Java 如何在给定的包中找到带注释的方法？
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How to find annotated methods in a given package?
提问by Jonik
I have a simple marker annotation for methods (similar to the first example in Item 35 in Effective Java(2nd ed)):
我有一个简单的方法标记注释（类似于Effective Java（第二版）第 35 条中的第一个示例）：
/**
* Marker annotation for methods that are called from installer's
* validation scripts etc.
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface InstallerMethod {
}
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.)
然后，在一个给定的包（比如com.acme.installer）中，它有几个包含大约 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的所有带注释的方法进行一些检查。）
What (if any) is the easiest way to do this? Preferably without adding new 3rd party libraries or frameworks.
什么（如果有）是最简单的方法？最好不要添加新的 3rd 方库或框架。
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.
编辑：澄清method.isAnnotationPresent(InstallerMethod.class)一下，显然将是检查方法是否具有注释的方法 - 但这个问题包括找到所有方法。
采纳答案by parkr
If you want to implement it yourself, these methods will find all the classes in a given package:
如果你想自己实现它，这些方法会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;
}
Then you can just filter on those classes with the given annotation:
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
}
}
回答by skaffman
If you're happy to use Spring, then that does something along these lines using it's context:component-scan functionality, where Spring scans for annotated classes in a given package. Under the covers, it's pretty gruesome, and involves grubbing about on the filesystem and in JAR files looking for classes in the package.
如果您乐于使用 Spring，那么可以使用它的 context:component-scan 功能执行这些操作，其中 Spring 扫描给定包中的带注释的类。在幕后，它非常可怕，涉及在文件系统和 JAR 文件中寻找包中的类。
Even if you can't use Spring directly, having a look through its source code might give you some ideas.
即使您不能直接使用 Spring，查看其源代码也可能会给您一些想法。
Certainly, the Java reflection APi is no use here, it specifically does not provide a means to obtain all classes in a package.
当然，Java 反射 API 在这里是没有用的，它具体没有提供获取包中所有类的方法。
回答by Aleksander Blomsk?ld
You should probably take a look at the open source Reflections library. With it you can easily achieve what you want with few lines of code:
您或许应该看看开源的Reflections 库。有了它，你可以用几行代码轻松实现你想要的：
Reflections reflections = new Reflections(
new ConfigurationBuilder().setUrls(
ClasspathHelper.forPackage( "com.acme.installer" ) ).setScanners(
new MethodAnnotationsScanner() ) );
Set<Method> methods = reflections.getMethodsAnnotatedWith(InstallerMethod.class);
