creating a build file with ant

Question

I am trying to work through the HelloWorld example on the Web that shows you how to create a build file using ANT in Eclipse. This is the project build file from the web example

<?xml version="1.0" encoding="UTF-8"?>
<project name="HW.makejar" default="makejar" basedir=".">
    <target name="makejar" description="Create a jar for the HW project">
        <jar jarfile="HelloWorld.jar" includes="*.class" basedir="."/>
    </target>
</project>

But when I run the resulting jar, I get this error message failed to load Main-Class manifest attribute from HelloWorld.jar.

So then I tried it like this:

<?xml version="1.0" encoding="UTF-8"?>
<project name="HW.makejar" default="makejar" basedir=".">
    <target name="makejar" description="Create a jar for the HW project">
        <jar jarfile="HelloWorld.jar" includes="*.class" basedir=".">
            <manifest>
                <attribute name="Main-Class" value="ami.HelloWorld" />
            </manifest>
        </jar>

    </target>
</project>

When I reran the resulting jar, I got the following error message:

Exception in thread "main" java.lang.NoClassDefFoundError: ami/HelloWorld

What am I doing wrong. By the way, when I manually compile the source and specify the Main.class within Eclipse, the resulting jar runs perfectly.

Answer 1

Does your jar file contain any class files? If not, try:

<jar jarfile="HelloWorld.jar" includes="**/*.class" basedir=".">

Answer 2

Is your basedir correct? If you jar tvf HelloWorld.jar is the class HelloWorld.class listed under the ami folder? If it is listed directly under the root you need to add it from its parent folder, not from the ami folder.