【Struts2源码】@Inject查找并缓存注入器

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注解@Inject的操作类是ContainerImpl，@Inject在Struts中用到了很多，主要用来构造函数、属性、方法及方法参数注入，当调用ContainerImpl的Inject方法时，这些部分就启动，ContainerImpl初始化时，缓存这些构建方法

这里我们只分析查找这些带@Inject的注入器，并把它们缓存起来。

1.初始化一个注入器Map，用来放置找到@Inject后实例化的注入器，这里使用ReferenceCache缓存类，在运行期构建map，核心方法create会调用addInjectors方法扫描所有注入器加入到ReferenceCache缓存Map里面，并且内部实现ThreadLocal模式规避多线程问题，

	/*** Field and method injectors.*/final Map<Class<?>, List<Injector>> injectors =new ReferenceCache<Class<?>, List<Injector>>() {@Overrideprotected List<Injector> create( Class<?> key ) {List<Injector> injectors = new ArrayList<Injector>();addInjectors(key, injectors);return injectors;}};

2.addInjectors()方法

	void addInjectors( Class clazz, List<Injector> injectors ) {if (clazz == Object.class) {return;}// Add injectors for superclass first.addInjectors(clazz.getSuperclass(), injectors);// TODO (crazybob): Filter out overridden members.addInjectorsForFields(clazz.getDeclaredFields(), false, injectors);addInjectorsForMethods(clazz.getDeclaredMethods(), false, injectors);}

	void addInjectorsForMethods( Method[] methods, boolean statics,List<Injector> injectors ) {addInjectorsForMembers(Arrays.asList(methods), statics, injectors,new InjectorFactory<Method>() {public Injector create( ContainerImpl container, Method method,String name ) throws MissingDependencyException {return new MethodInjector(container, method, name);}});}void addInjectorsForFields( Field[] fields, boolean statics,List<Injector> injectors ) {addInjectorsForMembers(Arrays.asList(fields), statics, injectors,new InjectorFactory<Field>() {public Injector create( ContainerImpl container, Field field,String name ) throws MissingDependencyException {return new FieldInjector(container, field, name);}});}

3. 找到有注解@Inject的成员，调用传入的injectorFactory.create方法创建真正的Injector实例 加入到注入器集合中

	<M extends Member & AnnotatedElement> void addInjectorsForMembers(List<M> members, boolean statics, List<Injector> injectors,InjectorFactory<M> injectorFactory ) {for ( M member : members ) {if (isStatic(member) == statics) {Inject inject = member.getAnnotation(Inject.class);if (inject != null) {try {injectors.add(injectorFactory.create(this, member, inject.value()));} catch ( MissingDependencyException e ) {if (inject.required()) {throw new DependencyException(e);}}}}}}

这样就可以无差别的在构造函数、属性、方法及方法参数处使用@Inject注解了

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