使用GZIPOutputStream时当前文件大小

Question

我正在以异步方式使用GZIPOutputStream将压缩数据写入磁盘。

我想知道已经写入的数据的大小，这样我就可以在文件达到极限时关闭它。

ByteBuffer src;
//..
//data added to src here
//..
File theFile = new File("hello.gz");
FileOutputStream fos = new FileOutputStream(theFile);
GZIPOutputStream zs = new GZIPOutputStream(fos);
BufferedWriter zipwriter = new BufferedWriter(new OutputStreamWriter(zs, "UTF-8"));

(while_more_data)
{
   zipwriter.write(src.get());
   // check current file size here and close file if limit is reached
}

Answer 1

将您的FileOutputStream封装到另一个输出流中，它能够计算写入的字节数，比如第三方库雅加达公域IO提供的CountingOutputStream，或者番石榴中的CountingOutputStream。

实现可以类似于：

ByteBuffer src;
//..
//data added to src here
//..
File theFile = new File("hello.gz");
try (FileOutputStream fos = new FileOutputStream(theFile);
     CountingOutputStream cos = new CountingOutputStream(fos);
     GZIPOutputStream zs = new GZIPOutputStream(cos);
     BufferedWriter zipwriter = new BufferedWriter(new OutputStreamWriter(zs, "UTF-8"))) {

    (while_more_data) {
        zipwriter.write(src.get());
        zipwriter.flush(); // make sure, data passes cos
        if (cos.getByteCount() >= limit) {
            // limit reached
        }
    }
}

Answer 2

或如果您不想进入整个库，如番石榴或公-IO，则只需扩展GZIPOutputStream并从关联的平移器获取数据，如下所示：

public class MyGZIPOutputStream extends GZIPOutputStream {

  public GZIPOutputStream(OutputStream out) throws IOException {
      super(out);
  }

  public long getBytesRead() {
      return def.getBytesRead();
  }

  public long getBytesWritten() {
      return def.getBytesWritten();
  }

  public void setLevel(int level) {
      def.setLevel(level);
  }
}