Struts里的ActionForm

　　前两天有位哥们问起Struts的ActionForm，翻了翻源码。

　　RequestProcessor的202与203行，以struts1.2为准。

       // Process any ActionForm bean related to this request
        ActionForm form = processActionForm(request, response, mapping);
        processPopulate(request, response, form, mapping);

　　330-331行
            // Create (if necessary) a form bean to use
        ActionForm instance = RequestUtils.createActionForm
            (request, mapping, moduleConfig, servlet);

　　RequestUtils的方法源码：

　　public static ActionForm 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);
    }

　RequestUtils另外一方法:

　  private static ActionForm lookupActionForm(HttpServletRequest request, String attribute, String scope)
    {
        // Look up any existing form bean instance
        if (log.isDebugEnabled()) {
            log.debug(
                    " Looking for ActionForm bean instance in scope '"
                    + scope
                    + "' under attribute key '"
                    + attribute
                    + "'");
        }
        ActionForm instance = null;
        HttpSession session = null;
        if ("request".equals(scope)) {
            instance = (ActionForm) request.getAttribute(attribute);
        } else {
            session = request.getSession();
            instance = (ActionForm) session.getAttribute(attribute);
        }

        return (instance);
    }

　　从以上可以看出，Struts先是到struts-config.xml配置的request或session里去拿，拿不到则创建。

　　需要注意的是，对DynaActionForm有一些处理上差异。