JSON in Java — Jackson, Gson & org.json

Java does not have built-in JSON support, but three libraries dominate: Jackson (most popular in enterprise), Gson (from Google, simple API), and org.json (lightweight, no dependencies).

Jackson — parse JSON into a POJO

Jackson's ObjectMapper is the standard choice for enterprise Java. Add com.fasterxml.jackson.core:jackson-databind to your build.

import com.fasterxml.jackson.databind.ObjectMapper;

public class User {
    public int id;
    public String name;
    public String email;
}

ObjectMapper mapper = new ObjectMapper();
String json = "{"id":1,"name":"Alice","email":"alice@example.com"}";
User user = mapper.readValue(json, User.class);
System.out.println(user.name); // Alice

Jackson — serialize to JSON

Use mapper.writeValueAsString() to serialize a POJO to a JSON string.

User user = new User();
user.id = 1;
user.name = "Alice";

String json = mapper.writeValueAsString(user);
// {"id":1,"name":"Alice","email":null}

// Pretty-print
String pretty = mapper
    .writerWithDefaultPrettyPrinter()
    .writeValueAsString(user);

Gson — parse and serialize

Gson is simpler for small projects. Add com.google.code.gson:gson to your build.

import com.google.gson.Gson;

Gson gson = new Gson();

// Parse
User user = gson.fromJson(json, User.class);

// Serialize
String output = gson.toJson(user);

Handle JSON parse errors in Java

Jackson throws JsonProcessingException (a checked exception) on parse failure. Always handle it.

import com.fasterxml.jackson.core.JsonProcessingException;

try {
    User user = mapper.readValue("{invalid}", User.class);
} catch (JsonProcessingException e) {
    System.err.println("Parse error: " + e.getOriginalMessage());
}

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Frequently Asked Questions

What is the best JSON library for Java?▾

Jackson (jackson-databind) is the most widely used in enterprise Java. Gson is simpler for smaller projects. For Spring Boot, Jackson is included by default.

How do I parse JSON in Java with Jackson?▾

Create an ObjectMapper and call mapper.readValue(jsonString, MyClass.class). Your class needs a no-arg constructor or Jackson annotations.

How do I ignore unknown JSON properties in Jackson?▾

Add @JsonIgnoreProperties(ignoreUnknown = true) to your class, or configure the ObjectMapper globally: mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false).

How do I serialize null fields in Jackson?▾

By default, null fields are included. To skip them globally: mapper.setSerializationInclusion(Include.NON_NULL). Or use @JsonInclude(Include.NON_NULL) on the class.

What is the difference between Jackson and Gson?▾

Jackson is faster and has more features (streaming API, tree model, extensive annotations). Gson is simpler to use with minimal configuration. For most Java/Spring projects, Jackson is the better choice.

JSON in Other Languages

JSON in Python →JSON in JavaScript →JSON in TypeScript →JSON in Go →JSON in PHP →JSON in Ruby →JSON in C# →JSON in Rust →JSON in Kotlin →JSON in Swift →JSON in Dart →JSON in Scala →JSON in Next.js →JSON in Express →JSON in FastAPI →JSON in Django →JSON in Terraform →

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