FastJson – Convert Java objects to / from JSON

By mkyong | Updated: May 3, 2019

Viewed: 3,962 (+134 pv/w)

Tags: fastjson java json

FastJson provides easily APIs to convert Java objects to / from JSON

• JSON.toJSONString – Java objects to JSON
• JSON.parseObject – JSON to Java objects
• JSON.parseArray – JSON array to List of Java objects

Overall, the FastJson is really simple and easy to convert JSON to / from objects, however, it lack of direct File support, especially the JSON.parseArray method, it needs some extra efforts to read from a JSON file. Hope the future APIs like parseObject and parseArray are able to support for sources like File or URL directly.

P.S Tested with FastJson 1.2.57

	<dependency>
		<groupId>com.alibaba</groupId>
		<artifactId>fastjson</artifactId>
		<version>1.2.57</version>
	</dependency>

1. POJO

A simple POJO, for JSON conversion.

package com.mkyong;

import java.math.BigDecimal;
import java.util.Arrays;
import java.util.Date;
import java.util.List;
import java.util.Map;

public class Staff {

    private String name;
    private int age;
    private String[] position;
    private List<String> skills;
    private Map<String, BigDecimal> salary;

    //getters, setters, toString, constructor
}

2. Java objects to JSON

package com.mkyong;

import com.alibaba.fastjson.JSON;

import java.io.IOException;
import java.math.BigDecimal;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.*;

public class FastJsonExample1 {

    public static void main(String[] args) {

        Staff staff = createStaff();

        // Java objects to JSON
        String json = JSON.toJSONString(staff);
        System.out.println(json);

        // Java objects to JSON, pretty-print
        String json2 = JSON.toJSONString(staff, true);
        System.out.println(json2);

        // Java objects to JSON, with formatted date
        String json3 = JSON.toJSONStringWithDateFormat(staff, "dd/MM/yyyy HH:mm:ss");
        System.out.println(json3);

        // List of Java objects to JSON Array
        List<Staff> list = Arrays.asList(createStaff(), createStaff());
        String json4 = JSON.toJSONStringWithDateFormat(list, "dd/MM/yyyy HH:mm:ss");
        System.out.println(json4);

        try {
            // can't find fastjson api to write files, np, just use the standard java.nio Files.write
            Files.write(Paths.get("c:\\projects\\staff.json"), json4.getBytes());
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    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"));
        staff.setJoinDate(new Date());

        return staff;

    }

}

Output

// json
{"age":38,"joinDate":1556870430099,"name":"mkyong","position":["Founder","CTO","Writer"],
"salary":{"2018":14000,"2012":12000,"2010":10000},"skills":["java","python","node","kotlin"]}

// json2
{
	"age":38,
	"joinDate":1556870430099,
	"name":"mkyong",
	"position":["Founder","CTO","Writer"],
	"salary":{
		"2018":14000,
		"2012":12000,
		"2010":10000
	},
	"skills":[
		"java",
		"python",
		"node",
		"kotlin"
	]
}

// json3 - format date
{"age":38,"joinDate":"03/05/2019 16:00:30","name":"mkyong","position":["Founder","CTO","Writer"],
"salary":{"2018":14000,"2012":12000,"2010":10000},"skills":["java","python","node","kotlin"]}

// json4 - JSON Array
[
	{
		"age":38,
		"joinDate":1556870630615,
		"name":"mkyong",
		"position":["Founder","CTO","Writer"],
		"salary":{
			"2018":14000,
			"2012":12000,
			"2010":10000
		},
		"skills":[
			"java",
			"python",
			"node",
			"kotlin"
		]
	},
	{
		"age":38,
		"joinDate":1556870630615,
		"name":"mkyong",
		"position":["Founder","CTO","Writer"],
		"salary":{
			"2018":14000,
			"2012":12000,
			"2010":10000
		},
		"skills":[
			"java",
			"python",
			"node",
			"kotlin"
		]
	}
]

3. JSON to Java objects

package com.mkyong;

import com.alibaba.fastjson.JSON;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class FastJsonExample2 {

    public static void main(String[] args) {

        // JSON string to Java object
        String jsonString = "{\"name\":38,\"name\":\"mkyong\"}";
        Staff staff = JSON.parseObject(jsonString, Staff.class);

        System.out.println(staff);

        // JSON array to Java object
        String jsonArray = "[{\"name\":38,\"name\":\"mkyong\"}, {\"name\":39,\"name\":\"mkyong2\"}]";
        List<Staff> staff1 = JSON.parseArray(jsonArray, Staff.class);

        System.out.println(staff1);

        // JSON array in File to Java object
        // staff.json contain JSON array
        try (Stream<String> lines = Files.lines(Paths.get("c:\\projects\\staff.json"))) {

            String content = lines.collect(Collectors.joining());
			// Hope parseArray() will support File or Reader in future.
            List<Staff> list = JSON.parseArray(content, Staff.class);
            System.out.println(list);

        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

References

• FastJson home page
• FastJson user guide
• FastJson data bind examples
• FastJson best practice (Chinese)
• Why FastJson is so fast? (Chinese)
• FastJson Stream API