Walk resource tree as directory in classpath

The two most frequent type of classpath URL we get when get it through ClassLoader#getResource(resourceName) is either file or jar entries. If we want to walk a resources that are stored in a directory, then we need to parse these differently. For file, it’s easy to do since we have java.io.File. As for jar, we would use JarFile. Here is a implementation.

public static void walkClasspathResDir(ClassLoader cl, String resDir, ConsumerEx<FileStream> fileConsumer) {
        // NOTE: JarEntry.isDirectory() used below requires input to ends with slash.
        if (!resDir.endsWith("/")) {
            resDir = resDir + "/";
        }

        URL url = cl.getResource(resDir);
        if (url == null) {
            throw new AppException("Resource directory " + resDir + " not found in classpath.");
        } else if ("file".equals(url.getProtocol())) {
            File dir = new File(url.getPath());
            if (!dir.isDirectory()) {
                throw new AppException("Resource is not a directory: " + resDir);
            }
            walkFileDir(dir, fileConsumer);
        } else if ("jar".equals(url.getProtocol())) {
            try {
                JarURLConnection conn = (JarURLConnection) url.openConnection();
                if (!(conn.getJarEntry().isDirectory())) {
                    throw new AppException("Resource is not a directory: " + resDir);
                }
                walkJarEntryDir(conn.getJarFile(), resDir, fileConsumer);
            } catch (Exception e) {
                throw new AppException("Unable to read resource: " + url, e);
            }
        } else {
            throw new AppException("Unsupported protocol " + url.getProtocol() + " for checking resource directory.");
        }
    }

    public static void walkFileDir(File dir, ConsumerEx<FileStream> fileConsumer) {
        try {
            Files.walkFileTree(dir.toPath(), new SimpleFileVisitor<Path>() {
                @Override
                public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
                    try (FileInputStream stream = new FileInputStream(file.toFile())) {
                        try {
                            String shortPath = file.toFile().getPath().substring(dir.getPath().length());
                            // Always convert path separator to Unix
                            shortPath = FilenameUtils.separatorsToUnix(shortPath);
                            // Remove leading '/' if there is any
                            if (shortPath.startsWith("/")) {
                                shortPath = shortPath.substring(1);
                            }
                            fileConsumer.accept(new FileStream(shortPath, stream));
                        } catch (Exception e) {
                            throw new AppException("Failed to process file: " + file, e);
                        }
                    }
                    return FileVisitResult.CONTINUE;
                }
            });
        } catch (IOException e) {
            throw new AppException("Failed to walk directory: " + dir, e);
        }
    }

    public static void walkJarEntryDir(JarFile jarFile, String entryName, ConsumerEx<FileStream> fileConsumer) {
        try {
            Enumeration<JarEntry> entries = jarFile.entries();
            while (entries.hasMoreElements()) {
                JarEntry jarEntry = entries.nextElement();
                if (jarEntry.getName().startsWith(entryName)) {
                    if (!jarEntry.isDirectory()) {
                        try (InputStream stream = jarFile.getInputStream(jarEntry)) {
                            try {
                                String shortPath = jarEntry.getName().substring(entryName.length());
                                fileConsumer.accept(new FileStream(shortPath, stream));
                            } catch (Exception e) {
                                throw new AppException("Failed to process jar entry: " + jarEntry.getName(), e);
                            }
                        }
                    }
                }
            }
        } catch (IOException e) {
            throw new AppException("Failed to walk jar directory entry: " + entryName, e);
        }
    }

Here the FileStream is just a POJO that holds a resource path name and the stream that points to it. One tricky part to above code is noted in comment:

// NOTE: JarEntry.isDirectory() used below requires input to ends with slash.

Now, here is how we can use it:

        ClassLoader cl = Thread.currentThread().getContextClassLoader();
        walkClasspathResDir(cl, "toolbox/templates/javaapp", (fileStream) -> {
            System.out.println(fileStream.getPath() + " " + fileStream.getStream());
        });
        System.out.println();