Java Examples in a Nutshell, 3rd Edition

Compressing Files and Directories

Example 3-5 demonstrates an interesting application of stream classes: compressing files and directories. The classes of interest in this example are not actually part of the java.io package, but instead part of the java.util.zip package. The Compress class defines two static methods, gzipFile( ), which compresses a file using GZIP compression format, and zipDirectory( ), which compresses the files (but not directories) in a directory using the ZIP archive and compression format. gzipFile( ) uses the GZIPOutputStream class, while zipDirectory( ) uses the ZipOutputStream and ZipEntry classes, all from java.util.zip.

This example demonstrates the versatility of the stream classes and shows again how streams can be wrapped around one another so that the output of one stream becomes the input of another. This technique makes it possible to achieve a great variety of effects. Notice again the while loop in both methods that does the actual copying of data from source file to compressed file. These methods do not attempt to handle exceptions; instead they just pass them on to the caller, which is often exactly the right thing to do.

Compress is meant to be used as a utility class by other programs, so it doesn’t itself include a main( ) method. The example does include an inner Compress.Test class, however, which has a main( ) method that can test the gzipFile( ) and zipDirectory( ) methods.

Example 3-5. Compress.java

package je3.io; import java.io.*; ...