文章目录

  • 前言
  • 一、什么是JSON对象?
  • 二、什么是json字符串?
  • 二、什么是JSON数组?
  • 三、复杂、嵌套的json字符串
  • 四、json字符串转换
    • 4.1 简单json字符串转换为java对象
    • 4.2 简单json字符串数组转换为list数组
    • 4.3 复杂嵌套json字符串数组转换为Java对象、list数组
      • 4.3.1 示例1
      • 4.3.2 示例2
  • 总结

前言

在开发中经常需要将json字符串转换为java对象或者list数组,这样方便我们来使用这些数据,下面就来介绍一下怎样将json字符串和json数组转换为Java对象或者list数组。

本次使用阿里巴巴的fastjson来解析json字符串,需要添加依赖:

        <dependency>            <groupId>com.alibaba</groupId>            <artifactId>fastjson</artifactId>            <version>1.2.8</version>        </dependency>

一、什么是JSON对象?

在大括号 {…} 中书写,包含多个 key/value(键/值)对,key 必须是字符串,value 可以是合法的 JSON 数据类型(字符串, 数字, 对象, 数组, 布尔值或 null)
例如一个最简单的没有嵌套的JSON对象:
{ “name”:“Sun”, “age”:18, “site”:null }

二、什么是json字符串?

书写格式和JSON对象一样,不过类型属于String,不能直接操作其中的各个属性,需要对其进行转换。在很多前后端交互传值之类的,都以json字符串的形式进行传递。,所以对json字符串进行转换非常有必要。

二、什么是JSON数组?

JSON 数组在中括号中书写,JSON 中数组值必须是合法的 JSON 数据类型(字符串, 数字, 对象, 数组, 布尔值或 null)。
简单的JSON数组:
[ “Google”, “Runoob”, “Taobao” ]

三、复杂、嵌套的json字符串

复杂的是json字符串里面嵌套json数组,这也是转换的重点,例如:
{
“student”: [
{
“name”: “Tom”,
“Grade”: 1,
“age”: 11,
“gender”: “M”
},
{
“name”: “Jerry”,
“Grade”: 1,
“age”: 10,
“gender”: “M”
}
],
“classroom”: {
“class1”: “room1”,
“class2”: “room2”
}
}

在这里推荐几个比较好用的json字符串校验和格式化的网站:
链接: http://www.kjson.com/
链接: https://www.bejson.com/

四、json字符串转换

4.1 简单json字符串转换为java对象

转换语句:

//方法1  将json字符串转换为java对象Student student =JSON.parseObject(jsonStr,Student .class);
//方法2   先将json字符串转换成JSONObject对象JSONObject jsonObject1 = new JSONObject(JSON.parseObject(jsonStr));//将转换后的JSONObject对象转换成Student对象Student  student1 = (Student) JSONObject.toJavaObject(jsonObject1,Student.class);

示例:解析如下json字符串
{
“name”: “Tom”,
“Grade”: 1,
“age”: 11,
“gender”: “M”
}

    首先创建一个对应的对象:
public class Student {    private String name;    private int grade;    private int age;    private String gender;    //省略get、set方法}
    public void testJson(){        String jsonStr = "{\n" +                "            \"name\": \"Tom\", \n" +                "            \"Grade\": 1, \n" +                "            \"age\": 11, \n" +                "            \"gender\": \"M\"\n" +                "        }";        JSONObject jsonObject = new JSONObject(JSON.parseObject(jsonStr));        System.out.println("jsonObject:"+jsonObject);        System.out.println("name:"+jsonObject.get("name"));        System.out.println("Grade:"+jsonObject.get("Grade"));        System.out.println("age:"+jsonObject.get("age"));        //方法1  将json字符串转换为java对象        Student student =JSON.parseObject(jsonStr,Student .class);        System.out.println("student:"+student);        //方法2   先将json字符串转换成JSONObject对象        JSONObject jsonObject1 = new JSONObject(JSON.parseObject(jsonStr));        //将转换后的JSONObject对象转换成Student对象        Student  student1 = (Student) JSONObject.toJavaObject(jsonObject1,Student.class);        System.out.println("student1:"+student1);        //转换为java对象之后可以利用对象的get方法来取值        System.out.println("age:"+student.getAge());    }

执行结果:

4.2 简单json字符串数组转换为list数组

使用语句:

 List<Student> studentList  = JSONObject.parseArray(jsonStr, Student.class);

示例:

[
{
“name”: “Tom”,
“Grade”: 1,
“age”: 11,
“gender”: “M”
},
{
“name”: “Jerry”,
“Grade”: 1,
“age”: 10,
“gender”: “M”
}
]

首先创建一个对应的java对象:

public class Student {    private String name;    private int grade;    private int age;    private String gender;    //省略get、set方法}
    public void testJson(){        String jsonStr = "[\n" +                "    {\n" +                "        \"name\": \"Tom\", \n" +                "        \"Grade\": 1, \n" +                "        \"age\": 11, \n" +                "        \"gender\": \"M\"\n" +                "    }, \n" +                "    {\n" +                "        \"name\": \"Jerry\", \n" +                "        \"Grade\": 1, \n" +                "        \"age\": 10, \n" +                "        \"gender\": \"M\"\n" +                "    }\n" +                "]";        List<Student> studentList  = JSONObject.parseArray(jsonStr, Student.class);        System.out.println("studentList:"+studentList);        for (int i = 0; i < studentList.size(); i++) {            System.out.println("name:"+studentList.get(i).getName());            System.out.println("Grade:"+studentList.get(i).getGender());            System.out.println("age:"+studentList.get(i).getAge());        }    }

运行结果:

4.3 复杂嵌套json字符串数组转换为Java对象、list数组

4.3.1 示例1

使用语句:
为4.1和4.2的嵌套使用

示例:
{
“student”: [
{
“name”: “Tom”,
“Grade”: 1,
“age”: 11,
“gender”: “M”
},
{
“name”: “Jerry”,
“Grade”: 1,
“age”: 10,
“gender”: “M”
}
],
“classroom”: {
“class1”: “fifth floor”,
“class2”: “seventh floor”
}
}

首先创建对应的java对象,上面的Student对象可以重复使用,这里需要再添加两个对象,一个整体的包含Student和Classroom的对象School ,一个Classroom对象:

public class School {//这里的Student和Classroom声明为Object类型    private Object Student;    private Object Classroom;         //省略get、set方法}
public class Classroom {    private String class1;    private String class2;      //省略get、set方法}

进行转换:

    public void testJson(){        String jsonStr = "{\n" +                "    \"student\": [\n" +                "        {\n" +                "            \"name\": \"Tom\", \n" +                "            \"Grade\": 1, \n" +                "            \"age\": 11, \n" +                "            \"gender\": \"M\"\n" +                "        }, \n" +                "        {\n" +                "            \"name\": \"Jerry\", \n" +                "            \"Grade\": 1, \n" +                "            \"age\": 10, \n" +                "            \"gender\": \"M\"\n" +                "        }\n" +                "    ], \n" +                "    \"classroom\": {\n" +                "        \"class1\": \"fifth floor\", \n" +                "        \"class2\": \"seventh floor\"\n" +                "    }\n" +                "}";        //方法1   调用JSON.parseObject方法将json字符串转换为java对象        School school =JSON.parseObject(jsonStr,School.class);        System.out.println("school:"+school);                //方法2   先将json字符串转换成JSONObject对象        JSONObject jsonObject = new JSONObject(JSON.parseObject(jsonStr));        //将转换后的JSONObject对象整体转换成School对象        School school1 = (School) JSONObject.toJavaObject(jsonObject,School.class);        System.out.println("school1:"+school1);        //将School中的student数组转换成list对象        List<Student> studentList  = JSONObject.parseArray(school.getStudent().toString(), Student.class);        System.out.println("studentList:"+studentList);        for (int i = 0; i < studentList.size(); i++) {            System.out.print("name:"+studentList.get(i).getName()+",");            System.out.print("Grade:"+studentList.get(i).getGender()+",");            System.out.println("age:"+studentList.get(i).getAge());        }        //将School中的classroom转换成java对象 与刚开始转换school的思路是一样的        //从school对象中getClassroom,返回的是一个Object对象类型        Object classroomObj = school.getClassroom();        //用toString()方法将Object对象转换成String        String strClassroom = school.getClassroom().toString();        //方法1   调用JSON.parseObject方法将json字符串转换为java对象        Classroom classroom1 =JSON.parseObject(strClassroom,Classroom.class);        System.out.println("classroom1:"+classroom1);        //方法2  先将json字符串转换成JSONObject对象        JSONObject jsonClassroom = new JSONObject(JSON.parseObject(strClassroom));        //再利用JSONObject.toJavaObject转换为java对象        Classroom classroom2 = (Classroom) JSONObject.toJavaObject(jsonClassroom,Classroom.class);        System.out.println("classroom2:"+classroom2);    }

运行结果:

4.3.2 示例2

使用语句:
在4.3.1的基础上新增了两个字段:schoolName和address。Student对象和Classroom对象可以使用,需要重新创建一个整体的对象HighSchool

示例:
{
“schoolName”: “ECNU”,
“address”: “Road”,
“student”: [{
“name”: “Tom”,
“Grade”: 1,
“age”: 11,
“gender”: “M”
},
{
“name”: “Jerry”,
“Grade”: 1,
“age”: 10,
“gender”: “M”
}
],
“classroom”: {
“class1”: “fifth floor”,
“class2”: “seventh floor”
}
}

首先创建对应的java对象,上面的Student对象可以重复使用,这里需要再添加两个对象,一个整体的包含Student和Classroom的对象,一个Classroom对象:

public class School {//这里的Student和Classroom声明为Object类型    private Object Student;    private Object Classroom;         //省略get、set方法}
public class Classroom {    private String class1;    private String class2;      //省略get、set方法}

进行转换:

       public void testJson(){        String jsonStr = "{\n" +                "    \"schoolName\": \"ECNU\", \n" +                "    \"address\": \"Road\", \n" +                "    \"student\": [\n" +                "        {\n" +                "            \"name\": \"Tom\", \n" +                "            \"Grade\": 1, \n" +                "            \"age\": 11, \n" +                "            \"gender\": \"M\"\n" +                "        }, \n" +                "        {\n" +                "            \"name\": \"Jerry\", \n" +                "            \"Grade\": 1, \n" +                "            \"age\": 10, \n" +                "            \"gender\": \"M\"\n" +                "        }\n" +                "    ], \n" +                "    \"classroom\": {\n" +                "        \"class1\": \"fifth floor\", \n" +                "        \"class2\": \"seventh floor\"\n" +                "    }\n" +                "}";        //方法1   调用JSON.parseObject方法将json字符串转换为java对象        HighSchool highSchool = JSON.parseObject(jsonStr,HighSchool.class);        System.out.println("highSchool:"+ highSchool);        System.out.println("schoolName:"+ highSchool.getSchoolName());        System.out.println("address:"+ highSchool.getAddress());        //方法2 与之前讲过的一样,这里就省略掉了        //将School中的student数组转换成list对象        List<Student> studentList  = JSONObject.parseArray(highSchool.getStudent().toString(), Student.class);        System.out.println("studentList:"+studentList);        for (int i = 0; i < studentList.size(); i++) {            System.out.print("name:"+studentList.get(i).getName()+",");            System.out.print("Grade:"+studentList.get(i).getGender()+",");            System.out.println("age:"+studentList.get(i).getAge());        }        //HighSchool 与刚开始转换school的思路是一样的        //从highSchool对象中getClassroom,返回的是一个Object对象类型        Object classroomObj = highSchool.getClassroom();        //用toString()方法将Object对象转换成String        String strClassroom = highSchool.getClassroom().toString();        //方法1   调用JSON.parseObject方法将json字符串转换为java对象        Classroom classroom1 =JSON.parseObject(strClassroom,Classroom.class);        System.out.println("classroom1:"+classroom1);        //方法2 与之前讲过的一样,这里就省略掉了    }

运行结果:


总结

转换大体上分为两种:
1、以{……}大括号包裹的数据要转换为java对象;
2、 以[ ] 中括号包裹的数据转换为list数组。

首先要明白,以 { } 开头的是JSONObject,以 [ ] 开头的是JSONArray,如果本身就是json字符串的格式(即格式类型为String),那就不用转换,直接使用转换方法进行转换。

但是如果是嵌套字符串的话,从第一次转换后的java对象中取出来的是Object类型,这时候需要先用toString方法转换为String类型,然后再调用方法。