Gson JsonReader and JsonWriter example

Gson provides APIs to read and write JSON as an object model or stream. The GSON JsonReader & JsonWriter use streaming model to process JSON.

To use Gson JsonReader & JsonWriter, you need to download gson-2.8.5.jar from gson-2.8.5.jar

1) JsonReader example

import java.io.IOException;
import java.io.StringReader;

import com.google.gson.stream.JsonReader;
	
public class TestGsonJsonReader {
    public static void main(String[] args) {
        String jsonString = "{\"id\":12345, \"name\":\"Jason Bourne\", \"age\":35, "
             + "\"roles\":[\"Actor\",\"Father\"]}";
        JsonReader jsonReader = new JsonReader(new StringReader(jsonString));

        try {
            jsonReader.beginObject();
            
            while(jsonReader.hasNext()){
                String key = jsonReader.nextName(); 
                if ("id".equals(key)){
                 System.out.println(jsonReader.nextInt());
                } else if("name".equals(key)){
                    System.out.println(jsonReader.nextString());
                } else if("age".equals(key)){
                    System.out.println(jsonReader.nextInt());
                } else if("roles".equals(key)){
                    jsonReader.beginArray();
                    
                    while (jsonReader.hasNext()) {
                        System.out.println(jsonReader.nextString());
                    }
                    
                    jsonReader.endArray();
                } else {
                    jsonReader.skipValue(); 
                }
            }
            
            jsonReader.endObject();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
	

Output :

12345
Jason Bourne
35
Actor
Father
    

2) JsonWriter example

import java.io.FileWriter;
import java.io.IOException;

import com.google.gson.stream.JsonWriter;
	
public class TestGsonJsonWriter {
    public static void main(String[] args) {
                
        try (JsonWriter writer = new JsonWriter(new FileWriter("C:\\actor.json"))) {

            writer.beginObject();                   
            writer.name("id").value(12345);    
            writer.name("name").value("Jason Bourne");         
            writer.name("age").value(35);    

            writer.name("roles");
            writer.beginArray(); 
            writer.value("Actor");                  
            writer.value("Father");                  
            writer.endArray();                      

            writer.endObject();                     

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
	

Output actor.json:

{"id":12345,"name":"Jason Bourne","age":35,"roles":["Actor","Father"]}