RequestProcessor类详解

Struts框架只允许应用中存在一个ActionServlet类,但是可以存在多个客户化的RequestProcessor类,每个子应用模块都可以有单独的RequestProcessor类,

ActionServlet主要负责初始化,以及介绍请求并找到合适的RequestRrocessor,之后真正干活的是RequestProecssor和Action.
上回说到ActionServlet的process方法最终会调用RequestProcessor类的process方法.下面介绍这个方法.
一.RequestProcessor的process方法

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);

    }

 
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);

    } 

1) 调用processMultipart()方法
如果HTTP请求方式为post,并且contentType为”multipart/form-data”开头,标准的HttpServletRequest对象将被重新包装,以方便处理”multipart”类型的HTTP请求.如果请求方式为get,或正congtentType属性不是”mulitipart”,就直接返回原始的HttpServletRequest对象.

2) 调用processPath()方法
获得请求的URI的路径,这一信息可用于选择合适的Struts Action组件.

3) 调用processLocale方法
当ControllerConfig对象的locale属性为true,将读取用户请求中包含的Locale信息,然后把Locale实例保存在session范围内.

4) 调用processContendType(contentType)方法
读取ControllerConfig对象的conttentType属性,然后调用response.setContentType(contentType)方法,设置响应结果的文档类型和字符编码.
processContent()方法如下

protected void processContent(HttpServletRequest request,
                                 HttpServletResponse response) {

       String contentType = moduleConfig.getControllerConfig().getContentType();
       if (contentType != null) {
           response.setContentType(contentType);
       }

   }

 protected void processContent(HttpServletRequest request,
                                  HttpServletResponse response) {

        String contentType = moduleConfig.getControllerConfig().getContentType();
        if (contentType != null) {
            response.setContentType(contentType);
        }

    } 

5) 调用processNoCache()方法
读取ControllerConfig对象的nocache属性,如果nocache属性为true,在响应结果中将加入特定的头参数:Pragma,Cache-Control和Expires,
防止页面被存储在客户的浏览器的缓存中,processNoCache方法的代码如下:

protected void processNoCache(HttpServletRequest request,
                                  HttpServletResponse response) {

        if (moduleConfig.getControllerConfig().getNocache()) {
            response.setHeader("Pragma", "No-cache");
            response.setHeader("Cache-Control", "no-cache,no-store,max-age=0");
            response.setDateHeader("Expires", 1);
        }
    }

protected void processNoCache(HttpServletRequest request,
                                  HttpServletResponse response) {

        if (moduleConfig.getControllerConfig().getNocache()) {
            response.setHeader("Pragma", "No-cache");
            response.setHeader("Cache-Control", "no-cache,no-store,max-age=0");
            response.setDateHeader("Expires", 1);
        }
    }

6)调用processPreprocess()方法
该方法不执行任何操作.直接返回true.子类可以覆盖这个方法.
执行客户化的预处理请求操作.

7)调用processMapping()方法
寻找和用户请求的URI匹配的ActionMapping,如果不存在这样的ActionMapping,则向用户返回恰当的错误信息.

8)调用processRoles()方法
先判断是否为Action配置了安全角色,如果配置了安全角色,就调用isUserInRole()方法判断当前用户是否具备必需的角色,如果不具备,就结束请求处理流程.,向用户返回恰当的错误消息.

9)调用processActionForm()方法
先判断是否为ActionMapping配置了ActionForm,如果配置了ActionForm,就先从ActionForm的存在范围内（request或session）寻找改ActionForm实例,如果不存在,就创建一个实例,接下来把它保存在合适的范围内,保存时使用的属性key为ActionMapping的name属性。

10）调用processPopulate()方法
如果为ActionMapping配置了ActionForm，就先调用ActionForm的reset（）方法，再把请求中的表单数据组装到ActionForm中。

11）调用processValidate（）方法
如果为ActionMapping配置了ActionForm，并且ActionMapping的validate属性为true，就调用ActionForm的validate（）方法，如果validate方法返回的ActionErrors对象中包含ActionMessage对象，说明表单验证失败。就把ActionErrors对象放在request范围内，再把请求转发到ActionMapping的input属性指定的Web组件。如果ActionForm的validate方法执行表单验证成功，就继续执行下面的处理流程。

12）调用processForward()方法
判断是否在ActionMapping中配置了forward属性。如果配置了这个属性，就调用RequestDispatcher的forward方法，请求处理流程结束。否则进行下一步。

13）调用processInclude()方法
判断是否在ActionMapping中配置了include属性。如果配置了这个属性，就调用RequestDispatcher的include方法，请求处理流程结束。否则进行下一步。

14）调用processActionCreate（）方法
先判断是否在Action缓存中存在这个Action实例，如果没有就新建一个Action实例，把它放在Action缓存中。可以看出Action也是只有一个实例在运行的。

15）调用processActionPerform
该方法调用Action实例的execute方法，该方法位于try/catch中，以及捕获异常。processActionPerform（）方放代码如下。

protected ActionForward
       processActionPerform(HttpServletRequest request,
                            HttpServletResponse response,
                            Action action,
                            ActionForm form,
                            ActionMapping mapping)
       throws IOException, ServletException {
       try {
           return (action.execute(mapping, form, request, response));
       } catch (Exception e) {
           return (processException(request, response,
                                    e, form, mapping));
       }

 protected ActionForward
        processActionPerform(HttpServletRequest request,
                             HttpServletResponse response,
                             Action action,
                             ActionForm form,
                             ActionMapping mapping)
        throws IOException, ServletException {
        try {
            return (action.execute(mapping, form, request, response));
        } catch (Exception e) {
            return (processException(request, response,
                                     e, form, mapping));
        }
} 

16)调用processActionForward方法
把你的Action的excute方法返回的ActionFoward对象作为参数传给它，processActionForward对象包的请求转发信息来执行请求转发或重定向。

在RequestProcessor类的process方法中，会访问ControllerConfig、ActionMappig和ActionForward实力的属性，ControllerConfig类和struts配置文件的<controlle>r元素对应，ActionMapping类和<action>元素对应，ActionForward和<forward>元素对应，process方法通过访问这三个类实例的属性来获得相关的配置信息。
写了这么多，RequestProcessor干得事够多的吧。

二．扩展RequestProcessor类
如果想修改RequestProcessor的一些默认功能,改易覆盖RequestProcessor基类中的相关方法.

Public class CustomRequestProcessor extends RequestProcessor{
  protected void processPreprocess (HttpServletRequest request,
                                 HttpServletResponse response) {
………………….
}
}

Public class CustomRequestProcessor extends RequestProcessor{
  protected void processPreprocess (HttpServletRequest request,
                                 HttpServletResponse response) { 
………………….
}
}

在struts配置文件中，<controller>元素的processorClass属性用于配置你自己的RequestProcessor类

</controller
contentType＝“text/html:charset=”GB2312”
locale=”true” nocache=”true” processorCalss=”com.test.CustomRequestProcessor”/>

</controller 
contentType＝“text/html:charset=”GB2312”
locale=”true” nocache=”true” processorCalss=”com.test.CustomRequestProcessor”/>