在提交响应后无法调用sendRedirect（）

HTTP状态500 - 内部服务器错误

输入例外报告

消息在提交响应后无法调用sendRedirect（）

说明服务器遇到意外情况，无法满足请求。

例外

java.lang.IllegalStateException：在提交响应后无法调用sendRedirect（）
org.apache.catalina.connector.ResponseFacade.sendRedirect（ResponseFacade.java:488）
servlet.RegistServlet.doGet（RegistServlet.java:116）
servlet.RegistServlet.doPost（RegistServlet.java:127）
javax.servlet.http.HttpServlet.service（HttpServlet.java:661）
javax.servlet.http.HttpServlet.service（HttpServlet.java:742）
org.apache.tomcat.websocket.server.WsFilter.doFilter（WsFilter.java:52）

注意服务器日志中提供了根本原因的完整堆栈跟踪。

Apache Tomcat / 8.5.38

package servlet;
import com.imooc.domain.User;

import utils.UploadUtils;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/*import org.apache.tomcat.util.http.fileupload.disk.DiskFileItemFactory;
import org.apache.tomcat.util.http.fileupload.servlet.ServletFileUpload;*/

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

/**
* 用户注册的Servlet
*/
@WebServlet("/RegistServlet")
public class RegistServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

  try {
   // 数据的接收
   // 文件上传基本操作:
   // 1.创建一个磁盘文件项工厂对象
   DiskFileItemFactory disFilieItemFactory = new DiskFileItemFactory();
   // 2.创建一个核心解析类
   ServletFileUpload servletFileUpload = new ServletFileUpload(disFilieItemFactory);
   // 3.解析request请求, 返回的是List集合中存放的是FileItem对象
   List<FileItem> list = servletFileUpload.parseRequest(request);
   //定义一个List集合,用于保存兴趣爱好数据:
   List<String> hobbyList = new ArrayList();
   Map<String,String> map = new HashMap();
   // 4.遍历集合,获得每个FileItem,判断是表单项还是文件上传项
      for(FileItem fileItem : list) {
       String url = null;   //存储图片路径
       //判断是表单项还是文件上传项
       if(fileItem.isFormField()) {
        //普通表单项
        //接收表单项参数值:
        String name = fileItem.getFieldName(); // 获得表单项的name属性的值
        String value = fileItem.getString("UTF-8"); // 获得表单项的值
        System.out.println(name+"\t"+value);
        //接收复选框的数据
        if("hobby".equals(name)) {
         String hobbyValue = fileItem.getString("UTF-8");
         //接收到一个值,将这个值存放到hobbyList集合中
         hobbyList.add(hobbyValue);
         hobbyValue = hobbyList.toString().substring(1,hobbyList.toString().length()-1);
         System.out.println(name+"\t"+hobbyValue);
         //将爱好的数据存入到Map集合中:
         map.put(name,hobbyValue);
        }else {
         //将数据存入到map集合中:
         map.put(name,value);
        }
       }else {
        // 文件上传项:
        // 文件上传功能
        //获取文件上传的名称:
        String fileName = fileItem.getName();
        if(fileName != null && !"".equals(fileName)) {
        //通过工具类获得唯一文件名:
        String uuidFileName = UploadUtils.getUUIDFileName(fileName);
        System.out.println(uuidFileName);
        //获得文件上传的数据:
        InputStream is = fileItem.getInputStream();
        //获得文件上传的路径:
        String path = this.getServletContext().getRealPath("/upload");
        //将输入流对接到输出流就可以了:
         url = path+"\\"+uuidFileName;
        OutputStream os = new FileOutputStream(url);
        int len = 0;
        byte[] b = new byte[1024];
        while((len = is.read(b)) != -1) {
         os.write(b,0,len);
        }
        is.close();
        os.close();
        }
       }
       System.out.println(map);
       //封装数据到User当中
       User user = new User();
       user.setUsername(map.get("username"));
       user.setPassword(map.get("password"));
       user.setSex(map.get("sex"));
       user.setNickname(map.get("nickname"));
       user.setHobby(map.get("hobby"));
       user.setPath(url);
       //将注册用户的信息存入到List集合中:
       List<User> userList = (List<User>) this.getServletContext().getAttribute("list");
       userList.add(user);
       for(User u : userList) {
        System.out.println(u);
       }

       this.getServletContext().setAttribute("list", userList);
       // 注册成功,跳转到登录页面
       request.getSession().setAttribute("username", user.getUsername());
       response.sendRedirect(request.getContextPath()+"/login.jsp");
      }
  } catch (FileUploadException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request,response);
}

}

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>注册</title>
<link rel="stylesheet" href="./css/reg.css">
</head>
<body>
    <div class="reg">
        <div class="header">
            <h1>
                <a href="./login.jsp">登录</a> <a href="./regist.jsp">注册</a>
            </h1>
        </div>
        
        <form action="/reg_login/RegistServlet" method="post" enctype="multipart/form-data">
            <table>
                <tr>
                    <td class="td1">用户名</td>
                    <td><input type="text" class="input1" name="username"></td>
                </tr>
                <tr>
                    <td class="td1">密码</td>
                    <td><input type="password" class="input1" name="password"></td>
                </tr>
                <tr>
                    <td class="td1">昵称</td>
                    <td><input type="text" class="input1" name="nickname"></td>
                </tr>
                <tr>
                    <td class="td1">性别</td>
                    <td>
                        <input type="radio" name="sex" value="male">男
                        <input type="radio" name="sex" value="female">女
                    </td>
                </tr>
                <tr>
                    <td class="td1">上传头像</td>
                    <td><input type="file" id="photo" name="upload"></td>
                </tr>
                <tr>
                    <td class="td1">兴趣爱好</td>
                    <td><label>
                        <input type="checkbox" name="hobby" value="篮球">篮球
                        <input type="checkbox" name="hobby" value="足球">足球
                        <input type="checkbox" name="hobby" value="排球">排球
                        <input type="checkbox" name="hobby" value="羽毛球">羽毛球
                    </label></td>
                </tr>
                <tr>
                    <td colspan="2">
                        <div class="btn-red">
                            <input type="submit" value="注册" id="reg-btn">
                        </div>
                    </td>
                </tr>
            </table>
        </form>
    </div>
</body>
</html>