如何将 Java 对象转换为 JSON？

要将 Java 对象或 POJO （普通旧 Java 对象）转换为 JSON，我们可以使用JSONObject将对象作为参数的构造函数之一。在下面的示例中，我们将StudentPOJO 转换为 JSON 字符串。Student类必须提供 getter 方法，JSONObject通过调用这些方法创建 JSON 字符串。

在此代码段中，我们执行以下操作：

• 使用 setter 方法创建Student对象并设置其属性。
• 创建JSONObject调用object并将Student对象用作其构造函数的参数。
• JSONObject使用 getter 方法生成 JSON 字符串。
• 调用object.toString()方法获取 JSON 字符串。

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.gson.Gson;
import org.json.JSONObject;

import java.util.Arrays;

public class PojoToJSON {

    public static void main(String[] args) throws JsonProcessingException {
        Student student = new Student();
        student.setId(1L);
        student.setName("Alice");
        student.setAge(20);
        student.setCourses(Arrays.asList("Engineering", "Finance", "Chemistry"));

        JSONObject object = new JSONObject(student);
        String json = object.toString();
        System.out.println(json);
        System.out.println(new Gson().toJson(student));
        // Creating Object of ObjectMapper define in Jackson API
        ObjectMapper Obj = new ObjectMapper();

        // Converting the Java object into a JSON string
        String jsonStr = Obj.writeValueAsString(student);
        // Displaying Java object into a JSON string
        System.out.println(jsonStr);

    }
}

运行此代码会产生以下结果：

{"courses":["Engineering","Finance","Chemistry"],"name":"Alice","id":1,"age":20}
{"id":1,"name":"Alice","age":20,"courses":["Engineering","Finance","Chemistry"]}
{"id":1,"name":"Alice","age":20,"courses":["Engineering","Finance","Chemistry"]}

上面代码中使用的Student类：

import java.util.List;

public class Student {

    private Long id;
    private String name;
    private int age;
    private List courses;

    public Student(Long id, String name, int age, List courses) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.courses = courses;
    }

    Student() {

    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public List getCourses() {
        return courses;
    }

    public void setCourses(List courses) {
        this.courses = courses;
    }

}

Maven 依赖项

    4.0.0
    com.example.javaobjectjson
    JavaObjectJSON
    1.0-SNAPSHOT
    

        
        
            org.json
            json
            20211205
        
        
        
            com.google.code.gson
            gson
            2.9.0
        
        
            com.fasterxml.jackson.core
            jackson-databind
            2.12.1