When no entry is specified on the URL, the entry name is null : JarURLConnection « Network « Java Tutorial

1. Java Tutorial
2. Network
3. JarURLConnection

import java.net.JarURLConnection;
import java.net.URL;

public class Main {
  public static void main(String[] argv) throws Exception {
    URL url = new URL("jar:file:/c://my.jar!/");
    JarURLConnection conn = (JarURLConnection) url.openConnection();

    String entryName = conn.getEntryName(); // null

  }
}