I'm pretty sure that JAR files are just TAR's, so if you can create those with Eclipse you're good to go. I don't have an installation on this comp to test, but I believe you can right click on ...

Click "OK" to add the JAR to the folder. Click the "Save" button and click the Eclipse toolbar's "Run" button. The JAR and other app Java files run in the emulator, so you can test the code.