Learning Java

Data Compression

The java.util.zip package contains classes you can use for data compression. In this section, we’ll talk about how to use these classes. We’ll also present two useful example programs that build on what you have just learned about streams and files.

The classes in the java.util.zip package support two widespread compression formats: GZIP and ZIP. Both of these are based on the ZLIB compression algorithm, which is discussed in RFC 1950, RFC 1951, and RFC 1952. These documents are available at http://www.faqs.org/rfcs. But you don’t need to read them unless you want to implement your own compression algorithm or otherwise extend the functionality of the java.util.zip package.

Compressing Data

The java.util.zip class provides two FilterOutputStream subclasses to write compressed data to a stream. To write compressed data in the GZIP format, simply wrap a GZIPOutputStream around an underlying stream and write to it. The following is a complete example that shows how to compress a file using the GZIP format:

//file: GZip.java import java.io.*; import java.util.zip.*; public class GZip { public static int sChunk = 8192; public static void main(String[] args) { if (args.length != 1) { System.out.println("Usage: GZip source"); return; } // create output stream String zipname = args[0] + ".gz"; GZIPOutputStream zipout; try { FileOutputStream out = new FileOutputStream(zipname); zipout = new GZIPOutputStream(out); } catch (IOException e) { System.out.println("Couldn't ...