InputStream which copies your available Data

CopyInputStream.java

import java.io.ByteArrayOutputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

public class CopyInputStream extends FilterInputStream {
	private final ByteArrayOutputStream _copyTo = new ByteArrayOutputStream();

	public CopyInputStream(InputStream in) {
		super(in);
	}

	@Override
	public int read() throws IOException {
		int ch = in.read();
		if (ch != -1) {
			_copyTo.write(ch);
		}
		return ch;
	}

	@Override
	public synchronized int read(byte[] b, int off, int len) throws IOException {
		int size = super.read(b, off, len);
		if (size != -1) {
			_copyTo.write(b, off, size);
		}

		return size;
	}

	public byte[] toByteArray() {
		return _copyTo.toByteArray();
	}
}

If we know the length, we could also copy it into a NIO ByteBuffer.