我如何从另一个jar内的shell脚本中调用jar内的java类

Question

I have a web application and inside a jar i have a shell script. From that shell script i want to execute a java class that is inside another jar file. I can actually execute, in a prompt, the class like this

/usr/bin/java -jar bar.foo.a.jar bar.foo.my.class

but the problem is when a task executes the script from inside the jar. Then the bar.foo.a.jar is not located because its not at the same level

i tried with

/usr/bin/java -jar ../../bar.foo.a.jar bar.foo.my.class

but i doesn't work, any suggestion on how could i achieve this? is there a better way to do something like this?

Answer 1

It is not clear from your question what you have actually tried, but here are a couple of pointers.

• You cannot execute a shell script that is inside a JAR file. You have to extract it to a free-standing file in the file system before you can execute it.

• You cannot use a JAR file that is nested inside another JAR file. (Or at least, you can't without creating a custom ClassLoader.) The nested JAR file needs to be extracted as a free-standing file.

• If your problem is with relative paths, you need to pay careful attention to what the "current directory" is at the point when the path is resolved. As an experiment, try replacing the relative path with the absolute path of the JAR file.

• The -jar option is not designed to work that way. Assuming that the JAR file really exists at the relative location you are using, you probably need to do this:

   /usr/bin/java -cp ../../bar.foo.a.jar bar.foo.MyClass 

  The -jar option tells the JVM to execute the JAR file as a command, using the Main-Class declared in the JAR file's manifest as the entry point. If you do this:

   /usr/bin/java -jar ../../bar.foo.a.jar bar.foo.MyClass 

  you will find that bar.foo.MyClass is passed to the declared main program as its first command-line argument.

---

My advice would be to take a few minutes to carefully read the manual pages for the java command, the jar command, and the linked pages that describe how the class path works, etc.

Answer 2

-jar option is a convenient way to execute a class inside a jar file, aka having an executable jar. But using -jar file will ignore user class paths.

It might be easier for you to define proper classpath variable and execute your command with

/usr/bin/java -cp $CLASSPATH bar.foo.my.class