结合源码浅析Struts2与Spring整合的原理
本文假设读者已经自己动手整合过Struts2和Spring这两个框架。我想说明的重点不是如何整合这两个框架，而是为什么经过配置之后Struts的Action等对象可以由Spring来管理，即找到两个框架的衔接点。
笔者用的是框架版本分别为Struts-2.3和Spring-4.1。
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文章的结构如下：
一、回顾Struts2与Spring整合的配置方法
二、（重点）对关键配置的分析
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一、回顾Struts2与Spring整合的配置方法
1. 创建一个普通的Web应用（含/WEB-INF/web.xml）
2. 配置Struts2
首先，我们要导入Struts2所需的Jar包（先不考虑整合用的包），导包的就不多说了。接下来，我们要创建struts.xml配置文件，我把配置文件放在CLASSPATH /src 中。这里我先创建一个测试用的package，配置文件的主要内容如下：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.3//EN" "http://struts.apache.org/dtds/struts-2.3.dtd" > 3 <struts> 4 <package name="test" extends="struts-default" namespace="/"> 5 </package> 6 </struts>
接下来，我们要在Web应用的配置文件web.xml中配置Struts2的过滤器StrutsPrepareAndExecuteFilter，用来过滤所有的请求，配置文件如下：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0"> 3 <display-name>ssh7</display-name> 4 <filter> 5 <filter-name>struts2</filter-name> 6 <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class> 7 </filter> 8 <filter-mapping> 9 <filter-name>struts2</filter-name> 10 <url-pattern>/*</url-pattern> 11 </filter-mapping> 12 </web-app>
Struts2配置到这里就可以了，启动一下，看看成不成功。if 成功 then 继续下一步，else 检查一下导的包对不对，或者配置文件的路径和内容有没有错。
3. 配置Spring
首先，导入Spring所需的Jar包（先不考虑整合所需的包）。
接下来，创建Spring配置文件，我创建的配置文件为applicationContext.xml，放在/WEB-INF目录下。配置文件如下：
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.1.xsd "> </beans>
4. 整合Struts2与Spring
1）在web.xml配置文件中配置一个上下文初始化参数(context-param)，配置片段如下：
<context-param> <param-name>contextConfigLocation</param-name><!--这个参数用于指定Spring配置文件的位置--> <param-value>/WEB-INF/applicationContext.xml</param-value> </context-param>
2）web.xml配置文件中配置监听器org.springframework.web.context.ContextLoaderListener，用于监听ServletContext的加载，配置文件片段如下：
<listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener>
3）导入Struts2的Spring插件包struts2-spring-plugin-2.3.16.3.jar，这是一个Struts2的插件包，用于在Struts2中引入Spring。
4）启动服务器，看看成功没有。（注意：检查一下有没有把需要的包都复制到/WEB-INF/lib中）
5. 创建一个测试用的Action，并在struts.xml和applicationContext.xml中配置，
Action类：
package way.blog.struts2spring.action; import com.opensymphony.xwork2.ActionSupport; public class TestAction extends ActionSupport{ private static final long serialVersionUID = 1L; public TestAction() { } public String execute(){ return "success"; } }
applicationContext.xml配置片段：
<bean id="testAction" class="way.blog.struts2spring.action.TestAction" scope="prototype">
</bean>
struts.xml配置片段：
<package name="test" extends="struts-default" namespace="/"> <!-- 这里action的class属性我们不填实现类的类名，而是填这个action在Spring配置中的bean的名称 --> <action name="testAction" class="testAction" method="execute"> <result name="success">/index.jsp</result> </action> </package>
运行服务器并访问该Action，页面成功跳转到/index.jsp，说明Struts2和Spring整合成功。
二、（重点）对关键配置的分析
1. 整合过程中，web.xml里添加的初始化参数(context-param) contextConfigLocation，是用来指定Spring配置文件的位置的，在这个例子中，参数的值为/WEB-INF/applicationContext.xml，那这个参数是被谁使用的呢？我们可以猜到可能与web.xml中添加的监听器有关，接着往下看。
2. web.xml中添加的监听器org.springframework.web.context.ContextLoaderListener，继承了ContextLoader类，实现了ServletContextListener接口，所以它是在监听Web应用的状态（启动和关闭），即监听ServletContext对象的状态（初始化和销毁），这里我查看Spring的源码：
ContextLoaderListener类片段：
/** * Initialize the root web application context. */ @Override public void contextInitialized(ServletContextEvent event) { initWebApplicationContext(event.getServletContext());
}
监听器监听ServletContext的初始化，在初始化完成后调用contextInitialized方法，contextInitialized方法中调用了父类ContextLoader中的initWebApplicationContext方法，并把初始化完成的ServletContext对象作为参数传入，我们看看ContextLoader的源码：
ContextLoader源码片段：
1 /** 2 * Initialize Spring's web application context for the given servlet context, 3 * using the application context provided at construction time, or creating a new one 4 * according to the "{@link #CONTEXT_CLASS_PARAM contextClass}" and 5 * "{@link #CONFIG_LOCATION_PARAM contextConfigLocation}" context-params. 6 * @param servletContext current servlet context 7 * @return the new WebApplicationContext 8 * @see #ContextLoader(WebApplicationContext) 9 * @see #CONTEXT_CLASS_PARAM 10 * @see #CONFIG_LOCATION_PARAM 11 */ 12 public WebApplicationContext initWebApplicationContext(ServletContext servletContext) { 13 if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) { 14 throw new IllegalStateException( 15 "Cannot initialize context because there is already a root application context present - " + 16 "check whether you have multiple ContextLoader* definitions in your web.xml!"); 17 } 18 19 Log logger = LogFactory.getLog(ContextLoader.class); 20 servletContext.log("Initializing Spring root WebApplicationContext"); 21 if (logger.isInfoEnabled()) { 22 logger.info("Root WebApplicationContext: initialization started"); 23 } 24 long startTime = System.currentTimeMillis(); 25 26 try { 27 // Store context in local instance variable, to guarantee that 28 // it is available on ServletContext shutdown. 29 if (this.context == null) { 30 this.context = createWebApplicationContext(servletContext); 31 } 32 if (this.context instanceof ConfigurableWebApplicationContext) { 33 ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context; 34 if (!cwac.isActive()) { 35 // The context has not yet been refreshed -> provide services such as 36 // setting the parent context, setting the application context id, etc 37 if (cwac.getParent() == null) { 38 // The context instance was injected without an explicit parent -> 39 // determine parent for root web application context, if any. 40 ApplicationContext parent = loadParentContext(servletContext); 41 cwac.setParent(parent); 42 } 43 configureAndRefreshWebApplicationContext(cwac, servletContext); 44 } 45 } 46 servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context); 47 48 ClassLoader ccl = Thread.currentThread().getContextClassLoader(); 49 if (ccl == ContextLoader.class.getClassLoader()) { 50 currentContext = this.context; 51 } 52 else if (ccl != null) { 53 currentContextPerThread.put(ccl, this.context); 54 } 55 56 if (logger.isDebugEnabled()) { 57 logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" + 58 WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]"); 59 } 60 if (logger.isInfoEnabled()) { 61 long elapsedTime = System.currentTimeMillis() - startTime; 62 logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms"); 63 } 64 65 return this.context; 66 } 67 catch (RuntimeException ex) { 68 logger.error("Context initialization failed", ex); 69 servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex); 70 throw ex; 71 } 72 catch (Error err) { 73 logger.error("Context initialization failed", err); 74 servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err); 75 throw err; 76 } 77 } 78 79 protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) { 80 if (ObjectUtils.identityToString(wac).equals(wac.getId())) { 81 // The application context id is still set to its original default value 82 // -> assign a more useful id based on available information 83 String idParam = sc.getInitParameter(CONTEXT_ID_PARAM); 84 if (idParam != null) { 85 wac.setId(idParam); 86 } 87 else { 88 // Generate default id... 89 wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + 90 ObjectUtils.getDisplayString(sc.getContextPath())); 91 } 92 } 93 94 wac.setServletContext(sc); 95 String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM); 96 if (configLocationParam != null) { 97 wac.setConfigLocation(configLocationParam); 98 } 99 100 // The wac environment's #initPropertySources will be called in any case when the context 101 // is refreshed; do it eagerly here to ensure servlet property sources are in place for 102 // use in any post-processing or initialization that occurs below prior to #refresh 103 ConfigurableEnvironment env = wac.getEnvironment(); 104 if (env instanceof ConfigurableWebEnvironment) { 105 ((ConfigurableWebEnvironment) env).initPropertySources(sc, null); 106 } 107 108 customizeContext(sc, wac); 109 wac.refresh(); 110 }
源码看起来很复杂，但是只是出于理解的目的，所以我们只看重点的地方。
以上第30行处创建了一个WebApplicationContext对象（其实，WebApplicationContext只是这个对象实现的接口之一，通过第33行的类型强转我们可以看出这个对象还实现了ConfigurableWebApplicationContext接口），这个对象就是Spring的上下文对象，通过这个对象我们可以获取Spring中定义的Bean（还记得单独使用Spring时用的ClassPathXmlApplicationContext或FileSystemXmlApplicationContext吗？）。
第43行处的configureAndRefreshWebApplicationContext方法使用ServletContext对象对WebApplicationContext对象进行配置。
第95行处获取了ServletContext中的初始化参数CONFIG_LOCATION_PARAM，并在97行将该参数的值设置为WebApplicationContext的配置文件位置。其实常量CONFIG_LOCATION_PARAM就是字符串"contextConfigLocation"，也就是说web.xml中配置的初始化参数在这里被用到了，这也印证了我们上面的猜想。
创建并配置了Spring的上下文对象之后，在46行处，ServletContext对象将该WebApplicationContext对象设置为自己的一个属性，属性名为WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE。
剩下的就是异常处理的代码了。
我们发现，在ContextLoaderListener监听到ServletContext初始化完成后，只不过是创建了一个Spring的上下文对象，并将其设置为ServletContext对象的一个属性而已。我们可以知道的是，这个Spring的上下文对象肯定会在创建Action对象的时候被用到，但是Struts2是在什么时候获取这个对象，并在哪里使用这个对象来获取Action对象的bean呢？
3. 为了确定Action对象的创建时机，我使用了一个小技巧，我在TestAction的构造方法中手动抛出了一个异常，这样我就可以根据异常信息跟踪调用创建Action对象的方法路径了。
修改后的TestAction构造方法：
1 public TestAction() throws Exception{ 2 throw new Exception("创建Action对象时手动抛出的异常"); 3 }
访问TestAction时的异常信息：
1 严重: Exception occurred during processing request: Unable to instantiate Action, testAction, defined for 'testAction' in namespace '/'Error creating bean with name 'testAction' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [way.blog.struts2spring.action.TestAction]: Constructor threw exception; nested exception is java.lang.Exception: 创建Action对象时手动抛出的异常 2 Unable to instantiate Action, testAction, defined for 'testAction' in namespace '/'Error creating bean with name 'testAction' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [way.blog.struts2spring.action.TestAction]: Constructor threw exception; nested exception is java.lang.Exception: 创建Action对象时手动抛出的异常 3 at com.opensymphony.xwork2.DefaultActionInvocation.createAction(DefaultActionInvocation.java:316) 4 at com.opensymphony.xwork2.DefaultActionInvocation.init(DefaultActionInvocation.java:397) 5 at com.opensymphony.xwork2.DefaultActionProxy.prepare(DefaultActionProxy.java:194) 6 at org.apache.struts2.impl.StrutsActionProxy.prepare(StrutsActionProxy.java:63) 7 at org.apache.struts2.impl.StrutsActionProxyFactory.createActionProxy(StrutsActionProxyFactory.java:37) 8 at com.opensymphony.xwork2.DefaultActionProxyFactory.createActionProxy(DefaultActionProxyFactory.java:58) 9 at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:552) 10 at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77) 11 at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99) 12 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) 13 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) 14 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220) 15 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122) 16 at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501) 17 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170) 18 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98) 19 at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950) 20 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116) 21 at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408) 22 at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040) 23 at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607) 24 at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313) 25 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) 26 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) 27 at java.lang.Thread.run(Thread.java:745) 28 Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'testAction' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [way.blog.struts2spring.action.TestAction]: Constructor threw exception; nested exception is java.lang.Exception: 创建Action对象时手动抛出的异常 29 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1101) 30 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1046) 31 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:504) 32 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476) 33 at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322) 34 at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194) 35 at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:956) 36 at com.opensymphony.xwork2.spring.SpringObjectFactory.buildBean(SpringObjectFactory.java:151) 37 at com.opensymphony.xwork2.ObjectFactory.buildBean(ObjectFactory.java:171) 38 at com.opensymphony.xwork2.factory.DefaultActionFactory.buildAction(DefaultActionFactory.java:22) 39 at com.opensymphony.xwork2.ObjectFactory.buildAction(ObjectFactory.java:141) 40 at com.opensymphony.xwork2.DefaultActionInvocation.createAction(DefaultActionInvocation.java:297) 41 ... 24 more 42 Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [way.blog.struts2spring.action.TestAction]: Constructor threw exception; nested exception is java.lang.Exception: 创建Action对象时手动抛出的异常 43 at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:163) 44 at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:89) 45 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1094) 46 ... 35 more 47 Caused by: java.lang.Exception: 创建Action对象时手动抛出的异常 48 at way.blog.struts2spring.action.TestAction.<init>(TestAction.java:13) 49 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) 50 at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) 51 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) 52 at java.lang.reflect.Constructor.newInstance(Constructor.java:526) 53 at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:147) 54 ... 37 more
异常信息很长，但是我们可以过滤掉一些跟我们本次分析无关的，只保留与Struts2和Spring有关的信息，即红色和蓝色字体部分。
通过第11行到第3行，我们可以看出从StrutsPrepareAndExecuteFilter的doFilter方法开始如何通过一层层调用来创建Action对象，意料之中的是，我们发现了Struts2和Spring的衔接点，即上面的35-37行（蓝色字体），Struts2调用了Spring上下文对象（AbstractApplicationContext对象，猜测应该就是上面ContextLoaderListener中创建的Spring上下文对象转换来的，下面将验证这一点）的getBean方法！！！
Struts2中的一个对象引起了我们的注意——SpringObjectFactory，正是这个对象的buildBean方法完成了对Spring上下文对象的调用。我们继续查看源码：
com.opensymphony.xwork2.SpringObjectFactory源码片段：
1 /** 2 * Simple implementation of the ObjectFactory that makes use of Spring's application context if one has been configured, 3 * before falling back on the default mechanism of instantiating a new class using the class name. <p/> In order to use 4 * this class in your application, you will need to instantiate a copy of this class and set it as XWork's ObjectFactory 5 * before the xwork.xml file is parsed. In a servlet environment, this could be done using a ServletContextListener. 6 * 7 * @author Simon Stewart (sms@lateral.net) 8 */ 9 public class SpringObjectFactory extends ObjectFactory implements ApplicationContextAware { 10 private static final Logger LOG = LoggerFactory.getLogger(SpringObjectFactory.class); 11 12 protected ApplicationContext appContext; 13 /* 14 * 省略............ 15 */ 16 /** 17 * Set the Spring ApplicationContext that should be used to look beans up with. 18 * 19 * @param appContext The Spring ApplicationContext that should be used to look beans up with. 20 */ 21 public void setApplicationContext(ApplicationContext appContext) 22 throws BeansException { 23 this.appContext = appContext; 24 autoWiringFactory = findAutoWiringBeanFactory(this.appContext); 25 } 26 /* 27 * 省略............ 28 */ 29 /** 30 * Looks up beans using Spring's application context before falling back to the method defined in the {@link 31 * ObjectFactory}. 32 * 33 * @param beanName The name of the bean to look up in the application context 34 * @param extraContext 35 * @return A bean from Spring or the result of calling the overridden 36 * method. 37 * @throws Exception 38 */ 39 @Override 40 public Object buildBean(String beanName, Map<String, Object> extraContext, boolean injectInternal) throws Exception { 41 Object o; 42 43 if (appContext.containsBean(beanName)) { 44 o = appContext.getBean(beanName); 45 } else { 46 Class beanClazz = getClassInstance(beanName); 47 o = buildBean(beanClazz, extraContext); 48 } 49 if (injectInternal) { 50 injectInternalBeans(o); 51 } 52 return o; 53 } 54 /* 55 * 省略............ 56 */ 57 }
以上只截取了SpringObjectFactory中与我们分析有关的部分。我们来分析一下，首先，这个类继承了Struts2的ObjectFactory类，而通过查看文档中的说明或者源码（这里就不粘出来了），我们可以发现，这个ObjectFactory类是Struts2很重要的一个类，它用于创建所有Struts2的核心对象，包括Action, Interceptor, Result等。而SpringObjectFactory继承了ObjectFactory，说明通过将Struts2默认的ObjectFactory类替换为SpringObjectFactory就可以实现由Spring来创建对象了。
看一看SpringObjectFactory的源码和注释，buildBean(String,Map<String,Object>,boolean)方法覆盖了ObjectFactory中的对应方法，它接收的第一个参数，即是我们在struts.xml配置文件中为action指定的class属性。我们看到，这个方法首先是尝试从appContext中获取对应名称的bean，如果失败，才把该名称当做类名去创建对象。还记得我们前面的一个问题吗？Struts2怎么知道什么时候把action配置中的class属性当做bean的名称，什么时候又把它当做类名？这里就是答案了。我们从方法注释上也可以看到，该方法先尝试从Spring的上下文中获取对应名称的对象，如果失败，才使用父类的方法根据类名去创建新的对象。
谜团已经逐步解开，但是还有一个问题。注意，SpringObjectFactory中的ApplicationContext对象appContext是通过setApplicationContext方法传入的，那是由谁传入的？传入的是不是前面在ContextLoaderListener中创建的那个WebApplicationContext对象呢？
4. 我为了解决上面的问题想了很久，最后才发现，我一直忽略了之前导入的struts2-spring-plugin-xxx.jar这个包，也许这就是问题的答案了。通过查看该包，发现一个StrutsSpringObjectFactory类，这个类继承了上面提到的SpringObjectFactory，
org.apache.struts2.spring.StrutsSpringObjectFactory源码片段：
1 /** 2 * Struts object factory that integrates with Spring. 3 * <p/> 4 * Spring should be loaded using a web context listener 5 * <code>org.springframework.web.context.ContextLoaderListener</code> defined in <code>web.xml</code>. 6 * 7 */ 8 public class StrutsSpringObjectFactory extends SpringObjectFactory { 9 private static final Logger LOG = LoggerFactory.getLogger(StrutsSpringObjectFactory.class); 10 /* 11 *省略... 12 */ 13 /** 14 * Constructs the spring object factory 15 * @param autoWire The type of autowiring to use 16 * @param alwaysAutoWire Whether to always respect the autowiring or not 17 * @param useClassCacheStr Whether to use the class cache or not 18 * @param servletContext The servlet context 19 * @since 2.1.3 20 */ 21 @Inject 22 public StrutsSpringObjectFactory( 23 @Inject(value=StrutsConstants.STRUTS_OBJECTFACTORY_SPRING_AUTOWIRE,required=false) String autoWire, 24 @Inject(value=StrutsConstants.STRUTS_OBJECTFACTORY_SPRING_AUTOWIRE_ALWAYS_RESPECT,required=false) String alwaysAutoWire, 25 @Inject(value=StrutsConstants.STRUTS_OBJECTFACTORY_SPRING_USE_CLASS_CACHE,required=false) String useClassCacheStr, 26 @Inject ServletContext servletContext, 27 @Inject(StrutsConstants.STRUTS_DEVMODE) String devMode, 28 @Inject Container container) { 29 30 super(); 31 boolean useClassCache = "true".equals(useClassCacheStr); 32 if (LOG.isInfoEnabled()) { 33 LOG.info("Initializing Struts-Spring integration..."); 34 } 35 36 Object rootWebApplicationContext = servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE); 37 38 if(rootWebApplicationContext instanceof RuntimeException){ 39 RuntimeException runtimeException = (RuntimeException)rootWebApplicationContext; 40 LOG.fatal(runtimeException.getMessage()); 41 return; 42 } 43 44 ApplicationContext appContext = (ApplicationContext) rootWebApplicationContext; 45 if (appContext == null) { 46 // uh oh! looks like the lifecycle listener wasn't installed. Let's inform the user 47 String message = "********** FATAL ERROR STARTING UP STRUTS-SPRING INTEGRATION **********\n" + 48 "Looks like the Spring listener was not configured for your web app! \n" + 49 "Nothing will work until WebApplicationContextUtils returns a valid ApplicationContext.\n" + 50 "You might need to add the following to web.xml: \n" + 51 " <listener>\n" + 52 " <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>\n" + 53 " </listener>"; 54 LOG.fatal(message); 55 return; 56 } 57 58 String watchList = container.getInstance(String.class, "struts.class.reloading.watchList"); 59 String acceptClasses = container.getInstance(String.class, "struts.class.reloading.acceptClasses"); 60 String reloadConfig = container.getInstance(String.class, "struts.class.reloading.reloadConfig"); 61 62 if ("true".equals(devMode) 63 && StringUtils.isNotBlank(watchList) 64 && appContext instanceof ClassReloadingXMLWebApplicationContext) { 65 //prevent class caching 66 useClassCache = false; 67 68 ClassReloadingXMLWebApplicationContext reloadingContext = (ClassReloadingXMLWebApplicationContext) appContext; 69 reloadingContext.setupReloading(watchList.split(","), acceptClasses, servletContext, "true".equals(reloadConfig)); 70 if (LOG.isInfoEnabled()) { 71 LOG.info("Class reloading is enabled. Make sure this is not used on a production environment!", watchList); 72 } 73 74 setClassLoader(reloadingContext.getReloadingClassLoader()); 75 76 //we need to reload the context, so our isntance of the factory is picked up 77 reloadingContext.refresh(); 78 } 79 80 this.setApplicationContext(appContext); 81 82 int type = AutowireCapableBeanFactory.AUTOWIRE_BY_NAME; // default 83 if ("name".equals(autoWire)) { 84 type = AutowireCapableBeanFactory.AUTOWIRE_BY_NAME; 85 } else if ("type".equals(autoWire)) { 86 type = AutowireCapableBeanFactory.AUTOWIRE_BY_TYPE; 87 } else if ("auto".equals(autoWire)) { 88 type = AutowireCapableBeanFactory.AUTOWIRE_AUTODETECT; 89 } else if ("constructor".equals(autoWire)) { 90 type = AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR; 91 } else if ("no".equals(autoWire)) { 92 type = AutowireCapableBeanFactory.AUTOWIRE_NO; 93 } 94 this.setAutowireStrategy(type); 95 96 this.setUseClassCache(useClassCache); 97 98 this.setAlwaysRespectAutowireStrategy("true".equalsIgnoreCase(alwaysAutoWire)); 99 100 if (LOG.isInfoEnabled()) { 101 LOG.info("... initialized Struts-Spring integration successfully"); 102 } 103 } 104 }
这个类中只有一个方法，就是构造方法，在36行处我们惊奇的发现，我们之前存入ServletContext对象中的属性ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE终于又出现了！！！该属性的值就是在ContextLoaderListener中创建的那个Spring上下文对象，这里将其获取出来，并在第80行处调用了父类，即SpringObjectFactory的setApplicationContext方法将其赋值给继承自父类的ApplicationContext类型成员变量appContext。到这里就解决了上面问题的，我们证明了SpringObjectFactory中用到的ApplicationContext对象就是之前ContextLoaderListener中创建的，而且该对象由StrutsSpringObjectFactory的构造方法中调用父类的setApplicationContext方法传入。
5. 通过上面的分析我们确定了最后会用StrutsSpringObjectFactory类代替Struts中原来的ObjectFactory。那么是在哪里发生替换的呢？我先看了看struts核心包中的struts-default.xml文件，发现了我们要找的默认的ObjectFactory的定义：
struts-default.xml片段：
<bean class="com.opensymphony.xwork2.ObjectFactory" name="struts"/>
我们再查看struts核心包中的default.properties文件中定义的常量，我们找到了这一段：
1 ### if specified, the default object factory can be overridden here 2 ### Note: short-hand notation is supported in some cases, such as "spring" 3 ### Alternatively, you can provide a com.opensymphony.xwork2.ObjectFactory subclass name here 4 # struts.objectFactory = spring
也就是说只要我们将struts.objectFactory常量的值覆盖，换成我们自己定义的ObjectFactory对象，就可以覆盖原来的默认ObjectFactory了。我们再看看struts2-spring-plugin-xxx.jar插件包中的struts-plugin.xml文件，真相大白了！！！！
struts-plugin.xml文件片段：
<bean type="com.opensymphony.xwork2.ObjectFactory" name="spring" class="org.apache.struts2.spring.StrutsSpringObjectFactory" /> <!-- Make the Spring object factory the automatic default --> <constant name="struts.objectFactory" value="spring" />
我们看到这里定义了一个名为"spring"的ObjectFactory对象，其实现类正是StrtutsSpringObjectFactory，并且接下来设置了struts.objectFactory常量，将其设置成了我们定义的"spring"对象。
我们知道，Struts2在加载配置文件的时候会在Classpath中的寻找struts-plugin.xml文件，并自动将其加载，这样就完成了将Struts2与Spring的整合了。
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这个过程我也是花了很久才整理出来的，因为忘记了struts-plugin.xml是自动加载的，所以我没有从struts-plugin.xml作为突破口，不然可能整个过程会顺利许多。不过这样一个探索的过程也是挺有趣的。这个过程中难免有些疏漏，或者说明不清楚，就请大家多多指教了，毕竟这是我第一篇博客，哈哈哈！！！
文章是原创的，大家可以自由修改完善并转发，转发时请注明出处，，谢谢。
