struts2 java.lang.IllegalStateException: getWriter() has already been called for this response(异常解决)

 预告： 重点请看最后面。

做excel导出时遇到的问题，很多时候会遇到此错误，异常如下:

java.lang.IllegalStateException: getWriter() has already been called for this response
at org.apache.catalina.connector.Response.getOutputStream(Response.java:628)
at org.apache.catalina.connector.ResponseFacade.getOutputStream(ResponseFacade.java:196)
at com.wrt.action.order.EndOrderAction.exportInfo(EndOrderAction.java:143)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:446)
at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:285)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242)
at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:176)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242)
at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:265)
at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242)
背景如下：
使用Struts2框架，点击某个按钮实现列表excel导出
2.大致代码如下

public void exportInfo(){
try {
//web对象
HSSFWorkbook wb = new HSSFWorkbook();
//创建表头等
HSSFSheet sheet = wb.createSheet("test1");
//创建行
HSSFRow row = sheet.createRow(0);
//创建列
HSSFCell cell = row.createCell(0);
//**************省略excel创建部分..
HttpServletResponse response = ServletActionContext.getResponse();
OutputStream output = getRepsonse().getOutputStream();
response.reset();
response.setHeader("Content-disposition", "attachment; filename=details.xls");
response.setContentType("application/msexcel");
wb.write(output);
output.close();
System.out.println("成功创建excel文件");
} catch (Exception e) {
e.printStackTrace();
}
}

 
最终解决方案，将response.reset(); 放到OutputStream output = getRepsonse().getOutputStream();前面，

HttpServletResponse response = ServletActionContext.getResponse();
response.reset();
OutputStream output = getRepsonse().getOutputStream();
response.setHeader("Content-disposition", "attachment; filename=details.xls");
response.setContentType("application/msexcel");

 运行效果如下成功。 
.


原因，避免可能出现未关闭的getWriter()，使用了response.reset();进行刷新，而此时却在未刷新的情况下进行了OutputStream output = getRepsonse().getOutputStream();操作.....    简之：就是位置放错了 

.

会出现如下异常的三种可能：
1.通过response.reset(); 刷新可能存在一些未关闭的getWriter().  来源：http://blog.csdn.net/wonder4/article/details/8476603
2.struts2请求方法中返回了success此类会返回数据或者界面的，举例如下：
public String saveSubmitOrder(){
return "success";
}

改成
public String saveSubmitOrder(){
return null;
}

或者void。
3.存在多个getWriter且未关闭状态，或者getWriter与OutputStream同时出现。

总之，一个请求过来只会有一个返回结果，如果存在两个或以上则会出现此异常.