JSON serialization and Deserialization

JSON serialization and Deserialization

 

JSON is stand for JavaScript Object Notation, it is a lightweight data-interchange format.

Persist JSON to Java Object /POJO called JSON serialization ( Storing object state in a file ).
Converting Java object / POJO to JSON object called JSON Deserialization ( reading/recreating from file to object ).

Gson ( Google JSON library) used to convert object to/from json.
Gson is easy to learn and implement, what we need to know are following two methods.

toJson() – Convert Java object to JSON format
fromJson() – Convert JSON into Java object

Maven dependency to add to POM.xml ( search for latest jar in maven central ..http://search.maven.org/#search%7Cga%7C1%7Cgson )

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.4</version>
</dependency>


POJO

import java.util.ArrayList;
import java.util.List;

public class VarObject {

private int var1= 1599;
private String var2 = "GsonWelcomesU";
private List<String> list = new ArrayList<String>() {
  {
add("String 1");
add("String 2");
add("String 3");
  }
};

//getter and setter methods

@Override
public String toString() {
   return "DataObject [var1=" + var1 + ", var2=" + var2 + ", list="
+ list + "]";
}

}
Serialize JSON  .. toJson()
Convert object to JSON string, and save it as “file.json“.

import java.io.FileWriter;
import java.io.IOException;
import com.google.gson.Gson;

public class SerializeJSON {
    public static void main(String[] args) {

 VarObject obj = new VarObject ();
  Gson gson = new Gson();

// convert java object to JSON format, and returned as JSON formatted string
String json = gson.toJson(obj);

try {
//write converted json data to a file named "file.json"
FileWriter writer = new FileWriter("c:\\file.json");
writer.write(json);
writer.close();

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

System.out.println(json);

    }
}
Output

{"var1":1599,"var2":"GsonWelcomesU","list":["String 1","String 2","String 3"]}

 

 

 

DeSerialize JSON  .. fromJson()
Convert JSON  to Java Object.

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import com.google.gson.Gson;

public class DeserializeJSON {

public static void main(String[] args) {

Gson gson = new Gson();

try {

BufferedReader br = new BufferedReader(
new FileReader("c:\\file.json"));

//convert the json string back to object
  VarObject obj = gson.fromJson(br, VarObject.class);

System.out.println(obj);

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

    }
}

Output

VarObject [var1=1599, var2=GsonWelcomesU, list=[String 1, String 2, String 3]]

Pretty Print JSON format
To enable pretty print, you should use GsonBuilder return a Gson object :

 Gson gson = new GsonBuilder().setPrettyPrinting().create();
 String json = gson.toJson(obj);
 System.out.println(json);

Output

{
  "var1": 1599,
  "var2": "GsonWelcomesU",
  "list": [
    "String 1",
    "String 2",
    "String 3"
  ]
}

 

********* How to convert a long JSON Array to Java Object  ?? *********