Dynamically exclude JSON fields with GSON from Object

In this tutorials we show you how to dynamically exclude JSON fields with GSON. When you have a use case that you want to exclude a field for whatever reason. You can create a custom JsonSerializer. With this serializer you can modify your exposed json object dynamically.

Dependencies

You must have the GSON dependency on your classpath.

<?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>exclusing-strategy</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <name>JSON - ${project.artifactId}</name>
    <url>https://memorynotfound.com</url>

    <properties>
        <gson.version>2.5</gson.version>
    </properties>

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

</project>

Object to be serialized

We will be serializing this product object.

package com.memorynotfound.json;

import java.util.Date;

public class Product {

    private long id;
    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;
    }

    public long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public Date getCreated() {
        return created;
    }

    public double getAmount() {
        return amount;
    }
}

Custom JsonSerializer

We can dynamically exclude a field with a custom JsonSerializer. We have a reference to our Product object which we can convert to a JsonObject. After this conversion we can check for certain conditions when we want to exclude a certain field dynamically.

package com.memorynotfound.json;

import com.google.gson.*;
import java.lang.reflect.Type;

public class ProductSerializer implements JsonSerializer<Product> {

    @Override
    public JsonElement serialize(Product product, Type type, JsonSerializationContext jsc) {
        JsonObject jObj = (JsonObject)new GsonBuilder().create().toJsonTree(product);
        if (product.getAmount() > 100){
            jObj.remove("amount");
        }
        return jObj;
    }
}

Dynamically exclude JSON fields with GSON

We can add our custom ProductSerializer with the .registerTypeAdapter() method.

package com.memorynotfound.json;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import java.util.Date;

public class ExcludeExposeGson {

    public static void main(String... args){
        Product product = new Product(1, "Playstation 4", new Date(), 499.99);

        // normal serialization
        Gson gson = new GsonBuilder().create();
        String result = gson.toJson(product);
        System.out.println(result);

        // dynamic serialization on product
        gson = new GsonBuilder()
                .registerTypeAdapter(Product.class, new ProductSerializer())
                .create();
        result = gson.toJson(product);
        System.out.println(result);
    }
}

Output

{"id":1,"name":"Playstation 4","created":"Dec 17, 2015 10:35:53 AM","amount":499.99}
{"id":1,"name":"Playstation 4","created":"Dec 17, 2015 10:35:53 AM"}

• GSON registerTypeAdapter JavaDoc
• GSON JsonSerializer JavaDoc

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