JSON操作

一、JSON形式

JSON键/值对由键和值组成，键必须是字符串，值可以是字符串（string）、数值(number) 、对象（object）、数组（array）、true、false、null。

例子：

{
    "name": "liuzijian",
    "age": 27,
    "hobby": ["basketball","running","swimming"],
    "istall": false,
    "isyoung": true,
    "money": null,
    "other": {
        "gender": "male",
        "city": "nanjing",
        "email": "liuzijian15@huawei.com"
    }
}

 二、JAVA中Json的操作

1、主要有四种jar包提供了json操作：

• JSON官方

  <dependency>
      <groupId>org.json</groupId>
      <artifactId>json</artifactId>
      <version>20180813</version>
  </dependency>

• GSON

  <dependency>
      <groupId>com.google.code.gson</groupId>
      <artifactId>gson</artifactId>
      <version>2.8.5</version>
  </dependency>

• FastJSON

  <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>fastjson</artifactId>
      <version>1.2.54</version>
  </dependency>

• jackson

  <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-core</artifactId>
      <version>2.9.8</version>
  </dependency>

2、定义实体类

Department类：

import lombok.Data;

@Data
public class Department
{
    private Integer departmentId;

    private String departmentName;

    public Department(Integer departmentId, String departmentName)
    {
        this.departmentId = departmentId;
        this.departmentName = departmentName;
    }
　　//默认构造函数，由jackson解析json字符串为对象时调用
    public Department()
    {

    }
}

Employee类：

import lombok.Data;

import java.util.List;

@Data
public class Employee
{
    private String name;

    private Integer id;

    private Integer age;

    private Double salary;

    private List<Department> departments;

    public Employee(String name, Integer id, Integer age, Double salary, List<Department> departments)
    {
        this.name = name;
        this.id = id;
        this.age = age;
        this.departments = departments;
    }

    public Employee()
    {

    }
}

3、JSON操作

　　 3.1定义JSON操作类

import java.util.ArrayList;
import java.util.List;

public class JSONTest
{
    private String json；private Employee employee;

    public void init()
    {

　　 　　json = "{"id":1,"name":"liuzijian","age":27,"salary":5000.1,"departments":[{"departmentId":1,"departmentName":"CBC"},{"departmentId":2,"departmentName":"SCB"}]}";

        Department department1 = new Department(1, "CBC");
        Department department2 = new Department(2, "SCB");
        List<Department> departments = new ArrayList<>();
        departments.add(department1);
        departments.add(department2);
        employee = new Employee("liuzijian", 1, 27, 5000.1, departments);
    }
}

　　下面开始在这个类中添加方法测试json操作。

 　　3.2 使用JSON官方包

　　1）解析json字符串

    public void testJsonToObjectInJson()
    {
        org.json.JSONObject jsonObject = new org.json.JSONObject(json);
        Employee employee = new Employee();
        employee.setId(jsonObject.getInt("id"));
        employee.setName(jsonObject.getString("name"));
        employee.setAge(jsonObject.getInt("age"));
        employee.setSalary(jsonObject.getDouble("salary"));

        List<Department> departments = new ArrayList<>();
        org.json.JSONArray jsonArray = jsonObject.getJSONArray("departments");
        for (int i = 0;i < jsonArray.length();i++)
        {
            org.json.JSONObject item = jsonArray.getJSONObject(i);
            Department department = new Department(item.getInt("departmentId"), item.getString("departmentName"));
            departments.add(department);
        }

        employee.setDepartments(departments);

        System.out.println(employee);
    }

　　2）使用官方包将对象解析为字符串比较麻烦

　　3.3 使用fastjson包

　　1）从json字符串中解析出对象

    public void testJsonToObjectInFastJson()
    {
        Employee employee = com.alibaba.fastjson.JSON.parseObject(json, Employee.class);
        System.out.println(employee);
    }

　　2）将对象解析为json字符串

    public void testObjectToJsonInFastJson()
    {
        String json = com.alibaba.fastjson.JSON.toJSONString(employee);
        System.out.println(json);
    }

　　3.4 使用gson包

　　1）将对象解析为json字符串

    public void testObjectToJsonInGson()
    {
        com.google.gson.Gson gson = new com.google.gson.Gson();
        String json = gson.toJson(employee);
        System.out.println(employee);
    }

　　2）从json字符串中解析出对象

    public void testJsonToObjectInGson()
    {
        com.google.gson.Gson gson = new com.google.gson.Gson();
        Employee employee = gson.fromJson(json, Employee.class);
        System.out.println(employee);
    }

　　3.5 使用jackson包，SpringMVC内置的解析器就是这个

　　1）从json字符串中解析出对象

    public void testJsonToObjectInJackson() throws Exception
    {
        com.fasterxml.jackson.databind.ObjectMapper mapper = new com.fasterxml.jackson.databind.ObjectMapper();
        Employee employee = mapper.readValue(json, Employee.class);
        System.out.println(employee);
    }

　　2）将对象解析为json字符串

    public void testObjectToJsonInJackson() throws JsonProcessingException
    {
        com.fasterxml.jackson.databind.ObjectMapper mapper = new com.fasterxml.jackson.databind.ObjectMapper();
        String json = mapper.writeValueAsString(employee);
        System.out.println(json);
    }

除了JSON官方的对类没有要求，剩下的都要求是标准的类，否则无法解析，因为都用到了反射。