java - Is it possible to package all the jar dependencies in one big jar?

Question

I know this isn't "best practice", but can I include all of the dependencies in one big jar?

Answer 1

My feeling is that calling One-Jar's performance awful and poor is unjust. For moderately sized application one can expect startup will take a couple of seconds longer (which does not affect JVM splash screen though). Memory overhead of tens of megabytes is negligible for most environments, except perhaps embedded systems. Also, One-Jar is capable of automatically extracting some files to the file system, which saves the need to develop an installer in my case.

Below is an attempt to quantify the performance impact introduced by One-Jar to my application. It is Swing-based GUI application, consists of 352 classes obfuscated with ProGuard 4.5b2. One-Jar 0.96 is used to bundle resulting classes with 12MB worth of libraries (ODFDOM, Saxon HE, Xerces, Jaxen, VLDocking, Apache Commons, etc). I have compared performance of the obfuscated jar with the same jar processed by One-Jar.

• From JVM start to the start of of main() method: 0.5s without One-Jar and 1.7s with One-Jar. From JVM start to the appearance of application window on the screen: 2.3s without One-Jar and 3.4s with One-Jar. So One-Jar adds 1.1s to startup time.
• One-Jar will not increase the delay between JVM start and splash image appearing on the screen (if implemented via jar manifest), so the startup time increase is not too annoying for interactive applications.
• We are talking about a class loader, so there should be no impact on code execution speed, unless you are extensively using dynamic class loading.
• Looking at JVM statistics (via jconsole) shows that One-Jar'red version takes more heap memory. For my application the overhead is in the order of tens of MBs. I saw figures like 16MB vs 40MB, 306MB vs 346MB, 131MB vs 138MB, depending on now much user data the application is handling and now long time ago garbage collector has been executed.

The above timing was obtained by taking a timestamp just before starting JVM from Linux shell, in beginning of main() method, and in windowOpened() event handler of my application window. The measurements were taken on a not particularly fast D820 laptop, with dual core 1GHz CPU and 2G or RAM running Ubuntu 8.04.

Hope it helps.