Изучение магии внедрения зависимости с использованием аннотаций — часть 2

public class JarFileSample {

  private static final String JAR_FILE_PACKAGE = "org.slf4j";

  private static final Pattern pattern = Pattern.compile("^" + JAR_FILE_PACKAGE + ".*");

  public static void main(String[] args) throws IOException, ClassNotFoundException {

    System.out.println("Finding all classes in jarfile package...");
    JarFileSample instance = new JarFileSample();

    List<Class<?>> result = instance.getClasses(JAR_FILE_PACKAGE);
    listResults(result);

    System.out.println("-- END --");
  }

  private List<Class<?>> getClasses(String packageName) throws ClassNotFoundException, IOException {

    String path = packageName.replace('.', '/'); // Convert the package name
    List<File> directories = getPackageDirectories(path);
    return walkJars(directories);
  }

  private List<File> getPackageDirectories(String path) throws IOException {

    List<File> files = new ArrayList<File>();
    ClassLoader classLoader = getClassLoader();
    Enumeration<URL> resources = classLoader.getResources(path);
    while (resources.hasMoreElements()) {
      URL resource = resources.nextElement();
      File file = getNextFile(resource);
      files.add(file);
    }
    return files;
  }

  private File getNextFile(URL resource) throws UnsupportedEncodingException {
    String fileNameDecoded = URLDecoder.decode(resource.getFile(), "UTF-8");
    fileNameDecoded = fileNameDecoded.substring(fileNameDecoded.indexOf(":") + 1, fileNameDecoded.indexOf("!"));
    return new File(fileNameDecoded);
  }

  private ClassLoader getClassLoader() {
    ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
    assert classLoader != null;
    return classLoader;
  }

  private List<Class<?>> walkJars(List<File> directories) throws IOException, ClassNotFoundException {

    List<Class<?>> classes = new ArrayList<Class<?>>();
    for (File directory : directories) {
      classes.addAll(walkJar(directory));
    }

    return classes;
  }

  private List<Class<?>> walkJar(File directory) throws IOException, ClassNotFoundException {

    List<Class<?>> classes = new ArrayList<Class<?>>();
    JarFile jarFile = new JarFile(directory);

    Enumeration<JarEntry> jarEntries = jarFile.entries();

    while (jarEntries.hasMoreElements()) {
      JarEntry jarEntry = jarEntries.nextElement();
      addClassFromJar(jarEntry, classes);
    }

    return classes;
  }

  private void addClassFromJar(JarEntry jarEntry, List<Class<?>> classes) {
    if (isMatchingClass(jarEntry)) {
      String fileName = jarEntry.getName();
      if (isValidClassName(fileName)) {
        Class<?> clazz = createClass(fileName);
        if (isNotNull(clazz)) {
          classes.add(clazz);
        }
      }
    }
  }

  private boolean isMatchingClass(JarEntry jarEntry) {

    boolean retVal = false;
    if (!jarEntry.isDirectory()) {
      String name = jarEntry.getName();
      Matcher matcher = pattern.matcher(name);
      retVal = matcher.matches();
    }
    return retVal;
  }

  private boolean isValidClassName(String fileName) {
    return fileName.endsWith(".class") && !fileName.contains("$");
  }

  private Class<?> createClass(String fileName) {

    try {
      String className = getClassName(fileName);
      return Class.forName(className);
    } catch (Throwable e) {
      e.printStackTrace();
      return null;
    }
  }

  private String getClassName(final String fileName) {

    String retVal = fileName.substring(0, fileName.length() - 6);
    retVal = retVal.replaceAll("/", ".");

    return retVal;
  }

  private boolean isNotNull(Object obj) {
    return obj != null;
  }

  private static void listResults(List<Class<?>> clazzes) {

    int i = 1;
    for (Class<?> clazz : clazzes) {
      System.out.println(i++ + ") Found: " + clazz.getName());
    }
  }
}