如何找到一个给定的包带注释的方法呢？ [英] How to find annotated methods in a given package?

问题描述

我有一个方法，一个简单的标记注释（类似于第一个例子中的35项的有效的Java 的（第二版））：

I have a simple marker annotation for methods (similar to the first example in Item 35 in Effective Java (2nd ed)):

/**
 * 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 com.acme.installer ），其中有一些含有20个班的几个子包，我想找到所有的方法注释都用它。 （因为我想要做的关于单元测试的所有注解的方法进行一些检查。）

Then, in a given package (say com.acme.installer), which has a few subpackages containing some 20 classes, I'd like to find all methods that are annotated with it. (Because I'd like to do some checks regarding all the annotated methods in a unit test.)

什么（如果有的话）是做最简单的方法？ preferably无需添加新的第三方库或框架。

What (if any) is the easiest way to do this? Preferably without adding new 3rd party libraries or frameworks.

修改：澄清一下，明明 method.isAnnotation present（InstallerMethod.class）将是检查是否有方法的方法有注解 - 但这个问题包括找到的所有方法

Edit: to clarify, obviously method.isAnnotationPresent(InstallerMethod.class) will be the way to check if a method has the annotation - but this problem includes finding all the methods.

推荐答案

如果你想自己实现它，这些方法会发现在一个给定的包中的所有类：

If you want to implement it yourself, these methods will find all the classes in a given 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();
        dirs.add(new File(resource.getFile()));
    }
    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，你可以在给定的注解这些类过滤器：

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

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

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