Java in a Nutshell, 5th Edition

Name

Package java.util.jar

Synopsis

The java.util.jar package contains classes for reading and writing Java archive, or JAR, files. A JAR file is nothing more than a ZIP file whose first entry is a specially named manifest file that contains attributes and digital signatures for the ZIP file entries that follow it. Many of the classes in this package are relatively simple extensions of classes from the java.util.zip package.

The easiest way to read a JAR file is with the random-access JarFile class. This class allows you to obtain the JarEntry that describes any named file within the JAR archive. It also allows you to obtain an enumeration of all entries in the archive and an InputStream for reading the bytes of a specific JarEntry. Each JarEntry describes a single entry in the archive and allows access to the Attributes and the digital signatures associated with the entry. The JarFile also provides access to the Manifest object for the JAR archive; this object contains Attributes for all entries in the JAR file. Attributes is a mapping of attribute name/value pairs, of course, and the inner class Attributes.Name defines constants for various standard attribute names.

You can also read a JAR file with JarInputStream. This class requires to you read each entry of the file sequentially, however. JarOutputStream allows you to write out a JAR file sequentially. Finally, you can also read an entry within a JAR file and manifest attributes for that entry with a java.net.JarURLConnection ...