ActionServlet.init()

 public void init() throws ServletException {
        final String configPrefix = "config/";
        final int configPrefixLength = configPrefix.length() - 1;

        // Wraps the entire initialization in a try/catch to better handle
        // unexpected exceptions and errors to provide better feedback
        // to the developer
        try {
            initInternal();
            initOther();
            initServlet();
            initChain();

            getServletContext().setAttribute(Globals.ACTION_SERVLET_KEY, this);
            initModuleConfigFactory();
            //讀取struts-config.xml，生成config物件，放入到moduleConfig中
            // Initialize modules as needed
            ModuleConfig moduleConfig = initModuleConfig("", config);
            //根據MessageResourcesConfigs生成MessageResources
            initModuleMessageResources(moduleConfig);
            //根據PlugInConfigs生產plugIns
            initModulePlugIns(moduleConfig);
            //初始化formbeanconfig，包括動態bean的配置
            initModuleFormBeans(moduleConfig);
            initModuleForwards(moduleConfig);
            initModuleExceptionConfigs(moduleConfig);
            initModuleActions(moduleConfig);
            moduleConfig.freeze();

            Enumeration names = getServletConfig().getInitParameterNames();

            while (names.hasMoreElements()) {
                String name = (String) names.nextElement();

                if (!name.startsWith(configPrefix)) {
                    continue;
                }

                String prefix = name.substring(configPrefixLength);

                moduleConfig =
                    initModuleConfig(prefix,
                        getServletConfig().getInitParameter(name));
                initModuleMessageResources(moduleConfig);
                initModulePlugIns(moduleConfig);
                initModuleFormBeans(moduleConfig);
                initModuleForwards(moduleConfig);
                initModuleExceptionConfigs(moduleConfig);
                initModuleActions(moduleConfig);
                moduleConfig.freeze();
            }

            this.initModulePrefixes(this.getServletContext());

            this.destroyConfigDigester();
        } catch (UnavailableException ex) {
            throw ex;
        } catch (Throwable t) {
            // The follow error message is not retrieved from internal message
            // resources as they may not have been able to have been
            // initialized
            log.error("Unable to initialize Struts ActionServlet due to an "
                + "unexpected exception or error thrown, so marking the "
                + "servlet as unavailable.  Most likely, this is due to an "
                + "incorrect or missing library dependency.", t);
            throw new UnavailableException(t.getMessage());
        }
    }
 

 protected void initModuleMessageResources(ModuleConfig config)
        throws ServletException {
	//struts-config.xml中配置的MessageResourcesConfig
        MessageResourcesConfig[] mrcs = config.findMessageResourcesConfigs();
        for (int i = 0; i < mrcs.length; i++) {
            if ((mrcs[i].getFactory() == null)
                || (mrcs[i].getParameter() == null)) {
                continue;
            }
            if (log.isDebugEnabled()) {
                log.debug("Initializing module path '" + config.getPrefix()
                    + "' message resources from '" + mrcs[i].getParameter()
                    + "'");
            }
<span style="white-space:pre">	</span>//這個預設是org.apache.struts.util.PropertyMessageResourcesFactory
            String factory = mrcs[i].getFactory();
            MessageResourcesFactory.setFactoryClass(factory);
<span style="white-space:pre">	</span>//預設是org.apache.struts.util.PropertyMessageResourcesFactory的例項
            MessageResourcesFactory factoryObject =
                MessageResourcesFactory.createFactory();
            factoryObject.setConfig(mrcs[i]);
<span style="white-space:pre">	</span>//parameter實際上是資原始檔路徑。MessageResources 是在第一次使用時載入的。
            MessageResources resources =
                factoryObject.createResources(mrcs[i].getParameter());
            resources.setReturnNull(mrcs[i].getNull());
            resources.setEscape(mrcs[i].isEscape());
            getServletContext().setAttribute(mrcs[i].getKey()
                + config.getPrefix(), resources);
        }
    }
 

protected void initModulePlugIns(ModuleConfig config)
        throws ServletException {
        if (log.isDebugEnabled()) {
            log.debug("Initializing module path '" + config.getPrefix()
                + "' plug ins");
        }
        PlugInConfig[] plugInConfigs = config.findPlugInConfigs();
        PlugIn[] plugIns = new PlugIn[plugInConfigs.length];
        getServletContext().setAttribute(Globals.PLUG_INS_KEY
            + config.getPrefix(), plugIns);
        for (int i = 0; i < plugIns.length; i++) {
            try {
                plugIns[i] =
                    (PlugIn) RequestUtils.applicationInstance(plugInConfigs[i]
                        .getClassName());
				//這個工具方法是把plugInConfigs[i].getProperties()這個鍵值對，賦值給plugIns[i]
				 BeanUtils.populate(plugIns[i], plugInConfigs[i].getProperties());
                // Pass the current plugIn config object to the PlugIn.
                // The property is set only if the plugin declares it.
                // This plugin config object is needed by Tiles
                try {
		//org.apache.struts.tiles.TilesPlugin初始化專用
		//TilesPlugin是tiles模板專用				
                    PropertyUtils.setProperty(plugIns[i],
                        "currentPlugInConfigObject", plugInConfigs[i]);
                } catch (Exception e) {
                    ;
                    // FIXME Whenever we fail silently, we must document a valid
                    // reason for doing so.  Why should we fail silently if a
                    // property can't be set on the plugin?

                    /**
                     * Between version 1.138-1.140 cedric made these changes.
                     * The exceptions are caught to deal with containers
                     * applying strict security. This was in response to bug
                     * #15736
                     *
                     * Recommend that we make the currentPlugInConfigObject part
                     * of the PlugIn Interface if we can, Rob
                     */
                }

                plugIns[i].init(this, config);
            } catch (ServletException e) {
                throw e;
            } catch (Exception e) {
                String errMsg =
                    internal.getMessage("plugIn.init",
                        plugInConfigs[i].getClassName());

                log(errMsg, e);
                throw new UnavailableException(errMsg);
            }
        }
   }
 

   protected void initModuleFormBeans(ModuleConfig config)
        throws ServletException {
        if (log.isDebugEnabled()) {
            log.debug("Initializing module path '" + config.getPrefix()
                + "' form beans");
        }

        // Process form bean extensions.
        FormBeanConfig[] formBeans = config.findFormBeanConfigs();

        for (int i = 0; i < formBeans.length; i++) {
            FormBeanConfig beanConfig = formBeans[i];
		//處理formbean的繼承關係，會把父類屬性copy到formbeanconfig
		//大致研究了一下，在配置formbean時，可以設定extends，值是formbean的name。不過dtd裡面限制了這個屬性（extends），可能是不推薦使用吧
            processFormBeanExtension(beanConfig, config);
        }

        for (int i = 0; i < formBeans.length; i++) {
            FormBeanConfig formBean = formBeans[i];

            // Verify that required fields are all present for the form config
            if (formBean.getType() == null) {
                handleValueRequiredException("type", formBean.getName(),
                    "form bean");
            }

            // ... and the property configs
            FormPropertyConfig[] fpcs = formBean.findFormPropertyConfigs();

            for (int j = 0; j < fpcs.length; j++) {
                FormPropertyConfig property = fpcs[j];

                if (property.getType() == null) {
                    handleValueRequiredException("type", property.getName(),
                        "form property");
                }
            }

            // Force creation and registration of DynaActionFormClass instances
            // for all dynamic form beans
            if (formBean.getDynamic()) {
			//動態bean配置，初始化dynaActionFormClass = new DynaActionFormClass(this);（this是指formBean）
                formBean.getDynaActionFormClass();
            }
        }
    }