JAVA之间的转换

 //1. 创建json数组格式
    let j1 = ["刘备","关羽","张飞"];
    console.log(j1[1]);
    //2. 创建json map格式
    let j2 = {"name":"曹操","age":18};
    console.log(j2.name);
    //3. 嵌套格式1
    let j3 = {"name":"曹操","age":18,"friends":["司马懿","曹植","曹丕"]};
    console.log(j3.friends[0]);
    //4. 嵌套格式2
    let j4 = [{"name":"刘德华","age":18},{"name":"张学友","age":38}];
    console.log(j4[0].name);

    //json字符串和json对象区别  从服务器返回的内容一般是json字符串
    let jsonString = '["刘备","关羽","张飞"]';
    console.log(jsonString)
    //将json字符串转成json对象
    let j5 = JSON.parse(jsonString);
    console.log(j5[0]);

      com.fasterxml.jackson.core
      jackson-databind
      2.10.1
    

 //将集合转成json字符串
ObjectMapper om = new ObjectMapper();
String jsonString = om.writevalueAsString(list);
 //将json返回给客户端
 //application/json 告诉客户端返回的是json对象,这样客户端接收到数据时
 //会自动将json字符串转成json对象 不用使用JSON.parse()方法自己转换了
 response.setContentType("application/json;charset=utf-8");
 PrintWriter pw = response.getWriter();

doGet请求获取参数时  在第一行  request.setCharacterEncoding("UTF-8");
给服务器端返回数据时:
response.setContentType("text/html;charset=utf-8");
PrintWriter pw = response.getWriter();

数组转 List：使用 Arrays. asList(array) 进行转换。
List 转数组：使用 List 自带的 toArray() 方法。