帮忙看下 struts2下PrintWriter out = response.getWriter();出错

Question

package com.sunmq.action;import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.http.HttpServletResponse;
import com.opensymphony.xwork2.ActionSupport;public class CheckUserAction extends ActionSupport  {
    private String type;
    
    public String execute() throws IOException {
     HttpServletResponse response=null;
     response.setContentType("text/html; charset=UTF-8");
PrintWriter out = response.getWriter();
out.print("<script>alert('成功');window.location.reload();</script>");
        return SUCCESS;
    } public String getType() {
return type;
} public void setType(String type) {
this.type = type;
}}出错如下
type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception java.lang.NullPointerException
com.sunmq.action.CheckUserAction.execute(CheckUserAction.java:23)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)
com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:452)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:291)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:254)

Answer 1

HttpServletResponse response=null;//你都把它设为null用 this.response 就可以获得到

Answer 2

HttpServletResponse response=null;
  response.setContentType("text/html; charset=UTF-8");
PrintWriter out = response.getWriter();你的response都还没有值 你就设置setContentType，你说他能不报错不？

Answer 3

 response.setContentType("text/html; charset=UTF-8");
去掉还是同样的错误

Answer 4

java.lang.NullPointerException
com.sunmq.action.CheckUserAction.execute(CheckUserAction.java:23)//这句空指针了，在23行。

Answer 5

java.lang.NullPointerException
HttpServletResponse response;
not
HttpServletResponse response=null;

Answer 6

这样才是实例了一个。不然你都设置为NUll了 你说怎么不为空呢？

Answer 7

HttpServletResponse response = ServletActionContext.getResponse();

Answer 8

还有如果你用的是struts2的话是不可以 return success的; 一定要return null 才会有值!!!!!!!