课题打卡~请老师检查

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <div style="width: 620px;">
        <form action="ajax/emp" method="get">
            <input style="width: 200px;" type="button" id="popular"
                name="popular" value="流行歌曲"> <input style="width: 200px;"
                type="button" id="classic" name="classic" value="经典歌曲"> <input
                style="width: 200px;" type="button" id="rock" name="rock"
                value="摇滚歌曲">
        </form>
    </div>
    <div style="width: 600px; text-align: center;">
        <div id="content"></div>
    </div>
    <script type="text/javascript" src="js/jquery-3.3.1.js"></script>
    <script type="text/javascript">
        $(function() {
            $("#popular").click(function() {
                initAjax("ajax/song","get","flag=popular","json");
            }); 
            $("#classic").click(function() {
                initAjax("ajax/song","get","flag=classic","json");
            }); 
            $("#rock").click(function() {
                initAjax("ajax/song","get","flag=rock","json");
            }); 
        });
        function initAjax(url,type,data,dataType){
            $.ajax({
                "url" : url,
                "type" : type,
                "data" : data,
                "dataType" : dataType,
                "success" : function(json) {
                    $("#content").text("");
                    console.log(json.length);
                    for(var i=0;i<json.length;i++){
                        $("#content").append("<h2><b>"+json[i].name+"</b></h2>");
                    }                                            
                },
                "error" : function(xmlhttp, errorText) {
                    console.log(xmlhttp);
                    console.log(errorText);
                    if(xmlhttp.status == 400){
                        alert("无效的请求");
                    }else if(xmlhttp.status == 404){
                        alert("无法找到文件");
                    }else if(xmlhttp.status == 500){
                        alert("内部服务器错误");
                    }
                }
            });
        }
    </script>
</body>
</html>

package com.imooc.ajax;
 
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
 
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 com.alibaba.fastjson.JSON;
 
/**
 * Servlet implementation class SongServlet
 */
@WebServlet("/ajax/song")
public class SongServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
 
    /**
     * @see HttpServlet#HttpServlet()
     */
    public SongServlet() {
        super();
        // TODO Auto-generated constructor stub
    }
 
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        List<Song> song = new ArrayList<Song>();
        String flag = request.getParameter("flag");
        if (flag.equals("popular")) {
            song.add(new Song(1, "稻香"));
            song.add(new Song(2, "晴天"));
            song.add(new Song(3, "告白气球"));
        } else if (flag.equals("classic")) {
            song.add(new Song(1, "千千阙歌"));
            song.add(new Song(2, "傻女"));
            song.add(new Song(3, "七友"));
        } else if (flag.equals("rock")) {
            song.add(new Song(1, "一块红布"));
            song.add(new Song(2, "假行憎"));
            song.add(new Song(3, "新长征路上的摇滚"));
        }
        String json = JSON.toJSONString(song);
        response.setContentType("text/html;charset=UTF-8");
        response.getWriter().println(json);
    }
 
}