深入浅出学习Struts框架（七）：分析Struts框架实例2

在上一篇博客中讲到ActionServlet是如何初始化的以及web.xml的配置信息的具体作用。今天我们讲继续讲解ActionServlet在初始化的时候如何读取/WEB-INF/struts-config.xml信息到内存中，如何将这些从配置文件读取的信息以Actionmapping的形式展现在内存中的。

 

由于这部分内容是比较繁琐的，所以我对这部分的深入分析也不能太详细，但是具体实现流程我会讲清晰，如果有兴趣研究的童鞋们希望能够继续深入，研究的非常透彻的时候，可以给我发邮件或Q我。

 

下面来开始今天的博客，我们先从ActionServlet源代码的init方法开始。因为ActionServlet就是一个Servlet，它也是具有典型的那几个方法init、doget、dopost等方法。既然是初始化，那么我们就要看init方法。Init方法的源代码如下：

   

/** * <p>Initialize this servlet. Most of the processing has been factored into * support methods so that you can overrideparticular functionality at a * fairly granular level.</p> * * @exception ServletException if we cannotconfigure ourselves correctly */ publicvoidinit() throwsServletException { // Wraps the entire initialization in a try/catch tobetter handle // unexpected exceptions and errors to provide better feedback // to the developer try { initInternal(); initOther(); initServlet(); getServletContext().setAttribute(Globals.ACTION_SERVLET_KEY, this); initModuleConfigFactory(); // Initialize modules as needed ModuleConfig moduleConfig =initModuleConfig("", config); initModuleMessageResources(moduleConfig); initModuleDataSources(moduleConfig); initModulePlugIns(moduleConfig); moduleConfig.freeze(); Enumeration names =getServletConfig().getInitParameterNames(); while (names.hasMoreElements()) { String name = (String)names.nextElement(); if (!name.startsWith("config/")) { continue; } String prefix =name.substring(6); moduleConfig = initModuleConfig (prefix,getServletConfig().getInitParameter(name)); initModuleMessageResources(moduleConfig); initModuleDataSources(moduleConfig); initModulePlugIns(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. Mostlikely, this is due to an " + "incorrect or missing library dependency.", t); throw new UnavailableException(t.getMessage()); } }

 

在解释这段代码的流程和意思之前，有必要说一句，就是当我们在eclipse里面看代码的时候，尤其是看一段生疏的很长的代码的时候，希望能够经常使用Ctrl键（多余的不解释）。

 

下面开始讲解这段代码的流程和具体每一步的含义，如果有不正确的地方，希望指正。

首先映入眼帘的是initInternal（）方法。这个方法的实现代码是：

代码段一：

/** * <p>Initialize our internal MessageResourcesbundle.</p> * * @exception ServletException if we cannotinitialize these resources */ protectedvoidinitInternal() throwsServletException { // :FIXME: Document UnavailableException try { internal = MessageResources.getMessageResources(internalName); } catch (MissingResourceException e) { log.error("Cannot load internal resources from '"+ internalName+ "'", e); throw new UnavailableException ("Cannot load internal resources from '"+ internalName+ "'"); } }

 

代码段二：

/** * Create and return an instance of <code>MessageResources</code> for the * created by the default <code>MessageResourcesFactory</code>. * * @param config Configuration parameterfor this message bundle. */ publicsynchronizedstaticMessageResources getMessageResources(String config) { if (defaultFactory == null) { defaultFactory =MessageResourcesFactory.createFactory(); } return defaultFactory.createResources(config); }

代码段三：

/** * Create and return a <code>MessageResourcesFactory</code> instance ofthe * appropriate class, which can be used tocreate customized * <code>MessageResources</code>instances. If no such factory can be * created, return <code>null</code> instead. */ publicstaticMessageResourcesFactory createFactory(){ // Construct a new instance of the specified factory class try { if (clazz == null) clazz = RequestUtils.applicationClass(factoryClass); MessageResourcesFactory factory = (MessageResourcesFactory) clazz.newInstance(); return (factory); } catch (Throwable t) { LOG.error("MessageResourcesFactory.createFactory",t); return (null); } }

这个方法的具体作用就是初始化MessageResources，具体实现是工厂模式，首先判断defaultFactory是否存在，不存在则创建工厂，

defaultFactory = MessageResourcesFactory.createFactory()，在通过工厂创建资源类defaultFactory.createResources(config);存在则直接创建资源类。

initOther（）的方法，主要是初始化其它的配置，获取我们自己的struts-config配置文件的路径，
而它的默认路径就是web-inf/struts-config.xml，另外这个方法还会注册一些转换类的。具体源代码是：

/** * <p>Initialize other global characteristics ofthe controller servlet.</p> * * @exception ServletException if we cannotinitialize these resources */ protectedvoidinitOther() throwsServletException { String value = null; value =getServletConfig().getInitParameter("config"); if (value != null) { config = value; } // Backwards compatibility for form beans of Java wrapper classes // Set to true for strict Struts 1.0 compatibility value =getServletConfig().getInitParameter("convertNull"); if ("true".equalsIgnoreCase(value) || "yes".equalsIgnoreCase(value) || "on".equalsIgnoreCase(value) || "y".equalsIgnoreCase(value) || "1".equalsIgnoreCase(value)) { convertNull = true; } if (convertNull) { ConvertUtils.deregister(); ConvertUtils.register(new BigDecimalConverter(null), BigDecimal.class); ConvertUtils.register(new BigIntegerConverter(null), BigInteger.class); ConvertUtils.register(new BooleanConverter(null), Boolean.class); ConvertUtils.register(new ByteConverter(null), Byte.class); ConvertUtils.register(new CharacterConverter(null), Character.class); ConvertUtils.register(new DoubleConverter(null), Double.class); ConvertUtils.register(new FloatConverter(null), Float.class); ConvertUtils.register(new IntegerConverter(null), Integer.class); ConvertUtils.register(new LongConverter(null), Long.class); ConvertUtils.register(new ShortConverter(null), Short.class); } }

initServlet()方法是利用digester读取web.xml文件并且放到servletContext中。具体实现源代码：

/** * <p>Initialize the servlet mapping under which our controller servlet * is being accessed. This will be used in the <code>&html:form></code> * tag to generate correct destination URLs for form submissions.</p> * * @throws ServletException if error happens while scanning web.xml */ protected void initServlet() throws ServletException { // Remember our servlet name this.servletName = getServletConfig().getServletName(); // Prepare a Digester to scan the web application deployment descriptor Digester digester = new Digester(); digester.push(this); digester.setNamespaceAware(true); digester.setValidating(false); // Register our local copy of the DTDs that we can find for (int i = 0; i < registrations.length; i += 2) { URL url = this.getClass().getResource(registrations[i+1]); if (url != null) { digester.register(registrations[i], url.toString()); } } // Configure the processing rules that we need digester.addCallMethod("web-app/servlet-mapping", "addServletMapping", 2); digester.addCallParam("web-app/servlet-mapping/servlet-name", 0); digester.addCallParam("web-app/servlet-mapping/url-pattern", 1); // Process the web application deployment descriptor if (log.isDebugEnabled()) { log.debug("Scanning web.xml for controller servlet mapping"); } InputStream input = getServletContext().getResourceAsStream("/WEB-INF/web.xml"); if (input == null) { log.error(internal.getMessage("configWebXml")); throw new ServletException(internal.getMessage("configWebXml")); } try { digester.parse(input); } catch (IOException e) { log.error(internal.getMessage("configWebXml"), e); throw new ServletException(e); } catch (SAXException e) { log.error(internal.getMessage("configWebXml"), e); throw new ServletException(e); } finally { try { input.close(); } catch (IOException e) { log.error(internal.getMessage("configWebXml"), e); throw new ServletException(e); } } // Record a servlet context attribute (if appropriate) if (log.isDebugEnabled()) { log.debug("Mapping for servlet '" + servletName + "' = '" + servletMapping + "'"); } if (servletMapping != null) { getServletContext().setAttribute(Globals.SERVLET_KEY, servletMapping); } }

 

这篇博客先介绍这几个方法，随着这些方法具体作用和具体实现的慢慢的我们就知道init方法的作用，也慢慢的就解开了当我们实例化ActionServlet的时候，digester是如何读取/WEB-INF/struts-config.xml的文件内容，并且放到了ActionMapping中。敬请期待！