Java™ Application Development on Linux - Dator

164Chapter 5The Sun Microsystems Java Software <strong>Development</strong> Kit-x-t-f-v-mExtract files from a JAR file.List files in a JAR.Specify the JAR filename.Be verbose—display descriptions of what the jar utility is doing as itdoes it.Add the contents of the named file to the manifest.5.12THE REST OF THE TOOLKITThere are additional utilities in the toolkit. Below is a capsule summary of themand their purposes.extcheckThis utility checks an applet JAR file for any extensions it requires that arein conflict with the current Java runtime environment. (But we don’tcover applets in this book.)jarsignerThis is a utility for digitally signing JAR file. Once a JAR is signed, anyonelooking at it can be sure of two things—first, the file was definitely preparedby the owner of the private key that matches the public key used toverify the signature; 29 and second, the JAR file has not been modified inany way since it was signed. In other words, depending upon the care withwhich the signer treats his/her private key, this certifies the authenticity29. A discussion of public/private keys as an authentication mechanism is beyond our scopehere. As a shameless plug, Mr. Schwarz would like to point you to Chapter 10 of his previousbook, Multitool Linux, which contains a beginner’s introduction to public key authenticationusing GnuPG. Of course, a quick Google search will find you many online descriptions thatare free.