How to parse JSON Array with Jackson

By mkyong | Updated: April 23, 2024

Viewed: 41,232 (+334 pv/w)

Tags: jackson java json json array parse json

This article uses the Jackson framework to parse JSON Array in Java.

Table of contents:

• 1. Download Jackson
• 2. Parse JSON Array with Jackson
• 3. Convert List of Objects to JSON Array
• 4. Write JSON Array with a list label
• 5. Parse JSON Array contains a list label
• 6. Download Source Code
• 7. References

P.S Tested with Jackson 2.17.0

1. Download Jackson

Simply declare jackson-databind in the pom.xml, and it will automatically pull in jackson-annotations, jackson-core, and other necessary dependencies.

  <dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.17.0</version>
  </dependency>

2. Parse JSON Array with Jackson

Below is a JSON array string.

[ 
    {
        "name" : "mkyong",
        "age" : 42
    }, 
    {
        "name" : "ah pig",
        "age" : 20
    } 
]

Create a Person object that matches the JSON property name.

package com.mkyong.json.model;

public class Person {

    private String name;
    private int age;

    public Person() {
    }

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // getters, setters, toString()
}

In Jackson, we can convert the JSON array to an Array or List.

package com.mkyong.json.jackson;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.mkyong.json.model.Person;

import java.util.List;

public class JsonArrayToObjectExample {

    public static void main(String[] args) throws JsonProcessingException {

        String jsonArray = "[{\"name\":\"mkyong\", \"age\":42}, {\"name\":\"ah pig\", \"age\":20}]";

        ObjectMapper mapper = new ObjectMapper();

        // 1. convert JSON array to Array objects
        Person[] person1 = mapper.readValue(jsonArray, Person[].class);
        for (Person p : person1) {
            System.out.println(p);
        }

        // 2. convert JSON array to List
        List<Person> person2 = mapper.readValue(jsonArray, new TypeReference<>() {
        });
        person2.forEach(System.out::println);

    }
}

output

Person{name='mkyong', age=42}
Person{name='ah pig', age=20}
Person{name='mkyong', age=42}
Person{name='ah pig', age=20}

3. Convert List of Objects to JSON Array

package com.mkyong.json.jackson;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.mkyong.json.model.Person;

import java.util.Arrays;
import java.util.List;

public class JsonArrayToObjectExample2 {

    public static void main(String[] args) throws JsonProcessingException {

        List<Person> list = Arrays.asList(
                new Person("mkyong", 42),
                new Person("ah pig", 20)
        );

        ObjectMapper mapper = new ObjectMapper();

        String result = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(list);

        System.out.println(result);

    }
}

Output

[ {
  "name" : "mkyong",
  "age" : 42
}, {
  "name" : "ah pig",
  "age" : 20
} ]

4. Write JSON Array with a list label

This example converts a list of Person objects to a JSON string with the list labeled as "Person":

package com.mkyong.json.jackson;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.mkyong.json.model.Person;

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class JsonArrayToObjectExample3 {

    public static void main(String[] args) throws JsonProcessingException {

        // Create a list of Person objects
        List<Person> people = Arrays.asList(
                new Person("mkyong", 42),
                new Person("ah pig", 20)
        );

        // Wrap the list in a Map with "Person" as the key
        Map<String, List<Person>> wrapper = new HashMap<>();
        wrapper.put("Person", people);

        // Create an ObjectMapper instance and convert the map to JSON
        ObjectMapper mapper = new ObjectMapper();

        String jsonOutput = mapper.writeValueAsString(wrapper);

        // Print the JSON output
        // {"Person":[{"name":"mkyong","age":42},{"name":"ah pig","age":20}]}
        System.out.println(jsonOutput);

    }
}

Output

{"Person":[{"name":"mkyong","age":42},{"name":"ah pig","age":20}]}

5. Parse JSON Array contains a list label

The technique is the same with the above example 4: first converts the JSON string to Map<String, List<Person>> and manually get the List<Person> later.

{
  "Person" : [ 
        {
            "name" : "mkyong",
            "age" : 42
        }, 
        {
            "name" : "ah pig",
            "age" : 20
        } 
    ]
}

package com.mkyong.json.jackson;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.mkyong.json.model.Person;

import java.util.List;
import java.util.Map;

public class JsonArrayToObjectExample4 {

    public static void main(String[] args) throws JsonProcessingException {

        String jsonInput = "{\"Person\":[{\"name\":\"mkyong\",\"age\":42},{\"name\":\"ah pig\",\"age\":20}]}";

        // Create ObjectMapper instance
        ObjectMapper mapper = new ObjectMapper();

        // Convert JSON string to Map<String, List<Person>>
        Map<String, List<Person>> result = mapper.readValue(jsonInput, new TypeReference<>() {
        });

        // Retrieve the list of persons
        List<Person> persons = result.get("Person");

        // Print the parsed persons
        for (Person person : persons) {
            System.out.println("Name: " + person.getName() + ", Age: " + person.getAge());
        }


    }
}

6. Download Source Code

7. References

• Jackson Github
• Jackson data-binding
• Jackson – Convert JSON string to Map
• Jackson Convert Java Object to / from JSON