如何将 Java 对象转换为 JSON？

太过爱你忘了你带给我的痛 2023-09-30 10:14 157阅读 0赞

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`Student`POJO 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<String> courses;
    
        public Student(Long id, String name, int age, List<String> 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<String> getCourses() {
            return courses;
        }
    
        public void setCourses(List<String> courses) {
            this.courses = courses;
        }
    
    }

**Maven 依赖项**

<?xml version="1.0" encoding="UTF-8"?>
    <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
        <modelVersion>4.0.0</modelVersion>
        <groupId>com.example.javaobjectjson</groupId>
        <artifactId>JavaObjectJSON</artifactId>
        <version>1.0-SNAPSHOT</version>
        <dependencies>
    
            
            <dependency>
                <groupId>org.json</groupId>
                <artifactId>json</artifactId>
                <version>20211205</version>
            </dependency>
            
            <dependency>
                <groupId>com.google.code.gson</groupId>
                <artifactId>gson</artifactId>
                <version>2.9.0</version>
            </dependency>
            <dependency>
                <groupId>com.fasterxml.jackson.core</groupId>
                <artifactId>jackson-databind</artifactId>
                <version>2.12.1</version>
            </dependency>  
    
        </dependencies>
    </project>