要将 Java 对象或 POJO (普通旧 Java 对象)转换为 JSON,定制小程序开发我们可以使用JSONObject
定制小程序开发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>
-
- <!-- https://mvnrepository.com/artifact/org.json/json -->
- <dependency>
- <groupId>org.json</groupId>
- <artifactId>json</artifactId>
- <version>20211205</version>
- </dependency>
- <!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
- <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>