Added MethodResolver strategy interface and two implementations: AnnotationMethodResolver and DefaultMethodResolver. The MessageMappingMethodInvoker no longer resolves based on Annotations. Instead, the component that delegates to the invoker is responsible for resolving the Method instance (e.g. ServiceActivator now does this when its single Object constructor is invoked).

org.springframework.integration/src/main/java/org/springframework/integration/endpoint/ServiceActivatorEndpoint.java

@@ -23,7 +23,8 @@ import org.springframework.integration.annotation.ServiceActivator;
 import org.springframework.integration.message.Message;
 import org.springframework.integration.message.MessageHandlingException;
 import org.springframework.integration.message.MessageMappingMethodInvoker;
-import org.springframework.integration.util.MethodUtils;
+import org.springframework.integration.util.DefaultMethodResolver;
+import org.springframework.integration.util.MethodResolver;
 import org.springframework.integration.util.MethodInvoker;
 import org.springframework.util.Assert;
 
@@ -32,8 +33,7 @@ import org.springframework.util.Assert;
  */
 public class ServiceActivatorEndpoint extends AbstractMessageHandlingEndpoint {
 
-	public static final String DEFAULT_LISTENER_METHOD = "handle";
-
+	private final MethodResolver methodResolver = new DefaultMethodResolver(ServiceActivator.class);
 
 	private final MethodInvoker invoker;
 
@@ -45,13 +45,7 @@ public class ServiceActivatorEndpoint extends AbstractMessageHandlingEndpoint {
 
 	public ServiceActivatorEndpoint(final Object object) {
 		Assert.notNull(object, "object must not be null");
-		Method method = MethodUtils.findMethodWithAnnotation(object.getClass(), ServiceActivator.class);
-		if (method == null) {
-			Method[] methods = MethodUtils.findPublicMethods(object.getClass(), false);
-			if (methods.length == 1) {
-				method = methods[0];
-			}
-		}
+		Method method = this.methodResolver.findMethod(object.getClass()); 
 		Assert.notNull(method, "unable to resolve ServiceActivator method on target class ["
 				+ object.getClass() + "]");
 		this.invoker = new MessageMappingMethodInvoker(object, method);

org.springframework.integration/src/main/java/org/springframework/integration/message/MessageMappingMethodInvoker.java

@@ -16,7 +16,6 @@
 
 package org.springframework.integration.message;
 
-import java.lang.annotation.Annotation;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.util.ArrayList;
@@ -26,7 +25,6 @@ import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
 import org.springframework.beans.factory.InitializingBean;
-import org.springframework.core.annotation.AnnotationUtils;
 import org.springframework.integration.util.DefaultMethodInvoker;
 import org.springframework.integration.util.MethodInvoker;
 import org.springframework.integration.util.NameResolvingMethodInvoker;
@@ -55,8 +53,6 @@ public class MessageMappingMethodInvoker implements MethodInvoker, InitializingB
 
 	private volatile String methodName;
 
-	private volatile Class<? extends Annotation> annotationType;
-
 	private volatile OutboundMessageMapper<Object[]> messageMapper;
 
 	private volatile MethodInvoker invoker;
@@ -81,12 +77,6 @@ public class MessageMappingMethodInvoker implements MethodInvoker, InitializingB
 		this.methodName = methodName;
 	}
 
-	public MessageMappingMethodInvoker(Object object, Class<? extends Annotation> annotationType) {
-		Assert.notNull(object, "object must not be null");
-		this.object = object;
-		this.annotationType = annotationType;
-	}
-
 
 	public void afterPropertiesSet() {
 		synchronized (this.initializationMonitor) {
@@ -97,38 +87,18 @@ public class MessageMappingMethodInvoker implements MethodInvoker, InitializingB
 				final List<Method> candidates = new ArrayList<Method>();
 				ReflectionUtils.doWithMethods(this.object.getClass(), new ReflectionUtils.MethodCallback() {
 					public void doWith(Method method) throws IllegalArgumentException, IllegalAccessException {
-						if (MessageMappingMethodInvoker.this.methodName != null) {
-							if (method.getName().equals(MessageMappingMethodInvoker.this.methodName)) {
-								candidates.add(method);
-							}
-						}
-						else if (MessageMappingMethodInvoker.this.annotationType != null) {
-							if (AnnotationUtils.findAnnotation(method, annotationType) != null) {
-								candidates.add(method);
-							}
+						if (method.getName().equals(MessageMappingMethodInvoker.this.methodName)) {
+							candidates.add(method);
 						}
 					}
 				});
 				if (candidates.size() == 0) {
-					String clause = "";
-					if (this.methodName != null) {
-						clause = " matching method name '" + this.methodName + "'";
-					}
-					else if (this.annotationType != null) {
-						clause = " matching annotation type '" + this.annotationType + "'";
-					}
-					throw new IllegalArgumentException("unable to find a candidate method"
-							+ clause + " on target class [" + this.object.getClass() + "]"); 
+					throw new IllegalArgumentException("unable to find a candidate method named '"
+							+ this.methodName + "'" + " on target class [" + this.object.getClass() + "]"); 
 				}
 				else if (candidates.size() == 1) {
 					this.method = candidates.get(0);
 				}
-				else if (this.annotationType != null) {
-					throw new IllegalArgumentException("unable to resolve method for annotation ["
-							+ this.annotationType + "], found " + candidates.size()
-							+ " candidates on target class [" + this.object.getClass() + "]: "
-							+ candidates);
-				}
 			}
 			if (this.method != null) {
 				Class<?>[] parameterTypes = this.method.getParameterTypes();

org.springframework.integration/src/main/java/org/springframework/integration/util/AnnotationMethodResolver.java

@@ -17,25 +17,42 @@
 package org.springframework.integration.util;
 
 import java.lang.annotation.Annotation;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Target;
 import java.lang.reflect.Method;
-import java.util.ArrayList;
-import java.util.List;
 import java.util.concurrent.atomic.AtomicReference;
 
 import org.springframework.core.annotation.AnnotationUtils;
 import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
 import org.springframework.util.ReflectionUtils;
 
 /**
- * Helper methods for detecting Methods.
+ * MethodResolver implementation that finds a <em>single</em> Method on the
+ * given Class that contains the specified annotation type.
  * 
  * @author Mark Fisher
  */
-public abstract class MethodUtils {
+public class AnnotationMethodResolver implements MethodResolver {
+
+	private Class<? extends Annotation> annotationType;
+
+
+	/**
+	 * Create a MethodResolver for the specified Method-level annotation type
+	 */
+	public AnnotationMethodResolver(Class<? extends Annotation> annotationType) {
+		Assert.notNull(annotationType, "annotationType must not be null");
+		Assert.isTrue(ObjectUtils.containsElement(
+				annotationType.getAnnotation(Target.class).value(), ElementType.METHOD),
+				"Annotation [" + annotationType + "] is not a Method-level annotation.");
+		this.annotationType = annotationType;
+	}
+
 
 	/**
 	 * Find a <em>single</em> Method on the given Class that contains the
-	 * specified annotation type.
+	 * annotation type for which this resolver is searching.
 	 * 
 	 * @param clazz the Class instance to check for the annotation
 	 * @param annotationType the Method-level annotation type
@@ -46,12 +63,11 @@ public abstract class MethodUtils {
 	 * @throws IllegalArgumentException if more than one Method has the
 	 * specified annotation
 	 */
-	public static <T extends Annotation> Method findMethodWithAnnotation(
-			final Class<?> clazz, final Class<T> annotationType) {
+	public Method findMethod(final Class<?> clazz) {
 		final AtomicReference<Method> annotatedMethod = new AtomicReference<Method>();
 		ReflectionUtils.doWithMethods(clazz, new ReflectionUtils.MethodCallback() {
 			public void doWith(Method method) throws IllegalArgumentException, IllegalAccessException {
-				T annotation = AnnotationUtils.findAnnotation(method, annotationType);
+				Annotation annotation = AnnotationUtils.findAnnotation(method, annotationType);
 				if (annotation != null) {
 					Assert.isNull(annotatedMethod.get(), "found more than one method on target class ["
 							+ clazz + "] with the annotation type [" + annotationType + "]");
@@ -62,25 +78,4 @@ public abstract class MethodUtils {
 		return annotatedMethod.get();
 	}
 
-	/**
-	 * Find all public Methods of a given Class.
-	 * 
-	 * @param clazz the class to search
-	 * @param includeMethodsDeclaredOnObject whether to include Methods
-	 * that are declared on the Object class
-	 * 
-	 * @return array of public Methods
-	 */
-	public static Method[] findPublicMethods(
-			final Class<?> clazz, final boolean includeMethodsDeclaredOnObject) {
-		final List<Method> methods = new ArrayList<Method>();
-		for (Method method : clazz.getMethods()) {
-			if (includeMethodsDeclaredOnObject
-					|| !method.getDeclaringClass().equals(Object.class)) {
-				methods.add(method);
-			}
-		}
-		return methods.toArray(new Method[methods.size()]);
-	}
-
 }

org.springframework.integration/src/main/java/org/springframework/integration/util/DefaultMethodResolver.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2002-2008 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.util;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Method;
+
+import org.springframework.util.Assert;
+
+/**
+ * Default MethodResolver implementation. It first checks for a single Method
+ * with the specified annotation (if not null), and then falls back to a single
+ * public Method if available.
+ * 
+ * @author Mark Fisher
+ */
+public class DefaultMethodResolver implements MethodResolver {
+
+	private final AnnotationMethodResolver annotationMethodResolver;
+
+
+	public DefaultMethodResolver() {
+		this(null);
+	}
+
+	public DefaultMethodResolver(Class<? extends Annotation> annotationType) {
+		this.annotationMethodResolver = (annotationType != null) ?
+				new AnnotationMethodResolver(annotationType) : null;
+	}
+
+
+	public Method findMethod(Class<?> clazz) {
+		Assert.notNull(clazz, "Class must not be null");
+		if (this.annotationMethodResolver != null) {
+			Method method = this.annotationMethodResolver.findMethod(clazz);
+			if (method != null) {
+				return method;
+			}
+		}
+		return this.findSinglePublicMethod(clazz);
+	}
+
+	private Method findSinglePublicMethod(Class<?> clazz) {
+		Method result = null;
+		for (Method method : clazz.getMethods()) {
+			if (!method.getDeclaringClass().equals(Object.class)) {
+				if (result != null) {
+					throw new IllegalArgumentException(
+							"Class [" + clazz + "] contains more than one public Method.");
+				}
+				result = method;
+			}
+		}
+		return result;
+	}
+
+}

org.springframework.integration/src/main/java/org/springframework/integration/util/MethodResolver.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2002-2008 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.util;
+
+import java.lang.reflect.Method;
+
+/**
+ * Strategy interface for detecting a single Method on a Class.
+ * 
+ * @author Mark Fisher
+ */
+public interface MethodResolver {
+
+	/**
+	 * Find a single Method on the provided Class that matches this resolver's
+	 * criteria.
+	 * 
+	 * @param clazz the Class on which to search for a Method
+	 * 
+	 * @return a single Method or <code>null</code> if no Method matching this
+	 * resolver's criteria can be found.
+	 * 
+	 * @throws IllegalArgumentException if more than one Method defined on the
+	 * given Class matches this resolver's criteria
+	 */
+	Method findMethod(Class<?> clazz) throws IllegalArgumentException;
+
+}

org.springframework.integration/src/test/java/org/springframework/integration/endpoint/ServiceActivatorMethodResolutionTests.java

@@ -0,0 +1,120 @@
+/*
+ * Copyright 2002-2008 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.endpoint;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+import org.springframework.integration.annotation.ServiceActivator;
+import org.springframework.integration.channel.QueueChannel;
+import org.springframework.integration.message.Message;
+import org.springframework.integration.message.StringMessage;
+
+/**
+ * @author Mark Fisher
+ */
+public class ServiceActivatorMethodResolutionTests {
+
+	@Test
+	public void singleAnnotationMatches() {
+		SingleAnnotationTestBean testBean = new SingleAnnotationTestBean();
+		ServiceActivatorEndpoint endpoint = new ServiceActivatorEndpoint(testBean);
+		QueueChannel outputChannel = new QueueChannel();
+		endpoint.setOutputChannel(outputChannel);
+		endpoint.afterPropertiesSet();
+		endpoint.onMessage(new StringMessage("foo"));
+		Message<?> result = outputChannel.receive(0);
+		assertEquals("FOO", result.getPayload());
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void multipleAnnotationFails() {
+		MultipleAnnotationTestBean testBean = new MultipleAnnotationTestBean();
+		new ServiceActivatorEndpoint(testBean);
+	}
+
+	@Test
+	public void singlePublicMethodMatches() {
+		SinglePublicMethodTestBean testBean = new SinglePublicMethodTestBean();
+		ServiceActivatorEndpoint endpoint = new ServiceActivatorEndpoint(testBean);
+		QueueChannel outputChannel = new QueueChannel();
+		endpoint.setOutputChannel(outputChannel);
+		endpoint.afterPropertiesSet();
+		endpoint.onMessage(new StringMessage("foo"));
+		Message<?> result = outputChannel.receive(0);
+		assertEquals("FOO", result.getPayload());
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void multiplePublicMethodFails() {
+		MultiplePublicMethodTestBean testBean = new MultiplePublicMethodTestBean();
+		new ServiceActivatorEndpoint(testBean);
+	}
+
+
+	private static class SingleAnnotationTestBean {
+
+		@ServiceActivator
+		public String upperCase(String s) {
+			return s.toUpperCase();
+		}
+
+		public String lowerCase(String s) {
+			return s.toLowerCase();
+		}
+	}
+
+
+	private static class MultipleAnnotationTestBean {
+
+		@ServiceActivator
+		public String upperCase(String s) {
+			return s.toUpperCase();
+		}
+
+		@ServiceActivator
+		public String lowerCase(String s) {
+			return s.toLowerCase();
+		}
+	}
+
+
+	private static class SinglePublicMethodTestBean {
+
+		public String upperCase(String s) {
+			return s.toUpperCase();
+		}
+
+		String lowerCase(String s) {
+			return s.toLowerCase();
+		}
+	}
+
+
+	private static class MultiplePublicMethodTestBean {
+
+		public String upperCase(String s) {
+			return s.toUpperCase();
+		}
+
+		public String lowerCase(String s) {
+			return s.toLowerCase();
+		}
+	}
+
+}

org.springframework.integration/src/test/java/org/springframework/integration/util/AnnotationMethodResolverTests.java

@@ -14,38 +14,42 @@
  * limitations under the License.
  */
 
-package org.springframework.integration.message;
+package org.springframework.integration.util;
 
-import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
 
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
+import java.lang.reflect.Method;
 
 import org.junit.Test;
 
 /**
  * @author Mark Fisher
  */
-public class MessageMappingMethodInvokerAnnotationTests {
+public class AnnotationMethodResolverTests {
 
 	@Test
-	public void singleAnnotationMatches() {
-		SingleAnnotationTestBean testBean = new SingleAnnotationTestBean();
-		MessageMappingMethodInvoker invoker =
-				new MessageMappingMethodInvoker(testBean, TestAnnotation.class);
-		invoker.afterPropertiesSet();
-		String result = (String) invoker.invokeMethod("foo");
-		assertEquals("FOO", result);
+	public void singleAnnotation() {
+		AnnotationMethodResolver resolver = new AnnotationMethodResolver(TestAnnotation.class);
+		Method method = resolver.findMethod(SingleAnnotationTestBean.class);
+		assertNotNull(method);
 	}
 
 	@Test(expected = IllegalArgumentException.class)
-	public void multipleAnnotationMatches() {
-		MultipleAnnotationTestBean testBean = new MultipleAnnotationTestBean();
-		MessageMappingMethodInvoker invoker =
-				new MessageMappingMethodInvoker(testBean, TestAnnotation.class);
-		invoker.afterPropertiesSet();
+	public void multipleAnnotations() {
+		AnnotationMethodResolver resolver = new AnnotationMethodResolver(TestAnnotation.class);
+		resolver.findMethod(MultipleAnnotationTestBean.class);
+	}
+
+	@Test
+	public void noAnnotations() {
+		AnnotationMethodResolver resolver = new AnnotationMethodResolver(TestAnnotation.class);
+		Method method = resolver.findMethod(NoAnnotationTestBean.class);
+		assertNull(method);
 	}
 
 
@@ -61,6 +65,10 @@ public class MessageMappingMethodInvokerAnnotationTests {
 		public String upperCase(String s) {
 			return s.toUpperCase();
 		}
+
+		public String lowerCase(String s) {
+			return s.toLowerCase();
+		}
 	}
 
 
@@ -77,4 +85,16 @@ public class MessageMappingMethodInvokerAnnotationTests {
 		}
 	}
 
+
+	private static class NoAnnotationTestBean {
+
+		public String upperCase(String s) {
+			return s.toUpperCase();
+		}
+
+		String lowerCase(String s) {
+			return s.toLowerCase();
+		}
+	}
+
 }

org.springframework.integration/src/test/java/org/springframework/integration/util/DefaultMethodResolverTests.java

@@ -0,0 +1,133 @@
+/*
+ * Copyright 2002-2008 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.util;
+
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import java.lang.reflect.Method;
+
+import org.junit.Test;
+
+/**
+ * @author Mark Fisher
+ */
+public class DefaultMethodResolverTests {
+
+	@Test
+	public void singleAnnotation() {
+		DefaultMethodResolver resolver = new DefaultMethodResolver(TestAnnotation.class);
+		Method method = resolver.findMethod(SingleAnnotationTestBean.class);
+		assertNotNull(method);
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void multipleAnnotations() {
+		DefaultMethodResolver resolver = new DefaultMethodResolver(TestAnnotation.class);
+		resolver.findMethod(MultipleAnnotationTestBean.class);
+	}
+
+	@Test
+	public void singlePublicMethod() {
+		DefaultMethodResolver resolver = new DefaultMethodResolver(TestAnnotation.class);
+		Method method = resolver.findMethod(SinglePublicMethodTestBean.class);
+		assertNotNull(method);
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void multiplePublicMethods() {
+		DefaultMethodResolver resolver = new DefaultMethodResolver(TestAnnotation.class);
+		resolver.findMethod(MultiplePublicMethodTestBean.class);
+	}
+
+	@Test
+	public void noPublicMethods() {
+		DefaultMethodResolver resolver = new DefaultMethodResolver(TestAnnotation.class);
+		Method method = resolver.findMethod(NoPublicMethodTestBean.class);
+		assertNull(method);
+	}
+
+
+	@Target(ElementType.METHOD)
+	@Retention(RetentionPolicy.RUNTIME)
+	private static @interface TestAnnotation {
+	}
+
+
+	private static class SingleAnnotationTestBean {
+
+		@TestAnnotation
+		public String upperCase(String s) {
+			return s.toUpperCase();
+		}
+
+		public String lowerCase(String s) {
+			return s.toLowerCase();
+		}
+	}
+
+
+	private static class MultipleAnnotationTestBean {
+
+		@TestAnnotation
+		public String upperCase(String s) {
+			return s.toUpperCase();
+		}
+
+		@TestAnnotation
+		public String lowerCase(String s) {
+			return s.toLowerCase();
+		}
+	}
+
+
+	private static class SinglePublicMethodTestBean {
+
+		public String upperCase(String s) {
+			return s.toUpperCase();
+		}
+
+		String lowerCase(String s) {
+			return s.toLowerCase();
+		}
+	}
+
+
+	private static class MultiplePublicMethodTestBean {
+
+		public String upperCase(String s) {
+			return s.toUpperCase();
+		}
+
+		public String lowerCase(String s) {
+			return s.toLowerCase();
+		}
+	}
+
+
+	private static class NoPublicMethodTestBean {
+
+		String lowerCase(String s) {
+			return s.toLowerCase();
+		}
+	}
+
+}