Serialize /convert list of objects to/from json in java (Gson & example)

Given an list of user defined objects, we would like to convert list of pojo objects to JSON (and JSON to list of objects).
We will use the Google gson library to achieve the conversion.
We will create Person class and we will perform the following operations with Person class
- Convert List of Person objects to JSON.
- Convert the JSON to List of Person objects

GSON maven dependency

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.5</version>
</dependency>

Program – convert list of objects to/from json in java (GSON & example)

1.) Person Class:

Person class containing firstName, lastName, age etc.
We have overloaded toString method to print person information.

package org.learn.gson;
 
public class Person {
    public String firstName;
    public String lastName;
    public int age;
    public String contact;
    public Person(String firstName, String lastName,
                int age, String contact) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
        this.contact = contact;
    }
    public String toString() {
        return "[" + firstName + " " + lastName +
               " " + age + " " +contact +"]";
    }
}

2.) JSONConverter Class:

JSONConverter is responsible for performing following operations.

Convert List of Person objects to JSON.
Convert the JSON to List of Person objects.

package org.learn.gson;
 
import java.lang.reflect.Type;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
 
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;
 
public class JSONConverter 
{
    public static void main( String[] args )
    {
        Gson objGson = new GsonBuilder().setPrettyPrinting().create();
             
        List  personList = Stream.of(
                new Person("Mike", "harvey", 34, "001894536"),
                new Person("Nick", "young", 75,  "005425676"),
                new Person("Jack", "slater", 21 ,"009654153"),
                new Person("gary", "hudson", 55,"00564536"),
                new Person("Mike", "harvey", 21 ,"003685417"),
                new Person("gary", "hudson", 25,"00452341"))
                .collect(Collectors.toList());
         
        //Convert list to json
        System.out.println("1. Convert list of person objects to Json");
        String json = objGson.toJson(personList);
        System.out.println(json);
         
        //Convert json back to list
        System.out.println("2. Convert JSON to list of person objects");
        Type listType = new TypeToken<List>() {}.getType();
        List readFromJson = objGson.fromJson(json, listType);
        readFromJson.forEach(System.out::println);
    }
}

Download Code – convert list of objects to/from json (GSON)

Output – convert list of objects to/from json in java (GSON & example)

1. Convert list of person objects to Json
[
{
"firstName": "Mike",
"lastName": "harvey",
"age": 34,
"contact": "001894536"
},
{
"firstName": "Nick",
"lastName": "young",
"age": 75,
"contact": "005425676"
},
{
"firstName": "Jack",
"lastName": "slater",
"age": 21,
"contact": "009654153"
},
{
"firstName": "gary",
"lastName": "hudson",
"age": 55,
"contact": "00564536"
},
{
"firstName": "Mike",
"lastName": "harvey",
"age": 21,
"contact": "003685417"
},
{
"firstName": "gary",
"lastName": "hudson",
"age": 25,
"contact": "00452341"
}
]
2. Convert JSON to list of person objects
[Mike harvey 34 001894536]
[Nick young 75 005425676]
[Jack slater 21 009654153]
[gary hudson 55 00564536]
[Mike harvey 21 003685417]
[gary hudson 25 00452341]

GSON maven dependency

Program – convert list of objects to/from json in java (GSON & example)

1.) Person Class:

2.) JSONConverter Class:

Output – convert list of objects to/from json in java (GSON & example)

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