Struts2中ActionContext.getContext().getParameters()异常

唉，发现自己好多的细节都没有能够有一个好的掌握，学艺不精，还需努力！

在action中获取参数的时候，一般常用两种方法：
一：使用ServletActionContext.getRequest().getParameter(“param”)根据参数名取得
二：使用ActionContext.getContext().getParameters()获取所有的请求参数

平常我用的最多的都是第一种，今天用了一下第二种：

Map<String, Object> map = ActionContext.getContext().getParameters()String name = (String) map.get("user");

但是在进行强制转换的时候出现的下面的异常信息：

严重: Exception occurred during processing request: [Ljava.lang.String; cannot be cast to java.lang.Stringjava.lang.ClassCastException: [Ljava.lang.String; cannot be cast to java.lang.String    at action.LoginAction.execute(LoginAction.java:30)    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)    at java.lang.reflect.Method.invoke(Unknown Source)    at ognl.OgnlRuntime.invokeMethod(OgnlRuntime.java:891)    at ognl.OgnlRuntime.callAppropriateMethod(OgnlRuntime.java:1293)    at ognl.ObjectMethodAccessor.callMethod(ObjectMethodAccessor.java:68)    at com.opensymphony.xwork2.ognl.accessor.XWorkMethodAccessor.callMethodWithDebugInfo(XWorkMethodAccessor.java:117)    at com.opensymphony.xwork2.ognl.accessor.XWorkMethodAccessor.callMethod(XWorkMethodAccessor.java:108)    at ognl.OgnlRuntime.callMethod(OgnlRuntime.java:1369)    at ognl.ASTMethod.getValueBody(ASTMethod.java:90)    at ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:212)    at ognl.SimpleNode.getValue(SimpleNode.java:258)    at ognl.Ognl.getValue(Ognl.java:494)    at ognl.Ognl.getValue(Ognl.java:458)    at com.opensymphony.xwork2.ognl.OgnlUtil$2.execute(OgnlUtil.java:309)    at com.opensymphony.xwork2.ognl.OgnlUtil.compileAndExecute(OgnlUtil.java:340)    at com.opensymphony.xwork2.ognl.OgnlUtil.getValue(OgnlUtil.java:307)    at com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:423)    at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:287)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:250)    at org.apache.struts2.interceptor.DeprecationInterceptor.intercept(DeprecationInterceptor.java:41)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:167)    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:265)    at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:76)    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229)    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229)    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:191)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:73)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at org.apache.struts2.interceptor.DateTextFieldInterceptor.intercept(DateTextFieldInterceptor.java:125)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:91)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:253)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:139)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:193)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:189)    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)    at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54)    at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:564)    at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:81)    at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99)    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)    at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:879)    at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:600)    at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1703)    at java.lang.Thread.run(Unknown Source)

经查找发现ActionContext.getContext().getParameters()中，返回的map的value是一个String数组。于是作如下处理：

Map<String, Object> map = ActionContext.getContext().getParameters();for (Entry<String, Object> entity : map.entrySet()) {    System.out.println("请求参数：" + entity.getKey()+" 值："+((String[])entity.getValue())[0]);}

好多东西用到的时候总是似曾相识，但是又没法准确的写出。多记笔记吧，希望能够提升自己。