java - Android - 从磁盘上传图像

Question

我在 Android 上上传文件时遇到了一些问题。我已经将应用程序的这一部分拼凑在一起，现在需要进行一些修改。

我正在尝试从 Uri 引用的磁盘图像上传文件到服务器。

在上传之前，我尝试将图像缩小到最大尺寸 1280。

这是一个示例类，其中包含我正在使用的实际代码。我敢肯定这是非常低效的:

/**
 * This is a fake class, this is actually spread across 2 or 3 files
 */
public class Temp
{
  /**
   * This is used to return an Input stream of known size
   */
  public static class KnownSizeInputStream extends InputStreamBody
  {
    private int mLength;

    public KnownSizeInputStream( final InputStream in, final int length, final String mimeType, final String filename )
    {
      super( in, mimeType, filename );
      mLength = length;
    }

    public long getContentLength()
    {
      return mLength;
    }
  }

  private static final int MAX_WIDTH  = 1280;
  private static final int MAX_HEIGHT = 1280;

  /**
   * Open up a file on disk and convert it into a stream of known size
   */
  public KnownSizeInputStream toStreamAio( Context c, Uri path )
  {
    /**
     * Scale down bitmap
     */
    Bitmap bitmapData = null;

    try
    {
      bitmapData = BitmapFactory.decodeStream( c.getContentResolver().openInputStream( path ) );
    }
    catch( Exception e )
    {
      e.printStackTrace();
    }

    int imgWidth = bitmapData.getWidth();
    int imgHeight = bitmapData.getHeight();

    // Constrain to given size but keep aspect ratio
    float scaleFactor = Math.min( ( ( float )MAX_WIDTH ) / imgWidth, ( ( float )MAX_HEIGHT ) / imgHeight );

    Matrix scale = new Matrix();
    scale.postScale( scaleFactor, scaleFactor );
    final Bitmap scaledImage = Bitmap.createBitmap( bitmapData, 0, 0, imgWidth, imgHeight, scale, false );

    try
    {
      bitmapData = scaledImage.copy( scaledImage.getConfig(), true );

      scaledImage.recycle();
    }
    catch( Exception e )
    {
      e.printStackTrace();
    }

    /**
     * To byte[]
     */
    byte[] byteData = null;

    ByteArrayOutputStream baos = new ByteArrayOutputStream();

    bitmapData.compress( Bitmap.CompressFormat.JPEG, 100, baos );

    byteData = baos.toByteArray();

    /**
     * To stream
     */
    return new KnownSizeInputStream( new ByteArrayInputStream( byteData ), byteData.length, "image/jpg", "Some image" );
  }

  /** 
   * Some pieces are removed, the main part is the addPart line
   */
  public void doUpload()
  {
    // create a new HttpPost, to our specified URI
    HttpPost post = new HttpPost( postUri );

    // org.apache.http.entity.mime
    MultipartEntity entity = new MultipartEntity( HttpMultipartMode.STRICT );


    // This line starts all of the issues
    entity.addPart( "file", toStreamAio( mContext, Uri.parse( "/some/file.jpg" ) ) );


    post.setEntity( entity );

    // send it
    HttpResponse response = client.execute( post );

  }
}

这是我遇到的异常，我从尝试分配图像的完整大小的调整大小中猜测:

Caused by: java.lang.OutOfMemoryError
 at android.graphics.Bitmap.nativeCopy(Native Method)
 at android.graphics.Bitmap.copy(Bitmap.java:403)
 at com.app.helper.UploadableImage.toScaledBitmap(UploadableImage.java:170)
 at com.app.helper.UploadableImage.toByteArray(UploadableImage.java:53)
 at com.app.helper.UploadableImage.toStream(UploadableImage.java:242)
 at com.app.rest.task.UploadContentTask.doInBackground(UploadContentTask.java:80)
 at com.app.rest.task.UploadContentTask.doInBackground(UploadContentTask.java:1)
 at android.os.AsyncTask$2.call(AsyncTask.java:264)
 at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
 ... 5 more

它是由这条线触发的:

data = scaledImage.copy( scaledImage.getConfig(), true );

我想我要问的主要问题是，如何从磁盘上的路径获取图像、缩放图像，以及我可以放入的流:

org.apache.http.entity.mime.MultipartEntity

通过:

.addPart("file", streamData);

最有效的，假设图像可以是巨大的(~6000px 是我迄今为止达到的最大尺寸)

Answer 1

首先，为什么要复制缩放后的位图？你不能像这样直接压缩缩放后的位图吗:

final Bitmap scaledImage = Bitmap.createBitmap(bitmapData, 0, 0,
        imgWidth, imgHeight, scale, false);
scaledImage.compress(Bitmap.CompressFormat.JPEG, 100, baos);

如果可以避免复制，则可以避免出现 OutOfMemoryError。

即使您使用 JPEG 压缩选择 95% 的质量(处理自然物体的照片时)，您也可以获得良好的压缩效果，质量损失微乎其微。您应该尝试质量设置并自行检查。