javaWeb用ajax传map数据怎么转换为json以及如何被后台进行拆分成java的map

$(".mod_post").click(function (e) {

    var id = $(".id").val(),
        name = $(".name").val(),
        english = $(".english").val(),
        chinese = $(".chinese").val(),
        math = $(".math").val(),
        total = $(".total").val();

    var map_data_o = {};

    var old_data = new Map();

    var new_data = new Map();

    if (id != idc) {
        new_data.set("id", id);

    } else {
        old_data.set("id", idc);
        map_data_o["id"]=idc;
    }

    if (name != namec) {
        new_data.set("name", name);
    } else {
        old_data.set("name", namec);
    }

    if (chinese != chinesec) {
        new_data.set("chinese", chinese);
    } else {
        old_data.set("chinese", chinesec);
    }

    if (math != mathc) {
        new_data.set("math", math);
    } else {
        old_data.set("math", mathc);
    }

    if (english != englishc) {
        new_data.set("english", english);
    } else {
        old_data.set("english", englishc);
    }

    if (total != totalc) {
        new_data.set("total", total);
    } else {
        old_data.set("total", totalc);
    }

    console.log(new_data);
    new_data.set("null","null");
    //为了区分新数据和老数据的分界线，
    //因为数据一旦用json传输的话就会把map转换为数组所以需要用这个来区分新数据和老数据
    console.log(old_data);

    // JSON.parse(JSON.stringify(new_data));
    // JSON.parse(JSON.stringify(old_data));
    console.log(JSON.parse(JSON.stringify(new_data)));
    console.log(JSON.parse(JSON.stringify(old_data)));
    $.ajax({
        type: "post",
        url: "/servlet_mod",
        data:{
            // n:Array.from(new_data),
            // o:Array.from(old_data)
           	n:Array.from(new_data),
            o:Array.from(old_data)
        },
        dataType: "json",
        success: function (response) {
        }
    });
})

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 java.io.IOException;
import java.util.*;
@WebServlet("/servlet_mod")
public class Mod_server_ajax extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        Map map = req.getParameterMap();
        Map n_val=new HashMap();
        Map o_val=new HashMap();
        boolean n_or_o= true;
        //遍历
        for (Iterator iter = map.entrySet().iterator(); iter.hasNext(); ) {
            Map.Entry element = (Map.Entry) iter.next();
            //key值
            //Object strKey = element.getKey();//获取的是o[0][] 或者是n[1][]的数据键值
            //value,数组形式的值，但是因为前端是map的原因所以0的位置存的是key 1的位置存的是value
            String[] value = (String[]) element.getValue();

            if (value[0].equals("null") && value[1].equals("null")) {
                n_or_o = false;
                continue;
            }
            if (n_or_o) {
                n_val.put(value[0],value[1]);
            } else {
                o_val.put(value[0],value[1] );
            }
        }

        Iterator it=n_val.keySet().iterator();

        while (it.hasNext()) {
            String key = it.next();
            String value= n_val.get(key);
            System.out.printf("%s : %sn",key,value);
        }

        it=o_val.keySet().iterator();
        while (it.hasNext()){
            String key = it.next();
            String value= o_val.get(key);
            System.out.printf("%s : %sn",key,value);
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}