Java中Jackson包使用总结 - 易学教程，面试笔记经验！

Jackson框架是基于Java平台的一套数据处理工具，它包含了3个核心库：streaming,databind,annotations，被称为“最好的Java Json解析器”。

Jackson下载

jackon包含三个核心类库：
jackson-core-2.14.1.jar 定义了底层的streaming API和实现了Json特性。
jackson-annotations-2.14.1.jar 包含了标准的Jackson注解。
jackson-databind-2.14.1.jar 实现了数据绑定和对象序列化，它依赖于streaming和annotations的包。

Jackson安装

1. Idea 中导入json包的方法。
ctrl+alt+shift+S 打开项目结构
Java中Jackson包

将刚才下载的jar文件导入我们的项目

Java中Jackson包

2. maven安装

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.14.1</version>
</dependency>
<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-annotations -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.14.1</version>
</dependency>
<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.14.1</version>
</dependency>

Java中Jackson将json转换成对象

json转Java对象

import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;

/**
 *JSON转java对象
 */
public class JSON2Class{
    //JSON转java对象
    public static void main(String[] args) {
        try {
            ObjectMapper objectMapper = new ObjectMapper();

            String json = "{\"name\":\"张三\",\"age\":23,\"address\":\"深圳市\"}";
            User zhang = objectMapper.readValue(json, User.class);
            System.out.println(zhang.getName() + "\n" + zhang.getAge() + "\n" + zhang.getAddress());
        } catch(IOException e) {
            e.printStackTrace();
        }
    }
}
//User.java
 class User {
    private String name;
    private Integer age;
    private String address;
    public User(){

    }
    public User(String name, Integer age, String address) {
        super();
        this.name = name;
        this.age = age;
        this.address = address;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
}

测试一下

输出

张三
23
深圳市

json转list对象

import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/**
 *2. json转list对象
 */
public class JSON2List {
    //JSON转java对象
    public static void main(String[] args) {
        try {
            ObjectMapper objectMapper = new ObjectMapper();
            //JSON转list
            String listJson = "[{\"name\":\"张三\",\"age\":21,\"address\":\"深圳\"}," + "{\"name\":\"李四\",\"age\":11,\"address\":\"武汉\"}," + "{\"name\":\"王五\",\"age\":31,\"address\":\"北京\"}]";
            JavaType javaType1 = objectMapper.getTypeFactory().constructParametricType(ArrayList.class, User.class);
            List< User > userList = (List < User > ) objectMapper.readValue(listJson, javaType1);
            for (User user1: userList) {
                System.out.println(user1.getName() + "\t" + user1.getAge() + "\t" + user1.getAddress());
            }
        } catch(IOException e) {
            e.printStackTrace();
        }
    }
}
//User.java
 class User {
    private String name;
    private Integer age;
    private String address;
    public User(){

    }
    public User(String name, Integer age, String address) {
        super();
        this.name = name;
        this.age = age;
        this.address = address;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
}

测试一下

输出

张三    21    深圳
李四    11    武汉
王五    31    北京

json转map对象

import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

/**
 *3. json转map对象
 */
public class json2map {
    //JSON转java对象
    public static void main(String[] args) {
        try {
            ObjectMapper objectMapper = new ObjectMapper();
            //JSON转map
            String mapJson = "{\"one\":{\"name\":\"张三\",\"age\":21,\"address\":\"深圳\"}," + "\"two\":{\"name\":\"李四\",\"age\":11,\"address\":\"武汉\"}," + "\"three\":{\"name\":\"王五\",\"age\":31,\"address\":\"北京\"}}";
            JavaType javaType2 = objectMapper.getTypeFactory().constructParametricType(HashMap.class, String.class, User.class);
            Map < String,User > userMap = (Map< String, User >) objectMapper.readValue(mapJson, javaType2);
            User one = userMap.get("one");
            User two = userMap.get("two");
            User three = userMap.get("three");
            System.out.println(one.getName() + "\t" + one.getAge() + "\t" + one.getAddress());
            System.out.println(two.getName() + "\t" + two.getAge() + "\t" + two.getAddress());
            System.out.println(three.getName() + "\t" + three.getAge() + "\t" + three.getAddress());
        } catch(IOException e) {
            e.printStackTrace();
        }
    }
}
//User.java
 class User {
    private String name;
    private Integer age;
    private String address;
    public User(){

    }
    public User(String name, Integer age, String address) {
        super();
        this.name = name;
        this.age = age;
        this.address = address;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
}

测试一下

Java中Jackson将对象转换成json

map对象转换成json

import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

/**
 *1. map对象转换成json
 */
public class map2json {
    //JSON转java对象
    public static void main(String[] args) {
        try {
            ObjectMapper objectMapper = new ObjectMapper();
            JsonGenerator jsonGenerator = objectMapper.getJsonFactory().createJsonGenerator(System.out, JsonEncoding.UTF8);
            //map转JSON
            Map < String,Object > map = new HashMap < String,Object > ();
            map.put("one", new User("张", 12, "深圳"));
            map.put("two", new User("李", 22, "武汉"));
            map.put("three", new User("王", 32, "北京"));
            System.out.println("ObjectMapper方式");
            objectMapper.writeValue(System.out, map);  
            System.out.println("JsonGenerator方式");
            jsonGenerator.writeObject(map);
        } catch(IOException e) {
            e.printStackTrace();
        }
    }

}
//User.java
 class User {
    private String name;
    private Integer age;
    private String address;
    public User(){

    }
    public User(String name, Integer age, String address) {
        super();
        this.name = name;
        this.age = age;
        this.address = address;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
}

测试一下

输出

ObjectMapper方式
{"one":{"name":"张","age":12,"address":"深圳"},"two":{"name":"李","age":22,"address":"武汉"},"three":{"name":"王","age":32,"address":"北京"}}

list对象转换成json

 import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/**
 *2. list对象转换成json
 */
public class ListToJSON {
    //JSON转java对象
    public static void main(String[] args) {
        try {
            ObjectMapper objectMapper = new ObjectMapper();
            JsonGenerator jsonGenerator = objectMapper.getJsonFactory().createJsonGenerator(System.out, JsonEncoding.UTF8);
            //list转JSON
            List< User > list = new ArrayList< User >();
            list.add(new User("张", 12, "深圳"));
            list.add(new User("李", 22, "武汉"));
            list.add(new User("王", 32, "北京"));
            System.out.println("ObjectMapper方式");
            objectMapper.writeValue(System.out, list);
            System.out.println("JsonGenerator方式");
            jsonGenerator.writeObject(list);
        } catch(IOException e) {
            e.printStackTrace();
        }
    }

}
//User.java
 class User {
    private String name;
    private Integer age;
    private String address;
    public User(){

    }
    public User(String name, Integer age, String address) {
        super();
        this.name = name;
        this.age = age;
        this.address = address;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
}

测试一下