ClassNotFoundException when loading JAR file with ClassLoader

Question

I picked up instructions (and code) here and there on creating and using a class from a jar file.

I created a Test.java file :

package a;
public class Test {
    public String print(){
        return "TestLALALA";
    }   
}

And created a jar file with :

jar cvf0 Test.jar Test.java

When I extract the jar (through command-line), the class is intact.

I put the jar in a "libs" folder in my Eclipse project. I can see it in the project "Build Path" under "Libraries".

The following code hits a ClassNotFoundException :

URL[] urls = new URL[1];
try {
    File file = new File("C:\\Eclipse\\Demo\\libs\\Test.jar");
    urls[0] = file.toURI().toURL();
} catch (MalformedURLException e1) {
    e1.printStackTrace();
}
URLClassLoader loader = new URLClassLoader (urls);
Class classToLoad = null;
if(loader!=null)
{
    try {
        classToLoad = loader.loadClass("a.Test");
    } catch (ClassNotFoundException e1) {
        e1.printStackTrace();
    }
}

What did I miss ?

Thank you!

Answer 1

It looks like you are adding only the uncompiled .java file to the JAR rather than the compiled .class file.

Also the file within the JAR should be a/Test.class so you need to make sure that the a directory is present in there to represent the package path. Currently it appears that the file exists in the root of the JAR rather than within a subdirectory.