在嵌入式jar中使用入口点创建可执行jar

Question

I have an Eclipse project that uses many .jar files as dependencies, but has no source files. There is a run configuration set up that defines the main method (entry point) as a method within one of the included jars. It runs fine within Eclipse, but when I try to use the executable jar wizard, I get the error "Could not find main method from given launch configuration."

According to this tutorial , one can use the jar command line tool to manually set the entrypoint of a jar, but what should I use as the path to the .class file for the main method, since I don't directly have any .class files, just embedded jars?

Alternatively, are there any other ways to get the entrypoint set correctly?

Answer 1

The standard JAR file format allows a manifest and a set of class/resource files. Of course, you can package up JAR files inside a JAR file, but the standard Java class loader is unable to load classes (from the embedded JAR files) that way. Thus, you'll need to expand all the JAR files and repackage them according to the packages. Again, this is true if you are not writing your own class loader.

If you are using Maven, fortunately, Maven provides a few plugins to do this repackaging task. See the Maven JAR plugin , or the Maven Shade Plugin that help creating the so-called Uber JAR which can optionally use a Main-Class manifest attribute. Alternatively, in the absence of Maven, you can always expand and rejar the classes by using a simple shell script.

Once you do that, you can use either java -jar myjar.jar , or java -cp myjar.jar my.main.Class .