Your Smart IOT

In this tutorial, we will show you how to use Jackson 2.x to convert Java object to / from JSON.
<h2>1. Quick Reference</h2>
1.1 Convert Java object to JSON, <code>writeValue(...)</code>
<div class="prism-show-language">
<div class="prism-show-language-label">Java</div>
</div>
<pre class=" language-java">
<code class=" language-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);
</code>
</pre>
1.2 Convert JSON to Java object, <code>readValue(...)</code>
<div class="prism-show-language">
<div class="prism-show-language-label">Java</div>
</div>
<pre class=" language-java">
<code class=" language-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);
</code>
</pre>
P.S All examples are tested with Jackson 2.6.3
<div class="note">Differences from Jackson 1.x 
Most of the APIs still maintains the same method name and signature, just the packaging is different.
<ol>
<li>Jackson 1.x – org.codehaus.jackson.map</li>
<li>Jackson 2.x – com.fasterxml.jackson.databind</li>
</ol>
</div>
<div>
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<h2>2. Jackson 2 Dependency</h2>
2.1 For Jackson 2.x, declares <code>jackson-databind</code>, it will download its dependencies – <code>jackson-core</code> and <code>jackson-annotations</code>
<div class="filename">pom.xml</div>
<div class="prism-show-language">
<div class="prism-show-language-label">Markup</div>
</div>
<pre class=" language-markup">
<code class=" language-markup"> <dependency>
 <groupId>com.fasterxml.jackson.core</groupId>
 <artifactId>jackson-databind</artifactId>
 <version>2.6.3</version>
 </dependency>
</code>
</pre>
2.2 Review the Jackson dependencies :
<div class="filename">mvn dependency:tree</div>
<div class="prism-show-language">
<div class="prism-show-language-label">Markup</div>
</div>
<pre class=" language-markup">
<code class=" language-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</code>
</pre>
<h2>3. POJO (Plain Old Java Object)</h2>
A simple pojo <code>Staff</code> object for testing.
<div class="filename">Staff.java</div>
<div class="prism-show-language">
<div class="prism-show-language-label">Java</div>
</div>
<pre class=" language-java">
<code class=" language-java">package com.mkyong.json;

public class Staff {

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

//getters and setters
</code>
</pre>
<h2>4. Java Object to JSON</h2>
Convert a <code>Staff</code> object into a JSON formatted string.
<div class="filename">Jackson2Example.java</div>
<div class="prism-show-language">
<div class="prism-show-language-label">Java</div>
</div>
<pre class=" language-java">
<code class=" language-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;

}

{
 "name" : "mkyong",
 "age" : 33,
 "position" : "Developer",
 "salary" : 7500,
 "skills" : [ "java", "python" ]
}
</code>
</pre>
<h2>5. JSON to Java Object</h2>
Read JSON string and convert it back to a Java object.
<div class="filename">Jackson2Example.java</div>
<div class="prism-show-language">
<div class="prism-show-language-label">Java</div>
</div>
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<pre class=" language-java">
<code class=" language-java">package com.mkyong.json;

public class Jackson2Example {

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();
 }
 }

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

{
 "name" : "mkyong",
 "age" : 0,
 "position" : null,
 "salary" : 7500,
 "skills" : [ "java", "python" ]
}
</code>
</pre>
<h2>6. @JsonView</h2>
<code>@JsonView</code>, 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).
<div class="filename">Views.java</div>
<div class="prism-show-language">
<div class="prism-show-language-label">Java</div>
</div>
<pre class=" language-java">
<code class=" language-java">package com.mkyong.json;

public class Views {

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

}
</code>
</pre>
6.2 For “Normal view”, salary will be hidden, for “Manager view”, display everything.
<div class="filename">Staff.java</div>
<div class="prism-show-language">
<div class="prism-show-language-label">Java</div>
</div>
<pre class=" language-java">
<code class=" language-java">package com.mkyong.json;

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

public class Staff {

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

@JsonView(Views.Normal.class)
 private List<String> skills;
</code>
</pre>
6.3 To enable the <code>@JsonView</code> features, use the following methods :
<ol>
<li>mapper.writerWithView(“view class”).writeValue()</li>
<li>mapper.readerWithView(“view class”).readValue()</li>
</ol>
<div class="filename">JacksonExample.java</div>
<div class="prism-show-language">
<div class="prism-show-language-label">Java</div>
</div>
<pre class=" language-java">
<code class=" language-java">package com.mkyong.json;

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

public class Jackson2Example {

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);

return staff;

}

}
</code>
</pre>
Output
<div class="prism-show-language">
<div class="prism-show-language-label">Bash</div>
</div>
<pre class=" language-bash">
<code class=" language-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]]
</code>
</pre>
<div class="note">Note 
Read this <a href="http://bit.ly/1qzNnwE" target="_blank">Spring MVC Ajax example</a> – This example demonstrate the use of <code>@JsonView</code> on Spring MVC framework.</div>
<h2>7. Misc Examples</h2>
Some commonly ask questions.
7.1 Convert a JSON Array format to a Java <code>List</code> object.
<div class="prism-show-language">
<div class="prism-show-language-label">Java</div>
</div>
<pre class=" language-java">
<code class=" language-java"> String json = "[{\"name\":\"mkyong\"}, {\"name\":\"laplap\"}]";
 List<Staff> list = mapper.readValue(json, new TypeReference<List<Staff>>(){});
</code>
</pre>
7.2 Convert a JSON to a <code>Map</code>
<div class="prism-show-language">
<div class="prism-show-language-label">Java</div>
</div>
<pre class=" language-java">
<code class=" language-java"> String json = "{\"name\":\"mkyong\", \"age\":33}";
 Map<String, Object> map = mapper.readValue(json, new TypeReference<Map<String,Object>>(){});</code>
</pre>
<pre class=" language-markup">
</pre>
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Jackson 2 – Convert Java Object to / from JSON

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...

Jackson 2 – Convert Java Object to / from JSON

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