Jackson 2 – Convert Java Object to / from JSON

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Title: Jackson 2 – Convert Java Object to / from JSON
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In this tutorial, we will show you how to use Jackson 2.x to convert Java object to / from JSON. 1. Quick Reference 1.1 Convert Java objec...

In this tutorial, we will show you how to use Jackson 2.x to convert Java object to / from JSON.

1. Quick Reference

1.1 Convert Java object to JSON, writeValue(...)

Java

ObjectMapper mapper = new ObjectMapper();
Staff obj = new Staff();

//Object to JSON in file
mapper.writeValue(new File("c:\\file.json"), obj);

//Object to JSON in String
String jsonInString = mapper.writeValueAsString(obj);

1.2 Convert JSON to Java object, readValue(...)

Java

ObjectMapper mapper = new ObjectMapper();
String jsonInString = "{'name' : 'mkyong'}";

//JSON from file to Object
Staff obj = mapper.readValue(new File("c:\\file.json"), Staff.class);

//JSON from URL to Object
Staff obj = mapper.readValue(new URL("http://bit.ly/1WH8gE6"), Staff.class);

//JSON from String to Object
Staff obj = mapper.readValue(jsonInString, Staff.class);

P.S All examples are tested with Jackson 2.6.3

Differences from Jackson 1.x
Most of the APIs still maintains the same method name and signature, just the packaging is different.

Jackson 1.x – org.codehaus.jackson.map
Jackson 2.x – com.fasterxml.jackson.databind

2. Jackson 2 Dependency

2.1 For Jackson 2.x, declares jackson-databind, it will download its dependencies – jackson-core and jackson-annotations

pom.xml

Markup

   <dependency>
                <groupId>com.fasterxml.jackson.core</groupId>
                <artifactId>jackson-databind</artifactId>
                <version>2.6.3</version>
        </dependency>

2.2 Review the Jackson dependencies :

mvn dependency:tree

Markup

[INFO] com.mkyong:json:jar:0.0.1-SNAPSHOT
[INFO] +- com.fasterxml.jackson.core:jackson-databind:jar:2.6.3:compile
[INFO] |  +- com.fasterxml.jackson.core:jackson-annotations:jar:2.6.0:compile
[INFO] |  \- com.fasterxml.jackson.core:jackson-core:jar:2.6.3:compile
[INFO] \- junit:junit:jar:3.8.1:test

3. POJO (Plain Old Java Object)

A simple pojo Staff object for testing.

Staff.java

Java

package com.mkyong.json;

import java.math.BigDecimal;
import java.util.List;

public class Staff {

        private String name;
        private int age;
        private String position;
        private BigDecimal salary;
        private List<String> skills;

        //getters and setters

4. Java Object to JSON

Convert a Staff object into a JSON formatted string.

Jackson2Example.java

Java

package com.mkyong.json;

import java.io.File;
import java.io.IOException;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Jackson2Example {

        public static void main(String[] args) {
                Jackson2Example obj = new Jackson2Example();
                obj.run();
        }

        private void run() {
                ObjectMapper mapper = new ObjectMapper();

                Staff staff = createDummyObject();

                try {
                        // Convert object to JSON string and save into a file directly
                        mapper.writeValue(new File("D:\\staff.json"), staff);

                        // Convert object to JSON string
                        String jsonInString = mapper.writeValueAsString(staff);
                        System.out.println(jsonInString);

                        // Convert object to JSON string and pretty print
                        jsonInString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(staff);
                        System.out.println(jsonInString);

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

        private Staff createDummyObject() {

                Staff staff = new Staff();

                staff.setName("mkyong");
                staff.setAge(33);
                staff.setPosition("Developer");
                staff.setSalary(new BigDecimal("7500"));

                List<String> skills = new ArrayList<>();
                skills.add("java");
                skills.add("python");

                staff.setSkills(skills);

                return staff;

        }

}

Output

Bash

//new json file is created in D:\\staff.json"

{"name":"mkyong","age":33,"position":"Developer","salary":7500,"skills":["java","python"]}

{
  "name" : "mkyong",
  "age" : 33,
  "position" : "Developer",
  "salary" : 7500,
  "skills" : [ "java", "python" ]
}

5. JSON to Java Object

Read JSON string and convert it back to a Java object.

Jackson2Example.java

Java

package com.mkyong.json;

import java.io.File;
import java.io.IOException;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Jackson2Example {

        public static void main(String[] args) {
                Jackson2Example obj = new Jackson2Example();
                obj.run();
        }

        private void run() {
                ObjectMapper mapper = new ObjectMapper();

                try {

                        // Convert JSON string from file to Object
                        Staff staff = mapper.readValue(new File("D:\\staff.json"), Staff.class);
                        System.out.println(staff);

                        // Convert JSON string to Object
                        String jsonInString = "{\"name\":\"mkyong\",\"salary\":7500,\"skills\":[\"java\",\"python\"]}";
                        Staff staff1 = mapper.readValue(jsonInString, Staff.class);
                        System.out.println(staff1);

                        //Pretty print
                        String prettyStaff1 = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(staff1);
                        System.out.println(prettyStaff1);
                        
                } catch (JsonGenerationException e) {
                        e.printStackTrace();
                } catch (JsonMappingException e) {
                        e.printStackTrace();
                } catch (IOException e) {
                        e.printStackTrace();
                }
        }

}

Output

Bash

Staff [name=mkyong, age=33, position=Developer, salary=7500, skills=[java, python]]

Staff [name=mkyong, age=0, position=null, salary=7500, skills=[java, python]]

{
  "name" : "mkyong",
  "age" : 0,
  "position" : null,
  "salary" : 7500,
  "skills" : [ "java", "python" ]
}

6. @JsonView

@JsonView, useful feature, it lets you control what fields to display.

6.1 A simple class, do nothing, just define two views (static classes as members).

Views.java

Java

package com.mkyong.json;

public class Views {

        public static class Normal{};
        
        public static class Manager extends Normal{};

}

6.2 For “Normal view”, salary will be hidden, for “Manager view”, display everything.

Staff.java

Java

package com.mkyong.json;

import java.math.BigDecimal;
import java.util.List;
import com.fasterxml.jackson.annotation.JsonView;

public class Staff {

        @JsonView(Views.Normal.class)
        private String name;

        @JsonView(Views.Normal.class)
        private int age;

        @JsonView(Views.Normal.class)
        private String position;

        @JsonView(Views.Manager.class)
        private BigDecimal salary;

        @JsonView(Views.Normal.class)
        private List<String> skills;

6.3 To enable the @JsonView features, use the following methods :

mapper.writerWithView(“view class”).writeValue()
mapper.readerWithView(“view class”).readValue()

JacksonExample.java

Java

package com.mkyong.json;

import java.io.IOException;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Jackson2Example {

        public static void main(String[] args) {
                Jackson2Example obj = new Jackson2Example();
                obj.run();
        }

        private void run() {
                ObjectMapper mapper = new ObjectMapper();

                Staff staff = createDummyObject();

                try {

                        // Salary will be hidden
                        System.out.println("Normal View");
                        String normalView = mapper.writerWithView(Views.Normal.class).writeValueAsString(staff);
                        System.out.println(normalView);

                        String jsonInString = "{\"name\":\"mkyong\",\"age\":33,\"position\":\"Developer\",\"salary\":7500,\"skills\":[\"java\",\"python\"]}";
                        Staff normalStaff = mapper.readerWithView(Views.Normal.class).forType(Staff.class).readValue(jsonInString);
                        System.out.println(normalStaff);

                        // Display everything
                        System.out.println("\nManager View");
                        String managerView = mapper.writerWithView(Views.Manager.class).writeValueAsString(staff);
                        System.out.println(managerView);

                        Staff managerStaff = mapper.readerWithView(Views.Manager.class).forType(Staff.class).readValue(jsonInString);
                        System.out.println(managerStaff);

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

        private Staff createDummyObject() {

                Staff staff = new Staff();

                staff.setName("mkyong");
                staff.setAge(33);
                staff.setPosition("Developer");
                staff.setSalary(new BigDecimal("7500"));

                List<String> skills = new ArrayList<>();
                skills.add("java");
                skills.add("python");

                staff.setSkills(skills);

                return staff;

        }

}

Output

Bash

Normal View
{"name":"mkyong","age":33,"position":"Developer","skills":["java","python"]}
Staff [name=mkyong, age=33, position=Developer, salary=null, skills=[java, python]]

Manager View
{"name":"mkyong","age":33,"position":"Developer","salary":7500,"skills":["java","python"]}
Staff [name=mkyong, age=33, position=Developer, salary=7500, skills=[java, python]]

Note
Read this Spring MVC Ajax example – This example demonstrate the use of @JsonView on Spring MVC framework.

7. Misc Examples

Some commonly ask questions.

7.1 Convert a JSON Array format to a Java List object.

Java

       String json = "[{\"name\":\"mkyong\"}, {\"name\":\"laplap\"}]";
        List<Staff> list = mapper.readValue(json, new TypeReference<List<Staff>>(){});

7.2 Convert a JSON to a Map

Java

       String json = "{\"name\":\"mkyong\", \"age\":33}";
        Map<String, Object> map = mapper.readValue(json, new TypeReference<Map<String,Object>>(){});

View more at: http://bit.ly/1XReQFr

Jackson 2 – Convert Java Object to / from JSON

1. Quick Reference

2. Jackson 2 Dependency

3. POJO (Plain Old Java Object)

4. Java Object to JSON

5. JSON to Java Object

6. @JsonView

7. Misc Examples

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Jackson 2 – Convert Java Object to / from JSON

1. Quick Reference

2. Jackson 2 Dependency

3. POJO (Plain Old Java Object)

4. Java Object to JSON

5. JSON to Java Object

6. @JsonView

7. Misc Examples

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