Java Gson write list example

In this example, we will learn how to write a list of JSON objects into a file using Gson library.

Check out top GSON tutorial at Google GSON Tutorial.

Java Gson Maven dependency

This is a Maven dependency for Gson:

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.2</version>
</dependency>

Java Gson write list example

The example writes JSON data into an items.json file.

import com.google.gson.Gson;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;

class Item {
    
    private final String name;
    private final int quantity;

    public Item(String name, int quantity) {
        this.name = name;
        this.quantity = quantity;
    }
}

public class GsonWriteList {

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

        String fileName = "src/main/resources/items.json";
        
        try (FileOutputStream fos = new FileOutputStream(fileName);
                OutputStreamWriter isr = new OutputStreamWriter(fos, 
                        StandardCharsets.UTF_8)) {
            
            Gson gson = new Gson();
            
            Item item1 = new Item("chair", 4);
            Item item2 = new Item("book", 5);
            Item item3 = new Item("pencil", 1);
            
            List<Item> items = new ArrayList<>();
            items.add(item1);
            items.add(item2);
            items.add(item3);
            
            gson.toJson(items, isr);
        }
        
        System.out.println("Items written to file");
    }
}

Output: Items written to file.