Learning Java, 4th Edition

Data Compression

The java.util.zip package contains classes you can use for data compression in streams or files. The classes in the java.util.zip package support two widespread compression formats: GZIP and ZIP. 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 learned in this chapter. After that, we’ll talk about a higher-level way to work with ZIP archives—as filesystems—introduced with Java 7.

Archives and Compressed Data

The java.util.zip package provides two filter streams for writing compressed data. The GZIPOutputStream is for writing data in GZIP compressed format. The ZIPOutputStream is for writing compressed ZIP archives, which can contain one or many files. 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, but the stream could just as well be sent over a network connection or to any other type of stream destination. Our GZip example is a command line utility that compresses a file.

    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 ...