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()
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.
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
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;
}
//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。
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：
