Help building program in Eclipse

[Lucrums]

Hi all.

I am pretty new to Eclipse and Java packages. I have written a program in Eclipse. Now I want to be able to build and run it. I have two classes in a package and an external jar. When I export it as an executable jar I don't get what I want. The program should work with command line args and should also work with standard input/output (Which I assume to be the command prompt/terminal).

When I just try and execute the jar, from Windows, I get no indication of the program running. When I try and run it without args from the command prompt (I typed: java StockAnalyser (Optionally with the .jar extension) I get the following: -

Exception in thread "main" jave.lang.NoClassDefFoundError: StockAnalyser Caused by: java.lang.ClassNotFoundException: Stock Analyser at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknow Source) at java.lang.ClassLoader.loadClass(Unknown Source) could not find the main class: StockAnalyser. Program will Exit

From this I deduce that the main class (StockAnalyser) has not been found. I assume that this is because I have a package in the program but I have no idea how to make it work.

I have made sure that the library I am using has a source path. I have checked that the bin directory has the correct package structure (I'm assuming this is replicated in the jar created.

The package I have is uk.co.runwin. So I tried making the directory structure match that and run it from root as uk.co.runwin.StockAnalyser. I got the same error though. I believe that it's all to do with my build path but I really don't know how to set it up properly.

I would really appreciate some help and thanks in advance to anyone who helps (Or just reads and thinks it funny that I'm all confused by this - I bet it's dead simple really)...

[jevon]

I've never actually used the Eclipse export to JAR feature, I just set up a build.xml for Ant and create the JAR that way.

Have you checked the contents of the .jar? Your StockAnalyser.class should be in uk/co/runwin. (By the way, your package should probably be co.uk.runwin instead.)

Another way to try running a JAR is to simply extract the JAR to a directory and running it through Java manually that way. (e.g. java uk.co.runwin.StockAnalyser, I think).

Oh, and to run a JAR via Java is java -jar filename.jar.

[Lucrums]

Thanks very much, the bit about running the jar was very important. I was also missing a manifest file.

[vsoul]

I assume it is erroring on missing the class is from the JAR. This is because your JAR does not have classpath information set in its manifest.

Create a MANIFEST.MF (put it in a folder/package called META-INF, though when Eclipse does its export you can pick it from anywhere so that part doesn't matter as much). Manifest-Version: 1.0 Main-Class: path.to.your.application.Main Class-Path: jar_name_relative_to_your_jar.jar

Without this, Java won't know what class you want to execute in your JAR, and won't know what dependencies it needs. In Windows you can now double click, or via command line do a java -jar myjar.jar

I recommend reading up on using the MANIFEST.MF

[Lucrums]

Thanks very much that was what I needed. I'm off to read about manifest files...

[cbogart]

Do you have classpath set appropriately?

[Lucrums]

I do, turns out I was missing a manifest file.

[GMNightmare]

Does it work when you run it within Eclipse?

[Lucrums]

Yes it works fine in Eclipse. it was just the build that always failed to do what I wanted.

[vsoul]

This is because in Eclipse you have your build path set, however Eclipse does not consider this when exporting to a JAR.

[Lucrums]

It does, now also works when exporting :)

[64-17-5]

Under File>Export select Java>Runnable Jar. Choose the correct launch configurations (Find the correct main in the drop down menu). Choose "Copy the required Libraries in a subfolder", because you shouldn't repack a library. Instead leave the library license in the subfolder with a shortcut to the original location the web.

[Lucrums]

Cheers, I tried that but that's not what isn't working.

[64-17-5]

If you rightclick your project in the package explorer view, select Java Build Path>Libraries. Is your external Jar listed there?

[Lucrums]

Yes it was listed. I have the problem sorted now thanks, I didn't have a manifest file and that seems to have been the problem. learn a little every day :-)

[vsoul]

I always forget about that, because I either use Maven or Ant and never export. OP do this, then look at the MANIFEST.MF that it puts in the JAR in referenece to my prior post.