深入浅出学习Struts1框架（七）：ActionServlet实例化之读取struts-config.xml配置文件

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！