的Java尋求與特定的註解和註釋元素的方法

Question

假設我有這樣的註解類

@Retention(RetentionPolicy.RUNTIME) 
@Target(ElementType.METHOD) 
public @interface MethodXY { 
    public int x(); 
    public int y(); 
} 

public class AnnotationTest { 
    @MethodXY(x=5, y=5) 
    public void myMethodA(){ ... } 

    @MethodXY(x=3, y=2) 
    public void myMethodB(){ ... } 
} 

那麼，有沒有辦法尋找到一個對象，「求」出與@MethodXY註釋的方法，其元素x = 3，y = 2，並調用它？

感謝

Answer 1

這裏有一個方法，它返回的具體註釋方法：

public static List<Method> getMethodsAnnotatedWith(final Class<?> type, final Class<? extends Annotation> annotation) { 
    final List<Method> methods = new ArrayList<Method>(); 
    Class<?> klass = type; 
    while (klass != Object.class) { // need to iterated thought hierarchy in order to retrieve methods from above the current instance 
     // iterate though the list of methods declared in the class represented by klass variable, and add those annotated with the specified annotation 
     final List<Method> allMethods = new ArrayList<Method>(Arrays.asList(klass.getDeclaredMethods()));  
     for (final Method method : allMethods) { 
      if (method.isAnnotationPresent(annotation)) { 
       Annotation annotInstance = method.getAnnotation(annotation); 
       // TODO process annotInstance 
       methods.add(method); 
      } 
     } 
     // move to the upper class in the hierarchy in search for more methods 
     klass = klass.getSuperclass(); 
    } 
    return methods; 
} 

它可以很容易地修改您的特定需求。請注意，所提供的方法遍歷類層次結構以查找具有所需註釋的方法。

這裏是您的特定需求的方法：

public static List<Method> getMethodsAnnotatedWithMethodXY(final Class<?> type) { 
    final List<Method> methods = new ArrayList<Method>(); 
    Class<?> klass = type; 
    while (klass != Object.class) { // need to iterated thought hierarchy in order to retrieve methods from above the current instance 
     // iterate though the list of methods declared in the class represented by klass variable, and add those annotated with the specified annotation 
     final List<Method> allMethods = new ArrayList<Method>(Arrays.asList(klass.getDeclaredMethods())); 
     for (final Method method : allMethods) { 
      if (method.isAnnotationPresent(MethodXY.class)) { 
       MethodXY annotInstance = method.getAnnotation(MethodXY.class); 
       if (annotInstance.x() == 3 && annotInstance.y() == 2) {   
        methods.add(method); 
       } 
      } 
     } 
     // move to the upper class in the hierarchy in search for more methods 
     klass = klass.getSuperclass(); 
    } 
    return methods; 
} 

對於發現的方法（S）的調用請參考一tutorial。這裏可能遇到的困難之一是方法參數的數量，這些參數可能因所找到的方法而異，因此需要一些額外的處理。

Answer 2

試試這個代碼示例：

import java.lang.annotation.Annotation; 
import java.lang.reflect.Method; 
import java.lang.annotation.Retention; 
import java.lang.annotation.RetentionPolicy; 
import java.lang.annotation.Target; 
import java.lang.annotation.ElementType; 
import java.lang.reflect.InvocationTargetException; 

class AnotTest { 
    public static void main(String... args) { 
     AnnotationTest at = new AnnotationTest(); 
     for (Method m : at.getClass().getMethods()) { 
      MethodXY mXY = (MethodXY)m.getAnnotation(MethodXY.class); 
      if (mXY != null) { 
       if (mXY.x() == 3 && mXY.y() == 2){ 
        try { 
         m.invoke(at); 
        } catch (IllegalAccessException e) { 
         //do nothing; 
        } catch (InvocationTargetException o) { 
         //do nothing; 
        } 
       } 
      } 
     } 
    } 
    @Retention(RetentionPolicy.RUNTIME) 
    @Target(ElementType.METHOD) 
    static public @interface MethodXY { 
     public int x(); 
     public int y(); 
    } 

    static class AnnotationTest { 
     @MethodXY(x=5, y=5) 
     public void myMethodA() { 
      System.out.println("boo"); 
     } 

     @MethodXY(x=3, y=2) 
     public void myMethodB() { 
      System.out.println("foo"); 
     } 
    } 
}