Convert Java Object To/From JSON (Gson)

How To Convert Java Object To/From JSON (Gson)

Gson is google library for internal use, but now you can use publically.
It is a lightweight data-interchange format.
Gson is easy to learn and implement, We need to know two methods given below.
1 : toJson() – Convert Java object to JSON format.
2 : fromJson() – Convert JSON into Java object.
A pojo, with initialized values, Later use Gson to convert this object to/from JSON formatted string.
package test.gson; import java.util.ArrayList; import java.util.List; public class DataObject { private int data1 = 100; private String data2 = "hello"; 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 [data1=" + data1 + ", data2=" + data2 + ", list=" + list + "]"; } }
toJson() Example:
Convert object to JSON string, and save it as test.json
package test.gson; import java.io.FileWriter; import java.io.IOException; import com.google.gson.Gson; public class GsonTest { public static void main(String[] args) { DataObject obj = new DataObject(); 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 "test.json" FileWriter writer = new FileWriter("d:\\test\\test.json"); writer.write(json); writer.close(); } catch (IOException e) { e.printStackTrace(); } System.out.println(json); } } Output is : {"data1":100,"data2":"hello","list":["String 1","String 2","String 3"]}
fromJson() Example: Read data from test.json , convert back to object.
package test.gson; import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; import com.google.gson.Gson; public class GsonTest1 { public static void main(String[] args) { Gson gson = new Gson(); try { BufferedReader br = new BufferedReader( new FileReader("d:\\test\\test.json")); //convert the json string back to object DataObject obj = gson.fromJson(br, DataObject.class); System.out.println(obj); } catch (IOException e) { e.printStackTrace(); } } } Output is : DataObject [data1=100, data2=hello, list=[String 1, String 2, String 3]]