SSH框架之Struts（3）——Struts的执行流程之核心方法

　　上篇讲了Tomcat实例化一个单例的ActionServlet。依据web.xml配置文件做好对应的初始化工作。

这时client产生一个.do结尾的request请求，採用get/post方式提交之后。不论哪种方式提交，都会进入到process核心方法中。

ActionServelt

　doGet（）和doPost（）方法

 　　　　　public void <strong>doGet</strong>(HttpServletRequest request,	HttpServletResponse response)
	        throws IOException, ServletException {

	        <strong>process</strong>(request, response);

	    }

	    public void <strong>doPost</strong>(HttpServletRequest request,      HttpServletResponse response)
	        throws IOException, ServletException {

	        <strong>process</strong>(request, response);

	    }

　process方法

	    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);

	    }

　　这种方法主要有两个作用：

　　首先调用org.apache.struts.util.ModuleUtils类的selectModule()方法。这种方法依据请求对象和servletContext选择负责处理当前请求所属的模块。然后把与该模块相关的ModuleConfig和MessageResources对象存储倒request范围中，这使得框架的其余组件能够方便地从request范围中读取这些对象，从而获取应用配置信息和消息资源。

　　其次， 实例化RequestProcessor类。然后调用RequestProcessor类的process()方法，来完毕十几的预处理请求操作。

RequestProcessor

　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);

    }

依照process（）方法的运行流程，

　　一、processMultipart();

　　　1、首先推断是否为post方式。假设不是post方式，则肯定不是上传请求。则直接返回request对象

	if (!"POST".equalsIgnoreCase(request.getMethod())) {
		return (request);

        }

　　　2、获取request对象的ContentType，假设ContentType为multipart/form-datade 话则 new 一个 MultipartRequestWrapper 对象返回。

否则直接返回request。

 String contentType = request.getContentType();        if ((contentType != null)
            && contentType.startsWith("multipart/form-data")) {
            return (new MultipartRequestWrapper(request));
        } else {
            return (request);
        }

　　　这里简答的来说，是用来推断是否有上传功能的需求。假设有上传功能的需求。那么必须把form的contentType改为multipart/form-data。而这种方法就是来解析并打包成一个实现HttpServletRequest的包，为上传文件服务的。

　　二、 processPath()

        String path = processPath(request, response);
        if (path == null) {
            return;
        }
        if (log.isDebugEnabled()) {
            log.debug("Processing a '" + request.getMethod() +
                      "' for path '" + path + "'");
        }

　　　通过调用processPath方法。获得訪问的详细action的名字

　　三、processLocale()

protected void processLocale(HttpServletRequest request,HttpServletResponse response) {

	        // Are we configured to select the Locale automatically?

if (!moduleConfig.getControllerConfig().getLocale()) {
	            return;
	        }
	        // Has a Locale already been selected?
	        HttpSession session = request.getSession();
	        if (session.getAttribute(Globals.LOCALE_KEY) != null) {
	            return;
	        }
	        // Use the Locale returned by the servlet container (if any)
	        Locale locale = request.getLocale();
	        if (locale != null) {
	            if (log.isDebugEnabled()) {
	                log.debug(" Setting user locale '" + locale + "'");
	            }
	            session.setAttribute(Globals.LOCALE_KEY, locale);
	        }
	    }

　　　

　　　是本地服务还是国际化服务，这是依据浏览器的设置的（确切的说是依据操作系统设置的）

　　四、processContent();processNoCache();

　　　当中processContent用来确定内容类型和编码类型

　　　processNoCache依据配置文件里的配置属性来确定某些内容是否进行缓存

　　五、 processMapping()

　　　依据request。response和action的名字去Struts.config.xml中获取相应的actionmapping，也就是将我们配置好的request要请求的action放入到ActionMapping对象中去。

　　1、首先去配置文件中找对应的配置信息

// Is there a mapping for this path?

ActionMapping mapping = (ActionMapping) moduleConfig.findActionConfig(path);

　　2、假设有配置则把它放入request。并返回。

        // If a mapping is found, put it in the request and return it
        if (mapping != null) {
            request.setAttribute(Globals.MAPPING_KEY, mapping);
            return (mapping);
        }

　　3、找到“未知的映射路径（假设有的话）”。相同找到了就放到request里并返回他。

        // Locate the mapping for unknown paths (if any)
        ActionConfig[] configs = moduleConfig.findActionConfigs();
        for (int i = 0; i < configs.length; i++) {
            if (configs[i].getUnknown()) {
                mapping = (ActionMapping) configs[i];
                request.setAttribute(Globals.MAPPING_KEY, mapping);
                return (mapping);
            }

        }

　　4、假设还是没有找到mapping信息则发送错误消息。并返回null

        // No mapping can be found to process this request
        String msg = getInternal().getMessage("processInvalid");
        log.error(msg + " " + path);
        response.sendError(HttpServletResponse.SC_NOT_FOUND, msg);

        return null;

　　此时。ActionMapping元素包括了如Action类的名称及在请求中用到的ActionForm的信息，另外还有配置在当前ActionMapping的里的ActionForwards信息。

　　六、processActionForm()

	 protected ActionForm processActionForm(HttpServletRequest request,
	                                           HttpServletResponse response,
	                                           ActionMapping mapping) {

	        // Create (if necessary) a form bean to use
	        ActionForm instance = RequestUtils.createActionForm
	            (request, mapping, moduleConfig, servlet);
	        if (instance == null) {
	            return (null);
	        }

	        // Store the new instance in the appropriate scope
	        if (log.isDebugEnabled()) {
	            log.debug(" Storing ActionForm bean instance in scope '" +
	                mapping.getScope() + "' under attribute key '" +
	                mapping.getAttribute() + "'");
	        }
	        if ("request".equals(mapping.getScope())) {
	            request.setAttribute(mapping.getAttribute(), instance);
	        } else {
	            HttpSession session = request.getSession();
	            session.setAttribute(mapping.getAttribute(), instance);
	        }
	        return (instance);

	    }

　　　查看mapping里是否配置name属性或attribute属性来指定ActionForm，假设配置了ActionForm就到session或是Request中进行查找，查到后进行返回；假设没有找到。依据ActionForm的路径进行创建并放入到scope域中。

　　七、processPopulate()

 protected void processPopulate(HttpServletRequest request,
                                   HttpServletResponse response,
                                   ActionForm form,
                                   ActionMapping mapping)
        throws ServletException {

        if (form == null) {
            return;
        }
        // Populate the bean properties of this ActionForm instance
        if (log.isDebugEnabled()) {
            log.debug(" Populating bean properties from this request");
        }
        form.setServlet(this.servlet);
        form.reset(mapping, request);

        if (mapping.getMultipartClass() != null) {
            request.setAttribute(Globals.MULTIPART_KEY,
                                 mapping.getMultipartClass());
        }
        RequestUtils.populate(form, mapping.getPrefix(), mapping.getSuffix(),
                              request);

        // Set the cancellation request attribute if appropriate
        if ((request.getParameter(Constants.CANCEL_PROPERTY) != null) ||
            (request.getParameter(Constants.CANCEL_PROPERTY_X) != null)) {
            request.setAttribute(Globals.CANCEL_KEY, Boolean.TRUE);
        }
    }

　　　这种方法主要是用来为ActionForm 填充数据，运行ActionForm的reset重置方法，之后获取到表单全部输入域的名称。依据request.getParameter获取输入域名称所相应的值，然后将输入域名称和值以键值对形式放入到map中，之后调用一个比較重要的第三方组件BeanUtils来实现属性的转换和拷贝到详细的ActionForm中

　　八、processValidate（）

　　　验证表单数据合法性，这个可用可不用的。假设使用了Struts的验证，这里会自己主动的运行该方法进行验证。

　　九、processForward（）

　　　处理mapping指定的forward 和 include，Struts检查<action>元素的forward和include属性的值。假如有配置。则把forward和include 请求放在配置的页面内，之后转发到详细的ActionServlet中进行详细业务逻辑的处理。

小结

　　至此，RequestProcessor的核心方法process运行完成。之后会到详细的Ａction中运行业务相关的操作。

纵观整个运行流程，其基本的方法无外乎两个，一个是AcionServlet中的process方法，还有一个是RequestProcessor的process()方法，至于其它的截取请求路径，填充actionForm。国际化等方法也都被用于外观模式封装在了process方法中。