How do I pretty-print JSON string in Google Gson?

In the following example you’ll see how to format JSON string using the Google Gson library. Here are the steps:

We create a Map.
Put a couple key-value pairs to it. We put a string, a LocalDate object and an array of String[].
Create a Gson object using the GsonBuilder. This allows us to configure the Gson object.
We use the setPrettyPrinting() to configure Gson to output pretty print.
The registerTypeAdapter() allows us to register custom serializer, in this case we use it to serialize LocalDate object.

Here is our code snippet:

package org.kodejava.gson;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonElement;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

import java.lang.reflect.Type;
import java.time.LocalDate;
import java.time.Month;
import java.time.format.DateTimeFormatter;
import java.util.HashMap;
import java.util.Map;

public class GsonPrettyPrint {
    public static void main(String[] args) {
        Map<String, Object> map = new HashMap<>();
        map.put("name", "Duke");
        map.put("address", "Menlo Park");
        map.put("dateOfBirth", LocalDate.of(2000, Month.FEBRUARY, 1));
        map.put("languages", new String[]{"Java", "Kotlin", "JavaScript"});

        Gson gson = new GsonBuilder()
                .setPrettyPrinting()
                .registerTypeAdapter(LocalDate.class, new LocaleDateAdapter())
                .create();
        String json = gson.toJson(map);
        System.out.println(json);
    }

    static class LocaleDateAdapter implements JsonSerializer<LocalDate> {
        @Override
        public JsonElement serialize(LocalDate date, Type type, JsonSerializationContext jsonSerializationContext) {
            return new JsonPrimitive(date.format(DateTimeFormatter.ISO_DATE));
        }
    }
}

Running this code produces the following result:

{
  "address": "Menlo Park",
  "languages": [
    "Java",
    "Kotlin",
    "JavaScript"
  ],
  "name": "Duke",
  "dateOfBirth": "2000-02-01"
}

Maven Dependencies

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.11.0</version>
</dependency>

Author
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Wayan

Founder at Kode Java

A programmer, runner and recreational diver, lives on the island of Bali, Indonesia. Programming in Java, Spring Framework, Hibernate / JPA, MySQL. To support me working on this project, buy me a cup of coffee, every little bit helps. Thank you.

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