import java.io.*;
import java.util.jar.*;
import java.util.*;
import java.net.*;

File file = new File( basedir, "target/no-appendAssemblyId-no-classifier-1.jar" );

System.out.println( "file: " + file + " exists? " + file.exists() );

JarFile jarFile = new JarFile( file );

JarEntry entry = jarFile.getEntry( "org/apache/maven/plugin/assembly/mojos/AbstractAssemblyMojo.class" );

return entry != null;