JAVA中的JSON之Jackson

最新推荐文章于 2025-03-24 11:22:02 发布

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本文深入讲解了Java中常用的Jackson库如何进行JSON数据的序列化和反序列化操作，包括实体类定义、依赖引入及核心类ObjectMapper的使用，演示了Java对象与JSON字符串之间的相互转换。

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什么是jackson

Java常见的Json类库。

jar包引入

<dependency>
	<groupId>com.fasterxml.jackson.core</groupId>
	<artifactId>jackson-core</artifactId>
	<version>2.9.1</version>
</dependency>
<dependency>
	<groupId>com.fasterxml.jackson.core</groupId>
	<artifactId>jackson-annotations</artifactId>
	<version>2.9.1</version>
</dependency>
<dependency>
	<groupId>com.fasterxml.jackson.core</groupId>
	<artifactId>jackson-databind</artifactId>
	<version>2.9.1</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

ObjectMapper是JSON操作的核心，Jackson的所有JSON操作都是在ObjectMapper中实现。
ObjectMapper是线程安全的。

public class APP {
	public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {
		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
		 ObjectMapper mapper = new ObjectMapper();  
		 String classJson = mapper.writeValueAsString(classes);
		 System.out.println(classJson);
		 
		// json转为java对象
		String json = "{\"id\":\"1\",\"name\":\"一班\",\"studentList\":[{\"id\":\"1\",\"name\":\"张三\",\"age\":20}]}";
		Classes classes2 = mapper.readValue(json, Classes.class);
		System.out.println(classes2);

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

		// json转为map
		JavaType jvt = mapper.getTypeFactory().constructParametricType(HashMap.class,String.class,Object.class);
		Map<String, Object> map = mapper.readValue(classJson, jvt);
		System.out.println(map);
		
		//结果
		//{"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]]]
		//[Student [id=1, name=张三, age=20]]
		//{name=一班, studentList=[{id=1, name=张三, age=20}], id=1}
	}
}