自学SSH框架之---struts（三）：源码分析struts1如何实现Action单例模式

      今天想说的是struts1和struts2的一个区别，就是Struts1 Action是单例模式并且必须是线程安全的，而Struts2 Action对象为每一个请求产生一个实例，因此没有线程安全问题。我们就简单分析源码看看struts1是如何实现Action单例模式的。

       我们借助于自学SSH框架之---struts（二）中的例子来简单分析下。先看看web.xml的配置，如下：

<?xml version="1.0" encoding="UTF-8"?><web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> <!-- Standard Action Servlet Configuration (with debugging) --> <servlet> <servlet-name>action</servlet-name> <servlet-class>org.apache.struts.action.ActionServlet</servlet-class> <init-param> <param-name>config</param-name> <param-value>/WEB-INF/struts-config.xml</param-value> </init-param> <init-param> <param-name>debug</param-name> <param-value>2</param-value> </init-param> <init-param> <param-name>detail</param-name> <param-value>2</param-value> </init-param> <load-on-startup>2</load-on-startup> </servlet> <!-- Standard Action Servlet Mapping --> <servlet-mapping> <servlet-name>action</servlet-name> <url-pattern>*.do</url-pattern> </servlet-mapping> </web-app>

<servlet-name>action</servlet-name>
    <servlet-class>org.apache.struts.action.ActionServlet</servlet-class>

 

<servlet-name>action</servlet-name>
    <url-pattern>*.do</url-pattern>

这段代码的意思是所有以.do结尾的请求都由ActionServlet来接收。

而请求的方式是什么呢，这个是在jsp页面表明的，先看上一篇博文的login.jsp中有这么一段代码：      <form action="login.do" method="post">，此处的post就表明它要调用ActionServlet的doPost方法。

      好，接下来我们就看看org.apache.struts.action.ActionServlet的doPost方法，

public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { process(request, response); }

可以看出通过request可以拿到所有的客户端数据，我们再继续看看process方法是什么

/** * <p>Perform the standard request processing for this request, and create * the corresponding response.</p> * * @param request The servlet request we are processing * @param response The servlet response we are creating * * @exception IOException if an input/output error occurs * @exception ServletException if a servlet exception is thrown */ protected void process(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { ModuleUtils.getInstance().selectModule(request, getServletContext()); ModuleConfig config = getModuleConfig(request); RequestProcessor processor = getProcessorForModule(config); if (processor == null) { processor = getRequestProcessor(config); } processor.process(request, response); }

这里面的RequestProcessor类的process方法是它的核心处理方法，继续跟进

/** * <p>Process an <code>HttpServletRequest</code> and create the * corresponding <code>HttpServletResponse</code> or dispatch * to another resource.</p> * * @param request The servlet request we are processing * @param response The servlet response we are creating * * @exception IOException if an input/output error occurs * @exception ServletException if a processing exception occurs */ public void process(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { // Wrap multipart requests with a special wrapper request = processMultipart(request); // Identify the path component we will use to select a mapping String path = processPath(request, response); if (path == null) { return; } if (log.isDebugEnabled()) { log.debug("Processing a '" + request.getMethod() + "' for path '" + path + "'"); } // Select a Locale for the current user if requested processLocale(request, response); // Set the content type and no-caching headers if requested processContent(request, response); processNoCache(request, response); // General purpose preprocessing hook if (!processPreprocess(request, response)) { return; } this.processCachedMessages(request, response); // Identify the mapping for this request ActionMapping mapping = processMapping(request, response, path); if (mapping == null) { return; } // Check for any role required to perform this action if (!processRoles(request, response, mapping)) { return; } // Process any ActionForm bean related to this request ActionForm form = processActionForm(request, response, mapping); processPopulate(request, response, form, mapping); // Validate any fields of the ActionForm bean, if applicable try { if (!processValidate(request, response, form, mapping)) { return; } } catch (InvalidCancelException e) { ActionForward forward = processException(request, response, e, form, mapping); processForwardConfig(request, response, forward); return; } catch (IOException e) { throw e; } catch (ServletException e) { throw e; } // Process a forward or include specified by this mapping if (!processForward(request, response, mapping)) { return; } if (!processInclude(request, response, mapping)) { return; } // Create or acquire the Action instance to process this request Action action = processActionCreate(request, response, mapping); if (action == null) { return; } // Call the Action instance itself ActionForward forward = processActionPerform(request, response, action, form, mapping); // Process the returned ActionForward instance processForwardConfig(request, response, forward); }

我们的一次请求就会到达上面的方法里面。

我们就简单说明一下这个方法，对于struts这个请求驱动框架，它会先截取路径，通过 String path = processPath(request, response);把URL截下来，也就是例子中的login ；

接下来通过ActionMapping mapping = processMapping(request, response, path);
        if (mapping == null) {
            return;
        }取得struts-config.xml的配置信息

<action-mappings>里面的
        <action path="/login"
                type="com.bjsxt.struts.LoginAction"
                name="loginForm"
                scope="request"
                validate="false"
        >
            <forward name="success" path="/login_success.jsp"/>
            <forward name="error" path="/login_error.jsp"/>
        </action>
       
    </action-mappings>，那么它是如何得到这些信息的呢？

它是在ActionServlet 第一次初始化的时候，也就是在执行它的init方法的时候，会将上面的xml文件读到内存里面，读到相应的数据结构里面，其中<action></action>内容是怎么读的呢？其实吧，每一个action都会对应一个ActionMapping实例，其中map的key值就是path，map的value就是actionmapping：

<action path="/login"
                type="com.bjsxt.struts.LoginAction"
                name="loginForm"
                scope="request"
                validate="false"
        >
            <forward name="success" path="/login_success.jsp"/>
            <forward name="error" path="/login_error.jsp"/>
        </action>

 

     所以当请求过来后，它会通过ActionMapping mapping = processMapping(request, response, path);去map里面，通过path来找到其对应的配置信息，放到mapping里面，拿到之后通过 ActionForm form = processActionForm(request, response, mapping);处理actionForm，在这里它会判断配置文件配置actionForm没，我们例子它配了  name="loginForm"，如果没有它会创建一个actionForm，名字是通过此处<form-bean name="loginForm" type="com.bjsxt.struts.LoginActionForm"/>配置而得的，然后将actionForm放到scope里面。此处要说明的是actionForm是可有可无的，因为有的请求不需要数据的，只是单纯页面的跳转。

 

      好，接下来跳过actionForm收集数据的过程和验证部分，接下来就会调用我们的action了，那么调用action会先创建action，那么怎么创建的呢？它会先拿到 type里面的“com.bjsxt.struts.LoginAction"，去map里面看有没有，如果有就直接返回，没有就创建，所以通过这种方式保证我们action是单实例的，好了今天就到此结束了吧，先饭饭了