[ACCEPTED]-How to find annotated methods in a given package?-annotations

Accepted answer
Score: 55

If you want to implement it yourself, these 3 methods will find all the classes in a given 2 package:

/**
 * Scans all classes accessible from the context class loader which belong
 * to the given package and subpackages.
 * 
 * @param packageName
 *            The base package
 * @return The classes
 * @throws ClassNotFoundException
 * @throws IOException
 */
private Iterable<Class> getClasses(String packageName) throws ClassNotFoundException, IOException
{
    ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
    String path = packageName.replace('.', '/');
    Enumeration<URL> resources = classLoader.getResources(path);
    List<File> dirs = new ArrayList<File>();
    while (resources.hasMoreElements())
    {
        URL resource = resources.nextElement();
        URI uri = new URI(resource.toString());
        dirs.add(new File(uri.getPath()));
    }
    List<Class> classes = new ArrayList<Class>();
    for (File directory : dirs)
    {
        classes.addAll(findClasses(directory, packageName));
    }

    return classes;
}

/**
 * Recursive method used to find all classes in a given directory and
 * subdirs.
 * 
 * @param directory
 *            The base directory
 * @param packageName
 *            The package name for classes found inside the base directory
 * @return The classes
 * @throws ClassNotFoundException
 */
private List<Class> findClasses(File directory, String packageName) throws ClassNotFoundException
{
    List<Class> classes = new ArrayList<Class>();
    if (!directory.exists())
    {
        return classes;
    }
    File[] files = directory.listFiles();
    for (File file : files)
    {
        if (file.isDirectory())
        {
            classes.addAll(findClasses(file, packageName + "." + file.getName()));
        }
        else if (file.getName().endsWith(".class"))
        {
            classes.add(Class.forName(packageName + '.' + file.getName().substring(0, file.getName().length() - 6)));
        }
    }
    return classes;
}

Then you can just filter on those 1 classes with the given annotation:

for (Method method : testClass.getMethods())
{
    if (method.isAnnotationPresent(InstallerMethod.class))
    {
        // do something
    }
}
Score: 37

You should probably take a look at the open 2 source Reflections library. With it you can easily achieve 1 what you want with few lines of code:

Reflections reflections = new Reflections( 
    new ConfigurationBuilder().setUrls( 
    ClasspathHelper.forPackage( "com.acme.installer" ) ).setScanners(
    new MethodAnnotationsScanner() ) );
Set<Method> methods = reflections.getMethodsAnnotatedWith(InstallerMethod.class);
Score: 1

If you're happy to use Spring, then that 12 does something along these lines using it's 11 context:component-scan functionality, where 10 Spring scans for annotated classes in a 9 given package. Under the covers, it's pretty 8 gruesome, and involves grubbing about on 7 the filesystem and in JAR files looking 6 for classes in the package.

Even if you can't 5 use Spring directly, having a look through 4 its source code might give you some ideas.

Certainly, the 3 Java reflection APi is no use here, it specifically 2 does not provide a means to obtain all classes 1 in a package.

More Related questions