Struts2源码阅读(五)_FilterDispatcher核心控制器

Dispatcher已经在之前讲过,这就好办了。FilterDispatcher是Struts2的核心控制器,首先看一下init()方法。

public void init(FilterConfig filterConfig) throws ServletException {     
    try {     
        this.filterConfig = filterConfig;     
        initLogging();     
     //创建dispatcher,前面都已经讲过啰     
        dispatcher = createDispatcher(filterConfig);     
        dispatcher.init();     
     //注入将FilterDispatcher中的变量通过container注入,如下面的staticResourceLoader     
        dispatcher.getContainer().inject(this);     
        //StaticContentLoader在BeanSelectionProvider中已经被注入了依赖关系:DefaultStaticContentLoader     
     //可以在struts-default.xml中的<bean>可以找到     
        staticResourceLoader.setHostConfig(new FilterHostConfig(filterConfig));     
    } finally {     
        ActionContext.setContext(null);     
    }     
}   

//下面来看DefaultStaticContentLoader的setHostConfig     
    public void setHostConfig(HostConfig filterConfig) {     
          //读取初始参数pakages,调用parse(),解析成类似/org/apache/struts2/static,/template的数组        
        String param = filterConfig.getInitParameter("packages");     
           //"org.apache.struts2.static template org.apache.struts2.interceptor.debugging static"     
        String packages = getAdditionalPackages();     
        if (param != null) {     
            packages = param + " " + packages;     
        }     
        this.pathPrefixes = parse(packages);     
        initLogging(filterConfig);     
    }       

现在回去doFilter的方法,每当有一个Request,都会调用这些Filters的doFilter方法

public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {     
    
    HttpServletRequest request = (HttpServletRequest) req;     
    HttpServletResponse response = (HttpServletResponse) res;     
    ServletContext servletContext = getServletContext();     
    
    String timerKey = "FilterDispatcher_doFilter: ";     
    try {     
    
        // FIXME: this should be refactored better to not duplicate work with the action invocation     
        //先看看ValueStackFactory所注入的实现类OgnlValueStackFactory     
     //new OgnlValueStack     
        ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack();     
        ActionContext ctx = new ActionContext(stack.getContext());     
        ActionContext.setContext(ctx);     
    
        UtilTimerStack.push(timerKey);     
    
 //如果是multipart/form-data就用MultiPartRequestWrapper进行包装     
//MultiPartRequestWrapper是StrutsRequestWrapper的子类,两者都是HttpServletRequest实现     
//此时在MultiPartRequestWrapper中就会把Files给解析出来,用于文件上传     
//所有request都会StrutsRequestWrapper进行包装,StrutsRequestWrapper是可以访问ValueStack     
//下面是参见Dispatcher的wrapRequest     
   // String content_type = request.getContentType();     
       //if(content_type!= null&&content_type.indexOf("multipart/form-data")!=-1){     
       //MultiPartRequest multi =getContainer().getInstance(MultiPartRequest.class);     
       //request =new MultiPartRequestWrapper(multi,request,getSaveDir(servletContext));     
       //} else {     
       //     request = new StrutsRequestWrapper(request);     
       // }     
         
        request = prepareDispatcherAndWrapRequest(request, response);     
        ActionMapping mapping;     
        try {     
         //根据url取得对应的Action的配置信息     
         //看一下注入的DefaultActionMapper的getMapping()方法.Action的配置信息存储在 ActionMapping对象中     
            mapping = actionMapper.getMapping(request, dispatcher.getConfigurationManager());     
        } catch (Exception ex) {     
            log.error("error getting ActionMapping", ex);     
            dispatcher.sendError(request, response, servletContext, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, ex);     
            return;     
        }     
    
     //如果找不到对应的action配置,则直接返回。比如你输入***.jsp等等                                      
     //这儿有个例外,就是如果path是以“/struts”开头,则到初始参数packages配置的包路径去查找对应的静态资源并输出到页面流中,当然.class文件除外。如果再没有则跳转到404       
        if (mapping == null) {     
            // there is no action in this request, should we look for a static resource?     
            String resourcePath = RequestUtils.getServletPath(request);     
    
            if ("".equals(resourcePath) && null != request.getPathInfo()) {     
                resourcePath = request.getPathInfo();     
            }     
    
            if (staticResourceLoader.canHandle(resourcePath)) {     
            // 在DefaultStaticContentLoader中:return serveStatic && (resourcePath.startsWith("/struts") || resourcePath.startsWith("/static"));     
                staticResourceLoader.findStaticResource(resourcePath, request, response);     
            } else {     
                // this is a normal request, let it pass through     
                chain.doFilter(request, response);     
            }     
            // The framework did its job here     
            return;     
        }     
        //正式开始Action的方法     
        dispatcher.serviceAction(request, response, servletContext, mapping);     
    
    } finally {     
        try {     
            ActionContextCleanUp.cleanUp(req);     
        } finally {     
            UtilTimerStack.pop(timerKey);     
        }     
    }     
}   


//下面是ActionMapper接口的实现类 DefaultActionMapper的getMapping()方法的源代码:     
    public ActionMapping getMapping(HttpServletRequest request,     
            ConfigurationManager configManager) {     
        ActionMapping mapping = new ActionMapping();     
        String uri = getUri(request);//得到请求路径的URI,如:testAtcion.action或testAction.do     
    
    
        int indexOfSemicolon = uri.indexOf(";");//修正url的带;jsessionid 时找不到而且的bug     
        uri = (indexOfSemicolon > -1) ? uri.substring(0, indexOfSemicolon) : uri;     
    
        uri = dropExtension(uri, mapping);//删除扩展名,默认扩展名为action     
        if (uri == null) {     
            return null;     
        }     
    
        parseNameAndNamespace(uri, mapping, configManager);//匹配Action的name和namespace     
    
        handleSpecialParameters(request, mapping);//去掉重复参数     
    
        //如果Action的name没有解析出来,直接返回     
    if (mapping.getName() == null) {     
      returnnull;     
    }     
     //下面处理形如testAction!method格式的请求路径     
    if (allowDynamicMethodCalls) {     
      // handle "name!method" convention.     
      String name = mapping.getName();     
      int exclamation = name.lastIndexOf("!");//!是Action名称和方法名的分隔符     
      if (exclamation != -1) {     
        mapping.setName(name.substring(0, exclamation));//提取左边为name     
        mapping.setMethod(name.substring(exclamation + 1));//提取右边的method     
      }     
    }     
    
        return mapping;     
    }   
从代码中看出,getMapping()方法返回ActionMapping类型的对象,该对象包含三个参数:Action的name、namespace和要调用的方法method。
  如果getMapping()方法返回ActionMapping对象为null,则FilterDispatcher认为用户请求不是Action,自然另当别论,FilterDispatcher会做一件非常有意思的事:如果请求以/struts开头,会自动查找在web.xml文件中配置的 packages初始化参数,就像下面这样:

<filter>    
       <filter-name>struts2</filter-name>    
       <filter-class>    
         org.apache.struts2.dispatcher.FilterDispatcher     
       </filter-class>    
       <init-param>    
         <param-name>packages</param-name>    
         <param-value>com.lizanhong.action</param-value>    
       </init-param>    
   </filter> 
FilterDispatcher会将com.lizanhong.action包下的文件当作静态资源处理,即直接在页面上显示文件内容,不过会忽略扩展名为class的文件。比如在com.lizanhong.action包下有一个aaa.txt的文本文件,其内容为“中华人民共和国”,访问  http://localhost:8081/Struts2Demo/struts/aaa.txt 时会输出txt中的内容
   FilterDispatcher.findStaticResource()方法

protected void findStaticResource(String name, HttpServletRequest request, HttpServletResponse response) throws IOException {     
    if (!name.endsWith(".class")) {//忽略class文件     
      //遍历packages参数     
      for (String pathPrefix : pathPrefixes) {     
        InputStream is = findInputStream(name, pathPrefix);//读取请求文件流     
        if (is != null) {     
          ...     
          // set the content-type header     
          String contentType = getContentType(name);//读取内容类型     
          if (contentType != null) {     
            response.setContentType(contentType);//重新设置内容类型     
          }     
         ...     
          try {     
           //将读取到的文件流以每次复制4096个字节的方式循环输出     
            copy(is, response.getOutputStream());     
          } finally {     
            is.close();     
          }     
          return;     
        }     
      }     
    }     
  }    
如果用户请求的资源不是以/struts开头——可能是.jsp文件,也可能是.html文件,则通过过滤器链继续往下传送,直到到达请求的资源为止。
如果getMapping()方法返回有效的ActionMapping对象,则被认为正在请求某个Action,将调用 Dispatcher.serviceAction(request, response, servletContext, mapping)方法,该方法是处理Action的关键所在。
下面就来看serviceAction,这又回到全局变量dispatcher中了
//Load Action class for mapping and invoke the appropriate Action method, or go directly to the Result.     
public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,     
                              ActionMapping mapping) throws ServletException {     
        //createContextMap方法主要把Application、Session、Request的key value值拷贝到Map中     
        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();     
            //创建一个Action的代理对象,ActionProxyFactory是创建ActionProxy的工厂     
            //参考实现类:DefaultActionProxy和DefaultActionProxyFactory     
            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!     
            //如果是Result,则直接转向,关于Result,ActionProxy,ActionInvocation下一讲中再分析     
            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) {     
                LOG.error("Could not find action or result", 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);     
        }     
    }    

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