JAVA中的JSON之Gson

什么是Gson

Gson 是 Google 提供的用来在 Java 对象和 JSON 数据之间进行映射的 Java 类库。可以将一个 JSON 字符串转成一个 Java 对象，或者反过来。

jar包引入

<dependency>
	<groupId>com.google.code.gson</groupId>
	<artifactId>gson</artifactId>
	<version>2.8.5</version>
</dependency>

实体类

public class Student {
	private String id;
	private String name;
	private int age;
	
	public String getId() {
		return id;
	}
	public void setId(String 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;
	}
	@Override
	public String toString() {
		return "Student [id=" + id + ", name=" + name + ", age=" + age + "]";
	}

}

public class Classes {
	private String id;
	private String name;
	private List<Student> studentList;
	
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public List<Student> getStudentList() {
		return studentList;
	}
	public void setStudentList(List<Student> studentList) {
		this.studentList = studentList;
	}
	@Override
	public String toString() {
		return "Classes [id=" + id + ", name=" + name + ", studentList=" + studentList + "]";
	}
}

转换操作

public class APP {
	public static void main(String[] args) {
		Student student = new Student();
		student.setId("1");
		student.setName("张三");
		student.setAge(20);

		List<Student> studentList = new ArrayList<Student>();
		studentList.add(student);

		Classes classes = new Classes();
		classes.setId("1");
		classes.setName("一班");
		classes.setStudentList(studentList);

		// java对象转为json
		String classesJson = new Gson().toJson(classes);
		System.out.println(classesJson);

		// json转为java对象
		String json = "{\"id\":\"1\",\"name\":\"一班\",\"studentList\":[{\"id\":\"1\",\"name\":\"张三\",\"age\":20}]}";
		Classes classes2 = new Gson().fromJson(json, Classes.class);
		System.out.println(classes2);

		// json转换为list
		String jsonList = "[{\"id\":\"1\",\"name\":\"张三\",\"age\":20}]";
		studentList = new Gson().fromJson(jsonList, new TypeToken<List<Student>>() {}.getType());
		System.out.println(studentList);

		// json转为map
		Map<String, Object> map = new Gson().fromJson(json, new TypeToken<Map<String, Object>>() {}.getType());
		System.out.println(map);
		
		//结果
		//[Student [id=1, name=张三, age=20]]
		//{"id":"1","name":"一班","studentList":[{"id":"1","name":"张三","age":20}]}
		//Classes [id=1, name=一班, studentList=[Student [id=1, name=张三, age=20]]]
		//{id=1, name=一班, studentList=[{id=1, name=张三, age=20.0}]}
	}