1.先创建一个工具类SaveImageUtils

public class SaveImageUtils {
    public static void saveImageToGallery(Context context, Bitmap bmp) {
        // 首先保存图片
        File appDir = new File(Environment.getExternalStorageDirectory(), "Boohee");
        if (!appDir.exists()) {
            appDir.mkdir();
        }
        String fileName = System.currentTimeMillis() + ".jpg";
        File file = new File(appDir, fileName);
        try {
            FileOutputStream fos = new FileOutputStream(file);
            bmp.compress(Bitmap.CompressFormat.JPEG, 100, fos);
            fos.flush();
            fos.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        // 其次把文件插入到系统图库
        try {
            MediaStore.Images.Media.insertImage(context.getContentResolver(),
                    file.getAbsolutePath(), fileName, null);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        // 最后通知图库更新
        context.sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.parse("file://" + file.getPath())));

    }
    public static void saveImageToGallerys(Context context, Bitmap bmp) {
        if (bmp == null){
            Toast.makeText(context, "保存出错了...", Toast.LENGTH_SHORT).show();
            return;
        }
        // 首先保存图片
//        File appDir = new File(BaseApplication.app.getTmpDir(), "ywq");
        File appDir = new File(Environment.getExternalStorageDirectory(), "Boohee");
        if (!appDir.exists()) {
            appDir.mkdir();
        }
        String fileName = System.currentTimeMillis() + ".jpg";
        File file = new File(appDir, fileName);
        try {
            FileOutputStream fos = new FileOutputStream(file);
            bmp.compress(Bitmap.CompressFormat.JPEG, 100, fos);
            fos.flush();
            fos.close();
        } catch (FileNotFoundException e) {
            Toast.makeText(context, "文件未发现...", Toast.LENGTH_SHORT).show();
            e.printStackTrace();
        } catch (IOException e) {
            Toast.makeText(context, "保存出错了...", Toast.LENGTH_SHORT).show();
            e.printStackTrace();
        }catch (Exception e){
            Toast.makeText(context, "保存出错了...", Toast.LENGTH_SHORT).show();
            e.printStackTrace();
        }

        // 最后通知图库更新
        try {
            MediaStore.Images.Media.insertImage(context.getContentResolver(), file.getAbsolutePath(), fileName, null);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
        Uri uri = Uri.fromFile(file);
        intent.setData(uri);
        context.sendBroadcast(intent);
        Toast.makeText(context, "保存出错了...", Toast.LENGTH_SHORT).show();
    }
}

2.MainActivity 调用

public class MainActivity extends AppCompatActivity {

    private Bitmap bitmap_image;

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

        //获得ID控件
        ImageView image = findViewById(R.id.image);

        //将ImageView 转换为 Bitmap
        bitmap_image = ((BitmapDrawable)image.getDrawable()).getBitmap();

        //长按保存
        image.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View v) {
                SaveImageUtils.saveImageToGallery(MainActivity.this, bitmap_image);
                return false;
            }
        });
    }
}