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Java Spring framework, Dependency Injection, DI, IoC, Inversion of Control


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Hi, I just prepared a presentation on Java Spring Framework, the topics covered include architecture of Spring framework and it's modules. Spring Core is explained in detail including but not limited to Inversion of Control (IoC), Dependency Injection (DI) etc. Thank you and happy learning. :)

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Java Spring framework, Dependency Injection, DI, IoC, Inversion of Control

  1. 1. Spring Framework Prepared & Presented by Arjun 1
  2. 2. Know your trainer Name: Arjun Phone : +91 9691053479 Email:  Freelance corporate trainer.  More than 2 years of strong hands-on experience in top MNCs in Java and related technologies.  More than 2 years of experience as a Java trainer. Clients / Previous Employers: 2
  3. 3. Agenda Topics to be covered are:      Introduction to Spring framework Benefits of Spring framework Spring framework architecture Inversion of Control (IoC) Dependency Injection (DI) 3
  4. 4. Spring Framework  Light-weight comprehensive framework for building Java SE and Java EE applications  Created by Rod Johnson  JavaBeans-based configuration management, applying Inversionof-Control principles, specifically using the Dependency Injection technique • Reduce dependencies of components on specific implmentation of other components. • A core bean factory, which is usable globally  Generic abstraction layer for database transaction management 4
  5. 5. Key Features  Built-in generic strategies for JTA and a single JDBC DataSource  This removes the dependency on a Java EE environment for transaction support.  Integration with persistence frameworks Hibernate, JDO and iBATIS.  MVC web application framework, built on core Spring functionality,  supporting many technologies for generating views, including JSP.  Extensive aspect-oriented programming (AOP) framework to provide  services such as transaction management.  As with the Inversion-of-Control parts of the system, this aims to improve the modularity of systems created using the framework. 5
  6. 6. Using Spring  Wiring of components through Dependency Injection  Promotes de-coupling among the parts that make the application  Test-Driven Development (TDD)  POJO classes can be tested without being tied up with the framework  Declarative programming through AOP  Easily configured aspects, esp. transaction support  Integration with other technologies  EJB for J2EE  Hibernate, iBatis, JDBC (for data access)  Velocity (for presentation)  Struts and WebWork (For web) 6
  7. 7. Spring Framework 7
  8. 8. Core Package  The fundamental part which provides the IoC and Dependency Injection features  BeanFactory, provides a sophisticated implementation of the factory pattern  Removes the need for programmatic singletons  Decouple the configuration and specification of dependencies in program logic. 8
  9. 9. Context Package  Provides a way to access objects in a framework-style  Inherits its features from the beans package and adds support for • internationalization (I18N) • event-propagation • resource-loading • transparent creation of contexts by 9
  10. 10. DAO Package  Provides a JDBC-abstraction layer that removes the need to do tedious  JDBC coding and parsing of database-vendor specific error codes  Programmatic as well as declarative transaction management for • classes implementing special interfaces • POJOs 10
  11. 11. ORM Package  The ORM package provides integration layers for popular objectrelational mapping APIs, including JPA, JDO, Hibernate, and iBatis.  Using the ORM package you can use all those O/R-mappers in combination with all the other features Spring offers, such as the simple declarative transaction management feature mentioned previously 11
  12. 12. AOP Package  Spring's AOP package provides an AOP Alliance-compliant aspectoriented programming implementation • method-interceptors and pointcuts to cleanly decouple code implementing functionality that should logically speaking be separated  Using source-level metadata functionality you can also incorporate all kinds of behavioral information into your code 12
  13. 13. MVC Package  Web package provides features, such as • multipart file-upload functionality, • the initialization of the IoC container using servlet listeners • A web-oriented application context. • Can be used together with WebWork or Struts,  Spring's MVC package provides a Model-View-Controller (MVC)  implementation for web applications  Provides a clean separation between domain model code and web forms, and allows all the other features of the Spring Framework. 13
  14. 14. IoC Container      Introduction Basic Containers and Beans Dependencies The Application Context Developing a Spring Application 14
  15. 15. Inversion of Control  The Spring IoC container makes use of Java POJO classes and configuration metadata.  It produces a fully configured and executable system or application. 15
  16. 16. Introduction to IoC  Traditional software is developed with the application code “in control” • The application defines the “main”function/method/entry point • Calls the application’s components to perform processing  Frameworks invert this relationship and call the application code • “Don’t call us we’ll call you” • Framework provides the “main”function/method/entry point • Application code fits into the framework and is called when the framework decides.  A particular variant of IoC is “dependency injection” 16
  17. 17. Dependency Injection  Most frameworks use the “Service Lookup” approach to allow application code to find its dependencies. • e.g. J2EE code looks up resources via JNDI • CORBA applications find services via a Naming Service • The lookup mechanism is hard coded into the application code  Dependency Injection frameworks supply the resources that a component needs when initialising it • Component declares resources required (usually as interface types) • Framework configuration defines concrete instances to use • Framework passes component the concrete resources at load time  “IoC containers” are “Dependency Injection” containers 17
  18. 18. Service Lookup vs. Dependency Injection 18
  19. 19. IoC Container  The org.springframework.beans and org.springframework.context packages provide the basis for the Spring Framework's IoC container.  BeanFactory interface provides an advanced configuration mechanism capable of managing  objects of any nature.  ApplicationContext interface , a sub interface of BeanFactory is used for • Easier integration with Spring's AOP features, • Message resource handling (in internationalization), • Event propagation • Specific contexts such as the WebApplicationContext 19
  20. 20. Container and Beans  A bean is simply an object that is instantiated, assembled and otherwise managed by a Spring IoC container  The beans, and the dependencies between them, are reflected in the configuration metadata used by a container.  org.springframework.beans.factory.BeanFactory is the representation of the Spring IoC container, it’s responsible for: • containing and managing beans, • instantiating or sourcing application objects • configuring such objects • assembling the dependencies between objects. 20
  21. 21. The Container  There are a number of implementations of the BeanFactory interface  The most commonly used BeanFactory implementation is the XmlBeanFactory class.  The XmlBeanFactory takes the XML configuration metadata and uses it to create a fully configured system or application. 21
  22. 22. Configuration Meta Data  The meta-data informs the Spring container as to how to “instantiate, configure, and assemble *the objects in your application+”.  XML-based metadata is the most commonly used form of configuration metadata.  Configuration consists of at least one bean definition that the container must manage, but could be more than one bean definition.  When using XML-based configuration metadata, these beans are configured as <bean/> elements inside a top-level <beans/> element. 22
  23. 23. Simple XML Configuration <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="" xmlns:xsi="" xsi:schemaLocation=""> <bean id="..." class="..."> <!--collaborators and configuration for this bean go here --> </bean> <bean id="..." class="..."> <!--collaborators and configuration for this bean go here --> </bean> <!--more bean definitions go here --> </beans> 23
  24. 24. Instantiating a Container ApplicationContext context = new ClassPathXmlApplicationContext( new String[] {"services.xml", "daos.xml"}); // an ApplicationContext is also a BeanFactory (via inheritance) BeanFactory factory = context; 24
  25. 25. The Bean  The container manages the beans , and they are are created using the configuration metadata.  Bean definitions are represented as BeanDefinition objects, which contain the following metadata:  package-qualified class name: typically this is the actual implementation class of the bean being defined.  bean behavioral configuration elements, • which state how the bean should behave in the container (scope, lifecycle callbacks etc.,).  references to other beans • which are needed for the bean to do its work; these references are also called collaborators or dependencies.  other configuration settings • An example would be the number of connections to use in a bean that manages a connection pool, or the size limit of the pool. 25
  26. 26. Benefits of Dependency Injection  Flexible • Avoid adding lookup code in business logic  Testable • No need to depend on external resources or containers for testing  Maintainable • Promotes a consistent approach across all applications and teams • Allows reuse in different application environments by changing configuration files instead of code 26
  27. 27. Dependency Injection     BeanFactory interface XmlBeanFactory implementation Bean configuration file Constructor dependency Injection • Dependencies are provided through the constructors of the component  Setter dependency injection • Dependencies are provided through the JavaBeanstyle setter methods of the component • More popular than Constructor dependency injection  Beans  Injection Parameters 27
  28. 28. BeanFactory Class  BeanFactory object is responsible for managing beans and their dependencies  Your application interacts with Spring's DI container through BeanFactory interface • BeanFactory object has to be created by the application typically XmlBeanFactory • BeanFactory object, when it gets created, read bean configuration file and performs the wiring • Once created, the application can access the beans via BeanFactory interface  XmlBeanFactory • Convenience extension of DefaultListableBeanFactory that reads bean definitions from an XML document 28
  29. 29. Beans  The term “bean” is used to refer any component managed by the BeanFactory  The “beans” are in the form of JavaBeans (in most cases) • no arg constructor • getter and setter methods for the properties  Beans are singletons by default  Properties • the beans may be simple values or references to other beans 29
  30. 30. The Bean – A Java Class public class Example { private int empid; private String empname; public int getEmpid() { return empid; } public void setEmpid(int empid) { this.empid = empid; } public String getEmpname() { return empname; } public void setEmpname(String empname) { this.empname = empname; } public Example() {super();}} // no arg constructor 30
  31. 31. Injecting Simple Values–XML File  Each bean is defined using <bean> tag under the root of the <beans> tag  The id attribute is used to give the bean its default name  The class attribute specifies the type of the bean <bean id="firstBean" class=""> <property name="empname"> <value>ramesh</value> </property> <property name="empid"><value>100</value></property> </bean> </beans> 31
  32. 32. Injecting Simple Values–XML File  Each bean is defined using <bean> tag under the root of the <beans> tag  The id attribute is used to give the bean its default name  The class attribute specifies the type of the bean <bean id="firstBean" class=""> <property name="empname"> <value>ramesh</value> </property> <property name="empid"><value>100</value></property> </bean> </beans> 32
  33. 33. Spring Application import org.springframework.beans.factory.BeanFactory; import org.springframework.beans.factory.xml.XmlBeanFactory; import; public class TestExample { public static void main(String[] args) { BeanFactory bfact = new XmlBeanFactory(new FileSystemResource("mybean.xml")); Example exObj = (Example)bfact.getBean("firstBean"); System.out.println(exObj.getEmpid()); System.out.println(exObj.getEmpname()); } } 33
  34. 34. Injection Parameter Types  Spring supports various kinds of injection parameters • Simple values • Beans in the same factory • Beans in another factory • Collections • Externally defined properties  You can use these types for both setter or constructor injections 34
  35. 35. Injecting Bean into the same Factory  Used when you need to inject one bean into another (target bean)  Configure both beans first  Configure an injection using <ref> tag in the target bean's <property> or <constructor-arg>  The type being injected does not have to be the exact type defined on the target  if the type defined on the target is an interface, the type being injected must be an implementation of it  if the type defined on the target is a class, the type being injected can be the same type or sub-type 35
  36. 36. Constructor Injection  All dependencies injected via constructor arguments – Requires potentially complex constructor argument lists  Avoids reliance on get/set naming conventions – e.g. addStateObserver()  Less flexible initialisation – Need a constructor per configuration option  Can be difficult to understand – Rely on ordering of parameters 36
  37. 37. Constructor Dependency Injection (code snippet) public class Invoice { private Items item; private String customer; private double amount; public Invoice(Items item) { this.item = item; } public Invoice() { super(); } // Set/Get Methods } public class Items { private int itemno; private String itemname; public Items() { super(); } // Set/Get Methods } 37
  38. 38. Constructor Dependency Injection (code snippet) public class TestConstDepend { public static void main(String[] args) { BeanFactory bf = new XmlBeanFactory(new FileSystemResource("mybeandef.xml")); Invoice inv = (Invoice)bf.getBean("Invoice"); System.out.println(inv.getItem()); System.out.println(inv.getCustomer()); System.out.println(inv.getAmount()); } } 38
  39. 39. Setter Injection  All dependencies injected via setter methods – No need for constructors  Allows flexible initialisation – Any set of properties can be initialised  Named properties allow for readable configuration data – Clear what is being injected  Requires JavaBean conventions to be followed – Non standard method names are problematic  Can result in invalid object configurations – Need post initialisation checking methods 39
  40. 40. Setter Injection (code snippet) public class Policy { private int policyCode; private String policyName; public Policy(int policyCode, String policyName) { this.policyCode = policyCode; this.policyName = policyName; } public Policy() { super(); } //SET-GET Methods } public class Insurance { private int policynumber; private Policy policyData; public Policy getPolicyData() { return policyData; } public void setPolicyData(Policy policyData) { this.policyData = policyData; } //SET-GET Methods } 40
  41. 41. Setter Injection (code snippet) public class TestSetterDependcy { public static void main(String[] args) { BeanFactory beanFact = new XmlBeanFactory (new FileSystemResource("myBean.xml")); Insurance ins =(Insurance)beanFact.getBean("Insurance"); System.out.println("Policy Number"+ins.getPolicynumber()); System.out.println("Policy Code“ + ins.getPolicyData().getPolicyCode()); System.out.println("Policy Holder Name"+ ins.getPolicyData().getPolicyName()); } } 41
  42. 42. Setter Injection (code snippet) <beans> <bean id="Insurance" class=""> <property name="policynumber“ <value>2345</value></property> <property name="policyData"><ref local="Policy"/></property> </bean> <bean id="Policy" class=""> <property name="policyCode"><value>100</value></property> <property name="policyName"><value>Life Insurance</value></property> </bean> </beans> 42
  43. 43. Thank You 43