How to Parse JSON in Java

Jackson — ObjectMapper

Maven: com.fasterxml.jackson.core:jackson-databind

import com.fasterxml.jackson.databind.ObjectMapper;

// Define a POJO
public class User {
    private String name;
    private int age;
    private boolean active;
    // getters and setters (or use @JsonProperty)
}

ObjectMapper mapper = new ObjectMapper();

// Deserialize JSON string to object
String json = "{"name":"Alice","age":30,"active":true}";
User user = mapper.readValue(json, User.class);

System.out.println(user.getName());   // Alice
System.out.println(user.getAge());    // 30

// Deserialize to List
String jsonArray = "[{"name":"Alice"},{"name":"Bob"}]";
List<User> users = mapper.readValue(
    jsonArray,
    mapper.getTypeFactory().constructCollectionType(List.class, User.class)
);

// Deserialize to Map (no POJO)
Map<String, Object> map = mapper.readValue(json, Map.class);

// Serialize object to JSON string
String output = mapper.writeValueAsString(user);

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

Gson (Google)

Maven: com.google.code.gson:gson

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import java.lang.reflect.Type;
import com.google.gson.reflect.TypeToken;

Gson gson = new Gson();

// Deserialize
String json = "{"name":"Alice","age":30}";
User user = gson.fromJson(json, User.class);

// Deserialize a List
String jsonArray = "[{"name":"Alice"},{"name":"Bob"}]";
Type listType = new TypeToken<List<User>>(){}.getType();
List<User> users = gson.fromJson(jsonArray, listType);

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

// Pretty-print
Gson prettyGson = new GsonBuilder().setPrettyPrinting().create();
String pretty = prettyGson.toJson(user);

Error Handling

// Jackson error handling
try {
    User user = mapper.readValue(json, User.class);
} catch (JsonParseException e) {
    System.err.println("JSON syntax error: " + e.getMessage());
} catch (JsonMappingException e) {
    System.err.println("Mapping error: " + e.getMessage());
} catch (IOException e) {
    System.err.println("IO error: " + e.getMessage());
}

// Gson error handling
try {
    User user = gson.fromJson(json, User.class);
} catch (com.google.gson.JsonSyntaxException e) {
    System.err.println("JSON syntax error: " + e.getMessage());
}

Parse JSON in Other Languages

FAQ