Making jar by hand, with dep

by Julien Diener on February 25, 2015 under blog-post

1 minute read

I happened to have problem running a jar with dependencies, and I found my-self wondering: Do I really know how it works?

I don’t remember having ever done it manually, so I tried. It is a good thing to be sure of what we know. Here is the code, lets two classes A and B. A’s got the main and requires B:

package one.pack;
 
import two.pack.B;
 
public class A{
    public static void main(String args[]){
        B b = new B();
        b.println("Hello world");
    }
}

package two.pack;
 
public class B{
    public void println(String message){
        System.out.println("B says: "+message);
    }
}

Now, let’s compile everything

# compile B.java into B.jar
javac B.java -d .    # "-d .": automatically create folders two/pack/
jar -cf B.jar two/     
 
# compile A.java into A.jar
javac -cp B.jar A.java -d .   # include B.jar in the classpath
jar -cf A.jar one/

Finally, move A.jar and run it

mv A.jar /somewhere/else
java -cp /somewhere/else/A.jar:B.jar one.pack.A

Output: B says: Hello world

Conclusion, it is just as expected but now at least I’m sure of it :-)

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