Guice is a dependency injection framework that helps solve problems like difficult code reuse and unclear class boundaries. It promotes modularity by separating implementation from interfaces and decoupling concrete classes. Guice uses dependency injection principles to allow reusable code and problem-specific code to develop independently. The framework constructs a graph of dependencies and uses binding resolution to instantiate objects through injection into constructors, methods or fields based on defined modules.

1. Guice in Athena
2014/11/28 datayes.com

2. • Request/Response Flow
• Init
• Guice
– Motivation? 解决什么问题
– 如何使用
– 原理和机制(Inside)

3. request/response flow
AthenaSer
vlet
doGet(res, resp)
Server
handle

4. request/response flow
GuiceFilter LogFilter JsonpFilter
GuiceCont
ainer
HttpServlet(servlet)
ServletContainer (Jersey)
NewsReso
urce
service(res, resp)
doFilter(res, resp)
doFilter(res, resp)
doFilter(res, resp)
Server
handle
dispatch

5. Request/Response Stack

6. No new instance
Jersey
Guice new NewsResource
new NewsMapper

7. Init
Server GuiceServletCo
doStart
ntextListener
contextInitialized
getInjector
Guice
createInjector
ServletContextListener(servlet)
InternalInjector
Creator
build
ConstructorInje
ctor
construct
MembersInject
or
NewsResource()
loadEagerSingletons
NewsReso
urce
memberInject
construct

8. Init

9. Guice : Motivation
• 我们遇到的问题
– Reused code seems hard
– Class and Package boundary/layer is vague/fuzzy

10. Guice : Motivation
• Why Guice?
Elasticsearch heavily build on Guice
InternalNode.java

11. Guice : Motivation
• dependency injection framework
• Easier to
– change
– unit test
– reuse in other contexts
• Modularity

12. Guice : Modularity
• Modularity
– Elasticsearch

13. Guice : Modularity
• Modularity
– Elasticsearch

14. Guice : Modularity

15. Guice : Modularity

16. Guice : principle (目的)
• Separate implementation from interface
• Decouple concrete from concrete
• IOC principle
– reusable code and the problem-specific code are developed
independently
• Dependency Inversion principle
– High-level modules should not depend on low-level
modules. Both should depend on abstractions.
– Abstractions should not depend on details. Details should
depend on abstractions.

17. Guice : DI (手段)
1
3
2
4
DI : client
service/service impl
injector

18. Guice : 如何使用
• 1) Inject
– Constructor
– Method
– Field
Athena 中主要是Field，如果构造函数中使用依赖，则到则使用Constructor

19. Guice : 如何使用
• 2) Binding
– Linked Bindings
• bindings map a type to its implementation
– Untargeted Bindings
• concrete classes and types annotated by either
@ImplementedBy or @ProvidedBy
– Binding Annotations

20. Guice : 如何使用
• 3) Module
– A module is a collection of bindings
– Install other modules
代码模块化
M
install
M1 M2 M3
type1
type2
bind
type3

21. Guice : 如何使用
• 4) Injector
– 传入一个/多个Module
Athena -> GuiceServletConfig

22. Guice : other
• Scopes
– @singleton
– @ RequestScoped
– @ SessionScoped
• AOP
– MethodInterceptor

23. Guice : Inside
• Injector
– Graph construction
– Binding Resolution
– ClassLoader
• AOP
– Reflection vs. codegen

24. Reference
• https://www.youtube.com/watch?v=hBVJbzAa
gfs
• http://www.infoq.com/presentations/Dagger