CODEWITHSUNDEEP
javaconfigurationbuildjar
IAmYourFaja
IAmYourFaja

Reputation: 56914

Compiling Java & JARs

I just asked a recent question about distributing executable JARs and their dependencies, and it made me realize that my understanding of JARs may be fundamentally flawed.

Thus, some might say "Hey now! This here is a duplicate question!" But I say nay, this question is a completely separate offshoot of this original question, and is concerned with Java fundamentals!

If I have an application that depends on, say, the Apache Commons CLI as well as JODA Time, and I pack this app up into a distributable JAR, my original question was: Without including the CLI and JODA JARs in my JAR, how does the program run on the client-side???

I am now thinking that since my code, which uses CLI and JODA, gets compiled into classfiles, and that bytecode is what gets packaged, then there is no need to include CLI or JODA (or any other 3rd party JAR) in my JAR, since it is all now functioning bytecode.

Can someone confirm or correct me? This revelation, though late in coming, has been staggering.

Upvotes: 1

Views: 165

Answers (2)

Liggy
Liggy

Reputation: 1201

The third party libraries (JodaTime, for example) need to be on the classpath during runtime. Not "packaged within your JAR".

If your app is launched from a JAR. You should specify the classpath in the manifest file which is packaged within the jar - http://download.oracle.com/javase/tutorial/deployment/jar/downman.html

You can have ANT generate the manifest classpath for you using the manifestclasspath element - http://ant.apache.org/manual/Tasks/manifestclasspath.html

Upvotes: 1

Chris Aldrich
Chris Aldrich

Reputation: 1922

No, that is not quite right. The key to everything is the classpath. Is all of the compiled code and/or other resources on the classpath? If you package everything up in one single jar, then yes, it is in the classpath and the JVM will locate all the resources to run. Otherwise, you need to specify (with a .bat or .sh file or something) all the resources that your application is dependent on, so the JVM will be able to appropriately look for those resources (be they Java code or properties files or whatever).

Also if I am reading your question right, are you assuming that the CLI and JODA code gets compiled into your code? If so, I hate to burst your bubble, but that is not the case. When your code compiles, it does not bring in dependencies (not in the sense you may be thinking). What it does at a conceptual level (correct me if I'm wrong JVM gurus) is it references other classes. Those references are what you are building when you code a class and compile it. At runtime the JVM will attempt to locate the compiled class behind the reference and THAT is where you either need the jar with those classes in the classpath OR you need those classes in your executable jar.

Make sense?

Upvotes: 1

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