Java seek a method with specific annotation and its annotation element

Question

Suppose I have this annotation class

 @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(){ ... } } 

So is there a way to look into an object, "seek" out the method with the @MethodXY annotation, where its element x = 3, y = 2, and invoke it?

Thanks

Answer 1

Here is a method, which returns methods with specific annotations:

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         for (final Method method : klass.getDeclaredMethods()) {             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; } 

It can be easily modified to your specific needs. Pls note that the provided method traverses class hierarchy in order to find methods with required annotations.

Here is a method for your specific needs:

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         for (final Method method : klass.getDeclaredMethods()) {             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; } 

For invocation of the found method(s) pls refer a tutorial. One of the potential difficulties here is the number of method arguments, which could vary between found methods and thus requiring some additional processing.

Answer 2

try this code sample:

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");         }     } }