Guice is a lightweight dependency injection framework for Java that allows configuring object bindings through modules. With Guice, classes declare their dependencies through constructor or field injection using the @Inject annotation rather than looking them up directly through factories. This improves testability. Modules map interfaces to implementations using a fluent binding API. At runtime, Guice uses this configuration to satisfy injection points. This reduces boilerplate code compared to manually wiring dependencies.
Guice is a lightweight Java dependency injection framework that allows developers to declare dependencies through modules and inject them using annotations. With Guice, developers can define bindings between interfaces and implementations, and annotate constructors and fields to specify injection points. This reduces boilerplate code compared to alternatives like implementing dependency injection by hand. Guice validates dependencies at startup and handles circular dependencies automatically.
This document introduces Google Guice, a dependency injection framework. It discusses dependency injection, benefits like separation of concerns and easier testing. It also covers disadvantages like potential maintenance issues. The document explores the Guice API including Injector, Module, Binder and different types of bindings like linked, annotated, instance and constructor bindings. It provides a simple example using traits, classes and annotations to demonstrate dependency injection with Guice. References for more information on Guice and dependency injection are also included.
This document provides an overview of Google Guice, an open source Java framework for dependency injection. It discusses key Guice concepts like dependency injection, bindings, providers, and scopes. It also covers advanced topics such as aspect-oriented programming with Guice, integration with other frameworks like Spring, and using Guice in servlets. The goal of Guice is to simplify dependency management and increase testability by removing hard-coded dependencies.
The document discusses Google Guice, an open source framework for dependency injection in Java. It provides an overview of dependency injection and what problem it aims to solve. The document then covers the key aspects of Google Guice, including how to define bindings between interfaces and implementations, different types of injections, and how to integrate Guice into applications and with other frameworks.
This document provides an overview of asynchronous JavaScript. It discusses how JavaScript uses a single thread and event queue. It introduces asynchronous functions and loading scripts asynchronously. It covers the requestIdleCallback function for background tasks. The document also provides an in-depth overview of promises in JavaScript for asynchronous code, including the promise lifecycle, then and catch methods, and creating promises using the Promise constructor.
The document provides a tutorial on using Google GIN (GWT INjection) for dependency injection in GWT client-side code. It explains that GIN is built on top of Guice and brings automatic dependency injection to GWT applications. It then outlines the 5 steps to implement GIN: 1) design interfaces, 2) create implementation classes, 3) configure bindings in a module, 4) define a Ginjector interface, and 5) generate and use the Ginjector. The steps are then explained in further detail with examples.
Developing enterprise applications today using JavaFX is a challenge. The industry has not matured enough to identify patterns and practices. Consequently practioners (architects and developers alike) commit the same mistakes again and again. There is a complete lack of non-UI frameworks that make JavaFX application development easy and fast. FxObjects attempts to address that gap. The 0.1 version released provides powerful features.
Bridging the communication Gap & Continuous Deliverymasoodjan
This is a case study of a top retailer in UK which was following Agile but not all the Agile practices. We will discuss how collaboration between business and engineering team improved using BDD and how it was used to generate automated acceptance tests. We will also discuss how continuous integration was implemented which laid foundation for continuous delivery.
Guice is a lightweight Java dependency injection framework that allows developers to declare dependencies through modules and inject them using annotations. With Guice, developers can define bindings between interfaces and implementations, and annotate constructors and fields to specify injection points. This reduces boilerplate code compared to alternatives like implementing dependency injection by hand. Guice validates dependencies at startup and handles circular dependencies automatically.
This document introduces Google Guice, a dependency injection framework. It discusses dependency injection, benefits like separation of concerns and easier testing. It also covers disadvantages like potential maintenance issues. The document explores the Guice API including Injector, Module, Binder and different types of bindings like linked, annotated, instance and constructor bindings. It provides a simple example using traits, classes and annotations to demonstrate dependency injection with Guice. References for more information on Guice and dependency injection are also included.
This document provides an overview of Google Guice, an open source Java framework for dependency injection. It discusses key Guice concepts like dependency injection, bindings, providers, and scopes. It also covers advanced topics such as aspect-oriented programming with Guice, integration with other frameworks like Spring, and using Guice in servlets. The goal of Guice is to simplify dependency management and increase testability by removing hard-coded dependencies.
The document discusses Google Guice, an open source framework for dependency injection in Java. It provides an overview of dependency injection and what problem it aims to solve. The document then covers the key aspects of Google Guice, including how to define bindings between interfaces and implementations, different types of injections, and how to integrate Guice into applications and with other frameworks.
This document provides an overview of asynchronous JavaScript. It discusses how JavaScript uses a single thread and event queue. It introduces asynchronous functions and loading scripts asynchronously. It covers the requestIdleCallback function for background tasks. The document also provides an in-depth overview of promises in JavaScript for asynchronous code, including the promise lifecycle, then and catch methods, and creating promises using the Promise constructor.
The document provides a tutorial on using Google GIN (GWT INjection) for dependency injection in GWT client-side code. It explains that GIN is built on top of Guice and brings automatic dependency injection to GWT applications. It then outlines the 5 steps to implement GIN: 1) design interfaces, 2) create implementation classes, 3) configure bindings in a module, 4) define a Ginjector interface, and 5) generate and use the Ginjector. The steps are then explained in further detail with examples.
Developing enterprise applications today using JavaFX is a challenge. The industry has not matured enough to identify patterns and practices. Consequently practioners (architects and developers alike) commit the same mistakes again and again. There is a complete lack of non-UI frameworks that make JavaFX application development easy and fast. FxObjects attempts to address that gap. The 0.1 version released provides powerful features.
Bridging the communication Gap & Continuous Deliverymasoodjan
This is a case study of a top retailer in UK which was following Agile but not all the Agile practices. We will discuss how collaboration between business and engineering team improved using BDD and how it was used to generate automated acceptance tests. We will also discuss how continuous integration was implemented which laid foundation for continuous delivery.
Code Camp 06 Model View Presenter Architecturebitburner93
This is the slide show I created for the first Twin Cities Code Camp in November of \'06 - I did this when I was working for Digineer and also used it in a Digi-U session that I put on for the other consultants.
How to build a react native app with the help of react native hooksKaty Slemon
How to build React Native application using React Hooks. Hire React Native developer to extract component logic into reusable functions without writing a class.
This document discusses dependency injection and inversion of control principles. It provides examples of how to implement dependency injection using interfaces, factories, and the Google Guice framework. The key points are:
1) Dependency injection loosens coupling between classes by allowing dependencies to be injected externally rather than created internally. This improves testability and flexibility.
2) Google Guice is an inversion of control framework that uses annotations and bindings to configure dependency injection. It handles object instantiation and wiring of dependencies.
3) With Guice, classes declare dependencies through interfaces or annotations rather than directly instantiating dependencies. This decouples classes and allows dependencies to vary without code changes.
Angularjs is a client side javascript framework that adds interactivity to HTML. It allows developers to create dynamic and interactive web applications. Some key features include directives, modules, controllers, expressions and data binding. Directives are HTML annotations that trigger javascript behaviors. Modules group application components. Controllers add application logic and behavior. Expressions display dynamic values in the HTML. Angularjs uses MVC architecture with the view being the DOM, controllers handling logic, and models storing data. It also utilizes dependency injection to manage dependencies between components.
The document discusses implementing inter-process communication (IPC) using Messenger in Android. It describes how a Messenger allows a service to expose a Handler to clients so they can send messages to be processed on the service's thread. The service returns a Messenger from onBind() and clients use it to send messages to the service's handler. The document provides code samples for implementing this in a service and client. It also compares Messenger to AIDL which allows concurrent IPC across processes but requires more setup.
Recently, our iOS team has prepared a report on the Combine Framework. We’ve discussed using the Combine framework, announced by Apple in 2019, while working with asynchronous code and how to use the delegate-pattern and callbacks as an alternative.
We’ve covered the following:
▪️ The comparison of Combine with other reactive paradigms, such as Rx and ReactiveSwift
▪️ Such entities as Publisher, Subscriber, Subject, Subscription, Scheduler
Lifecycle subscription and Backpressure work
▪️ Operators work
▪️ Debugging of the Reactive approach
▪️ Error handling
▪️ Usage of Combine with Foundation
▪️ Practical usage of Combine in typical situations
The report will be useful to those who:
▪️ Wants to stop using third-party dependencies such as Rx and ReactiveSwift
▪️ Wants to follow a declarative approach to programming in the future, but with a native framework.
This document provides an overview of Asp.Net MVC and how it compares to traditional Asp.Net web forms. Some key points:
- Asp.Net MVC follows the MVC pattern, separating concerns into models, views, and controllers, allowing for cleaner code and easier testing compared to Asp.Net web forms.
- In Asp.Net MVC, controllers handle requests and return action results, views are responsible for the UI, and models represent application data. This separation of concerns is more aligned with HTTP concepts.
- Asp.Net MVC aims to be more flexible, maintainable, and testable than web forms. It allows for tighter control over HTML and adheres to conventions over configurations
Neoito — Design patterns and depenedency injectionNeoito
Dependency injection is a software design pattern that allows someone to remove hard-coded dependencies and makes it possible to change them. Dependencies can be injected to the object via the constructor or via defined method or a setter property.
Faiz Mohamed Haneef is currently the CEO and Chief Technology Architect at Neoito. He's a former Architect at Lowe's, Hallmark and Infosys.
Dependency injection in Java, from naive to functionalMarian Wamsiedel
The presentation contains more approaches to implement inversion of control (dependency injection). There is a naive implementation, a standard guice implementation and two functional solutions.
The code samples are available on a github repository.
This document provides step by step instructions on how to achieve dependency injection using dagger 2. The code is written in java. The code content is courtesy of Coding In Flow - You can check out this channel for in-depth explanation. https://www.youtube.com/watch?v=ZZ_qek0hGkM&list=PLrnPJCHvNZuA2ioi4soDZKz8euUQnJW65
The document discusses test driven development (TDD) and how it can be used with Visual Studio 2010. It defines TDD as a process where developers write a failing test first, then code to pass the test, and refactor the code. The document outlines benefits of TDD like reduced bugs and defects, increased code flexibility, and easier addition of new features. It provides some advice on writing tests and using tools in Visual Studio 2010 like code coverage and contracts to help focus on TDD. Demo code is shown using unit testing and web testing in Visual Studio 2010.
The document discusses working with forms and events in ReactJS. It explains that HTML input elements like <input>, <textarea>, and <select> have their own state and need to be updated using the setState() method when a user interacts. Events in ReactJS work the same as in JavaScript and all JavaScript event handlers can be used. The setState() method is used to update state when a user interacts with an HTML element. An example component is provided that manages form state with an input field and button that updates state on change and click events.
The document discusses exceptions in SObjectizer-5.5. It explains that SObjectizer uses exceptions instead of return codes to prevent errors from being ignored. It describes the main exception class used by SObjectizer and how exceptions from agents are handled. It also covers how to set exception reactions for coops and the entire SObjectizer environment.
This document provides an overview and crash course on AngularJS. It begins with an introduction to key AngularJS concepts like data binding, expressions, scopes, directives, modules, dependency injection, controllers, services, factories and directives. It then covers these topics in more depth, explaining how directives extend HTML, how data binding works, the role of the $scope object, and how to create and inject dependencies using modules. The document also discusses controllers, services, factories and the differences between them. It concludes with brief sections on unit testing with Karma and end-to-end testing with Protractor.
Este documento descreve um sistema de marketing multinível que permite ganhar dinheiro indicando novos membros. Os membros ativos ganham uma porcentagem das vendas de produtos e serviços de pessoas em seus grupos de divulgação, que podem incluir até 5 níveis. Com todos os níveis preenchidos, a renda mensal pode chegar a R$8.818,25. Detalha os ganhos sobre indicações diretas e indiretas de novos membros.
This document discusses Klang and Little India in Malaysia, noting that Klang is a hot spot for locals and tourists rich in different cultures, while Little India has a high flow of people and is rich in Indian culture, with different types of buildings. It then provides steps to research locations, visit places, analyze and categorize photos, and choose captions to document the areas.
This 1 sentence document describes a puzzle game where a ball bounces between two sides like in the game Pong. The ball would bounce from one side to the other side similar to how the ball in Pong bounces between paddles on opposite sides of the screen.
Civilizations of East Asia
During the Song dynasty in China, gunpowder was invented over 500 years before Europe. In feudal Japan, the emperor was a figurehead and real power lay with the shoguns or supreme military commanders. Practiced mainly in Japan, Shinto is a religion that focuses on worshipping the divine forces of nature in mountains, trees, and rocks.
Dave Doyle needed a video surveillance solution to monitor activity and address
an outbreak of inventory and cashier-related shrinkage at his two Grande
Prairie Pita Pit stores. Dave turned to SNAP Security, a member organization of the Rogers Data
Alliance Program that provides mobile network video security solutions for
retail customers.
Code Camp 06 Model View Presenter Architecturebitburner93
This is the slide show I created for the first Twin Cities Code Camp in November of \'06 - I did this when I was working for Digineer and also used it in a Digi-U session that I put on for the other consultants.
How to build a react native app with the help of react native hooksKaty Slemon
How to build React Native application using React Hooks. Hire React Native developer to extract component logic into reusable functions without writing a class.
This document discusses dependency injection and inversion of control principles. It provides examples of how to implement dependency injection using interfaces, factories, and the Google Guice framework. The key points are:
1) Dependency injection loosens coupling between classes by allowing dependencies to be injected externally rather than created internally. This improves testability and flexibility.
2) Google Guice is an inversion of control framework that uses annotations and bindings to configure dependency injection. It handles object instantiation and wiring of dependencies.
3) With Guice, classes declare dependencies through interfaces or annotations rather than directly instantiating dependencies. This decouples classes and allows dependencies to vary without code changes.
Angularjs is a client side javascript framework that adds interactivity to HTML. It allows developers to create dynamic and interactive web applications. Some key features include directives, modules, controllers, expressions and data binding. Directives are HTML annotations that trigger javascript behaviors. Modules group application components. Controllers add application logic and behavior. Expressions display dynamic values in the HTML. Angularjs uses MVC architecture with the view being the DOM, controllers handling logic, and models storing data. It also utilizes dependency injection to manage dependencies between components.
The document discusses implementing inter-process communication (IPC) using Messenger in Android. It describes how a Messenger allows a service to expose a Handler to clients so they can send messages to be processed on the service's thread. The service returns a Messenger from onBind() and clients use it to send messages to the service's handler. The document provides code samples for implementing this in a service and client. It also compares Messenger to AIDL which allows concurrent IPC across processes but requires more setup.
Recently, our iOS team has prepared a report on the Combine Framework. We’ve discussed using the Combine framework, announced by Apple in 2019, while working with asynchronous code and how to use the delegate-pattern and callbacks as an alternative.
We’ve covered the following:
▪️ The comparison of Combine with other reactive paradigms, such as Rx and ReactiveSwift
▪️ Such entities as Publisher, Subscriber, Subject, Subscription, Scheduler
Lifecycle subscription and Backpressure work
▪️ Operators work
▪️ Debugging of the Reactive approach
▪️ Error handling
▪️ Usage of Combine with Foundation
▪️ Practical usage of Combine in typical situations
The report will be useful to those who:
▪️ Wants to stop using third-party dependencies such as Rx and ReactiveSwift
▪️ Wants to follow a declarative approach to programming in the future, but with a native framework.
This document provides an overview of Asp.Net MVC and how it compares to traditional Asp.Net web forms. Some key points:
- Asp.Net MVC follows the MVC pattern, separating concerns into models, views, and controllers, allowing for cleaner code and easier testing compared to Asp.Net web forms.
- In Asp.Net MVC, controllers handle requests and return action results, views are responsible for the UI, and models represent application data. This separation of concerns is more aligned with HTTP concepts.
- Asp.Net MVC aims to be more flexible, maintainable, and testable than web forms. It allows for tighter control over HTML and adheres to conventions over configurations
Neoito — Design patterns and depenedency injectionNeoito
Dependency injection is a software design pattern that allows someone to remove hard-coded dependencies and makes it possible to change them. Dependencies can be injected to the object via the constructor or via defined method or a setter property.
Faiz Mohamed Haneef is currently the CEO and Chief Technology Architect at Neoito. He's a former Architect at Lowe's, Hallmark and Infosys.
Dependency injection in Java, from naive to functionalMarian Wamsiedel
The presentation contains more approaches to implement inversion of control (dependency injection). There is a naive implementation, a standard guice implementation and two functional solutions.
The code samples are available on a github repository.
This document provides step by step instructions on how to achieve dependency injection using dagger 2. The code is written in java. The code content is courtesy of Coding In Flow - You can check out this channel for in-depth explanation. https://www.youtube.com/watch?v=ZZ_qek0hGkM&list=PLrnPJCHvNZuA2ioi4soDZKz8euUQnJW65
The document discusses test driven development (TDD) and how it can be used with Visual Studio 2010. It defines TDD as a process where developers write a failing test first, then code to pass the test, and refactor the code. The document outlines benefits of TDD like reduced bugs and defects, increased code flexibility, and easier addition of new features. It provides some advice on writing tests and using tools in Visual Studio 2010 like code coverage and contracts to help focus on TDD. Demo code is shown using unit testing and web testing in Visual Studio 2010.
The document discusses working with forms and events in ReactJS. It explains that HTML input elements like <input>, <textarea>, and <select> have their own state and need to be updated using the setState() method when a user interacts. Events in ReactJS work the same as in JavaScript and all JavaScript event handlers can be used. The setState() method is used to update state when a user interacts with an HTML element. An example component is provided that manages form state with an input field and button that updates state on change and click events.
The document discusses exceptions in SObjectizer-5.5. It explains that SObjectizer uses exceptions instead of return codes to prevent errors from being ignored. It describes the main exception class used by SObjectizer and how exceptions from agents are handled. It also covers how to set exception reactions for coops and the entire SObjectizer environment.
This document provides an overview and crash course on AngularJS. It begins with an introduction to key AngularJS concepts like data binding, expressions, scopes, directives, modules, dependency injection, controllers, services, factories and directives. It then covers these topics in more depth, explaining how directives extend HTML, how data binding works, the role of the $scope object, and how to create and inject dependencies using modules. The document also discusses controllers, services, factories and the differences between them. It concludes with brief sections on unit testing with Karma and end-to-end testing with Protractor.
Este documento descreve um sistema de marketing multinível que permite ganhar dinheiro indicando novos membros. Os membros ativos ganham uma porcentagem das vendas de produtos e serviços de pessoas em seus grupos de divulgação, que podem incluir até 5 níveis. Com todos os níveis preenchidos, a renda mensal pode chegar a R$8.818,25. Detalha os ganhos sobre indicações diretas e indiretas de novos membros.
This document discusses Klang and Little India in Malaysia, noting that Klang is a hot spot for locals and tourists rich in different cultures, while Little India has a high flow of people and is rich in Indian culture, with different types of buildings. It then provides steps to research locations, visit places, analyze and categorize photos, and choose captions to document the areas.
This 1 sentence document describes a puzzle game where a ball bounces between two sides like in the game Pong. The ball would bounce from one side to the other side similar to how the ball in Pong bounces between paddles on opposite sides of the screen.
Civilizations of East Asia
During the Song dynasty in China, gunpowder was invented over 500 years before Europe. In feudal Japan, the emperor was a figurehead and real power lay with the shoguns or supreme military commanders. Practiced mainly in Japan, Shinto is a religion that focuses on worshipping the divine forces of nature in mountains, trees, and rocks.
Dave Doyle needed a video surveillance solution to monitor activity and address
an outbreak of inventory and cashier-related shrinkage at his two Grande
Prairie Pita Pit stores. Dave turned to SNAP Security, a member organization of the Rogers Data
Alliance Program that provides mobile network video security solutions for
retail customers.
SDS in mental health: Finding things you can changeOutside the Box
The document discusses improving support systems for people with mental health problems. It notes that current systems are not working well based on feedback. The Social Care (Self-directed Support) Act aims to empower people through more choice and control over their care arrangements. However, simply providing more choices may not be enough if the underlying mindsets do not change. The document urges various groups, including people who use services, frontline practitioners, managers, and commissioners, to find creative ways to support people in pursuing different options and taking control of their lives rather than just focusing on traditional support models. Small changes by many individuals are needed to drive real progress in the system.
The document provides a transcript of two phone calls where the caller dials the wrong number but is trying to reach someone at the same office. In the first call, Michelle dials 5558790 trying to reach Rachel Allsop, but is told by the man who answers that she has the wrong number. In the second call, Ruth dials the same wrong number 5558790 trying to reach Paul Richards, and the man helps transfer her to Paul's direct number. Both callers apologize for dialing the wrong number.
UPS comenzó en 1907 como American Messenger Company y ha crecido para convertirse en un líder mundial en paquetería y logística. Ofrece entrega de paquetes en todo el mundo a través de operaciones terrestres, aéreas y marítimas. Ha innovado con sistemas de rastreo en línea que permiten a los clientes monitorear el estado de envío de más de 100 paquetes a la vez. En 2010, UPS generó $7.4 mil millones en ingresos netos y procesó 26.2 millones de solicitudes de rastreo
5th International Disaster and Risk Conference IDRC 2014 Integrative Risk Management - The role of science, technology & practice 24-28 August 2014 in Davos, Switzerland
The impact of Cheshire West; DoL & Court of Protection and liabilities - Elde...Browne Jacobson LLP
This document summarizes key points about deprivation of liberty and the impact of the Cheshire West ruling:
- It discusses the legal context around deprivation of liberty under the Mental Capacity Act and Article 5 of the European Convention on Human Rights.
- It explains that while the MCA allows for restraint believed necessary to prevent harm, deprivation of liberty requires authorization through the Deprivation of Liberty Safeguards or a court order.
- It notes that the Cheshire West Supreme Court ruling in 2014 established that authorities must "err on the side of caution" in identifying situations that amount to a deprivation of liberty and trigger safeguards for vulnerable people.
- Contact information is provided for any questions.
Peatlands cover one third of Scotland's land area and store the largest terrestrial carbon store in the UK. They face many pressures including drainage, burning, and development. Current research projects at the Environmental Research Institute are studying how peatland microbial communities and desmid diversity respond to disturbances like drainage, burning, and forestation. They are also examining how peatland-derived dissolved organic matter transports iron from land to sea. There is a need for more research on intact peatlands as baselines and on the impacts of different management practices to help inform sustainable peatland policy and management.
The document discusses China's interactions with neighboring regions like Korea, Vietnam, Japan, and nomadic groups to the north from the Sui to Song dynasties. It describes how China influenced these neighbors by spreading its culture, technology, and Buddhism while also adopting foreign aspects. China viewed itself as the central power and established a tributary system where it exchanged gifts for recognition of Chinese supremacy. However, the nomads also exerted influence on China at times through conquests and cultural diffusion.
Guice is a lightweight Java dependency injection framework that allows developers to declare dependencies through modules and inject them using annotations. With Guice, developers can define bindings between interfaces and implementations, and annotate constructors and fields to have dependencies automatically injected without needing to manually wire objects together. This reduces boilerplate code and makes applications easier to test by simplifying mocking of dependencies.
Guice is a lightweight Java dependency injection framework that allows developers to declare dependencies through annotations rather than through manual wiring code. With Guice, classes declare their dependencies through constructor injection using the @Inject annotation. Modules are implemented to map interfaces to implementations, specifying scopes. At runtime, Guice handles satisfying all declared dependencies through its generated injector without additional factory code. This reduces boilerplate and makes dependencies explicit and easy to manage.
The document discusses Google Guice, an open source framework for Java that supports dependency injection. It provides examples of how to use Guice to inject dependencies into classes through field injection, method injection, and constructor injection. It also covers how to define modules to configure dependency bindings and scopes like singletons. The document is intended to introduce developers to the basics of using Guice for dependency injection in Java applications.
This document discusses testability and provides lessons learned around testability. It begins with an introduction of the speaker and their background in testing. It then outlines some common testability problems like statics, singletons, and tight coupling. Solutions discussed include dependency injection and using mocks/fakes to isolate units for testing. The document provides an example of refactoring a weather application to make it more testable and enables the use of mocks for testing.
This document provides an overview of the Guice and Gin dependency injection frameworks. It discusses key features of Guice like annotation-based configuration, scopes, and type-safe injection. It compares Guice to Spring, noting Guice's simpler configuration. It also covers using Guice and Gin in web applications and GWT clients. Additional topics include the Warp utilities, configuration options like @Named, and limitations of Gin for GWT apps.
This document provides an overview of the Guice and Gin dependency injection frameworks. It discusses key features and differences between the two, including how Guice supports both server-side and client-side Java applications while Gin is tailored specifically for GWT client-side apps. Examples are given of basic usage and configuration for common tasks like singleton scopes and dependency injection.
Services in Grails are the place to put the majority of the logic in your application, leaving controllers responsible for handling request flow with redirects and so on.
How to implement dependency injection in c#Priyank Mittal
This slide explains the usage of dependency injection in order to write more precise code.
More Details: https://www.loginworks.com/technical-blogs/implement-dependency-injection-c/
In this presentation, Juhi Rathi of Valuebound has discussed “Dependency Module in Drupal 8.” It is a technique that introduces the service container, which ensures that all the dependencies will be available with the client.
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A service is a component that performs long-running operations in the background independently of any activity. There are two types of services: started services, which run indefinitely until stopped, and bound services, which are attached to components and stop when all components detach. Services must be declared in the manifest and have lifecycle methods like onStartCommand(), onBind(), onCreate(), and onDestroy().
This document discusses Grails services, including:
- Services are used to separate business logic from controllers and provide transaction support.
- Services can be created using the "grails create-service" command and are transactional by default.
- Methods on services can be annotated with @Transactional to control transaction behavior on a per-method level.
- Services provide dependency injection and support different scopes like prototype, request, and singleton.
Dependency Injection pattern in AngularAlexe Bogdan
The document discusses dependency injection (DI) in Angular and how it is used to configure services. It provides examples of different service types - constant, value, factory, service, and provider - and how they are registered and injected. The ngRoute module is also summarized as the core routing module in Angular that uses directives to render templates based on routes.
This document discusses effective practices for dependency injection (DI). It begins with a quick DI refresher and then provides guidelines for DI such as: explicitly defining dependencies, injecting exactly what is needed, preferring constructor injection, avoiding work in constructors, and avoiding direct dependencies on the injector. It also discusses testing code using DI, applying DI to existing code, and techniques for migrating code to use DI such as bottom-up or top-down approaches.
It's about how to involve unit-testing into an existing application.
Unit-testing is never easy to be approached, there's some experience about how to begin within it.
Stopping the Rot - Putting Legacy C++ Under TestSeb Rose
The document discusses introducing unit testing to legacy C++ code. It covers choosing a testing framework, writing initial tests and mocks, and various refactoring techniques like wrapping dependencies, extracting components, and adding non-intrusive C seams to facilitate testing. The goal is to incrementally make the code more testable while maintaining functionality through practices like test-driven development.
This document provides an overview of Angular, including what it is, why it is useful, its key features, and how to get started using it. Angular is a client-side framework written in JavaScript that makes it easy to build dynamic web applications. It provides features like separation of concerns, Ajax services, dependency injection, and browser history out of the box. The document demonstrates how to set up an Angular application and introduces concepts like views, directives, data binding, controllers, scopes, modules, and providers to help structure applications. It also covers validation and animation in Angular.
Java 9 brings modules as a core concept to the platform, but it’s more than just a language feature. With modules in Java 9, we can improve the design of code to increase maintainability and extensibility. As with every design principle, modularity requires thought and trade-offs to really reap the benefits. This session covers design practices for making codebases more maintainable and extensible. You will also find out about trade-offs to help you make the best choices. Topics include hiding implementations, using services for extensibility, API modules, avoiding cycles, optional dependencies, and dynamically loading modules. Familiarity with modules is helpful but not required. The speakers are the authors of Java 9 Modularity (O’Reilly).
Also see https://javamodularity.com
This document provides answers to 15 questions from a final exam on Angular. The questions cover topics like the defer attribute, comparison operators, variable scoping, strict mode, the DOM, adding events, event bubbling, timeouts vs intervals, JSON parsing, AJAX calls, coding style guidelines, and more. For each question, a concise answer is provided explaining the key concept or resolving the example code provided.
Android services allow long-running tasks to perform work in the background independently of an application's user interface. There are two main types of services: started services which can perform operations indefinitely even if the starting component is destroyed, and bound services which offer a client-server interface between a component and the service. Services must be started with startService() or bound to with bindService() and have lifecycle callback methods like onStartCommand(), onBind(), onCreate(), and onDestroy(). The IntentService class simplifies started service implementation. Bound services can expose interfaces using Binder, Messenger, or AIDL to allow inter-process communication.
Dependency injection is a design pattern that removes tight coupling between objects and their dependencies. It allows for objects to have their dependencies satisfied externally rather than internally. There are three main types of dependency injection: constructor injection, setter injection, and interface injection. Constructor injection passes dependencies through a class's constructor, while setter injection uses properties, and interface injection relies on implementing a common interface. Dependency injection promotes loose coupling, testability, and flexibility between classes.
5 key differences between Hard skill and Soft skillsRuchiRathor2
𝐓𝐡𝐞 𝐏𝐞𝐫𝐟𝐞𝐜𝐭 𝐁𝐥𝐞𝐧𝐝:
𝐖𝐡𝐲 𝐘𝐨𝐮 𝐍𝐞𝐞𝐝 𝐁𝐨𝐭𝐡 𝐇𝐚𝐫𝐝 & 𝐒𝐨𝐟𝐭 𝐒𝐤𝐢𝐥𝐥𝐬 𝐭𝐨 𝐓𝐡𝐫𝐢𝐯𝐞 💯
In today's dynamic and competitive market, a well-rounded skillset is no longer a luxury - it's a necessity.
While technical expertise (hard skills) is crucial for getting your foot in the door, it's the combination of hard and soft skills that propels you towards long-term success and career advancement. ✨
Think of it like this: Imagine a highly skilled carpenter with a masterful understanding of woodworking (hard skills). But if they struggle to communicate effectively with clients, collaborate with builders, or adapt to project changes (soft skills), their true potential remains untapped. 😐
The synergy between hard and soft skills is what creates true value in the workplace. Strong communication allows you to clearly articulate your technical expertise, while problem-solving skills help you navigate complex challenges alongside your team. 💫
By actively developing both sets of skills, you position yourself as a well-rounded professional who can not only perform tasks efficiently but also contribute meaningfully to a collaborative and dynamic work environment.
Go through the carousel and let me know your views 🤩
Khushi Saini, An Intern from The Sparks Foundationkhushisaini0924
This is my first task as an Talent Acquisition(Human resources) Intern in The Sparks Foundation on Recruitment, article and posts.
I invitr everyone to look into my work and provide me a quick feedback.
Parabolic antenna alignment system with Real-Time Angle Position FeedbackStevenPatrick17
Introduction
Parabolic antennas are a crucial component in many communication systems, including satellite communications, radio telescopes, and television broadcasting. Ensuring these antennas are properly aligned is vital for optimal performance and signal strength. A parabolic antenna alignment system, equipped with real-time angle position feedback and fault tracking, is designed to address this need. This document delves into the components, design, and implementation of such a system, highlighting its significance and applications.
Importance of Parabolic Antenna Alignment
The alignment of a parabolic antenna directly affects its performance. Even minor misalignments can lead to significant signal loss, which can degrade the quality of the received signal or cause communication failures. Proper alignment ensures that the antenna's focal point is accurately directed toward the signal source, maximizing the antenna's gain and efficiency. This precision is especially crucial in applications like satellite communications, where the antenna must track geostationary satellites with high accuracy.
Components of a Parabolic Antenna Alignment System
A parabolic antenna alignment system typically includes the following components:
Parabolic Dish: The primary reflector that collects and focuses incoming signals.
Feedhorn and Low Noise Block (LNB): Positioned at the dish's focal point to receive signals.
Stepper or Servo Motors: Adjust the azimuth (horizontal) and elevation (vertical) angles of the antenna.
Microcontroller (e.g., Arduino, Raspberry Pi): Processes sensor data and controls the motors.
Potentiometers: Provide feedback on the antenna's current angle positions.
Fault Detection Sensors: Monitor for potential faults such as cable discontinuities or LNB failures.
Control Software: Runs on the microcontroller, handling real-time processing and decision-making.
Real-Time Angle Position Feedback
Real-time feedback on the antenna's angle position is essential for maintaining precise alignment. This feedback is typically provided by potentiometers or rotary encoders, which continuously monitor the azimuth and elevation angles. The microcontroller reads this data and adjusts the motors accordingly to keep the antenna aligned with the signal source.
Fault Tracking in Antenna Alignment Systems
Fault tracking is vital for the reliability and performance of the antenna system. Common faults include cable discontinuities, LNB malfunctions, and motor failures. Sensors integrated into the system can detect these faults and either notify the user or initiate corrective actions automatically.
Design and Implementation
1. Parabolic Dish and Feedhorn
The parabolic dish is designed to reflect incoming signals to a focal point where the feedhorn and LNB are located. The dish's size and shape depend on the specific application and frequency range.
2. Motors and Position Control
Stepper motors or servo motors are used to control the azimuth and elevation of
LinkedIn Strategic Guidelines for June 2024Bruce Bennett
LinkedIn is a powerful tool for networking, researching, and marketing yourself to clients and employers. This session teaches strategic practices for building your LinkedIn internet presence and marketing yourself. The use of # and @ symbols is covered as well as going mobile with the LinkedIn app.
1. http://code.google.com/p/google-guice/
Java on Guice
Guice 1.0 User's Guide
Guice (pronounced "juice") is an ultra-lightweight, next-generation dependency
injection container for Java 5 and later.
Introduction
The enterprise Java community exerts a lot of effort toward wiring objects
together. How does your web application get access to a middle tier service, or
your service to the logged in user or transaction manager? You'll find many
general and specific solutions to this problem. Some rely on patterns. Others use
frameworks. All result in varying degrees of testability and some amount of
boilerplate code. You'll soon see that Guice enables the best of all worlds: easy
unit testing, maximal flexibility and maintainability, and minimal repetition.
We'll use an unrealistically simple example to illustrate the benefits of Guice over
some classic approaches which you're probably already familiar with. The
following example is so simple in fact that, even though it will show immediate
benefits, we won't actually do Guice justice. We hope you'll see that as your
application grows, Guice's benefits accelerate.
In this example, a client depends on a service interface. This could be any
arbitrary service. We'll just call it Service.
public interface Service {
void go();
}
2. We have a default implementation of this service which the client should not
depend directly on. If we decide to use a different service implementation in the
future, we don't want to go around and change all of our clients.
public class ServiceImpl implements Service {
public void go() {
...
}
}
We also have a mock service which we can use in unit tests.
public class MockService implements Service {
private boolean gone = false;
public void go() {
gone = true;
}
public boolean isGone() {
return gone;
}
}
Plain Old Factories
Before we discovered dependency injection, we mostly used the factory pattern.
In addition to the service interface, you have a service factory which provides the
service to clients as well as a way for tests to pass in a mock service. We'll make
the service a singleton so we can keep this example as simple as possible.
public class ServiceFactory {
private ServiceFactory() {}
private static Service instance = new ServiceImpl();
3. public static Service getInstance() {
return instance;
}
public static void setInstance(Service service) {
instance = service;
}
}
Our client goes directly to the factory every time it needs a service.
public class Client {
public void go() {
Service service = ServiceFactory.getInstance();
service.go();
}
}
The client is simple enough, but the unit test for the client has to pass in a mock
service and then remember to clean up afterwards. This isn't such a big deal in
our simple example, but as you add more clients and services, all this mocking
and cleaning up creates friction for unit test writing. Also, if you forget to clean up
after your test, other tests may succeed or fail when they shouldn't. Even worse,
tests may fail depending on which order you run them in.
public void testClient() {
Service previous = ServiceFactory.getInstance();
try {
final MockService mock = new MockService();
ServiceFactory.setInstance(mock);
Client client = new Client();
client.go();
assertTrue(mock.isGone());
}
finally {
ServiceFactory.setInstance(previous);
}
}
Finally, note that the service factory's API ties us to a singleton approach. Even if
getInstance() could return multiple instances, setInstance() ties our hands.
Moving to a non-singleton implementation would mean switching to a more
4. complex API.
Dependency Injection By Hand
The dependency injection pattern aims in part to make unit testing easier. We
don't necessarily need a specialized framework to practice dependency injection.
You can get roughly 80% of the benefit writing code by hand.
While the client asked the factory for a service in our previous example, with
dependency injection, the client expects to have its dependency passed in. Don't
call me, I'll call you, so to speak.
public class Client {
private final Service service;
public Client(Service service) {
this.service = service;
}
public void go() {
service.go();
}
}
This simplifies our unit test considerably. We can just pass in a mock service and
throw everything away when we're done.
public void testClient() {
MockService mock = new MockService();
Client client = new Client(mock);
client.go();
assertTrue(mock.isGone());
}
We can also tell from the API exactly what the client depends on.
Now, how do we connect the client with a service? When implementing
dependency injection by hand, we can move all dependency logic into factory
classes. This means we need a factory for our client, too.
public static class ClientFactory {
private ClientFactory() {}
public static Client getInstance() {
Service service = ServiceFactory.getInstance();
return new Client(service);
}
}
5. Implementing dependency injection by hand requires roughly the same number
of lines of code as plain old factories.
Dependency Injection with Guice
Writing factories and dependency injection logic by hand for every service and
client can become tedious. Some other dependency injection frameworks even
require you to explicitly map services to the places where you want them
injected.
Guice aims to eliminate all of this boilerplate without sacrificing maintainability.
With Guice, you implement modules. Guice passes a binder to your module, and
your module uses the binder to map interfaces to implementations. The following
module tells Guice to map Service to ServiceImpl in singleton scope:
public class MyModule implements Module {
public void configure(Binder binder) {
binder.bind(Service.class)
.to(ServiceImpl.class)
.in(Scopes.SINGLETON);
}
}
A module tells Guice what we want to inject. Now, how do we tell Guice where we
want it injected? With Guice, you annotate constructors, methods and fields with
@Inject.
public class Client {
private final Service service;
@Inject
public Client(Service service) {
this.service = service;
}
public void go() {
service.go();
}
}
The @Inject annotation makes it clear to a programmer editing your class which
members are injected.
For Guice to inject Client, we must either directly ask Guice to create a Client
instance for us, or some other class must have Client injected into it.
6. Guice vs. Dependency Injection By Hand
As you can see, Guice saves you from having to write factory classes. You don't
have to write explicit code wiring clients to their dependencies. If you forget to
provide a dependency, Guice fails at startup. Guice handles circular dependencies
automatically.
Guice enables you to specify scopes declaratively. For example, you don't have to
write the same code to store an object in the HttpSession over and over.
In the real world, you often don't know an implementation class until runtime.
You need meta factories or service locators for your factories. Guice addresses
these problems with minimal effort.
When injecting dependencies by hand, you can easily slip back into old habits and
introduce direct dependencies, especially if you're new to the concept of
dependency injection. Using Guice turns the tables and makes doing the right
thing easier. Guice helps keep you on track.
More Annotations
When possible, Guice enables you to use annotations in lieu of explicit bindings
and eliminate even more boilerplate code. Back to our example, if you need an
interface to simplify unit testing but you don't care about compile time
dependencies, you can point to a default implementation directly from your
interface.
@ImplementedBy(ServiceImpl.class)
public interface Service {
void go();
}
If a client needs a Service and Guice can't find an explicit binding, Guice will
inject an instance of ServiceImpl.
By default, Guice injects a new instance every time. If you want to specify a
different scope, you can annotate the implementation class, too.
@Singleton
public class ServiceImpl implements Service {
public void go() {
...
}
}
Architectural Overview
We can break Guice's architecture down into two distinct stages: startup and
7. runtime. You build an Injector during startup and use it to inject objects at
runtime.
Startup
You configure Guice by implementing Module. You pass Guice a module, Guice
passes your module a Binder, and your module uses the binder to configure
bindings. A binding most commonly consists of a mapping between an interface
and a concrete implementation. For example:
public class MyModule implements Module {
public void configure(Binder binder) {
// Bind Foo to FooImpl. Guice will create a new
// instance of FooImpl for every injection.
binder.bind(Foo.class).to(FooImpl.class);
// Bind Bar to an instance of Bar.
Bar bar = new Bar();
binder.bind(Bar.class).toInstance(bar);
}
}
Guice can look at the classes you tell it about during this stage and any classes
those classes know about, and tell you whether or not you're missing any
dependencies. For example, in a Struts 2 application, Guice knows about all of
your actions. Guice can validate your actions and anything they transitively
depend on, and fail early if necessary.
Creating an Injector entails the following steps:
1. First, create an instance of your module and pass it to Guice.createInjector().
8. 2. Guice creates a Binder and passes it to your module.
3. Your module uses the binder to define bindings.
4. Based on the bindings you specified, Guice creates an Injector and returns it to
you.
5. You use the injector to inject an object.
Runtime
We can now use the injector we created during the first stage to inject objects
and introspect on our bindings. Guice's runtime model consists of an injector
which contains some number of bindings.
A Key uniquely identifies each binding. The key consists of a type which the client
depends on and an optional annotation. You can use an annotation to
differentiate multiple bindings to the same type. The key's type and annotation
correspond to the type and annotation at a point of injection.
Each binding has a provider which provides instances of the necessary type. You
can provide a class, and Guice will create instances of it for you. You can give
Guice an instance of the type you're binding to. You can implement your own
provider, and Guice can inject dependencies into it.
Each binding also has an optional scope. Bindings have no scope by default, and
Guice creates a new instance for every injection. A custom scope enables you to
control whether or not Guice creates a new instance. For example, you can create
one instance per HttpSession.
Bootstrapping Your Application
The idea of bootstrapping is fundamental to dependency injection. Always
explicitly asking the Injector for dependencies would be using Guice as a service
locator, not a dependency injection framework.
Your code should deal directly with the Injector as little as possible. Instead,
you want to bootstrap your application by injecting one root object. The container
can further inject dependencies into the root object's dependencies, and so on
9. recursively. In the end, your application should ideally have one class (if that
many) which knows about the Injector, and every other class should expect to
have dependencies injected.
For example, a web application framework such as Struts 2 bootstraps your
application by injecting all of your actions. You might bootstrap a web service
framework by injecting your service implementation classes.
Dependency injection is viral. If you're refactoring an existing code base with a
lot of static methods, you may start to feel like you're pulling a never-ending
thread. This is a Good Thing. It means dependency injection is making your code
more flexible and testable.
If you get in over your head, rather than try to refactor an entire code base all in
one shot, you might temporarily store a reference to the Injector in a static field
somewhere or use static injection. Name the field's class clearly though:
InjectorHack and GodKillsAKittenEveryTimeYouUseMe come to mind. Keep in
mind that you you'll have to mock this class, and your unit tests will have to
install an Injector here by hand, and remember to clean up afterwards.
Binding Dependencies
How does Guice know what to inject? For starters, a Key composed of a type and
an optional annotation uniquely identifies a dependency. Guice refers to the
mapping between a key and an implementation as a Binding. An implementation
can consist of a single object, a class which Guice should also inject, or a custom
provider.
When injecting a dependency, Guice first looks for an explicit binding, a binding
which you specified using the Binder. The Binder API uses the builder pattern to
create a domain-specific expression language. Different methods return different
objects depending on the context limiting you to appropriate methods.
For example, to bind an interface Service to a concrete implementation
ServiceImpl, call:
binder.bind(Service.class).to(ServiceImpl.class);
This binding matches the following the method:
@Inject
void injectService(Service service) {
...
}
10. Note: In contrast to some other frameworks, Guice gives no
special treatment to "setter" methods. Guice will inject any
method with any number of parameters so long as the method
has an @Inject annotation, even if the method is in a
superclass.
DRY (Don't Repeat Yourself)
Repeating "binder" over and over for each binding can get a little tedious. Guice
provides a Module support class named AbstractModule which implicitly gives
you access to Binder's methods. For example, we could extend AbstractModule
and rewrite the above binding as:
bind(Service.class).to(ServiceImpl.class);
We'll use this syntax throughout the rest of the guide.
Annotating Bindings
If you need multiple bindings to the same type, you can differentiate the bindings
with annotations. For example, to bind an interface Service and annotation
@Blue to the concrete implementation BlueService, call:
bind(Service.class)
.annotatedWith(Blue.class)
.to(BlueService.class);
This binding matches the following the method:
@Inject
void injectService(@Blue Service service) {
...
}
Notice that while @Inject goes on the method, binding annotations such as
@Blue go directly on the parameter. The same goes for constructors. When using
field injection, both annotations can apply directly to the field, as in this example:
@Inject @Blue Service service;
Creating Binding Annotations
Where did this @Blue annotation just mentioned come from? You can create such
an annotation easily, although the standard incantation you have to use is
unfortunately a little complex:
11. /**
* Indicates we want the blue version of a binding.
*/
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.PARAMETER})
@BindingAnnotation
public @interface Blue {}
Luckily, we don't really have to understand it all just to use it. But for the curious,
here's what all this boilerplate means:
• @Retention(RUNTIME) allows your annotation to be visible at runtime.
• @Target({FIELD, PARAMETER}) is a courtesy to your users; it prevents
@Blue from being applied to methods, types, local variables, and other
annotations, where it would serve no purpose.
• @BindingAnnotation is a Guice-specific signal that you wish your
annotation to be used in this way. Guice will produce an error whenever
user applies more than one binding annotation to the same injectable
element.
Annotations With Attributes
If you can get by with marker annotations alone, feel free to skip to the next
section.
You can also bind to annotation instances, i.e. you can have multiple bindings
with the same type and annotation type, but with different annotation attribute
values. If Guice can't find a binding to an annotation instance with the necessary
attribute values, it will look for a binding to the annotation type instead.
Say for example we have a binding annotation @Named with a single string
attribute value.
@Retention(RUNTIME)
@Target({ FIELD, PARAMETER })
@BindingAnnotation
public @interface Named {
String value();
}
If we want to bind to @Named("Bob"), we first need an implementation of Named.
Our implementation must abide by the Annotation contract, specifically the
implementations of hashCode() and equals().
class NamedAnnotation implements Named {
final String value;
public NamedAnnotation(String value) {
this.value = value;
12. }
public String value() {
return this.value;
}
public int hashCode() {
// This is specified in java.lang.Annotation.
return 127 * "value".hashCode() ^ value.hashCode();
}
public boolean equals(Object o) {
if (!(o instanceof Named))
return false;
Named other = (Named) o;
return value.equals(other.value());
}
public String toString() {
return "@" + Named.class.getName() + "(value=" + value + ")";
}
public Class<? extends Annotation> annotationType() {
return Named.class;
}
}
Now we can use this annotation implementation to create bindings to @Named.
bind(Person.class)
.annotatedWith(new NamedAnnotation("Bob"))
.to(Bob.class);
This may seem like a lot of work compared to string based identifiers used by
other frameworks, but keep in mind that you can't do this at all with string-based
identifiers. Also, you'll find that you get a lot of reuse out of binding annotations.
Since identifying a binding by name is such a common use case, Guice provides a
production-worthy implementation of @Named in com.google.inject.name.
Implicit Bindings
As we saw in the introduction, you don't always have to declare bindings
explicitly. In the absence of an explicit binding, Guice will try to inject and create
a new instance of the class you depend on. If you depend on an interface, Guice
will look for an @ImplementedBy annotation which points to the concrete
implementation. Take the following explicit binding to a concrete, injectable class
named Concrete for example. It basically says, bind Concrete to Concrete.
That's explicit, but also a little redundant.
bind(Concrete.class);
13. Removing the binding above would not affect the behavior of this class:
class Mixer {
@Inject
Mixer(Concrete concrete) {
...
}
}
So, take your pick: explicit or brief. In the event of an error, Guice will produce
helpful messages either way.
Injecting Providers
Sometimes a client needs multiple instances of a dependency per injection. Other
times a client may not want to actually retrieve an object until some time after
the actual injection (if at all). For any binding of type T, rather than inject an
instance of T directly, you can inject a Provider<T>. Then call
Provider<T>.get() as necessary. For example:
@Inject
void injectAtm(Provider<Money> atm) {
Money one = atm.get();
Money two = atm.get();
...
}
As you can see, the Provider interface couldn't get much simpler so it doesn't
get in the way of easy unit testing.
Injecting Constant Values
When it comes to constant values, Guice gives special treatment to several types:
• Primitive types (int, char, ...)
• Primitive wrapper types (Integer, Character, ...)
• Strings
• Enums
• Classes
First, when binding to constant values of these types, you needn't specify the
type you're binding to. Guice can figure it out from the value. For example, given
a binding annotation named TheAnswer:
bindConstant().annotatedWith(TheAnswer.class).to(42);
14. Has the same effect as:
bind(int.class).annotatedWith(TheAnswer.class).toInstance(42);
When it comes time to inject a value of one of these types, if Guice can't find an
explicit binding for a primitive type, it will look for a binding to the corresponding
wrapper type and vice versa.
Converting Strings
If Guice still can't find an explicit binding for one of the above types, it will look
for a constant String binding with the same binding annotation and try to
convert its value. For example:
bindConstant().annotatedWith(TheAnswer.class).to("42"); //
String!
Will match:
@Inject @TheAnswer int answer;
When converting, Guice will try to look up enums and classes by name. Guice
converts a value once at startup which also means you get up front type
checking. This feature comes in especially handy if the binding value comes from
a properties file for example.
Custom Providers
Sometimes you need to create your objects manually rather than let Guice create
them. For example, you might not be able to add @Inject annotations to the
implementation class as it came from a 3rd party. In these cases, you can
implement a custom Provider. Guice can even inject your provider class. For
example:
class WidgetProvider implements Provider<Widget> {
final Service service;
@Inject
WidgetProvider(Service service) {
this.service = service;
}
public Widget get() {
return new Widget(service);
}
}
15. You bind Widget to WidgetProvider like so:
bind(Widget.class).toProvider(WidgetProvider.class);
Injecting the custom providers enables Guice to check the types and
dependencies up front. Custom providers can reside in any scope independent of
the scope of the objects they provide. By default, Guice creates a new provider
instance for every injection. In the above example, if each Widget needs its own
instance of Service, our code will work fine. You can specify a different scope for
a custom factory using a scope annotation on the factory class or by creating a
separate binding for the factory.
Example: Integrating With JNDI
Say for example we want to bind to objects from JNDI. We could implement a
reusable custom provider similar to the one below. Notice we inject the JNDI
Context:
package mypackage;
import com.google.inject.*;
import javax.naming.*;
class JndiProvider<T> implements Provider<T> {
@Inject Context context;
final String name;
final Class<T> type;
JndiProvider(Class<T> type, String name) {
this.name = name;
this.type = type;
}
public T get() {
try {
return type.cast(context.lookup(name));
}
catch (NamingException e) {
throw new RuntimeException(e);
}
}
/**
* Creates a JNDI provider for the given
* type and name.
*/
static <T> Provider<T> fromJndi(
Class<T> type, String name) {
return new JndiProvider<T>(type, name);
16. }
}
Thanks to generic type erasure, we must pass in the class at runtime. You could
skip this step, but tracking down type casting errors later might be a little tricky
(i.e. if JNDI returns an object of the wrong type).
We can use our custom JndiProvider to bind DataSource to an object from
JNDI:
import com.google.inject.*;
import static mypackage.JndiProvider.fromJndi;
import javax.naming.*;
import javax.sql.DataSource;
...
// Bind Context to the default InitialContext.
bind(Context.class).to(InitialContext.class);
// Bind to DataSource from JNDI.
bind(DataSource.class)
.toProvider(fromJndi(DataSource.class, "..."));
Scoping Bindings
By default, Guice creates a new object for every injection. We refer to this as
having "no scope." You can specify a scope when you configure a binding. For
example, to inject the same instance every time:
bind(MySingleton.class).in(Scopes.SINGLETON);
As an alternative, you can use an annotation on your implementation class to
specify the scope. Guice supports @Singleton by default:
@Singleton
class MySingleton {
...
}
The annotation approach works with implicit bindings as well but requires that
Guice create your objects. On the other hand, calling in() works with almost any
binding type (binding to a single instance being an obvious exception) and
overrides annotations when present. in() also accepts annotations if you don't
want a compile time dependency on your scope implementation.
Specify annotations for custom scopes using Binder.bindScope(). For example,
given an annotation @SessionScoped and a Scope implementation
ServletScopes.SESSION:
17. binder.bindScope(SessionScoped.class, ServletScopes.SESSION);
Creating Scope Annotations
Annotations used for scoping should:
• Have a @Retention(RUNTIME) annotation so we can see the annotation at
runtime.
• Have a @Target({TYPE}) annotation. Scope annotations only apply to
implementation classes..
• Have a @ScopeAnnotation meta-annotation. Only one such annotation can
apply to a given class.
For example:
/**
* Scopes bindings to the current transaction.
*/
@Retention(RUNTIME)
@Target({TYPE})
@ScopeAnnotation
public @interface TransactionScoped {}
Eagerly Loading Bindings
Guice can wait to load singleton objects until you actually need them. This helps
speed up development because your application starts faster and you only
initialize what you need. However, sometimes you always want to load an object
at startup. You can tell Guice to always eagerly load a singleton like so:
bind(StartupTask.class).asEagerSingleton();
We frequently use this to implement initialization logic for our application. You
can control the ordering of your initialization by creating dependencies on
singletons which Guice must instantiate first.
Injecting Between Scopes
You can safely inject objects from a larger scope into an object from a smaller
scope, or the same scope. For example, you can inject an Http session-scoped
object into an HTTP request-scoped object. However, injecting into objects with
larger scopes is a different story. For example, if you injected a request-scoped
object into a singleton, at best, you would get an error due to not running within
an HTTP request, and at worst your singleton object would always reference an
object from the first request. In these cases, you should inject a Provider<T>
18. instead and use it to retrieve the object from the smaller scope as necessary.
Then, you should be certain to never invoke this provider when you are outside of
T's scope (for example, when you are not servicing an HTTP request, and T is
request-scoped).
Development Stages
Guice is aware that your application goes through different stages of
development. You can tell it which stage the application is running in when you
create a container. Guice currently supports "development" and "production."
We've found that tests usually fall under one stage or the other.
During development, Guice will load singleton objects on demand. This way, your
application starts up fast and only loads the parts you're testing.
In production, Guice will load all your singleton objects at startup. This helps
catch errors early and takes any performance hits up front.
Your modules can also apply method interceptors and other bindings based on
the current stage. For example, an interceptor might verify that you don't use
your objects out of scope during development.
Intercepting Methods
Guice supports simple method interception using the AOP Alliance API. You can
bind interceptors from your modules using Binder. For example, to apply a
transaction interceptor to methods annotated with @Transactional:
import static com.google.inject.matcher.Matchers.*;
...
binder.bindInterceptor(
any(), // Match classes.
annotatedWith(Transactional.class), // Match methods.
new TransactionInterceptor() // The interceptor.
);
Try to shoulder as much of the filtering as is possible on the matchers rather than
in the interceptor's body as the matching code runs only once at startup.
Static Injection
Static fields and methods make testing and reusing more difficult, but there are
19. times where your only choice is to keep a static reference to the Injector.
For these situations, Guice supports injecting less accessible static members. For
example, HTTP session objects often need to be serializable to support
replication, but what if your session object depends on a container-scoped object?
We can keep a transient reference to the object, but how do we look it up again
upon deserialization?
We've found the most pragmatic solution to be static injection:
@SessionScoped
class User {
@Inject
static AuthorizationService authorizationService;
...
}
Guice never performs static injection automatically. You must use Binder to
explicitly request that the Injector inject your static members after startup:
binder.requestStaticInjection(User.class);
Static injection is a necessary evil, which makes testing more difficult. If you can
find a way to avoid using it, you'll probably be glad you did.
Optional Injection
Sometimes your code should work whether a binding exists or not. In these
cases, you can use @Inject(optional=true) and Guice can override your default
implementation with a bound implementation when available. For example:
@Inject(optional=true) Formatter formatter = new
DefaultFormatter();
If someone creates a binding for Formatter, Guice will inject an instance from
that binding. Otherwise, assuming Formatter isn't injectable itself (see Implicit
Bindings), Guice will skip the optional member.
Optional injection applies only to fields and methods, not constructors. In the
case of methods, if a binding for one parameter is missing, Guice won't inject the
method at all, even if bindings to other parameters are available.
Binding to Strings
We try to avoid using strings whenever possible as they're prone to misspellings,
not tool friendly, and so on, but using strings instead of creating custom
annotations can prove useful for quick and dirty code. For these situations, Guice
20. provides @Named and Names. For example, a binding to a string name like:
import static com.google.inject.name.Names.*;
...
bind(named("bob")).to(10);
Will match injection points like:
@Inject @Named("bob") int score;
Struts 2 Support
To install the Guice Struts 2 plugin with Struts 2.0.6 or later, simply include
guice-struts2-plugin-1.0.jar in your web application's classpath and select
Guice as your ObjectFactory implementation in your struts.xml file:
<constant name="struts.objectFactory" value="guice" />
Guice will inject all of your Struts 2 objects including actions and interceptors.
You can even scope your actions. You can optionally specify a Module for Guice to
install in your struts.xml file:
<constant name="guice.module" value="mypackage.MyModule"/>
If all of your bindings are implicit, you can get away without defining a module at
all.
A Counting Example
Say for example that we want to count the number of requests in a session.
Define a Counter object which will live on the session:
@SessionScoped
public class Counter {
int count = 0;
/** Increments the count and returns the new value. */
public synchronized int increment() {
return count++;
}
}
Next, we can inject our counter into an action:
public class Count {
21. final Counter counter;
@Inject
public Count(Counter counter) {
this.counter = counter;
}
public String execute() {
return SUCCESS;
}
public int getCount() {
return counter.increment();
}
}
Then create a mapping for our action in our struts.xml file:
<action name="Count"
class="mypackage.Count">
<result>/WEB-INF/Counter.jsp</result>
</action>
And a JSP to render the result:
<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
<body>
<h1>Counter Example</h1>
<h3><b>Hits in this session:</b>
<s:property value="count"/></h3>
</body>
</html>
We actually made this example more complicated than necessary in an attempt
to illustrate more concepts. In reality, we could have done away with the
separate Counter object and applied @SessionScoped to our action directly.
JMX Integration
See com.google.inject.tools.jmx.
Appendix: How the Injector resolves injection requests
The injector's process of resolving an injection request depends on the bindings
that have been made and the annotations found on the types involved. Here is a
22. summary of how an injection request is resolved:
1. Observe the Java type and the optional "binding annotation" of the element
to be injected. If the type is com.google.inject.Provider<T>, perform
resolution for the type indicated by T instead. Find a binding for this (type,
annotation) pair. If none, skip to #4.
2. Follow transitive bindings. If this binding links to another binding, follow this
edge and check again, repeating until we reach a binding which does not link
to any other binding. We are now at the most specific explicit binding for this
injection request.
3. If this binding specifies an instance or a Provider instance, we're done; use
this to fulfill the request.
4. If, at this point, the injection request used an annotation type or value, we
have failed and we produce an error.
5. Otherwise examine the Java type for this binding; if an @ImplementedBy
annotation is found, instantiate the referenced type. If a @ProvidedBy
annotation is found, instantiate the referenced provider and use it to obtain
the desired object. Otherwise attempt to instantiate the type itself.