Struts2源码阅读(六)_ActionProxy&ActionInvocation

下面开始讲一下主菜ActionProxy了.在这之前最好先去了解一下动态Proxy的基本知识.

ActionProxy是Action的一个代理类，也就是说Action的调用是通过ActionProxy实现的，其实就是调用了ActionProxy.execute()方法，而该方法又调用了ActionInvocation.invoke()方法。归根到底，最后调用的是DefaultActionInvocation.invokeAction()方法。

DefaultActionInvocation()->init()->createAction()。

最后通过调用ActionProxy.exute()-->ActionInvocation.invoke()-->Intercepter.intercept()-->ActionInvocation.invokeActionOnly()-->invokeAction()

这里的步骤是先由ActionProxyFactory创建ActionInvocation和ActionProxy.

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public ActionProxy createActionProxy(String namespace, String actionName, String methodName, Map<String, Object> extraContext, boolean executeResult, boolean cleanupContext) {

ActionInvocation inv = new DefaultActionInvocation(extraContext, true);

container.inject(inv);

return createActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext);

}

下面先看DefaultActionInvocation的init方法

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public void init(ActionProxy proxy) {

this.proxy = proxy;

Map<String, Object> contextMap = createContextMap();

// Setting this so that other classes, like object factories, can use the ActionProxy and other

// contextual information to operate

ActionContext actionContext = ActionContext.getContext();

if (actionContext != null) {

actionContext.setActionInvocation(this);

}

//创建Action,struts2中每一个Request都会创建一个新的Action

createAction(contextMap);

if (pushAction) {

stack.push(action);

contextMap.put("action", action);

}

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<InterceptorMapping> interceptorList = new ArrayList<InterceptorMapping>(proxy.getConfig().getInterceptors());

interceptors = interceptorList.iterator();

}

protected void createAction(Map<String, Object> contextMap) {

// load action

String timerKey = "actionCreate: " + proxy.getActionName();

try {

UtilTimerStack.push(timerKey);

//默认为SpringObjectFactory:struts.objectFactory=spring.这里非常巧妙,在struts.properties中可以重写这个属性

//在前面BeanSelectionProvider中通过配置文件为ObjectFactory设置实现类

//这里以Spring为例,这里会调到SpringObjectFactory的buildBean方法,可以通过ApplicationContext的getBean()方法得到Spring的Bean

action = objectFactory.buildAction(proxy.getActionName(), proxy.getNamespace(), proxy.getConfig(), contextMap);

} catch (InstantiationException e) {

throw new XWorkException("Unable to intantiate Action!", e, proxy.getConfig());

} catch (IllegalAccessException e) {

throw new XWorkException("Illegal access to constructor, is it public?", e, proxy.getConfig());

} catch (Exception e) {

...

} finally {

UtilTimerStack.pop(timerKey);

}

if (actionEventListener != null) {

action = actionEventListener.prepare(action, stack);

}

}

//SpringObjectFactory

public Object buildBean(String beanName, Map<String, Object> extraContext, boolean injectInternal) throws Exception {

Object o = null;

try {

//SpringObjectFactory会通过web.xml中的context-param:contextConfigLocation自动注入ClassPathXmlApplicationContext

o = appContext.getBean(beanName);

} catch (NoSuchBeanDefinitionException e) {

Class beanClazz = getClassInstance(beanName);

o = buildBean(beanClazz, extraContext);

}

if (injectInternal) {

injectInternalBeans(o);

}

return o;

}

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//接下来看看DefaultActionInvocation 的invoke方法

public String invoke() throws Exception {

String profileKey = "invoke: ";

try {

UtilTimerStack.push(profileKey);

if (executed) {

throw new IllegalStateException("Action has already executed");

}

//递归执行interceptor

if (interceptors.hasNext()) {

//interceptors是InterceptorMapping实际上是像一个像FilterChain一样的Interceptor链

//通过调用Invocation.invoke()实现递归牡循环

final InterceptorMapping interceptor = (InterceptorMapping) interceptors.next();

String interceptorMsg = "interceptor: " + interceptor.getName();

UtilTimerStack.push(interceptorMsg);

try {

//在每个Interceptor的方法中都会return invocation.invoke()

resultCode = interceptor.getInterceptor().intercept(DefaultActionInvocation.this);

}

finally {

UtilTimerStack.pop(interceptorMsg);

}

} else {

//当所有interceptor都执行完,最后执行Action,invokeActionOnly会调用invokeAction()方法

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

//在Result返回之前调用preResultListeners

//通过executed控制,只执行一次

if (!executed) {

if (preResultListeners != null) {

for (Object preResultListener : preResultListeners) {

PreResultListener listener = (PreResultListener) preResultListener;

String _profileKey = "preResultListener: ";

try {

UtilTimerStack.push(_profileKey);

listener.beforeResult(this, resultCode);

}

finally {

UtilTimerStack.pop(_profileKey);

}

}

}

// now execute the result, if we're supposed to

//执行Result

if (proxy.getExecuteResult()) {

executeResult();

}

executed = true;

}

return resultCode;

}

finally {

UtilTimerStack.pop(profileKey);

}

}

//invokeAction

protected String invokeAction(Object action,ActionConfig actionConfig)throws Exception{

String methodName = proxy.getMethod();

String timerKey = "invokeAction: " + proxy.getActionName();

try {

UtilTimerStack.push(timerKey);

boolean methodCalled = false;

Object methodResult = null;

Method method = null;

try {

//java反射机制得到要执行的方法

method = getAction().getClass().getMethod(methodName, new Class[0]);

} catch (NoSuchMethodException e) {

// hmm -- OK, try doXxx instead

//如果没有对应的方法，则使用do+Xxxx来再次获得方法

try {

String altMethodName = "do" + methodName.substring(0, 1).toUpperCase() + methodName.substring(1);

method = getAction().getClass().getMethod(altMethodName, new Class[0]);

} catch (NoSuchMethodException e1) {

// well, give the unknown handler a shot

if (unknownHandlerManager.hasUnknownHandlers()) {

try {

methodResult = unknownHandlerManager.handleUnknownMethod(action, methodName);

methodCalled = true;

} catch (NoSuchMethodException e2) {

// throw the original one

throw e;

}

} else {

throw e;

}

}

}

//执行Method

if (!methodCalled) {

methodResult = method.invoke(action, new Object[0]);

}

//从这里可以看出可以Action的方法可以返回String去匹配Result,也可以直接返回Result类

if (methodResult instanceof Result) {

this.explicitResult = (Result) methodResult;

// Wire the result automatically

container.inject(explicitResult);

return null;

} else {

return (String) methodResult;

}

} catch (NoSuchMethodException e) {

throw new IllegalArgumentException("The " + methodName + "() is not defined in action " + getAction().getClass() + "");

} catch (InvocationTargetException e) {

// We try to return the source exception.

Throwable t = e.getTargetException();

if (actionEventListener != null) {

String result = actionEventListener.handleException(t, getStack());

if (result != null) {

return result;

}

}

if (t instanceof Exception) {

throw (Exception) t;

} else {

throw e;

}

} finally {

UtilTimerStack.pop(timerKey);

}

}

action执行完了，还要根据ResultConfig返回到view，也就是在invoke方法中调用executeResult方法。

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private void executeResult() throws Exception {

//根据ResultConfig创建Result

result = createResult();

String timerKey = "executeResult: " + getResultCode();

try {

UtilTimerStack.push(timerKey);

if (result != null) {

//开始执行Result,

//可以参考Result的实现，如用了比较多的ServletDispatcherResult,ServletActionRedirectResult,ServletRedirectResult

result.execute(this);

} else if (resultCode != null && !Action.NONE.equals(resultCode)) {

throw new ConfigurationException("No result defined for action " + getAction().getClass().getName()

+ " and result " + getResultCode(), proxy.getConfig());

} else {

if (LOG.isDebugEnabled()) {

LOG.debug("No result returned for action " + getAction().getClass().getName() + " at " + proxy.getConfig().getLocation());

}

}

} finally {

UtilTimerStack.pop(timerKey);

}

}

public Result createResult() throws Exception {

//如果Action中直接返回的Result类型,在invokeAction()保存在explicitResult

if (explicitResult != null) {

Result ret = explicitResult;

explicitResult = null;

return ret;

}

//返回的是String则从config中得到当前Action的Results列表

ActionConfig config = proxy.getConfig();

Map<String, ResultConfig> results = config.getResults();

ResultConfig resultConfig = null;

synchronized (config) {

try {

//通过返回的String来匹配resultConfig

resultConfig = results.get(resultCode);

} catch (NullPointerException e) {

// swallow

}

if (resultConfig == null) {

// If no result is found for the given resultCode, try to get a wildcard '*' match.

//如果找不到对应name的ResultConfig，则使用name为*的Result

//说明可以用*通配所有的Result

resultConfig = results.get("*");

}

}

if (resultConfig != null) {

try {

//创建Result

return objectFactory.buildResult(resultConfig, invocationContext.getContextMap());

} catch (Exception e) {

LOG.error("There was an exception while instantiating the result of type " + resultConfig.getClassName(), e);

throw new XWorkException(e, resultConfig);

}

} else if (resultCode != null && !Action.NONE.equals(resultCode) && unknownHandlerManager.hasUnknownHandlers()) {

return unknownHandlerManager.handleUnknownResult(invocationContext, proxy.getActionName(), proxy.getConfig(), resultCode);

}

return null;

}

public Result buildResult(ResultConfig resultConfig, Map<String, Object> extraContext) throws Exception {

String resultClassName = resultConfig.getClassName();

Result result = null;

if (resultClassName != null) {

//buildBean中会用反射机制Class.newInstance来创建bean

result = (Result) buildBean(resultClassName, extraContext);

Map<String, String> params = resultConfig.getParams();

if (params != null) {

for (Map.Entry<String, String> paramEntry : params.entrySet()) {

try {

//reflectionProvider参见OgnlReflectionProvider；

//resultConfig.getParams()就是result配置文件里所配置的参数<param></param>

//setProperties方法最终调用的是Ognl类的setValue方法

//这句其实就是把param名值设置到根对象result上

reflectionProvider.setProperty(paramEntry.getKey(), paramEntry.getValue(), result, extraContext, true);

} catch (ReflectionException ex) {

if (LOG.isErrorEnabled())

LOG.error("Unable to set parameter [#0] in result of type [#1]", ex,

paramEntry.getKey(), resultConfig.getClassName());

if (result instanceof ReflectionExceptionHandler) {

((ReflectionExceptionHandler) result).handle(ex);

}

}

}

}

}

return result;

}

最后看一张在网上看到的一个调用流程图作为参考：