问如何在android图库中保存图片

EN

OutputStream output;
       // Find the SD Card path
        File filepath = Environment.getExternalStorageDirectory();

      // Create a new folder in SD Card
     File dir = new File(filepath.getAbsolutePath()
              + "/WhatSappIMG/");
        dir.mkdirs(); 

     // Retrieve the image from the res folder
        BitmapDrawable drawable = (BitmapDrawable) principal.getDrawable();
        Bitmap bitmap1 = drawable.getBitmap();

        // Create a name for the saved image
        File file = new File(dir, "Wallpaper.jpg" );

        try {

            output = new FileOutputStream(file);

            // Compress into png format image from 0% - 100%
            bitmap1.compress(Bitmap.CompressFormat.JPEG, 100, output);
            output.flush();
            output.close();

        }

        catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }