How to convert HASHMAP to JSON using GSON in Android?

GSON is java library, It is used to convert OBJECT to JSON and JSON to Object. Internally it going to work based on serialization and deserialization.

This example demonstrates how to convert HASHAMP to JSON using GSON library.

Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.

Step 2 − Add the following code in build.gradle.

apply plugin: 'com.android.application'

android {
   compileSdkVersion 28
   defaultConfig {
      applicationId "com.example.andy.myapplication"
      minSdkVersion 15
      targetSdkVersion 28
      versionCode 1
      versionName "1.0"
      testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
   }
   buildTypes {
      release {
         minifyEnabled false
         proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
      }
   }
}

dependencies {
   implementation fileTree(dir: 'libs', include: ['*.jar'])
   implementation 'com.android.support:appcompat-v7:28.0.0'
   implementation 'com.google.code.gson:gson:2.8.5'
   implementation 'com.android.support.constraint:constraint-layout:1.1.3'
   testImplementation 'junit:junit:4.12'
   androidTestImplementation 'com.android.support.test:runner:1.0.2'
   androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}

In the above code we have added GSON latest library.

Step 3 − Add the following code to res/layout/activity_main.xml.

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
   xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context=".MainActivity">
   <TextView
      android:id="@+id/result"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Result Data"
      app:layout_constraintBottom_toBottomOf="parent"
      app:layout_constraintLeft_toLeftOf="parent"
      app:layout_constraintRight_toRightOf="parent"
      app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

In the above code we have added textview, This text view going to show result data.

Step 4 − Add the following code to src/MainActivity.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;
import android.widget.Toast;
import com.google.gson.Gson;
import java.util.ArrayList;
import java.util.HashMap;

public class MainActivity extends AppCompatActivity {
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      TextView result=findViewById(R.id.result);
      HashMap<String,String> hashMap=new HashMap<>();
      hashMap.put("JAVA","NetBeans");
      hashMap.put("Android","Android Studio");
      hashMap.put("Kotlin", "Notepad ++");
      Gson gson=new Gson();
      String MapData=gson.toJson(hashMap);
      result.setText(MapData);
   }
}

Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click Run icon from the toolbar.