android javaでユーザからカメラ、写真フォルダへの許可を取る方法

import android.Manifest;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.pm.PackageManager;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.PermissionChecker;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {

    private static final int REQUEST_CODE_CAMERA_PERMISSION = 1000;
    private static final int REQUEST_CODE_WRITE_EXTERNAL_STORAGE_PERMISSION = 2000;

    String title = "権限チェック";
    String message = "この機能を使用する際には権限を許可する必要があります。";

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

        Button requestButtonCamera = (Button) findViewById(R.id.requestButton1);
        requestButtonCamera.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // カメラの権限状態取得
                int permissionCamera = PermissionChecker.checkSelfPermission(MainActivity.this, Manifest.permission.CAMERA);

                // カメラの権限確認
                if (permissionCamera != PackageManager.PERMISSION_GRANTED) {
                    requestPermission(REQUEST_CODE_CAMERA_PERMISSION);
                }

               // TODO : アクセス後の処理

            }
        });

        Button requestButtonWriteExternalStoragePermission = (Button) findViewById(R.id.requestButton2);
        requestButtonWriteExternalStoragePermission.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // カメラロールの権限状態取得
                int permissionWriteExternalStorage = PermissionChecker.checkSelfPermission(MainActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE);

                // カメラロールの権限確認
                if (permissionWriteExternalStorage != PackageManager.PERMISSION_GRANTED) {
                    requestPermission(REQUEST_CODE_WRITE_EXTERNAL_STORAGE_PERMISSION);
                }

                // TODO : アクセス後の処理

            }
        });

    }

    // Permission handling for Android 6.0
    private void requestPermission(int requestCode) {

        // 権限チェックした結果、持っていない場合はダイアログを出す
        switch (requestCode) {

            case REQUEST_CODE_CAMERA_PERMISSION:
                    alert(requestCode,new String[]{Manifest.permission.CAMERA},title, message);
                break;

            case REQUEST_CODE_WRITE_EXTERNAL_STORAGE_PERMISSION:
                    alert(requestCode,new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},title, message);
                break;
        }
    }

    private void alert(final int requestCode,final String[] manifestPermission, String title,String message){

        DialogInterface.OnClickListener dialog = new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                ActivityCompat.requestPermissions(MainActivity.this,
                        manifestPermission,
                        requestCode);
            }
        };

        new AlertDialog.Builder(this)
                .setTitle(title).setMessage(message)
                .setPositiveButton(android.R.string.ok,dialog).create().show();
    }
}