问题提出:
1、Struts2框架在什么时候将Action对象放到了值栈ValueStack的栈顶了?2、在哪里设置Debug断点能够最恰当的观察到这一过程?
问题解决:
2、我们知道,在值栈ValueStack中有两个逻辑部分Map栈和对象栈ObjectStack,而Action对象是被默认放在了对象栈的栈顶的(这一点我们通过<s:debug/>标签可以在页面中看到),因此我们将该断点设置在对象栈所对应的类CompoundRoot的push方法中最合适。
1、通过Debug过程来分析值栈ValueStack的变化过程:
1)当我们在CompoundRoot类的push方法中打上断点后,程序执行到此处,如下图:
2)这时,我们从Struts2框架的入口StrutsPrepareAndExecuteFilter类开始分析。在Debug视图中,我们将程序定位到StrutsPrepareAndExecuteFilter类,如下图:
附上StrutsPrepareAndExecuteFilter中doFilter()方法的源代码:
- public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
-
- HttpServletRequest request = (HttpServletRequest) req;
- HttpServletResponse response = (HttpServletResponse) res;
-
- try {
- prepare.setEncodingAndLocale(request, response);
- prepare.createActionContext(request, response);
- prepare.assignDispatcherToThread();
- if (excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) {
- chain.doFilter(request, response);
- } else {
- request = prepare.wrapRequest(request);
- ActionMapping mapping = prepare.findActionMapping(request, response, true);
- if (mapping == null) {
- boolean handled = execute.executeStaticResourceRequest(request, response);
- if (!handled) {
- chain.doFilter(request, response);
- }
- } else {
- execute.executeAction(request, response, mapping);
- }
- }
- } finally {
- prepare.cleanupRequest(request);
- }
- }
这里我们可以看到,doFilter()方法中通过调用execute对象的executeAction()方法来执行Action,接下来我们继续看一看executeAction()方法,如下图:
可以看出executeAction()方法中只是调用了dispatcher对象的serviceAction()方法,因此,我们再继续查看serviceAction()方法,如下图:
可以看到,在serviceAction()方法中实际上是创建了一个Action的代理类ActionProxy的对象,而并没有直接去执行Action。这是因为在执行Action之前Struts2还要去调用许多的拦截器,因此创建了Action的代理类。
附Dispatcher类中serviceAction()方法的源代码:
- public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,
- ActionMapping mapping) throws ServletException {
-
- Map<String, Object> extraContext = createContextMap(request, response, mapping, context);
-
-
- ValueStack stack = (ValueStack) request.getAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY);
- boolean nullStack = stack == null;
- if (nullStack) {
- ActionContext ctx = ActionContext.getContext();
- if (ctx != null) {
- stack = ctx.getValueStack();
- }
- }
- if (stack != null) {
- extraContext.put(ActionContext.VALUE_STACK, valueStackFactory.createValueStack(stack));
- }
-
- String timerKey = "Handling request from Dispatcher";
- try {
- UtilTimerStack.push(timerKey);
- String namespace = mapping.getNamespace();
- String name = mapping.getName();
- String method = mapping.getMethod();
-
- Configuration config = configurationManager.getConfiguration();
- ActionProxy proxy = config.getContainer().getInstance(ActionProxyFactory.class).createActionProxy(
- namespace, name, method, extraContext, true, false);
-
- request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, proxy.getInvocation().getStack());
-
-
- if (mapping.getResult() != null) {
- Result result = mapping.getResult();
- result.execute(proxy.getInvocation());
- } else {
- proxy.execute();
- }
-
-
- if (!nullStack) {
- request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack);
- }
- } catch (ConfigurationException e) {
-
- if (devMode) {
- String reqStr = request.getRequestURI();
- if (request.getQueryString() != null) {
- reqStr = reqStr + "?" + request.getQueryString();
- }
- LOG.error("Could not find action or result\n" + reqStr, e);
- } else {
- if (LOG.isWarnEnabled()) {
- LOG.warn("Could not find action or result", e);
- }
- }
- sendError(request, response, context, HttpServletResponse.SC_NOT_FOUND, e);
- } catch (Exception e) {
- if (handleException || devMode) {
- sendError(request, response, context, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);
- } else {
- throw new ServletException(e);
- }
- } finally {
- UtilTimerStack.pop(timerKey);
- }
- }
继续往下进行,如下图:
我们可以看到在上面的执行过程中,主要工作都是在创建Action的代理类对象proxy,在创建完成之后,该代理类对象proxy调用prepare()方法做了一些初始化的工作。
继续往下查看prepare()方法:
在prepare()方法(这是StrutsActionProxy的父类DefaultActionProxy的prepare()方法)中可以看到,其执行了invocation对象的init()方法,在该方法中this就是StrutsActionProxy类的对象,也即ActionProxy类的对象,就是Action的代理类。继续来看init()方法的具体实现:
到这里我们已经能够比较清楚的看到了Struts2框架将Action对象放到值栈中。注意,这里的Action对象中的相关属性(如提交的表单中的参数)并没有被赋上值,直到真正的执行Action对象中相应的方法时,其相关属性才被赋值。
附DefaultActionInvocation类中init()方法与createAction()方法的源代码:
- public void <span style="background-color: rgb(255, 0, 0);">init</span>(ActionProxy proxy) {
- this.proxy = proxy;
- Map<String, Object> contextMap = createContextMap();
-
-
-
- ActionContext actionContext = ActionContext.getContext();
-
- if (actionContext != null) {
- actionContext.setActionInvocation(this);
- }
-
- <span style="background-color: rgb(51, 255, 51);">createAction(contextMap);</span>
-
- if (pushAction) {
- <span style="background-color: rgb(51, 255, 51);">stack.push(action);</span>
- <span style="background-color: rgb(51, 255, 51);">contextMap.put("action", action);</span>
- }
-
- invocationContext = new ActionContext(contextMap);
- invocationContext.setName(proxy.getActionName());
-
-
- List<InterceptorMapping> interceptorList = new ArrayList<InterceptorMapping>(proxy.getConfig().getInterceptors());
- interceptors = interceptorList.iterator();
- }
- protected void <span style="background-color: rgb(255, 0, 0);">createAction</span>(Map<String, Object> contextMap) {
-
- String timerKey = "actionCreate: " + proxy.getActionName();
- try {
- UtilTimerStack.push(timerKey);
- <span style="background-color: rgb(51, 255, 51);">action = objectFactory.buildAction(proxy.getActionName(), proxy.getNamespace(), proxy.getConfig(), contextMap);</span>
- } 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) {
- String gripe;
-
- if (proxy == null) {
- gripe = "Whoa! No ActionProxy instance found in current ActionInvocation. This is bad ... very bad";
- } else if (proxy.getConfig() == null) {
- gripe = "Sheesh. Where'd that ActionProxy get to? I can't find it in the current ActionInvocation!?";
- } else if (proxy.getConfig().getClassName() == null) {
- gripe = "No Action defined for '" + proxy.getActionName() + "' in namespace '" + proxy.getNamespace() + "'";
- } else {
- gripe = "Unable to instantiate Action, " + proxy.getConfig().getClassName() + ", defined for '" + proxy.getActionName() + "' in namespace '" + proxy.getNamespace() + "'";
- }
-
- gripe += (((" -- " + e.getMessage()) != null) ? e.getMessage() : " [no message in exception]");
- throw new XWorkException(gripe, e, proxy.getConfig());
- } finally {
- UtilTimerStack.pop(timerKey);
- }
-
- if (actionEventListener != null) {
- <span style="background-color: rgb(51, 255, 51);">action = actionEventListener.prepare(action, stack);</span>
- }
- }
查看值栈OgnlValueStack类的push()方法,如下图:可以看到,它确实是调用了CompoundRoot对象的push()方法将Action对象放到了值栈中对象栈ObjectStack的栈顶。
收获:
1、分析问题的方法;
2、通过该过程清楚了Struts2值栈的变化过程;
2、进一步学习了Eclipse的debug使用方法。