Search for "Java Zero-Copy Buffers" or "Java NIO" or "Java Netty".
Here is a slide show about Netty and zero-copy : http://www.slideshare.net/danbim/zerocopy-eventdriven-servers-with-netty . Here is an example project with Netty.
Or you can go lower level and use the java.nio.channels classes, which you can read about here http://www.ibm.com/developerworks/linux/library/j-zerocopy/