In org.jboss.modules.JarFileResourceLoader#getResource() there is the following lines:

String jarFilePath = new File(jarFile.getName()).toURI().toString();
return new JarEntryResource(jarFile, entry, new URI("jar", jarFilePath + "!/" + entry.getName(), null).toURL());

Assuming I have AS7 in "/jboss as"
The first line results in a String of the form:

file:/jboss%20as/modules/org/jboss/as/jmx/main/jboss-as-jmx-7.1.0.Final-SNAPSHOT.jar

The second line escapes the string a second time:

jar:file:/jboss%2520as/modules/org/jboss/as/jmx/main/jboss-as-jmx-7.1.0.Final-SNAPSHOT.jar!/META-INF/services/javax.management.MBeanServerBuilder