compression on java nio direct buffers

问题

The gzip input/output stream dont operate on Java direct buffers.

Is there any compression algorithm implementation out there that operates directly on direct buffers?

This way there would be no overhead of copying a direct buffer to a java byte array for compression.

回答1:

I don't mean to detract from your question, but is this really a good optimization point in your program? Have you verified with a profiler that you indeed have a problem? Your question as stated implies you have not done any research, but are merely guessing that you will have a performance or memory problem by allocating a byte[]. Since all the answers in this thread are likely to be hacks of some sort, you should really verify that you actually have a problem before fixing it.

Back to the question, if you're wanting to compress the data "in place" in on a ByteBuffer, the answer is no, there is no capability to do that built into Java.

If you allocated your buffer like the following:

byte[] bytes = getMyData();
ByteBuffer buf = ByteBuffer.wrap(bytes);

You can filter your byte[] through a ByteBufferInputStream as the previous answer suggested.

回答2:

If you are using ByteBuffers you can use some simple Input/OutputStream wrappers such as these:

public class ByteBufferInputStream extends InputStream {

    private ByteBuffer buffer = null;

    public ByteBufferInputStream( ByteBuffer b) {
        this.buffer = b;
    }

    @Override
    public int read() throws IOException {
        return (buffer.get() & 0xFF);
    }
}

public class ByteBufferOutputStream extends OutputStream {

    private ByteBuffer buffer = null;

    public ByteBufferOutputStream( ByteBuffer b) {
        this.buffer = b;
    }

    @Override
    public void write(int b) throws IOException {
        buffer.put( (byte)(b & 0xFF) );
    }

}

Test:

ByteBuffer buffer = ByteBuffer.allocate( 1000 );
ByteBufferOutputStream bufferOutput = new ByteBufferOutputStream( buffer );
GZIPOutputStream output = new GZIPOutputStream( bufferOutput );
output.write("stackexchange".getBytes());
output.close();

buffer.position( 0 );

byte[] result = new byte[ 1000 ];

ByteBufferInputStream bufferInput = new ByteBufferInputStream( buffer );
GZIPInputStream input = new GZIPInputStream( bufferInput );
input.read( result );

System.out.println( new String(result));

来源：https://stackoverflow.com/questions/8766351/compression-on-java-nio-direct-buffers

标签

java

compression

gzip

nio