Tomcat请求处理流程

Tomcat+Struts1.x默认的ReqeustProcessor的请求处理流程

Tomcat+Struts+Spring2.5.x提供的DelegatingRequestProcessor的请求处理流程

Struts1.x默认的RequestProcessor得到Action的方法：processActionCreate

processActionCreate(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping)：

/**
* <p>Return an <code>Action</code> instance that will be used to process
* the current request, creating a new one if necessary.</p>
*
* @param request  The servlet request we are processing
* @param response The servlet response we are creating
* @param mapping  The mapping we are using
* @return An <code>Action</code> instance that will be used to process
*         the current request.
* @throws IOException if an input/output error occurs
*/
protected Action processActionCreate(HttpServletRequest request,
HttpServletResponse response, ActionMapping mapping)
throws IOException {
// Acquire the Action instance we will be using (if there is one)
String className = mapping.getType();

if (log.isDebugEnabled()) {
log.debug(" Looking for Action instance for class " + className);
}

// If there were a mapping property indicating whether
// an Action were a singleton or not ([true]),
// could we just instantiate and return a new instance here?
Action instance;

synchronized (actions) {
// Return any existing Action instance of this class
instance = (Action) actions.get(className);

if (instance != null) {
if (log.isTraceEnabled()) {
log.trace("  Returning existing Action instance");
}

return (instance);
}

// Create and return a new Action instance
if (log.isTraceEnabled()) {
log.trace("  Creating new Action instance");
}

try {
instance = (Action) RequestUtils.applicationInstance(className);

// Maybe we should propagate this exception
// instead of returning null.
} catch (Exception e) {
log.error(getInternal().getMessage("actionCreate",
mapping.getPath()), e);

response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
getInternal().getMessage("actionCreate", mapping.getPath()));

return (null);
}

actions.put(className, instance);
}

if (instance.getServlet() == null) {
instance.setServlet(this.servlet);
}

return (instance);
}

Spring的DelegatingRequestProcessor得到Action的方法：

processActionCreate(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping)：

/**
* Override the base class method to return the delegate action.
* @see #getDelegateAction
*/
protected Action processActionCreate(
HttpServletRequest request, HttpServletResponse response, ActionMapping mapping)
throws IOException {
//先试图从Sping的Action容器中获取对应的Action，如果没有找到，再调用Strut提供的RequestProcessor的processActionCreate方法得到对应的Action。
Action action = getDelegateAction(mapping);
if (action != null) {
return action;
}//如果没有找到，再调用Strut提供的RequestProcessor的processActionCreate方法得到对应的Action。
return super.processActionCreate(request, response, mapping);
}

/**
* Return the delegate <code>Action</code> for the given mapping.
* <p>The default implementation determines a bean name from the
* given <code>ActionMapping</code> and looks up the corresponding
* bean in the <code>WebApplicationContext</code>.
* @param mapping the Struts <code>ActionMapping</code>
* @return the delegate <code>Action</code>, or <code>null</code> if none found
* @throws BeansException if thrown by <code>WebApplicationContext</code> methods
* @see #determineActionBeanName
*/
protected Action getDelegateAction(ActionMapping mapping) throws BeansException {
String beanName = determineActionBeanName(mapping);
if (!getWebApplicationContext().containsBean(beanName)) {
return null;
}
return (Action) getWebApplicationContext().getBean(beanName, Action.class);
}