如何在给定的包中找到带注释的方法？

Question

我有一个方法的简单标记注释(类似于Effective Java(第2版)第35项中的第一个例子):

/**
 * Marker annotation for methods that are called from installer's 
 * validation scripts etc. 
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface InstallerMethod {
}

然后,在一个给定的包(比如说com.acme.installer)中,它有几个包含20个类的子包,我想找到所有用它注释的方法.(因为我想对单元测试中所有带注释的方法进行一些检查.)

什么(如果有的话)是最简单的方法呢？最好不要添加新的第三方库或框架.

编辑:澄清,显然method.isAnnotationPresent(InstallerMethod.class)将是检查方法是否具有注释的方法 - 但是这个问题包括找到所有方法.

Answer 1

如果您想自己实现它,这些方法将找到给定包中的所有类:

/**
 * 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;
}

然后,您可以使用给定的注释过滤这些类:

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

Answer 2

你应该看一下开源的Reflections库.有了它,您只需几行代码即可轻松实现您的目标:

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