如何將Java對象轉換為JSON實例詳解
要將 Java 對象或 POJO (普通舊 Java 對象)轉換為 JSON,我們可以使用JSONObject
將對象作為參數的構造函數之一。在下面的示例中,我們將Student
POJO 轉換為 JSON 字符串。Student
類必須提供 getter 方法,JSONObject
通過調用這些方法創建 JSON 字符串。
在此代碼段中,我們執行以下操作:
- 使用 setter 方法創建
Student
對象並設置其屬性。 - 創建
JSONObject
調用object
並將Student
對象用作其構造函數的參數。 JSONObject
使用 getter 方法生成 JSON 字符串。- 調用
object.toString()
方法獲取 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); } }
運行此代碼會產生以下結果:
{"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"]}
上面代碼中使用的Student類:
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 依賴項
<?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>
總結
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