Question

I actualy have 2 problems

I use eclipse -> export project to generate a jar file for my simple desktop (GUI) program
It generates a jar file and an ant script.

first problem:
the generated jar works fine when double-clicked.
When I use the generated ant script to generate the jar
by myself, it doesn’t work.
What can be wrong with a target like this (assuming that all dependencies are met)

 <target name="create_run_jar">
        <jar destfile="G:/dev/myproj/myproj.jar">
            <manifest>
                <attribute name="Main-Class" value="view.myproj"/>
                <attribute name="Class-Path" value=". myproj_lib/grouplayout.jar"/>
            </manifest>
            <fileset dir="G:/dev/myproj/bin"/>
        </jar>
        <delete dir="G:/dev/myproj/myproj_lib"/>
        <mkdir dir="G:/dev/myproj/myproj_lib"/>
        <copy file="G:/dev/.metadata/.plugins/org.dyno.visual.swing/layoutext/grouplayout.jar" todir="G:/dev/myproj/myproj"/>
    </target>  

//nevemind
//Second problem:
//when I double click on the auto-generated jar file the program launches and works fine.
//when I do java myjar from the command-line I get main class not found exception..
//weird huh?

Answer 1

I suggest that you take the JAR files generated the two ways, use the jar command to expand them into temporary directories, and then use diff in recursive mode to compare them.

However, I suspect that @Pace has put his finger on the problem; i.e. that you are using relative paths in the Class-Path manifest entry and this is liable to cause problems.