ActionServlet中的一个方法processActionForm

先来看具体struts中processActionForm方法的具体实现：

 

 

/**

     * <p>Retrieve and return the <code>ActionForm</code> associatedwith

     * this mapping, creating and retaining oneif necessary. If there is no

     * <code>ActionForm</code> associated with this mapping,return

     * <code>null</code>.</p>

     *

     * @param request The servlet request weare processing

     * @param response The servlet response weare creating

     * @param mapping The mapping we are using

     */

   protectedActionForm processActionForm(HttpServletRequestrequest,

                                          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);



}

/** * <p>Retrieve and return the <code>ActionForm</code> associatedwith * this mapping, creating and retaining oneif necessary. If there is no * <code>ActionForm</code> associated with this mapping,return * <code>null</code>.</p> * * @param request The servlet request weare processing * @param response The servlet response weare creating * @param mapping The mapping we are using */ protectedActionForm processActionForm(HttpServletRequestrequest, 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); }

 

        这个方法的大体流程是：根据ActionMapping中的name名称查找ActionForm，如果配置了ActionForm,那么就到request或session中查找，如果在request或session中存在已经创建的ActionForm，那么将返回。如果不存在那么会根据ActionForm的完成路径采用反射进行创建，再将创建好的ActionForm放到request或session中，之后返回ActionForm。

 

        具体我们可以跟随断点调试来看看这个方法是如何运行的。

 

        首先还是同上篇博客中的方法一样，先设置断点，之后进入processActionForm方法。

 

        第一个步骤就是创建ActionForm：

 

 

// Create (if necessary) a formbean to use

        ActionForm instance = RequestUtils.createActionForm

            (request, mapping, moduleConfig, servlet);

        if (instance == null) {

            return (null);

       }

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

 

        通过调用RequestUtils.createActionForm的方法把ActionMapping中的ActionForm字符串生成对象，并且返回。进入这段代码中：

 

 

publicstaticActionForm createActionForm(

            HttpServletRequest request,

            ActionMapping mapping,

            ModuleConfig moduleConfig,

            ActionServlet servlet) {



        // Is there a form bean associated with this mapping?

        String attribute = mapping.getAttribute();

        if (attribute == null) {

            return (null);

        }



        // Look up the form bean configuration information to use

        String name = mapping.getName();

        FormBeanConfig config =moduleConfig.findFormBeanConfig(name);

        if (config == null) {

            log.warn("No FormBeanConfig found under '"+ name + "'");

            return (null);

        }



        ActionForm instance = lookupActionForm(request,attribute, mapping.getScope());



        // Can we recycle the existing form bean instance (if there is one)?

        try {

            if (instance != null && canReuseActionForm(instance,config)) {

                return (instance);

            }

        } catch(ClassNotFoundException e) {

            log.error(servlet.getInternal().getMessage("formBean",config.getType()), e);

            return (null);

        }



        return createActionForm(config,servlet);

}

publicstaticActionForm createActionForm( HttpServletRequest request, ActionMapping mapping, ModuleConfig moduleConfig, ActionServlet servlet) { // Is there a form bean associated with this mapping? String attribute = mapping.getAttribute(); if (attribute == null) { return (null); } // Look up the form bean configuration information to use String name = mapping.getName(); FormBeanConfig config =moduleConfig.findFormBeanConfig(name); if (config == null) { log.warn("No FormBeanConfig found under '"+ name + "'"); return (null); } ActionForm instance = lookupActionForm(request,attribute, mapping.getScope()); // Can we recycle the existing form bean instance (if there is one)? try { if (instance != null && canReuseActionForm(instance,config)) { return (instance); } } catch(ClassNotFoundException e) { log.error(servlet.getInternal().getMessage("formBean",config.getType()), e); return (null); } return createActionForm(config,servlet); }

 

    

        方法首先定义变量nama，并且从mapping中获取值，String name = mapping.getName();也就是我们实例中的LoginForm字符串。之后通过调用FormBeanConfig config =moduleConfig.findFormBeanConfig(name);这句话把相应的LoginForm字符串生成相应的对象。

        这里要说明的是我们在struts-config配置文件中，配置过这样一个标签信息：

 

<form-beans>

       <form-bean name="loginForm" type="com.bjpowernode.struts.LoginActionForm"/>

    </form-beans>

<form-beans> <form-bean name="loginForm" type="com.bjpowernode.struts.LoginActionForm"/> </form-beans>

 

        这个标签在服务器一启动的时候就会利用digester读取这里的配置信息，并且放在FormBeanConfig类中，这样我们可以通过上面那一句话就可以把LoginForm字符串生成相应的对象。

 

       之后调用了ActionForm instance = lookupActionForm(request,attribute, mapping.getScope());这个方法，这个方法主要是查找scope属性中有没有存在ActionForm。具体实现：

 

 

if ("request".equals(scope)){

            instance = (ActionForm)request.getAttribute(attribute);

        } else {

            session = request.getSession();

            instance = (ActionForm)session.getAttribute(attribute);

        }

if ("request".equals(scope)){ instance = (ActionForm)request.getAttribute(attribute); } else { session = request.getSession(); instance = (ActionForm)session.getAttribute(attribute); }

 

        这里判断scope属性值是否为request，如果是则从request中读出ActionForm，如果不是则从session中读出。程序如果是第一次执行，那么ActionForm会是为空的。因为这里的ActionForm为空，所以就进入了if判断语句中，最后通过调用return createActionForm(config, servlet);创建ActionForm并且返回。

 

        之后processActionForm就会把返回来的ActionForm放入request或者session中。具体实现就是：

 

 

if ("request".equals(mapping.getScope())){

           request.setAttribute(mapping.getAttribute(), instance);

        } else {

            HttpSession session =request.getSession();

           session.setAttribute(mapping.getAttribute(), instance);

        }

if ("request".equals(mapping.getScope())){ request.setAttribute(mapping.getAttribute(), instance); } else { HttpSession session =request.getSession(); session.setAttribute(mapping.getAttribute(), instance); }

 

        到此为止，ActionForm就创建完成