2-6自由编程

为什么在返回答案的时候会出现乱码？

这是答案返回Servlet类：daanfanhui.java

package com.winking.ServletProj.change;
 
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
/**
 * Servlet implementation class daanfanhui
 */
@WebServlet("/mun")
public class daanfanhui extends HttpServlet {
    private static final long serialVersionUID = 1L;
        
    /**
     * @see HttpServlet#HttpServlet()
     */
    public daanfanhui() {
        super();
        // TODO Auto-generated constructor stub
    }
 
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         
        int mun=(int)request.getAttribute("reqn");
         
        response.getWriter().println("这是累加的和："+mun);
        response.setContentType("text/html;charset=utf-8");
    }
 
}

这是请求获取Servlet：getnum.java

package com.winking.ServletProj.change;
 
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
/**
 * Servlet implementation class getnum
 */
@WebServlet("/get")
public class getnum extends HttpServlet {
    private static final long serialVersionUID = 1L;
        
    /**
     * @see HttpServlet#HttpServlet()
     */
    public getnum() {
        super();
        // TODO Auto-generated constructor stub
    }
 
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String n =request.getParameter("n");
        int a=Integer.parseInt(n);
        int i=0;
        int umn=0;
        while(i<=a) {
            umn=umn+i;
            i++;
        }
        request.setAttribute("reqn", umn);
        request.getRequestDispatcher("/mun").forward(request, response);
         
    }
 
}

这是html的代码：computer.html

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="http://localhost:8080/FirstServlet/get">
<input type="text" name="n" "/>
<input type="submit" value="求累加和"/>
</form>
</body>
</html>