struts2 spring 整合 action 依赖注入异常

今天在进行struts2加spring整合的过程中，出现了空指针错误，错误信息如下“：

java.lang.NullPointerException

    com.action.UserAction.deal(UserAction.java:31)    com.action.UserAction$$FastClassBySpringCGLIB$$898dd58c.invoke()    org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)    org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:720)    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)    org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99)    org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:281)    org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)    org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)    org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:655)    com.action.UserAction$$EnhancerBySpringCGLIB$$b82da6c_2.deal()    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)    java.lang.reflect.Method.invoke(Method.java:498)    com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:450)    com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:289)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:252)    org.apache.struts2.interceptor.DeprecationInterceptor.intercept(DeprecationInterceptor.java:41)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:167)    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:265)    org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:249)    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:249)    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:191)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:73)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:91)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:252)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:139)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:193)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:189)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)    org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54)    org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:562)    org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)    org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99)    org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)    org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)    org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)    org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)    org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)    org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)    org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:452)    org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1087)    org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)    org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2536)    org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2525)    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)    java.lang.Thread.run(Thread.java:745)

开始我以为是配置问题导致struts2没有整合spring，然后在myeclipse上进行了单元测试，发现单元测试结果正常，action的usermanager能正常注入，说明此时action的确是由spring产生的，但是在web上就会出现空指针错误。在网上查阅大量资料后发现网上说的各种情况都不符合，最后查到说action的usermanager的变量名要和usermanager类在spring容器中的ID相同才行，只有action的usermanager的变量名和usermanager类的ID相同时 才不会出错，如果变量名和ID不相同，即使在action的usermanager的set方法上使用resource注解并指定usermanager类的ID，也会出错。比如action的变量名为user，注解为resource（name="userManager"）,usermanager类的ID为userManager,也还是会报错，只有把变量名改成userManager或把usermanager类的ID改成user才能去掉异常。

今天偶然发现在action中的变量名和对应类的ID相同的情况下，即使没有加resource也能成功注入,也就是其实userManager的注入不是因为rrsource.其实，在struts2-spring-plugin中有一个autowire的设置，

这个autowire的值默认是设为name,说明struts2和spring整合后会根据action的属性的名字去spring的容器里查找ID和它一样的类，如果找到就会自动装配上。这也是为什么去掉resource后还能成功注入的原因。那为什么resource不起作用呢？在网上查找后发现，struts.xml配置文件里的action配置有问题，在正常情况下的配置是这样的：

     <action name="user"  class="com.action.UserAction" >
    <result>/front/registersuccess.jsp</result>
    <result name="fail">/front/registerfail.jsp</result>
    <result name="list">/front/userlist.jsp</result>
    </action> 

class属性填入的是包名加类名，但是整合之后应该是这样：

     <action name="user"  class="userAction" >
    <result>/front/registersuccess.jsp</result>
    <result name="fail">/front/registerfail.jsp</result>
    <result name="list">/front/userlist.jsp</result>
    </action> 

在class里填入的应该是UserAction在spring容器里的ID名，其实就是把com.action.UserAction改成userAction,就行了。然后在UserAction中的属性的set方法里加上resource注解，这样即使属性名和类名不一样也能成功注入。

这其实是两种不同的设置action的方式，一种是struts配置文件中class还是用全限定名，struct自己产生action对象，然后利用spring插件的自动装配功能完成注入，也就是autowire方式，这种方法不用写spring注释（component,scope,resource）。另一种则是把action也交给spring管理，由spring产生和装配，这时的XML配置文件中的class要使用action类在spring容器中的ID名,要写component，scope，resouce。

另外，注意使用autowire方式注入时可能发生一种难以发现的异常，就是spring插件把类型不同但名称相同的类租入了导致类型转换错误，比如action类里有一User类型的变量叫user，spring容器中有一UserManager类型的类的ID也叫user，spring就会把UserManager付给User，然后抛出类型错误异常，提示不能从UserManager类转成User类。