Java 如何获取被注解的类元素

Question

比如定义了一个@controller的注解 然后有如下代码@controller
public class Test1{}
@controller
public class Test2{}
@controller
public class Test3{}
现在怎么在main方法获取到所有被@controller注解的类 

Answer 1

先取package信息，然后把所有class找到,接着挨个class看是否有你指定的annotation.
例子：
    private List<Class> getClassesForPackage(String pckgname)
            throws ClassNotFoundException {
        //There may be more than one if a package is split over multiple jars/paths
        List<Class> classes = new ArrayList<Class>();
        String className = "";
        try {
            ClassLoader cld = Thread.currentThread().getContextClassLoader();
            if (cld == null) {
                throw new ClassNotFoundException("Can't get class loader.");
            }            String pckgnmePathStr = pckgname.replace('.', '/');
            // Ask for all resources for the path
            Enumeration<URL> resources = cld.getResources(pckgnmePathStr);
            
            while (resources.hasMoreElements()) {
                URL res = resources.nextElement();
                if (res.getProtocol().equalsIgnoreCase("jar")){
                    JarURLConnection conn = (JarURLConnection) res.openConnection();
                    JarFile jar = conn.getJarFile();
                    for (JarEntry e:Collections.list(jar.entries())){                        if (e.getName().startsWith(pckgnmePathStr)
                            && e.getName().endsWith(".class") && !e.getName().contains("$")){
                            String name = e.getName().substring(pckgnmePathStr.length() + 1);
                            
                            // Do not discover classes in the sub-package
                            if(name.indexOf('/') > -1) continue;
                            className =
                                    e.getName().replace("/",".").substring(0,e.getName().length() - 6);
                            try {
                                classes.add(Class.forName(className));
                            }catch(NoClassDefFoundError ncdfe) {}
                        }
                    }
                }
            }
        } catch (NullPointerException x) {
            throw new ClassNotFoundException(pckgname + " does not appear to be " +
                    "a valid package (Null pointer exception)");
        } catch (UnsupportedEncodingException encex) {
            throw new ClassNotFoundException(pckgname + " does not appear to be " +
                    "a valid package (Unsupported encoding)");
        } catch (IOException ioex) {
            throw new ClassNotFoundException("IOException was thrown when trying " +
                    "to get all resources for " + pckgname, ioex);
        } catch (Throwable te){
            throw new ClassNotFoundException("IOException was thrown when trying " +
                    "to get all resources for " + pckgname + className, te);
        }        return classes;
    }    private static Map<String, NamedQueryDefinition> extractNamedQueries(List<Class> classes) {
        HashMap<String, NamedQueryDefinition> queryDefs = new HashMap<String, NamedQueryDefinition>();        for(Class clz : classes) {
            controller queries = (JpaQueries)clz.getAnnotation(controller.class);
            if(queries != null) {
                JpaQuery[] queryArray = queries.value();
                for(int i = 0; i < queryArray.length; i++) {
                    queryDefs.put(queryArray[i].name(), new NamedQueryDefinition(
                            queryArray[i].query(), false, null, null, null, null, null));                }
            }
        }
        return queryDefs;
    }in your main:List<Class> classes = getClassesForPackage("com.your.package.name");
config.getNamedQueries().putAll(extractNamedQueries(classes));

Answer 2

不否认这段代码满足一部分情况 
但在某些特殊场合不行
比如maven项目在cmd 用tomcat:run启动的时候应该跟注释有关的类什么的 比如注释处理器什么的