EasyPermissions

Library on GitHub with dependency + instructions:

github.com/googlesamples/easypermissions

<?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="com.codinginflow.easypermissionsexample.MainActivity">

    <Button
        android:id="@+id/button_open_camera"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Open camera"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

package com.codinginflow.easypermissionsexample;

import android.Manifest;
import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import java.util.List;

import pub.devrel.easypermissions.AfterPermissionGranted;
import pub.devrel.easypermissions.AppSettingsDialog;
import pub.devrel.easypermissions.EasyPermissions;

public class MainActivity extends AppCompatActivity implements EasyPermissions.PermissionCallbacks {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button buttonOpenCamera = findViewById(R.id.button_open_camera);
        buttonOpenCamera.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                openCamera();
            }
        });
    }

    @AfterPermissionGranted(123)
    private void openCamera() {
        String[] perms = {Manifest.permission.CAMERA, Manifest.permission.READ_EXTERNAL_STORAGE};
        if (EasyPermissions.hasPermissions(this, perms)) {
            Toast.makeText(this, "Opening camera", Toast.LENGTH_SHORT).show();
        } else {
            EasyPermissions.requestPermissions(this, "We need permissions because this and that",
                    123, perms);
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);

        EasyPermissions.onRequestPermissionsResult(requestCode, permissions, grantResults, this);
    }

    @Override
    public void onPermissionsGranted(int requestCode, @NonNull List<String> perms) {

    }

    @Override
    public void onPermissionsDenied(int requestCode, @NonNull List<String> perms) {
        if (EasyPermissions.somePermissionPermanentlyDenied(this, perms)) {
            new AppSettingsDialog.Builder(this).build().show();
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == AppSettingsDialog.DEFAULT_SETTINGS_REQ_CODE) {

        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.codinginflow.easypermissionsexample">

    <uses-permission android:name="android.permission.CAMERA" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>