json转java
步骤：
1.导入jackson相关jar包
2.创建Jackson核心对象 ObjectMapper
3.调用ObjectMapper的相关方法进行转换
1.readValue( json字符串数据，Class )
//json转java
@Test
public void test5() throws Exception {
//1.初始化JSON字符串
String json = "{\"gender\":\"男\",\"name\":\"张三\",\"age\":\"20\"}";
//2.创建一个ObjectMapper对象
ObjectMapper mapper = new ObjectMapper();
//3.转换为java对象 Person对象
Person person = mapper.readValue(json, Person.class);
System.out.println(person);// Person{name='张三', age=20, gender='男', birthday=null}
}
案例-校验用户名是否存在
服务器响应的数据，在客户端使用时，要想当做json数据格式使用
1.$.get ( type )：将最后一个参数type指定为" json "
2.在服务器设置MIME类型
resp.setContentType("application/json;charset=utf-8");
案例实现：
regist.html：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>注册页面</title>
<script src="js/jquery-3.3.1.min.js"></script>
<script>
$(function () {
//给username绑定blur事件
$("#username").blur(function () {
//获取username文本输入框的值
let username = $(this).val();
//发送ajax请求
//期望服务器响应回的数据格式：{"userExsit":true,"msg":此用户太受欢迎，请更换一个}
// {"userExsit":false,"msg":用户名可用}
$.get("findUserServlet", {username: username}, function (data) {
//判断userExsit键的值是否是true
let span = $("s_username");
if (data.userExsit) {
//用户名存在
span.css("color","red")
span.html(data.msg);
} else {
//用户名不存在
span.css("color","green")
span.html(data.msg);
}
},"json");// 响应格式
});
});
</script>
</head>
<body>
<input type="text" id="username" name="username" placeholder="请输入用户名">
<span id="s_username"></span>
<br>
<input type="password" name="password" placeholder="请输入密码">
<br>
<input type="submit" value="注册">
</body>
</html>
FindUserServlet：
package com.example.servlet;
import com.fasterxml.jackson.databind.ObjectMapper;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.util.HashMap;
@WebServlet(name = "findUserServlet", value = "/findUserServlet")
public class FindUserServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//1.获取用户名
String username = req.getParameter("username");
//2.调用service层判断用户名是否存在
//期望服务器响应回的数据格式：{"userExsit":true,"msg":此用户太受欢迎，请更换一个}
// {"userExsit":false,"msg":用户名可用}
//设置编码
// resp.setContentType("text/html;charset=utf-8");
resp.setContentType("application/json;charset=utf-8");
HashMap<String, Object> map = new HashMap<>();
if ("tom".equals(username)){
//存在
map.put("userExsit",true);
map.put("msg","此用户太受欢迎，请更换一个");
}else {
//不存在
map.put("userExsit",false);
map.put("msg","用户名可用");
}
//将map转为json，并且传递给客户端
//将map转为json
ObjectMapper mapper = new ObjectMapper();
//并且传递给客户端
mapper.writeValue(resp.getWriter(), map);
}
}
标签：username,map,用户名,java,校验,json,msg,ObjectMapper From： https://www.cnblogs.com/qihaokuan/p/17105659.html