Convert JSON to Java Object using Jackson

Jackson provides APIs which is a high-performance JSON processor for Java. Using Jackson APIs, you can easily convert a JSON to Java objects and vice-versa.

First you need to download following jars or using maven dependency

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.8
</dependency>   

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.9.8</version>
</dependency>    

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.9.8</version>
</dependency>    

{
    "id":12345, 
    "name":"Pierce Brosnan",
    "age":35,
    "emailaddress":["p.brosnan@gmail.com", "p.brosnan@yahoo.com"]
}    

Java POJO class used to convert JSON String to object and vice-versa.

import java.util.List;
    
public class Actor {
    
    private int id;
    private String name;
    private int age;
    private List<String> emailaddress;
      
    // removed getter and setter      
    
    @Override
    public String toString() {
        return "Employee [id=" + id + ", name=" + name + ","
            +" age=" + age + ", emailaddress=" + emailaddress + "]";
    }    
    
}    

1) Convert JSON string to Java object using Jackson.

// Parses JSON String using Jackson Parser    
import java.io.IOException;

import com.fasterxml.jackson.databind.ObjectMapper;
    
public class JsonToObject {
    public static void main(String[] args) {
        String jsonString = "{\"id\":12345, \"name\":\"Pierce Brosnan\", \"age\":35,"
            + " \"emailaddress\":[\"p.brosnan@gmail.com\", \"p.brosnan@yahoo.com\"]}";
            
        ObjectMapper mapper = new ObjectMapper();
        Actor actor = null;

        try {
            actor = mapper.readValue(jsonString, Actor.class);
        } catch (IOException e) {
            e.printStackTrace();
        } 
        System.out.println(actor);   
    }
}    

Output :

Actor [id=12345, name=Pierce Brosnan, age=35, emailaddress=[p.brosnan@gmail.com, p.brosnan@yahoo.com]]    

2) Reads JSON file and converts it to Java object using Jakckson.

// Parses JSON File using Jackson Parser    
import java.io.File;
import java.io.IOException;

import com.fasterxml.jackson.databind.ObjectMapper;
    
public class JsonToObject {
    public static void main(String[] args) {
        File file = new File("c://actors.json"); // to read from file
        ObjectMapper mapper = new ObjectMapper();
        Actor actor = null;

        try {
            actor = mapper.readValue(jsonString, Actor.class);
        } catch (IOException e) {
            e.printStackTrace();
        } 
        System.out.println(actor);    
    }
}
    

Output :

Actor [id=12345, name=Pierce Brosnan, age=35, emailaddress=[p.brosnan@gmail.com, p.brosnan@yahoo.com]]    

3) Convert Java object to JSON string using Jackson.

// Converts Java object to JSON string using Jackson   
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import com.fasterxml.jackson.databind.ObjectMapper;

public class ObjectToJson {
    public static void main(String[] args) {
        Actor actor = new Actor();
        actor.setId(1234);
        actor.setName("Pierce Brosnan");
        actor.setAge(40);
        
        List<String> emailaddress = new ArrayList<>();
        emailaddress.add("p.brosnan@yahoo.com");
        emailaddress.add("p.brosnan@gmail.com");
        actor.setEmailaddress(emailaddress);
            
        ObjectMapper mapper = new ObjectMapper();
        String jsonString = "";

        try {
            jsonString = mapper.writeValueAsString(actor);
            System.out.println(jsonString);   
            // Enable pretty print
            jsonString = mapper.writerWithDefaultPrettyPrinter().
                writeValueAsString(actor);
            System.out.println("Prettyfied output");
            System.out.println(jsonString); 
        }  catch (IOException e) {
            e.printStackTrace();
        } 
        
    }
}    

Output :

{"id":1234,"name":"Pierce Brosnan","age":40,"emailaddress":["p.brosnan@yahoo.com","p.brosnan@gmail.com"]}
Prettyfied output
{
  "id" : 1234,
  "name" : "Pierce Brosnan",
  "age" : 40,
  "emailaddress" : [ "p.brosnan@yahoo.com", "p.brosnan@gmail.com" ]
}   

4) Convert JSON to Map object

Map<String, String> map = new HashMap<>();
try {
    map = mapper.readValue(jsonString, Map.class);
} catch (IOException e) {
    e.printStackTrace();
}
System.out.println(map); 

Output :

{id=12345, name=Pierce Brosnan, age=35, emailaddress=[p.brosnan@gmail.com, p.brosnan@yahoo.com]}    

5) Convert Map object to JSON string

// Converts Map to JSON String
import java.io.IOException;
import java.util.Map;
import java.util.HashMap;

import com.fasterxml.jackson.databind.ObjectMapper;
    
public class TestJsonJackson {
    public static void main(String[] args) {
        Map<String, String> map = new HashMap<>();
        map.put("id", "12345");
        map.put("name", "Pierce Brosnan");
        map.put("age", "36");
            
        try {
            jsonString = mapper.writeValueAsString(map);
            System.out.println(jsonString);	
            
            // Pretty JSON
            jsonString = mapper.writerWithDefaultPrettyPrinter()
                .writeValueAsString(map);
            System.out.println(jsonString);	
        }  catch (IOException e) {
            e.printStackTrace();
        } 
    }
}    

Output :

{
    "name" : "Pierce Brosnan",
    "id" : "12345",
    "age" : "36"
}    

6) Below example shows how to convert JSON Array String to List object

Java class used to convert JSON Array String to List.

    
public class Employee {
    
    private int id;
    private String name;
    private int age;
        
    // removed getter and setter      
   
    @Override
    public String toString() {
        return "Employee [id=" + id + ", name=" + name + "," +" age=" + age + "]";
    }  
}  

// Converts JSON Array String to List  
import java.io.IOException;
import java.util.Arrays;
import java.util.List;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
    
public class TestJsonJackson {
    public static void main(String[] args) {
        String jsonString = "[{\"id\":\"12345\", \"name\":\"Jason Bourne\", \"age\":\"35\"},"
            + "{\"id\":\"12346\", \"name\":\"James Bond\", \"age\":\"38\"}]";
            
        ObjectMapper mapper = new ObjectMapper();

        try {
            Employee[] employee = mapper.readValue(jsonString, Employee[].class);
            System.out.println(Arrays.toString(employee));            
            
            List<Employee> employeeList = Arrays.asList(mapper.readValue(jsonString, Employee[].class));
            System.out.println(employeeList);
            
            employeeList = mapper.readValue(jsonString, new TypeReference<List<Employee>>() {});
            System.out.println(employeeList);
        } catch (JsonGenerationException e) {
            e.printStackTrace();
        } catch (JsonMappingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } 
    }
}    

Output :

[Employee [id=12345, name=Jason Bourne, age=35], Employee [id=12346, name=James Bond, age=38]]
[Employee [id=12345, name=Jason Bourne, age=35], Employee [id=12346, name=James Bond, age=38]]
[Employee [id=12345, name=Jason Bourne, age=35], Employee [id=12346, name=James Bond, age=38]]