Styjun

So, I have a main application that should load a jar that contains code and other resources (i.e.: jar files, text files, java properties etc.). I use:

JarFile jar = new JarFile(jar);
Enumeration<JarEntry> entries = jar.entries();

int URLsize = 1;
while (entries.hasMoreElements())
 if (entries.nextElement().getName().startsWith("foo/bar/foobar"))
 URLsize++;

entries = jar.entries();

URL[] urls = new URL[URLsize];
urls[0] = patch.toURI().toURL();

int count = 1;
while (entries.hasMoreElements())

 JarEntry nextElement = entries.nextElement();
 if (nextElement.getName().startsWith("foo/bar/foobar"))
 
 urls[count] = new URL("jar:file:/"+ jar.getAbsolutePath() + "!/" + nextElement.getName());

 count++;
 

to load the resources of the jar, and an URLClassLoader plus some reflection to get all resources together and execute the jar's main class, like this:

URLClassLoader loader = new URLClassLoader (urls);
Thread.currentThread().setContextClassLoader(loader);

Class<?> jarC = Class.forName ("foo.bar.barfoo.Main", true, loader);
Constructor<?> cons = jarC.getConstructor(String.class, String.class, Properties.class, Properties.class, String[].class);
Object instance = cons.newInstance (systemPath, programPath, config, some_data, args);

Method method = jarC.getMethod ("Main");

method.invoke (instance);

Now the problem is that inside the loaded jar's code when I try to load a bunch of files (resources) from a package inside the jar (e.g.: /foo/bar/foobar) it throws a NullPointerException.

private static InputStream getResourceAsStream(String resource) 
 try 
 return Thread.currentThread().getContextClassLoader().getResource(resource).openStream();
 catch (IOException e) 
 e.printStackTrace();
 

 return null;
 

That's how I try to get the package that than gets parsed with a BufferedReader and an InputStreamReader to get the names of each resource inside the package.
Okay, maybe a bit too detailed (this is just one way I use the getResourceAsStream method), but I hope I made myself understood, the ContextClassLoader doesn't contain the resources I loaded in the application that runs this jar within itself, so what do I need to do to get those from within the loaded jar?

EDIT: Calling the getResourceAsStream method:

private static List<String> getResourceFiles(String path) throws IOException 
 List<String> filenames = new ArrayList<>();

 try (
 InputStream in = getResourceAsStream(path);
 BufferedReader br = new BufferedReader(new InputStreamReader(in))) 
 String resource;

 while ((resource = br.readLine()) != null) 
 filenames.add(resource);
 
 

 return filenames;

And where the getResourceFiles method is called:

List<String> names = Foo.getResourceFiles("/foo/bar/foobar");

Why do you even do all this? Why not just add URL to JAR to the URLClassLoader?

E.g.

URLClassLoader loader = new URLClassLoader(new File(jar).toURI().toURL());

Also you should probably make that URLClassLoader have your current classloader as parent, e.g.

URLClassLoader loader = new URLClassLoader(new File(jar).toURI().toURL(), Thread.currentThread().getContextClassLoader());