Android實戰技巧之三十七：圖片的Base64編解碼

通經常使用Base64這樣的編解碼方式將二進制數據轉換成可見的字符串格式，就是我們常說的大串。10塊錢一串的那種，^_^。

Android的android.util包下直接提供了一個功能十分完備的Base64類供我們使用，以下就演示一下怎樣將一張圖片進行Base64的編解碼。

1.找到那張圖片

public void onEncodeClicked(View view) {

        //select picture
        Intent intent = new Intent();
        intent.setType("image/*");
        intent.setAction(Intent.ACTION_GET_CONTENT);
        startActivityForResult(intent, OPEN_PHOTO_FOLDER_REQUEST_CODE);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if(OPEN_PHOTO_FOLDER_REQUEST_CODE == requestCode && RESULT_OK == resultCode) {

            //encode the image
            Uri uri = data.getData();
            try {
                //get the image path
                String[] projection = {MediaStore.Images.Media.DATA};
                CursorLoader cursorLoader = new CursorLoader(this,uri,projection,null,null,null);
                Cursor cursor = cursorLoader.loadInBackground();
                int column_index = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
                cursor.moveToFirst();

                String path = cursor.getString(column_index);
                Log.d(TAG,"real path: "+path);
                encode(path);
            } catch (Exception ex) {
                Log.e(TAG, "failed." + ex.getMessage());
            }
        }
    }

2.將圖片轉換成bitmap並編碼

private void encode(String path) {
                //decode to bitmap
                Bitmap bitmap = BitmapFactory.decodeFile(path);
                Log.d(TAG, "bitmap width: " + bitmap.getWidth() + " height: " + bitmap.getHeight());
                //convert to byte array
                ByteArrayOutputStream baos = new ByteArrayOutputStream();
                bitmap.compress(Bitmap.CompressFormat.PNG, 100, baos);
                byte[] bytes = baos.toByteArray();

                //base64 encode
                byte[] encode = Base64.encode(bytes,Base64.DEFAULT);
                String encodeString = new String(encode);
                mTvShow.setText(encodeString);
}

3.將大串還原成圖片

    public void onDecodeClicked(View view) {
        byte[] decode = Base64.decode(mTvShow.getText().toString(),Base64.DEFAULT);
        Bitmap bitmap = BitmapFactory.decodeByteArray(decode, 0, decode.length);
        //save to image on sdcard
        saveBitmap(bitmap);
    }

    private void saveBitmap(Bitmap bitmap) {
        try {
            String path = Environment.getExternalStorageDirectory().getPath()
                    +"/decodeImage.jpg";
            Log.d("linc","path is "+path);
            OutputStream stream = new FileOutputStream(path);
            bitmap.compress(Bitmap.CompressFormat.JPEG, 90, stream);
            stream.close();
            Log.e("linc","jpg okay!");
        } catch (IOException e) {
            e.printStackTrace();
            Log.e("linc","failed: "+e.getMessage());
        }
    }

須要注意的是，一張圖片的編碼速度會非常慢，假設圖片非常大就更慢了。畢竟手機的處理能力有限。只是decode的速度確實相當的快，超出你的想象。好了，就是這樣簡單，今天就到這里了，晚安！