【Struts2源码】@Inject查找并缓存注入器

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>>() {
				@Override
				protected 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