ActionInvocation实现分析

ActionInvocation是ActionProxy中非常重要的变量。在产生ActionProxy之后，调用proxy.prepare()来产生ActionInvocation的实例。
从ActionInvocation类的说明中，我们可以看到ActionInvocation包括拦截器和Action的实例。
An ActionInvocation represents the execution state of an Action. It holds the Interceptors and the Action instance. By repeated re-entrant execution of the invoke() method, initially by the ActionProxy, then by the Interceptors, the Interceptors are all executed, and then the Action and the Result.
那么他们是怎么实现的呢？来分析DefaultActionInvocation
DefaultActionInvocation包括如下的域：

    protected Object action;//Object getAction()
    protected ActionProxy proxy;//ActionProxy getProxy()
    protected List preResultListeners;//void addPreResultListener(PreResultListener listener)
    protected Map extraContext;
    protected ActionContext invocationContext;
    protected Iterator interceptors;
    protected ValueStack stack;//ValueStack getStack();
    protected Result result;//Result getResult()
    protected String resultCode;//String getResultCode()
    protected boolean executed = false;//boolean isExecuted();
    protected boolean pushAction = true;
    protected ObjectFactory objectFactory;
    protected ActionEventListener actionEventListener;//void setActionEventListener(ActionEventListener listener)

    protected UnknownHandler unknownHandler;

不能从域中直接得到的接口方法是：

String invoke() throws Exception;
String invokeActionOnly() throws Exception;

在它的构造器中

/**
在构造器的参数列表中，只有proxy能比较明确知道它的含义。
*/
protected DefaultActionInvocation(final ObjectFactory objectFactory, final UnknownHandler handler, final ActionProxy proxy, final Map extraContext, final boolean pushAction, final ActionEventListener actionEventListener) throws Exception {
    	UtilTimerStack.profile("create DefaultActionInvocation: ", 
    			new UtilTimerStack.ProfilingBlock<Object>() {
					public Object doProfiling() throws Exception {
						DefaultActionInvocation.this.proxy = proxy;
                        DefaultActionInvocation.this.objectFactory = objectFactory;
				        DefaultActionInvocation.this.extraContext = extraContext;
				        DefaultActionInvocation.this.pushAction = pushAction;
                        DefaultActionInvocation.this.unknownHandler = handler;
                        DefaultActionInvocation.this.actionEventListener = actionEventListener;
                        init();
						return null;
					}
    			});
    }

再来看init()方法：

private void init() throws Exception {
        [//把extraContext放入contextMap，并把DefaultActionInvocation本身也放到contextMap中。还有对stack域的赋值。如果extraContext不存在ValueStack，则新产生一个。http://dl.iteye.com/upload/attachment/479236/fa9d2253-5ad4-3400-bb4f-b2a42cc91861.png
        Map contextMap = createContextMap();
        //主要是利用传递进来的objectFactory来产生Action实例。objectFactory.buildAction(proxy.getActionName(), proxy.getNamespace(), proxy.getConfig(), contextMap); 这个方法生成proxy.getConfig().getClassName()的实例，并把contextMap inject到其中。 inject的实现没看懂 http://dl.iteye.com/upload/attachment/479248/1ee39aa5-5898-3508-a818-5b4fac28fab2.png
        createAction(contextMap);
        //如果需要向stack中推入action实例，则推入。
        if (pushAction) {
            stack.push(action);
        }
        //ActionContext其实就是一map，核心就只有Map context;其它就是定义的编译时常量和一个管理各个线程的ActionContext的实例的静态ThreadLocal域。
        invocationContext = new ActionContext(contextMap);
        invocationContext.setName(proxy.getActionName());

        // get a new List so we don't get problems with the iterator if someone changes the list
        List interceptorList = new ArrayList(proxy.getConfig().getInterceptors());
        interceptors = interceptorList.iterator();
    }

再来看一个这个类的核心invoke()方法：

    public String invoke() throws Exception {
    	String profileKey = "invoke: ";
    	try {
    		UtilTimerStack.push(profileKey);
    		
    		if (executed) {
    			throw new IllegalStateException("Action has already executed");
    		}

    		if (interceptors.hasNext()) {
    			final InterceptorMapping interceptor = (InterceptorMapping) interceptors.next();
    			UtilTimerStack.profile("interceptor: "+interceptor.getName(), 
    					new UtilTimerStack.ProfilingBlock<String>() {
							public String doProfiling() throws Exception {
				    			resultCode = interceptor.getInterceptor().intercept(DefaultActionInvocation.this);
				    			return null;
							}
    			});
    		} else {
                        //在调用完所有Interceptor之后，调用此。即invokeAction(getAction(), proxy.getConfig());又即method.invoke(action,new Object[0]);
    			resultCode = invokeActionOnly();
    		}

    		// this is needed because the result will be executed, then control will return to the Interceptor, which will
    		// return above and flow through again
    		if (!executed) {
    			if (preResultListeners != null) {
    				for (Iterator iterator = preResultListeners.iterator();
    					iterator.hasNext();) {
    					PreResultListener listener = (PreResultListener) iterator.next();
    					
    					String _profileKey="preResultListener: ";
    					try {
    						UtilTimerStack.push(_profileKey);
    						listener.beforeResult(this, resultCode);
    					}
    					finally {
    						UtilTimerStack.pop(_profileKey);
    					}
    				}
    			}

    			// now execute the result, if we're supposed to
    			if (proxy.getExecuteResult()) {
    				executeResult();
    			}

    			executed = true;
    		}

    		return resultCode;
    	}
    	finally {
    		UtilTimerStack.pop(profileKey);
    	}
    }