.NET與java的MVC模式:struts2核心工作流程與原理

iDotNetSpace發表於2009-01-05
做為一名技術人員,聽到太多關於.net和java的比較的話題。我想對那些技術人員說,請先了解一下什麼是java(或者.net)吧,其實你根本不瞭解。

  這是Struts2官方站點提供的Struts 2 的整體結構。

  一個請求在Struts2框架中的處理大概分為以下幾個步驟:

  1. 客戶端提起一個(HttpServletRequest)請求,如上文在瀏覽器中輸入”http://localhost:8080/TestMvc/add.action”就是提起一個(HttpServletRequest)請求。
  2. 請求被提交到一系列(主要是三層)的過濾器(Filter),如(ActionContextCleanUp、其他過濾器(SiteMesh等)、 FilterDispatcher)。注意這裡是有順序的,先ActionContextCleanUp,再其他過濾器(SiteMesh等)、最後到FilterDispatcher。
  3. FilterDispatcher是控制器的核心,就是mvc中c控制層的核心。下面粗略的分析下我理解的FilterDispatcher工作流程和原理:FilterDispatcher進行初始化並啟用核心doFilter

    其程式碼如下:

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException ...{
            HttpServletRequest request = (HttpServletRequest) req;
            HttpServletResponse response = (HttpServletResponse) res;
            ServletContext servletContext = filterConfig.getServletContext();
            // 在這裡處理了HttpServletRequest和HttpServletResponse。
            DispatcherUtils du = DispatcherUtils.getInstance();
            du.prepare(request, response);//正如這個方法名字一樣進行locale、encoding以及特殊request parameters設定
            try ...{
                request = du.wrapRequest(request, servletContext);//對request進行包裝
            } catch (IOException e) ...{
                String message = "Could not wrap servlet request with MultipartRequestWrapper!";
                LOG.error(message, e);
                throw new ServletException(message, e);
            }
                    ActionMapperIF mapper = ActionMapperFactory.getMapper();//得到action的mapper
            ActionMapping mapping = mapper.getMapping(request);// 得到action 的 mapping
            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 ("true".equals(Configuration.get(WebWorkConstants.WEBWORK_SERVE_STATIC_CONTENT))
                        && resourcePath.startsWith("/webwork")) ...{
                    String name = resourcePath.substring("/webwork".length());
                    findStaticResource(name, response);
                } else ...{
                    // this is a normal request, let it pass through
                    chain.doFilter(request, response);
                }
                // WW did its job here
                return;
            }
            Object o = null;
            try ...{
                //setupContainer(request);
                o = beforeActionInvocation(request, servletContext);
    //整個框架最最核心的方法,下面分析
                du.serviceAction(request, response, servletContext, mapping);
            } finally ...{
                afterActionInvocation(request, servletContext, o);
                ActionContext.setContext(null);
            }
        }
    du.serviceAction(request, response, servletContext, mapping);
    //這個方法詢問ActionMapper是否需要呼叫某個Action來處理這個(request)請求,如果ActionMapper決定需要呼叫某個Action,FilterDispatcher把請求的處理交給ActionProxy

    public void serviceAction(HttpServletRequest request, HttpServletResponse response, String namespace, String actionName, Map requestMap, Map parameterMap, Map sessionMap, Map applicationMap) ...{
            HashMap extraContext = createContextMap(requestMap, parameterMap, sessionMap, applicationMap, request, response, getServletConfig());  //例項化Map請求 ,詢問ActionMapper是否需要呼叫某個Action來處理這個(request)請求
            extraContext.put(SERVLET_DISPATCHER, this);
            OgnlValueStack stack = (OgnlValueStack) request.getAttribute(ServletActionContext.WEBWORK_VALUESTACK_KEY);
            if (stack != null) ...{
                extraContext.put(ActionContext.VALUE_STACK,new OgnlValueStack(stack));
            }
            try ...{
                ActionProxy proxy = ActionProxyFactory.getFactory().createActionProxy(namespace, actionName, extraContext);
    //這裡actionName是通過兩道getActionName解析出來的, FilterDispatcher把請求的處理交給ActionProxy,下面是ServletDispatcher的 TODO:
                request.setAttribute(ServletActionContext.WEBWORK_VALUESTACK_KEY, proxy.getInvocation().getStack());
                proxy.execute();
             //通過代理模式執行ActionProxy
                if (stack != null)...{
                    request.setAttribute(ServletActionContext.WEBWORK_VALUESTACK_KEY,stack);
                }
            } catch (ConfigurationException e) ...{
                log.error("Could not find action", e);
                sendError(request, response, HttpServletResponse.SC_NOT_FOUND, e);
            } catch (Exception e) ...{
                log.error("Could not execute action", e);
                sendError(request, response, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);
            }
    }
  4. FilterDispatcher詢問ActionMapper是否需要呼叫某個Action來處理這個(request)請求,如果ActionMapper決定需要呼叫某個Action,FilterDispatcher把請求的處理交給ActionProxy。
  5. ActionProxy通過Configuration Manager(struts.xml)詢問框架的配置檔案,找到需要呼叫的Action類.
    如上文的struts.xml配置

     
     
        
        
                          class="edisundong.AddAction" >
                 add.jsp
            
       
        

     

    如果提交請求的是add.action,那麼找到的Action類就是edisundong.AddAction。
  6. ActionProxy建立一個ActionInvocation的例項,同時ActionInvocation通過代理模式呼叫Action。但在呼叫之前ActionInvocation會根據配置載入Action相關的所有Interceptor。(Interceptor是struts2另一個核心級的概念)

    下面我們來看看ActionInvocation是如何工作的:

    ActionInvocation 是Xworks 中Action 排程的核心。而對Interceptor 的排程,也正是由ActionInvocation負責。ActionInvocation 是一個介面, 而DefaultActionInvocation 則是Webwork 對ActionInvocation的預設實現。

    Interceptor 的排程流程大致如下:
    1. ActionInvocation初始化時,根據配置,載入Action相關的所有Interceptor。
    2. 通過ActionInvocation.invoke方法呼叫Action實現時,執行Interceptor。

    Interceptor將很多功能從我們的Action中獨立出來,大量減少了我們Action的程式碼,獨立出來的行為具有很好的重用性。XWork、WebWork的許多功能都是有Interceptor實現,可以在配置檔案中組裝Action用到的Interceptor,它會按照你指定的順序,在Action執行前後執行。
    那麼什麼是攔截器。
    攔截器就是AOP(Aspect-Oriented Programming)的一種實現。(AOP是指用於在某個方法或欄位被訪問之前,進行攔截然後在之前或之後加入某些操作。)
    攔截器的例子這裡就不展開了。
    struts-default.xml檔案摘取的內容:
    < interceptor name ="alias" class ="com.opensymphony.xwork2.interceptor.AliasInterceptor" />
    < interceptor name ="autowiring" class ="com.opensymphony.xwork2.spring.interceptor.ActionAutowiringInterceptor" />
    < interceptor name ="chain" class ="com.opensymphony.xwork2.interceptor.ChainingInterceptor" />
    < interceptor name ="conversionError" class ="org.apache.struts2.interceptor.StrutsConversionErrorInterceptor" />
    < interceptor name ="createSession" class ="org.apache.struts2.interceptor.CreateSessionInterceptor" />
    < interceptor name ="debugging" class ="org.apache.struts2.interceptor.debugging.DebuggingInterceptor" />
    < interceptor name ="external-ref" class ="com.opensymphony.xwork2.interceptor.ExternalReferencesInterceptor" />
    < interceptor name ="execAndWait" class ="org.apache.struts2.interceptor.ExecuteAndWaitInterceptor" />
    < interceptor name ="exception" class ="com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor" />
    < interceptor name ="fileUpload" class ="org.apache.struts2.interceptor.FileUploadInterceptor" />
    < interceptor name ="i18n" class ="com.opensymphony.xwork2.interceptor.I18nInterceptor" />
    < interceptor name ="logger" class ="com.opensymphony.xwork2.interceptor.LoggingInterceptor" />
    < interceptor name ="model-driven" class ="com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor" />
    < interceptor name ="scoped-model-driven" class ="com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor" />
    < interceptor name ="params" class ="com.opensymphony.xwork2.interceptor.ParametersInterceptor" />
    < interceptor name ="prepare" class ="com.opensymphony.xwork2.interceptor.PrepareInterceptor" />
    < interceptor name ="static-params" class ="com.opensymphony.xwork2.interceptor.StaticParametersInterceptor" />
    < interceptor name ="scope" class ="org.apache.struts2.interceptor.ScopeInterceptor" />
    < interceptor name ="servlet-config" class ="org.apache.struts2.interceptor.ServletConfigInterceptor" />
    < interceptor name ="sessionAutowiring" class ="org.apache.struts2.spring.interceptor.SessionContextAutowiringInterceptor" />
    < interceptor name ="timer" class ="com.opensymphony.xwork2.interceptor.TimerInterceptor" />
    < interceptor name ="token" class ="org.apache.struts2.interceptor.TokenInterceptor" />
    < interceptor name ="token-session" class ="org.apache.struts2.interceptor.TokenSessionStoreInterceptor" />
    < interceptor name ="validation" class ="com.opensymphony.xwork2.validator.ValidationInterceptor" />
    < interceptor name ="workflow" class ="com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor" />
    < interceptor name ="store" class ="org.apache.struts2.interceptor.MessageStoreInterceptor" />
    < interceptor name ="checkbox" class ="org.apache.struts2.interceptor.CheckboxInterceptor" />
    < interceptor name ="profiling" class ="org.apache.struts2.interceptor.ProfilingActivationInterceptor" />
  7.  一旦Action執行完畢,ActionInvocation負責根據struts.xml中的配置找到對應的返回結果。如上文中將結構返回“add.jsp”,但大部分時候都是返回另外一個action,那麼流程又得走一遍………

  總結:

  Struts2的工作流就只有這7步,比起Struts1簡單了很多(本人能力有限,struts2更多的東西現在還看不明白)。網上有很多很多的關於.net和java的比較之類的文章,可是有幾個作者是真正用過java和.net的呢?更多的評論都是人云亦云,想當然的評論java和.net。作為技術人千萬不要屁股決定腦袋,關於web的設計模式上.net也不是那麼一無是處,java也不是那麼完美無缺。下一篇分析下ASP.NET的設計模式(生命週期)。

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