Java JSON-Convert Java Object To/From JSON (Jackson)

Java JSON-Convert Java Object To/From JSON (Jackson)

JSON (JavaScript Object Notation) is a lightweight data exchange language based on text and easy to read. Although JSON is a subset of Javascript, JSON is a language-independent text format and is similar to the C language family. Wikipedia-http://zh.wikipedia.org/wiki/JSON

Jackson is a High-performance JSON processor Java library -- Jackson is a High-performance JSON-parsed Java lib

Core code:

//1. Convert Java object to JSON formatObjectMapper mapper = new ObjectMapper();mapper.writeValue(new File("c:\\user.json"), user);

//2. Convert JSON to Java objectObjectMapper mapper = new ObjectMapper();User user = mapper.readValue(new File("c:\\user.json"), User.class);

The following is an example:

I. POJOUser. java

package com.jiangge.jkstest;import java.util.ArrayList;import java.util.List;public class User {private int age = 23;private String name = "jiangge";private String qqNum = "499065469";private List
 
   message = new ArrayList
  
   () {{add("msg 1");add("msg 2");add("msg 3");}};public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public List
   
     getMessage() {return message;}public void setMessage(List
    
      message) {this.message = message;}public String getqqNum() {return qqNum;}public void setqqNum(String qq) {this.qqNum = qq;}@Overridepublic String toString() {return "User [age=" + age + ", name=" + name + ", message=" + message+ "]";}}
    
   
  
 

Ii. Java Object to JSON
Convert an "user" object into JSON formatted string, and save it into a file "user. json".

package com.jiangge.jkstest;import java.io.File;import java.io.IOException;import com.fasterxml.jackson.core.JsonGenerationException;import com.fasterxml.jackson.databind.JsonMappingException;import com.fasterxml.jackson.databind.ObjectMapper;//To make this work with the latest (1.9.3) Jackson, //there must be getters and setters for the members in the User class.public class JacksonExampleToJson {public static void main(String[] args) { User user = new User();ObjectMapper objMapper = new ObjectMapper();try {// convert user object to json string, and save to a fileobjMapper.writeValue(new File("c:\\user.json"), user);// display to consoleSystem.out.println(objMapper.writeValueAsString(user));} catch (JsonGenerationException e) {e.printStackTrace();} catch (JsonMappingException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace(); }   }}

Console output:

{"Age": 23, "name": "jiangge", "qqNum": "499065469", "message": ["msg 1", "msg 2 ", "msg 3"]}

Iii. JSON to Java Object
Read JSON string from file "user. json", and convert it back to Java object.

package com.jiangge.jkstest;import java.io.File;import java.io.IOException;import com.fasterxml.jackson.core.JsonGenerationException;import com.fasterxml.jackson.databind.JsonMappingException;import com.fasterxml.jackson.databind.ObjectMapper;public class JacksonExampleRead {public static void main(String[] args) { ObjectMapper objMapper = new ObjectMapper();try {// read from file, convert it to user classUser user = objMapper.readValue(new File("c:\\user.json"), User.class);// display to consoleSystem.out.println(user); } catch (JsonGenerationException e) {e.printStackTrace();} catch (JsonMappingException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}   } }

Console output:

User [age = 23, name = jiangge, message = [msg 1, msg 2, msg 3]

References:

Http://www.mkyong.com/java/how-to-convert-java-object-to-from-json-jackson/

For more information, see:

Http://www.mkyong.com/tutorials/java-json-tutorials/