JsonParser : Parse json file using gson library

In this post, I am going to explain, how can you parse a json file using gson library.

For example, consider below json file.

testApp.json

{
 "login" : {
  "userName" : "krishna",
  "password" : "krishna"
 },

 "homePage" : {
  "welcomeMessage" : "Hello Krishna",
  "buttonId" : "saveYourChanges"
 }
}

Below step-by-step procedure explains, how to parse login element from testApp.json file.

Step 1: Create the instance of JsonParser.

JsonParser jsonParser = new JsonParser();

Step 2: Read the json data from given file.

String jsonData = new String(Files.readAllBytes(Paths.get(jsonFilePath)));

Step 3: Get the root element by parsing the data.

JsonObject rootElement = (JsonObject)jsonParser.parse(jsonData);

Step 4: Now you can parse the element by using element name.

For example, below statement retrieves the json element with name 'login'.

JsonObject loginElement =  (JsonObject)jsonParser.parse(rootElement.get("login").toString());

Find the below working application.

Test.java

package com.sample.files;

import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Map;
import java.util.Set;

import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;

public class Test {

 private static String jsonFilePath = "C:\\Users\\krishna\\testApp.json";
 
 public static void main(String args[]) throws Exception {
 
  JsonParser jsonParser = new JsonParser();
  
  String jsonData = new String(Files.readAllBytes(Paths.get(jsonFilePath)));
  
  JsonObject rootElement = (JsonObject)jsonParser.parse(jsonData);
  
  JsonObject loginElement =  (JsonObject)jsonParser.parse(rootElement.get("login").toString());
  
  Set<Map.Entry<String, JsonElement>> entrySet = loginElement.entrySet();
  
  for(Map.Entry<String, JsonElement> entry : entrySet){
   String key = entry.getKey();
   String value = entry.getValue().getAsString();
   System.out.println("key : " + key + ", value : " + value);
  }

 }
}

Output

key : userName, value : krishna
key : password, value : krishna

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