Parse JSON in Java using Google's Gson and Jackson Library

This post will discuss how to parse JSON in Java using Google’s Gson and Jackson library.

Nowadays, almost all RESTful web services consume and produce JSON data instead of XML. Unfortunately, Java SE doesn’t support converting JSON to Java Object (and vice-versa). But there are many third-party libraries available that are very reliable and offer high performance.

To use Gson or Jackson library, we need to create POJO (Plain Old Java Object) with the same JSON structure. POJO is simply a class with private fields and public “getter” and “setter” methods. We recommend this online tool jsonschema2pojo for quickly generating POJO from json or json schema with Jackson/Gson annotation style.

1. Using Gson

Google’s Gson is one of the best libraries for parsing a JSON into POJO. It is very easy to learn and implement. We can use the Gson#fromJson() method to convert our JSON string into a Java object.

The following code decodes the given json string with the help of the Gson library:

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import com.google.gson.Gson;

import com.google.gson.annotations.Expose;

import com.google.gson.annotations.SerializedName;

import java.util.Arrays;

import java.util.List;

class Person

{

@SerializedName("name")

@Expose

private String name;

@SerializedName("age")

@Expose

private Integer age;

@SerializedName("student")

@Expose

private Student student;

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public Integer getAge() {

return age;

}

public void setAge(Integer age) {

this.age = age;

}

public Student getStudent() {

return student;

}

public void setStudent(Student student) {

this.student = student;

}

@Override

public String toString() {

return Arrays.asList(name, String.valueOf(age), student.toString()).toString();

}

class Student

{

@SerializedName("id")

@Expose

private String id;

@SerializedName("subjects")

@Expose

private List<String> subjects = null;

public String getId() {

return id;

}

public void setId(String id) {

this.id = id;

}

public List<String> getSubjects() {

return subjects;

}

public void setSubjects(List<String> subjects) {

this.subjects = subjects;

}

@Override

public String toString() {

return Arrays.asList(id, subjects.toString()).toString();

}

// Parse JSON using Google's Gson library

class Main

{

public static void main(String[] args)

{

// JSON string

String jsonString = "{\"name\":\"Jon Snow\",\"age\":22," +

"\"student\":{\"id\":\"Jon_Snow_22\"," +

"\"subjects\":[\"Maths\",\"Science\"]}}";

System.out.println("JSON string is: " + jsonString);

// Parse JSON string to `Person` object using Google's Gson library

Gson gson = new Gson();

Person person = gson.fromJson(jsonString, Person.class);

System.out.println("Person object: " + person);

}

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Output:
JSON string is: {"name":"Jon Snow","age":22,"student":{"id":"Jon_Snow_22","subjects":["Maths","Science"]}} Person object: [Jon Snow, 22, [Jon_Snow_22, [Maths, Science]]]

2. Using Jackson

Jackson is a multi-purpose, high-performance Java library for processing JSON. It provides Data Binding functionality that can be used for binding a JSON string into a POJO. All we need is to call the readValue() method of Jackson’s ObjectMapper class to convert our JSON string into the specified Java object.

Consider the following code, which parses the given json string using the Jackson library:

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import org.codehaus.jackson.JsonGenerationException;

import org.codehaus.jackson.annotate.*;

import org.codehaus.jackson.map.JsonMappingException;

import org.codehaus.jackson.map.ObjectMapper;

import java.io.IOException;

import java.util.Arrays;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

@JsonPropertyOrder({

"name",

"age",

"student"

})

class Person

{

@JsonProperty("name")

private String name;

@JsonProperty("age")

private Integer age;

@JsonProperty("student")

private Student student;

@JsonIgnore

private Map<String, Object> additionalProperties = new HashMap<>();

@JsonProperty("name")

public String getName() {

return name;

}

@JsonProperty("name")

public void setName(String name) {

this.name = name;

}

@JsonProperty("age")

public Integer getAge() {

return age;

}

@JsonProperty("age")

public void setAge(Integer age) {

this.age = age;

}

@JsonProperty("student")

public Student getStudent() {

return student;

}

@JsonProperty("student")

public void setStudent(Student student) {

this.student = student;

}

@JsonAnyGetter

public Map<String, Object> getAdditionalProperties() {

return this.additionalProperties;

}

@JsonAnySetter

public void setAdditionalProperty(String name, Object value) {

this.additionalProperties.put(name, value);

}

@Override

public String toString()

{

return Arrays.asList(name, String.valueOf(age), student.toString())

.toString();

}

@JsonPropertyOrder({

"id",

"subjects"

})

class Student

{

@JsonProperty("id")

private String id;

@JsonProperty("subjects")

private List<String> subjects = null;

@JsonIgnore

private Map<String, Object> additionalProperties = new HashMap<>();

@JsonProperty("id")

public String getId() {

return id;

}

@JsonProperty("id")

public void setId(String id) {

this.id = id;

}

@JsonProperty("subjects")

public List<String> getSubjects() {

return subjects;

}

@JsonProperty("subjects")

public void setSubjects(List<String> subjects) {

this.subjects = subjects;

}

@JsonAnyGetter

public Map<String, Object> getAdditionalProperties() {

return this.additionalProperties;

}

@JsonAnySetter

public void setAdditionalProperty(String name, Object value) {

this.additionalProperties.put(name, value);

}

@Override

public String toString() {

return Arrays.asList(id, subjects.toString()).toString();

}

// Parse JSON using the Jackson library

class Main

{

public static void main(String[] args)

{

// JSON string

String jsonString = "{\"name\":\"Jon Snow\",\"age\":22," +

"\"student\":{\"id\":\"Jon_Snow_22\"," +

"\"subjects\":[\"Maths\",\"Science\"]}}";

System.out.println("JSON string is: " + jsonString);

ObjectMapper mapper = new ObjectMapper();

Person person = null;

try {

// Parse JSON string to `Person` object using the Jackson library

person = mapper.readValue(jsonString, Person.class);

}

catch (JsonMappingException e) {

e.printStackTrace();

}

catch (IOException e) {

e.printStackTrace();

}

System.out.println("Person object: " + person);

}

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Output:

JSON string is: {"name":"Jon Snow","age":22,"student":{"id":"Jon_Snow_22","subjects":["Maths","Science"]}} Person object: [Jon Snow, 22, [Jon_Snow_22, [Maths, Science]]]

Useful JSON Tools:

That’s all about parsing JSON in Java using Google’s Gson and Jackson Library.

Parse JSON in Java using Google’s Gson and Jackson Library

1. Using Gson

2. Using Jackson

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