Up to JDK8, I could use the following to iterate on rt.jar classes. Given a single class, I could find all others like this :
final URL location = clazz.getProtectionDomain().getCodeSource().getLocation();
final File file = new File(location.toURI());
try (JarFile jarFile = new JarFile(file)) {
final Enumeration<JarEntry> entries = jarFile.entries();
while (entries.hasMoreElements()) {
final JarEntry jarEntry = entries.nextElement();
// do something...
}
}
After JDK8, using this clazz.getProtectionDomain().getCodeSource().getLocation()
isn't valid anymore:
java.lang.NullPointerException: Cannot invoke "java.security.CodeSource.getLocation()" because the return value of "java.security.ProtectionDomain.getCodeSource()" is null
Is there good replacement for this ? I'm thinking of doing a special case like this:
if (clazz.getProtectionDomain().getCodeSource() == null) {
// find URL to the jmod ...
}
However a solution that will work in both cases would be preferable.
CodePudding user response:
There’s a wrong assumption in your question, as classes are never loaded from a .jmod file.
You can get the location of a module like
Module m = clazz.getModule();
System.out.println(m.getLayer().configuration()
.findModule(m.getName()).flatMap(rm -> rm.reference().location())
.orElse(null));
which doesn’t work for the “unnamed module”, read classes loaded through the classpath, so you would have to resort to .getProtectionDomain().getCodeSource().getLocation()
if m.isNamed()
is false
.
However, for the built-in modules, the URI will always be jrt:/module-name
, so to iterate over the platform classes, you don’t need this at all.
For example, this code snippet lists all classes in the java.lang
package:
try(var list = Files.list(Paths.get(URI.create("jrt:/java.base/java/lang")))) {
list.map(p -> p.getFileName().toString())
.filter(s -> s.endsWith(".class"))
.map(s -> "java.lang." s.substring(0, s.length() - 6))
.forEach(System.out::println);
}
and to get the class file bytes for java.lang.Object
, you can simply use
byte[] objectClassFile = Files.readAllBytes(
Paths.get(URI.create("jrt:/java.base/java/lang/Object.class")));