ここで非常に古いスレッドを復活させていることに気付きましたが、今日グーグルで見つけたので...
進行状況を監視したい場合は、転送を最適化できるように、システムにチャンク サイズを処理させることを EJP が提案しているように、より良い方法です。監視する方法は、そのメソッドが呼び出されるReadableByteChannelたびに進行状況メッセージを渡すために使用するラッパー クラスを作成することです。read次に例を示します。
package download.progress.example;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;
public class DownloadProgressExample {
public static void main( String[] args ) {
new Downloader( "/tmp/foo.mp3", "http://example.com/bar.mp3" );
}
private interface RBCWrapperDelegate {
// The RBCWrapperDelegate receives rbcProgressCallback() messages
// from the read loop. It is passed the progress as a percentage
// if known, or -1.0 to indicate indeterminate progress.
//
// This callback hangs the read loop so a smart implementation will
// spend the least amount of time possible here before returning.
//
// One possible implementation is to push the progress message
// atomically onto a queue managed by a secondary thread then
// wake that thread up. The queue manager thread then updates
// the user interface progress bar. This lets the read loop
// continue as fast as possible.
public void rbcProgressCallback( RBCWrapper rbc, double progress );
}
private static final class Downloader implements RBCWrapperDelegate {
public Downloader( String localPath, String remoteURL ) {
FileOutputStream fos;
ReadableByteChannel rbc;
URL url;
try {
url = new URL( remoteURL );
rbc = new RBCWrapper( Channels.newChannel( url.openStream() ), contentLength( url ), this );
fos = new FileOutputStream( localPath );
fos.getChannel().transferFrom( rbc, 0, Long.MAX_VALUE );
} catch ( Exception e ) {
System.err.println( "Uh oh: " + e.getMessage() );
}
}
public void rbcProgressCallback( RBCWrapper rbc, double progress ) {
System.out.println( String.format( "download progress %d bytes received, %.02f%%", rbc.getReadSoFar(), progress ) );
}
private int contentLength( URL url ) {
HttpURLConnection connection;
int contentLength = -1;
try {
HttpURLConnection.setFollowRedirects( false );
connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod( "HEAD" );
contentLength = connection.getContentLength();
} catch ( Exception e ) { }
return contentLength;
}
}
private static final class RBCWrapper implements ReadableByteChannel {
private RBCWrapperDelegate delegate;
private long expectedSize;
private ReadableByteChannel rbc;
private long readSoFar;
RBCWrapper( ReadableByteChannel rbc, long expectedSize, RBCWrapperDelegate delegate ) {
this.delegate = delegate;
this.expectedSize = expectedSize;
this.rbc = rbc;
}
public void close() throws IOException { rbc.close(); }
public long getReadSoFar() { return readSoFar; }
public boolean isOpen() { return rbc.isOpen(); }
public int read( ByteBuffer bb ) throws IOException {
int n;
double progress;
if ( ( n = rbc.read( bb ) ) > 0 ) {
readSoFar += n;
progress = expectedSize > 0 ? (double) readSoFar / (double) expectedSize * 100.0 : -1.0;
delegate.rbcProgressCallback( this, progress );
}
return n;
}
}
}