拦截器、执行-Struts2拦截器原理-by小雨

发一下牢骚和主题无关：

    

Struts2拦截器理原  

    

 

    拦截器是struts2处置的心核，本文主要说struts2的拦截器的基本理原/实现，其它框架处置的货色就不说了，得自己再看了。
struts2本版：2.2.3

    

    当一个求请来了后，从org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter 开始处置

    

public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {         HttpServletRequest request = (HttpServletRequest) req;         HttpServletResponse response = (HttpServletResponse) res;         try {             //设置码编             prepare.setEncodingAndLocale(request, response);             //建创actionContext             prepare.createActionContext(request, response);             prepare.assignDispatcherToThread();    //如果不是struts的求请则续继由其它过滤器执行             if ( excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) {                 chain.doFilter(request, response);             } else { //包装request，对有文件上传的特别处置下                 request = prepare.wrapRequest(request); //查找对应的ActionMapping                 ActionMapping mapping = prepare.findActionMapping(request, response, true); //如果找不到ActionMapping则作当静态资源来处置                 if (mapping == null) {                     boolean handled = execute.executeStaticResourceRequest(request, response);                     if (!handled) {                         chain.doFilter(request, response);                     }                 } else {    //应用ActionMapping来执行action                     execute.executeAction(request, response, mapping);                 }             }         } finally {             prepare.cleanupRequest(request);         }     }

   
踪跟execute.executeAction()，则到了 org.apache.struts2.dispatcher.Dispatcher，如下：

    

public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,                               ActionMapping mapping) throws ServletException {         Map<String, Object> extraContext = createContextMap(request, response, mapping, context);         // If there was a previous value stack, then create a new copy and pass it in to be used by the new Action         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();    //应用StrutsActionProxyFactory(ActionProxyFactory的一个实现 )建创action代理对象    //proxy实际上是org.apache.struts2.impl.StrutsActionProxy类型             ActionProxy proxy = config.getContainer().getInstance(ActionProxyFactory.class).createActionProxy(                     namespace, name, method, extraContext, true, false);             request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, proxy.getInvocation().getStack());             // if the ActionMapping says to go straight to a result, do it!             if (mapping.getResult() != null) {                 Result result = mapping.getResult();                 result.execute(proxy.getInvocation());             } else { //执行action                 proxy.execute();             }             // If there was a previous value stack then set it back onto the request             if (!nullStack) {                 request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack);             }         } catch (ConfigurationException e) {             // WW-2874 Only log error if in devMode             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 {                 LOG.warn("Could not find action or result", e);             }             sendError(request, response, context, HttpServletResponse.SC_NOT_FOUND, e);         } catch (Exception e) {             sendError(request, response, context, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);         } finally {             UtilTimerStack.pop(timerKey);         }     }

    
DefaultActionProxyFactory建创ActionProxy，在com.opensymphony.xwork2.DefaultActionProxyFactory：

    

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);     }

      

    接下来看看 

    org.apache.struts2.impl.StrutsActionProxy的execute()方法，如下：

    

public String execute() throws Exception {         ActionContext previous = ActionContext.getContext();         ActionContext.setContext(invocation.getInvocationContext());         try {        //这里就是调用拦截器的入口了             return invocation.invoke();         } finally {             if (cleanupContext)                 ActionContext.setContext(previous);         }     }

   
最关键的，com.opensymphony.xwork2.DefaultActionInvocation.invoke()方法，这个DefaultActionInvocation是ActionInvocation的一个实现类，如下：

    

//保存了执行当前action方法时需要调用的拦截器栈，按照struts.xml中配制的拦截器顺序，从前到后，依次加入到了这个Iterator里面   protected Iterator<InterceptorMapping> interceptors;    public String invoke() throws Exception {         String profileKey = "invoke: ";         try {             UtilTimerStack.push(profileKey);             if (executed) {                 throw new IllegalStateException("Action has already executed");             }             //如果当前还有下一个，则续继执行拦截器             if (interceptors.hasNext()) {                 final InterceptorMapping interceptor = (InterceptorMapping) interceptors.next();                 String interceptorMsg = "interceptor: " + interceptor.getName();                 UtilTimerStack.push(interceptorMsg);                 try {      //执行拦截器的intercept()方法，并将当前ActionInvocation对象传递给这个方法      //这样，当一个拦截器执行完自己的处置后，需要让框架续继执行下一个拦截器的时候，直接应用actionInvocation.invoke()方法，当前这个方法又会被调一次，这其实就是一个递归了，递归方法是ActionInvocation.invoke()，结束条件是interceptors.hasNext()                                 resultCode = interceptor.getInterceptor().intercept(DefaultActionInvocation.this);                             }                 finally {                     UtilTimerStack.pop(interceptorMsg);                 }             } else { //拦截器全部都执行了，那么最后来执行action，跳出递归了                 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 (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                 if (proxy.getExecuteResult()) {                     executeResult();                 }                 executed = true;             }             return resultCode;         }         finally {             UtilTimerStack.pop(profileKey);         }     }

   
基本理原到此为止，下面弄个小例子再说明一下：

    

//拦截器，相当于struts2的拦截器  public interface Interceptor {     String intercept(InvocationContext context); } //很多拦截器的实现 public class ExceptionInterceptor implements Interceptor {     public String intercept(InvocationContext context) {         // 对异常的处置         System.out.println("\t\t\tExceptionInterceptor 处置异常");         return context.invoke();     } } public class FileUploadInterceptor implements Interceptor {     public String intercept(InvocationContext context) {         // 处置文件上传相关         System.out.println("\t\t\tFileUploadInterceptor 处置文件上传");         return context.invoke();     } } public class ParameterInterceptor implements Interceptor {     public String intercept(InvocationContext context) {         // 处置求请的参数         System.out.println("\t\t\tParameterInterceptor 处置求请参数");         return context.invoke();     } } //执行拦截器的invocation上下文，相当于struts2的ActionInvocation public class InvocationContext {     // 这里存放当前执行当前action所需要执行的拦截器栈     private Iterator<Interceptor> interceptorIterator = null;     private String prefix = "";     public InvocationContext() {         // 模拟从配制文件中相应的规则取拦截器栈         ArrayList<Interceptor> list = new ArrayList<Interceptor>();         list.add(new ExceptionInterceptor());         list.add(new FileUploadInterceptor());         list.add(new ParameterInterceptor());         interceptorIterator = list.iterator();     }     public String invoke() {         // 是否还有拦截器需要执行         if (interceptorIterator.hasNext()) {             // 获取下一个需要执行的拦截器             Interceptor interceptor = interceptorIterator.next();             String name = interceptor.getClass().getName();             name = prefix + name;             System.out.println(name + " intercept start...");             prefix += "\t";             // Interceptor的所有intercept方法实现里面，最后都调用了InvocationContext.invoke()方法             // 其实就是一个递归，只不过invoke()的下一个递归是在Interceptor.intercept()里面调用的             // 所以说为什么Interceptor.intercept()方法要加个InvocationContext的参数呢，作用就在于此             String result = interceptor.intercept(this);             System.out.println(name + " intercept end...");             return result;         } else {// 所有的拦截器都执行完了，那就来执行action对应的方法             return executeAction();         }     }     private String executeAction() {         System.out.println(prefix + "executeAction success.");         return "success";     } } //模拟求请进行测试 public class Test {     public static void main(String[] args) {         InvocationContext context = new InvocationContext();         System.out.println("求请开始了...");         context.invoke();         System.out.println("求请处置完了...");     } } 输出结果：

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