Struts版本——1.2.9
Digester版本——1.6
初始化ModuleConfig就是指Struts将struts-config.xml初始化为ModuleConfig对象,实现这个动作的代码在ActionServlet的init()方法中,如下:
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();
实际上,初始化ModuleConfig对象的过程仅仅在第3行的那句代码里,这里之所以列出这么多代码,是因为这段代码所做的事情可看成一个整体。对于这段代码的概括描述可参见Struts源码学习 — ActionServlet的初始化
将第3行代码里的initModuleConfig()方法挖开,如下:
/** * <p>Initialize the module configuration information for the * specified module.</p> * * @param prefix Module prefix for this module * @param paths Comma-separated list of context-relative resource path(s) * for this modules's configuration resource(s) * * @exception ServletException if initialization cannot be performed * @since Struts 1.1 */ protected ModuleConfig initModuleConfig(String prefix, String paths) throws ServletException { // :FIXME: Document UnavailableException? (Doesn't actually throw anything) if (log.isDebugEnabled()) { log.debug( "Initializing module path '" + prefix + "' configuration from '" + paths + "'"); } // Parse the configuration for this module ModuleConfigFactory factoryObject = ModuleConfigFactory.createFactory(); ModuleConfig config = factoryObject.createModuleConfig(prefix); // Configure the Digester instance we will use Digester digester = initConfigDigester(); // Process each specified resource path while (paths.length() > 0) { digester.push(config); String path = null; int comma = paths.indexOf(','); if (comma >= 0) { path = paths.substring(0, comma).trim(); paths = paths.substring(comma + 1); } else { path = paths.trim(); paths = ""; } if (path.length() < 1) { break; } this.parseModuleConfigFile(digester, path); } getServletContext().setAttribute( Globals.MODULE_KEY + config.getPrefix(), config); // Force creation and registration of DynaActionFormClass instances // for all dynamic form beans we wil be using FormBeanConfig fbs[] = config.findFormBeanConfigs(); for (int i = 0; i < fbs.length; i++) { if (fbs[i].getDynamic()) { fbs[i].getDynaActionFormClass(); } } return config; }
首先27、28两行,创建ModuleConfigFactory对象,其默认的实现是org.apache.struts.config.impl.DefaultModuleConfigFactory,可在web.xml中通过设置ActionServlet的configFactory初始化参数来改变实现类。然后由ModuleConfigFactory创建ModuleConfig对象,DefaultModuleConfigFactory的实现就是new一个org.apache.struts.config.impl.ModuleConfigImpl的对象,以prefix为构造方法的参数。
然后初始化Digester对象(后面详细说)。
因为参数paths可以是以逗号为分隔符的,多个struts-config.xml文件的路径,所以接下来的循环是用Digester对象分别对这多个struts-config.xml文件进行解析,解析的过程会将每个struts-config.xml文件里的元素都初始化为相应的XXXConfig对象,并将这些对象装进之前创建的ModuleConfig对象里。
然后将这个ModuleConfig对象放到ServletContext里。
59-64行,这一段是检查struts-config.xml文件里的所有form-bean元素,如果其type属性指定的类是动态FormBean,即org.apache.struts.action.DynaActionForm类或它的子类,就初始化FormBeanConfig的dynaActionFormClass字段。
最重要的代码在31行的initConfigDigester()方法里,挖开如下:
/** * <p>Create (if needed) and return a new <code>Digester</code> * instance that has been initialized to process Struts module * configuration files and configure a corresponding <code>ModuleConfig</code> * object (which must be pushed on to the evaluation stack before parsing * begins).</p> * * @exception ServletException if a Digester cannot be configured * @since Struts 1.1 */ protected Digester initConfigDigester() throws ServletException { // :FIXME: Where can ServletException be thrown? // Do we have an existing instance? if (configDigester != null) { return (configDigester); } // Create a new Digester instance with standard capabilities configDigester = new Digester(); configDigester.setNamespaceAware(true); configDigester.setValidating(this.isValidating()); configDigester.setUseContextClassLoader(true); configDigester.addRuleSet(new ConfigRuleSet()); for (int i = 0; i < registrations.length; i += 2) { URL url = this.getClass().getResource(registrations[i+1]); if (url != null) { configDigester.register(registrations[i], url.toString()); } } this.addRuleSets(); // Return the completely configured Digester instance return (configDigester); }
这个方法初始化Digester对象,就是这个Digester将struts-config.xml解析为ModuleConfig对象的。
Digester类的完全限定名为org.apache.commons.digester.Digester,来自于Apache Commons Digester,它是一个将XML映射到Java对象的工具。该工具底层还是使用SAX来解析XML,只是它在SAX的基础上,提出了一个Rule的概念。所谓Rule,通俗的解释就是“当扫描XML遇到某些结点时要做的事情”。Digester类根据这些Rule来解析XML,因此,解析之前需要给Digester添加这些Rule,Digester类里定义了一系列方法用来直接添加Rule。
也可以将添加Rule的繁琐工作委托给RuleSet来做,然后Digester调用addRuleSet(RuleSet)方法就行了。上面代码的25行就是这样做的,如何将struts-config.xml解析为ModuleConfig对象的Rule就是在ConfigRuleSet类的addRuleInstances()方法里添加到Digester的,该方法代码如下:
/** * <p>Add the set of Rule instances defined in this RuleSet to the * specified <code>Digester</code> instance, associating them with * our namespace URI (if any). This method should only be called * by a Digester instance. These rules assume that an instance of * <code>org.apache.struts.config.ModuleConfig</code> is pushed * onto the evaluation stack before parsing begins.</p> * * @param digester Digester instance to which the new Rule instances * should be added. */ public void addRuleInstances(Digester digester) { digester.addObjectCreate ("struts-config/data-sources/data-source", "org.apache.struts.config.DataSourceConfig", "className"); digester.addSetProperties ("struts-config/data-sources/data-source"); digester.addSetNext ("struts-config/data-sources/data-source", "addDataSourceConfig", "org.apache.struts.config.DataSourceConfig"); digester.addRule ("struts-config/data-sources/data-source/set-property", new AddDataSourcePropertyRule()); digester.addRule ("struts-config/action-mappings", new SetActionMappingClassRule()); digester.addFactoryCreate ("struts-config/action-mappings/action", new ActionMappingFactory()); digester.addSetProperties ("struts-config/action-mappings/action"); digester.addSetNext ("struts-config/action-mappings/action", "addActionConfig", "org.apache.struts.config.ActionConfig"); digester.addSetProperty ("struts-config/action-mappings/action/set-property", "property", "value"); digester.addObjectCreate ("struts-config/action-mappings/action/exception", "org.apache.struts.config.ExceptionConfig", "className"); digester.addSetProperties ("struts-config/action-mappings/action/exception"); digester.addSetNext ("struts-config/action-mappings/action/exception", "addExceptionConfig", "org.apache.struts.config.ExceptionConfig"); digester.addSetProperty ("struts-config/action-mappings/action/exception/set-property", "property", "value"); digester.addFactoryCreate ("struts-config/action-mappings/action/forward", new ActionForwardFactory()); digester.addSetProperties ("struts-config/action-mappings/action/forward"); digester.addSetNext ("struts-config/action-mappings/action/forward", "addForwardConfig", "org.apache.struts.config.ForwardConfig"); digester.addSetProperty ("struts-config/action-mappings/action/forward/set-property", "property", "value"); digester.addObjectCreate ("struts-config/controller", "org.apache.struts.config.ControllerConfig", "className"); digester.addSetProperties ("struts-config/controller"); digester.addSetNext ("struts-config/controller", "setControllerConfig", "org.apache.struts.config.ControllerConfig"); digester.addSetProperty ("struts-config/controller/set-property", "property", "value"); digester.addRule ("struts-config/form-beans", new SetActionFormBeanClassRule()); digester.addFactoryCreate ("struts-config/form-beans/form-bean", new ActionFormBeanFactory()); digester.addSetProperties ("struts-config/form-beans/form-bean"); digester.addSetNext ("struts-config/form-beans/form-bean", "addFormBeanConfig", "org.apache.struts.config.FormBeanConfig"); digester.addObjectCreate ("struts-config/form-beans/form-bean/form-property", "org.apache.struts.config.FormPropertyConfig", "className"); digester.addSetProperties ("struts-config/form-beans/form-bean/form-property"); digester.addSetNext ("struts-config/form-beans/form-bean/form-property", "addFormPropertyConfig", "org.apache.struts.config.FormPropertyConfig"); digester.addSetProperty ("struts-config/form-beans/form-bean/form-property/set-property", "property", "value"); digester.addSetProperty ("struts-config/form-beans/form-bean/set-property", "property", "value"); digester.addObjectCreate ("struts-config/global-exceptions/exception", "org.apache.struts.config.ExceptionConfig", "className"); digester.addSetProperties ("struts-config/global-exceptions/exception"); digester.addSetNext ("struts-config/global-exceptions/exception", "addExceptionConfig", "org.apache.struts.config.ExceptionConfig"); digester.addSetProperty ("struts-config/global-exceptions/exception/set-property", "property", "value"); digester.addRule ("struts-config/global-forwards", new SetActionForwardClassRule()); digester.addFactoryCreate ("struts-config/global-forwards/forward", new GlobalForwardFactory()); digester.addSetProperties ("struts-config/global-forwards/forward"); digester.addSetNext ("struts-config/global-forwards/forward", "addForwardConfig", "org.apache.struts.config.ForwardConfig"); digester.addSetProperty ("struts-config/global-forwards/forward/set-property", "property", "value"); digester.addObjectCreate ("struts-config/message-resources", "org.apache.struts.config.MessageResourcesConfig", "className"); digester.addSetProperties ("struts-config/message-resources"); digester.addSetNext ("struts-config/message-resources", "addMessageResourcesConfig", "org.apache.struts.config.MessageResourcesConfig"); digester.addSetProperty ("struts-config/message-resources/set-property", "property", "value"); digester.addObjectCreate ("struts-config/plug-in", "org.apache.struts.config.PlugInConfig"); digester.addSetProperties ("struts-config/plug-in"); digester.addSetNext ("struts-config/plug-in", "addPlugInConfig", "org.apache.struts.config.PlugInConfig"); digester.addRule ("struts-config/plug-in/set-property", new PlugInSetPropertyRule()); }
这里的所有addXXX()方法都是在添加Rule,只不过其中不叫addRule的方法是添加Digester的内置Rule的便捷方法。所有方法的第一个参数都是一个XPath格式的String,这些String看着都很眼熟吧,没错,都是struts-config.xml里的。
先说说Digester是如何使用Rule来解析XML的,执行Digester类的parse()方法来扫描解析XML,当扫描XML遇到匹配某个XPath的标签,就开始使用Digester里对应于这个XPath的Rule。碰到开始标签时,调用Rule的begin()方法;标签如果有体,调用Rule的body()方法;碰到结束标签时,调用Rule的end()方法。如果对应于某个XPath有多个Rule,就有个调用顺序的问题了。对于begin()方法,是按照Rule添加到Digester里的顺序调用;end()方法调用顺序与begin()相反。这点跟栈的思想一样。
这段代码里使用到的一些Digester内置Rule有:
ObjectCreateRule:创建对象并压栈。
FactoryCreateRule:由工厂来创建对象并压栈。
SetPropertiesRule:将标签属性值设置到栈顶对象的属性里。
SetPropertyRule:设置栈顶对象的单个属性的值。
SetNextRule:调用栈顶第2个元素的指定方法来建立它和栈顶元素的关系。
一般对标签的处理方式是,先用ObjectCreateRule或FactoryCreateRule创建对象,然后用SetPropertiesRule或SetPropertyRule设置对象的属性值,最后用SetNextRule建立该标签和父标签的关系。上面的代码基本就是这个套路,另外还加入了一些Struts自定义的Rule,如下:
AddDataSourcePropertyRule:设置DataSource的属性。
PlugInSetPropertyRule:设置PlugIn的属性。
SetActionMappingClassRule:根据struts-config/action-mappings标签的type属性,设置ActionConfig的实现类。
SetActionFormBeanClassRule:根据struts-config/form-beans标签的type属性,设置FormBeanConfig的实现类。
SetActionForwardClassRule:根据struts-config/global-forwards标签的type属性,设置ForwardConfig的实现类。
对于ActionConfig、FormBeanConfig、ForwardConfig,有3种方式可以改变这3个XXXConfig的实现类。
1. 使用自定义的ModuleConfig实现类,在其中定义XXXConfig的实现类,这个改变影响范围最大,针对于整个应用的XXXConfig。Struts默认的ModuleConfig实现类是org.apache.struts.config.impl.ModuleConfigImpl,这个类里面定义了XXXConfig的默认实现类,分别是org.apache.struts.action.ActionMapping、org.apache.struts.action.ActionFormBean、org.apache.struts.action.ActionForward。
2. 象上面最后的3个Rule说明中提到的那样,设置type属性,这个改变只针对于单个struts-config.xml中的XXXConfig。
3. 具体到单个struts-config.xml中的单个XXXConfig配置,设置它的className属性,来改变单个XXXConfig的实现类,这个改变影响最小,只针对单个XXXConfig。
正因为它们的实现类可以这样灵活的改变,所以上面代码在为Digester添加创建它们实例的Rule时,使用的是FactoryCreateRule,而不是ObjectCreateRule。要构造一个FactoryCreateRule,需要为它提供一个ObjectCreationFactory,前者将创建对象的工作委托给后者。Struts提供了创建这3种Config对象的ObjectCreationFactory——ActionMappingFactory、ActionFormBeanFactory、ActionForwardFactory、GlobalForwardFactory。如果标签给出了className属性,这些Factory就以该属性值创建对象;如果没有,就以之前设置的实现类创建对象。