Custom JSON field naming using GSON

Gson supports custom naming for JSON fields. You can annotate your fields with @SerializedName to provide this functionality. If there is an error in the naming of the field, it’ll throw a Runtime exception. In this tutorial we will show you how you can change the name of a field inside your Java Class.

Maven dependencies

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>
    <groupId>com.memorynotfound.json.gson</groupId>
    <artifactId>custom-namet</artifactId>
    <version>1.0.0-SNAPSHOT</version>

    <properties>
        <gson.version>2.3.1</gson.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>${gson.version}</version>
        </dependency>
    </dependencies>
</project>

Object to be Serialised/Deserialised

Gson has special annotations that you can define on a per field basis. If an invalid field name is provided it could produce a “Runtime” excepetion.

package com.memorynotfound.json;

import com.google.gson.annotations.SerializedName;

import java.util.Date;

public class Product {

    private long id;
    @SerializedName("item")
    private String name;
    private Date created;
    private double amount;

    public Product(long id, String name, Date created, double amount) {
        this.id = id;
        this.name = name;
        this.created = created;
        this.amount = amount;
    }
}

Custom JSON field naming using GSON

The following is an example of how to use both Gson naming policy feature and custom naming.: Gson supports a couple of pre-defined field naming policies to convert the standard Java field names.

• FieldNamingPolicy.UPPER_CAMEL_CASE
• FieldNamingPolicy.LOWER_CASE_WITH_DASHES
• FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES
• FieldNamingPolicy.UPPER_CAMEL_CASE_WITH_SPACES

See the GSON FieldNamingPolicy JavaDoc for more information.

package com.memorynotfound.json;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.util.Date;

public class CustomNameGson {

    public static void main(String... args){
        Product product = new Product(1, "Playstation 4", new Date(), 499.99);
        Gson gson = new GsonBuilder().setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE).create();
        String result = gson.toJson(product);
        System.out.println(result);
    }
}

Output

{"Id":1,"item":"Playstation 4","Created":"Dec 26, 2014 3:00:01 PM","Amount":499.99}

References

• GSON Deserialise Object
• GSON FieldNamingPolicy JavaDoc