JSON.simple – How to parse JSON

In this tutorial, we will show you how to parse JSON with JSON.simple

P.S Tested with json-simple 3.1.0

1. Download JSON.simple

	<dependency>
		<groupId>com.github.cliftonlabs</groupId>
		<artifactId>json-simple</artifactId>
		<version>3.1.0</version>
	</dependency>

2. POJO + Jsonable

2.1 To convert Java objects to/from JSON, The JSON.simple requires POJO to implement Jsonable, and override toJson()

package com.mkyong;
import com.github.cliftonlabs.json_simple.JsonObject;
import com.github.cliftonlabs.json_simple.Jsonable;
import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;
import java.math.BigDecimal;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
public class Staff implements Jsonable {
    private String name;
    private int age;
    private String[] position;
    private List<String> skills;
    private Map<String, BigDecimal> salary;
    //..getters setters
    @Override
    public String toJson() {
        final StringWriter writable = new StringWriter();
        try {
            this.toJson(writable);
        } catch (final IOException e) {
        return writable.toString();
    @Override
    public void toJson(Writer writer) throws IOException {
        final JsonObject json = new JsonObject();
        json.put("name", this.getName());
        json.put("age", this.getAge());
        json.put("position", this.getPosition());
        json.put("skills", this.getSkills());
        json.put("salary", this.getSalary());
        json.toJson(writer);

3. Java objects to JSON

3.1 Convert a Java object to JSON string and save as .json file.

package com.mkyong;
import com.github.cliftonlabs.json_simple.Jsoner;
import java.io.FileWriter;
import java.io.IOException;
import java.math.BigDecimal;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
public class JsonSimple1 {
    public static void main(String[] args) throws IOException {
        Staff staff = createStaff();
        // Java objects to JSON String
        String json = Jsoner.serialize(staff);
        // pretty print
        json = Jsoner.prettyPrint(json);
        System.out.println(json);
        // Java objects to JSON file
        try (FileWriter fileWriter = new FileWriter("C:\\projects\\user3.json")) {
            Jsoner.serialize(staff, fileWriter);
    private static Staff createStaff() {
        Staff staff = new Staff();
        staff.setName("mkyong");
        staff.setAge(38);
        staff.setPosition(new String[]{"Founder", "CTO", "Writer"});
        Map<String, BigDecimal> salary = new HashMap() {{
            put("2010", new BigDecimal(10000));
            put("2012", new BigDecimal(12000));
            put("2018", new BigDecimal(14000));
        }};
        staff.setSalary(salary);
        staff.setSkills(Arrays.asList("java", "python", "node", "kotlin"));
        return staff;

Output

	"skills":[
		"java",
		"python",
		"node",
		"kotlin"
	],
	"name":"mkyong",
	"position":[
		"Founder",
		"CTO",
		"Writer"
	],
	"salary":{
		"2018":14000,
		"2012":12000,
		"2010":10000
	},
	"age":38

{"skills":["java","python","node","kotlin"],"name":"mkyong","position":["Founder","CTO","Writer"],"salary":{"2018":14000,"2012":12000,"2010":10000},"age":38}

3.2 Convert list of objects to JSON array and save as .json file.

	Staff staff = createStaff();
	List<Staff> list = Arrays.asList(createStaff(), createStaff());
	// list of Java objects to JSON file 
	try (FileWriter fileWriter = new FileWriter("C:\\projects\\user4.json")) {
		Jsoner.serialize(list, fileWriter);

Output

{"skills":["java","python","node","kotlin"],"name":"mkyong","position":["Founder","CTO","Writer"],"salary":{"2018":14000,"2012":12000,"2010":10000},"age":38},
{"skills":["java","python","node","kotlin"],"name":"mkyong","position":["Founder","CTO","Writer"],"salary":{"2018":14000,"2012":12000,"2010":10000},"age":38}

4. JSON to Java objects

4.1 To convert JSON back to Java objects, we need help from dozer third party library to copy the object properties.

	<dependency>
		<groupId>net.sf.dozer</groupId>
		<artifactId>dozer</artifactId>
		<version>5.5.1</version>
	</dependency>

4.2 JSON string to Java object.

package com.mkyong;
import com.github.cliftonlabs.json_simple.JsonException;
import com.github.cliftonlabs.json_simple.JsonObject;
import com.github.cliftonlabs.json_simple.Jsoner;
import org.dozer.DozerBeanMapper;
import org.dozer.Mapper;
import java.io.FileReader;
import java.io.IOException;
public class JsonSimple2 {
    public static void main(String[] args) throws IOException, JsonException {
		// The file `user3.json` is generated from above example 3.1 
        try (FileReader fileReader = new FileReader(("C:\\projects\\user3.json"))) {
            JsonObject deserialize = (JsonObject) Jsoner.deserialize(fileReader);
			// need dozer to copy object to staff, json_simple no api for this?
            Mapper mapper = new DozerBeanMapper();
			// JSON to object
            Staff staff = mapper.map(deserialize, Staff.class);
            System.out.println(staff);

Output

Staff{name='mkyong', age=38, position=[Founder, CTO, Writer], 
	skills=[java, python, node, kotlin], salary={2018=14000, 2012=12000, 2010=10000}}

4.3 JSON array to Java object.

package com.mkyong;
import com.github.cliftonlabs.json_simple.JsonArray;
import com.github.cliftonlabs.json_simple.JsonException;
import com.github.cliftonlabs.json_simple.Jsoner;
import org.dozer.DozerBeanMapper;
import org.dozer.Mapper;
import java.io.FileReader;
import java.io.IOException;
import java.util.List;
import java.util.stream.Collectors;
public class JsonSimple3 {
    public static void main(String[] args) throws IOException, JsonException {
		// The file `user4.json` is generated from above example 3.2
        try (FileReader fileReader = new FileReader(("C:\\projects\\user4.json"))) {
            JsonArray objects = Jsoner.deserializeMany(fileReader);
            Mapper mapper = new DozerBeanMapper();
            JsonArray o = (JsonArray) objects.get(0);
            List<Staff> collect = o.stream()
				.map(x -> mapper.map(x, Staff.class)).collect(Collectors.toList());
            collect.forEach(x -> System.out.println(x));

Output

Staff{name='mkyong', age=38, position=[Founder, CTO, Writer], skills=[java, python, node, kotlin], salary={2018=14000, 2012=12000, 2010=10000}}
Staff{name='mkyong', age=38, position=[Founder, CTO, Writer], skills=[java, python, node, kotlin], salary={2018=14000, 2012=12000, 2010=10000}}