Added PayloadTypeMatchingHandlerMethodResolver.

org.springframework.integration/src/main/java/org/springframework/integration/handler/PayloadTypeMatchingHandlerMethodResolver.java

@@ -0,0 +1,135 @@
+/*
+ * 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.handler;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Method;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+import org.springframework.integration.core.Message;
+import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
+
+/**
+ * An implementation of {@link HandlerMethodResolver} that matches the payload
+ * type of the Message against the expected type of its candidate methods.
+ * 
+ * @author Mark Fisher
+ */
+public class PayloadTypeMatchingHandlerMethodResolver implements HandlerMethodResolver {
+
+	private final Map<Class<?>, Method> methodMap = new HashMap<Class<?>, Method>();
+
+	private volatile Method fallbackMethod;
+
+
+	public PayloadTypeMatchingHandlerMethodResolver(Method... candidates) {
+		Assert.notEmpty(candidates, "candidates must not be empty");
+		this.initMethodMap(candidates);
+	}
+
+
+	public Method resolveHandlerMethod(Message<?> message) {
+		Class<?> payloadType = message.getPayload().getClass();
+		Method method = this.methodMap.get(payloadType);
+		if (method == null) {
+			method = this.findClosestMatch(payloadType);
+			if (method == null) {
+				method = this.fallbackMethod;
+			}
+		}
+		return method;
+	}
+
+	private void initMethodMap(Method[] candidates) {
+		for (Method method : candidates) {
+			Class<?> expectedPayloadType = this.determineExpectedPayloadType(method);
+			if (expectedPayloadType == null) {
+				Assert.isTrue(fallbackMethod == null,
+						"At most one method can expect only Message headers rather than a payload, " +
+						"but found two: [" + method + "] and [" + this.fallbackMethod + "]");
+				this.fallbackMethod = method;
+			}
+			else {
+				Assert.isTrue(!this.methodMap.containsKey(expectedPayloadType),
+						"More than one method matches payload type [" + expectedPayloadType +
+						"]. Consider using annotations or providing a method name.");
+				this.methodMap.put(expectedPayloadType, method);
+			}
+		}
+	}
+
+	private Class<?> determineExpectedPayloadType(Method method) {
+		Class<?> expectedPayloadType = null;
+		Class<?>[] parameterTypes = method.getParameterTypes();
+		Annotation[][] parameterAnnotations = method.getParameterAnnotations();
+		for (int i = 0; i < parameterTypes.length; i++) {
+			if (!HandlerMethodUtils.containsHeaderAnnotation(parameterAnnotations[i])) {
+				Assert.isTrue(expectedPayloadType == null,
+						"Message-handling method must only have one parameter expecting a payload. Other " +
+						"parameters may be included but only if they have @Header or @Headers annotations.");
+				expectedPayloadType = parameterTypes[i];
+			}
+		}
+		return expectedPayloadType;
+	}
+
+	private Method findClosestMatch(Class<?> payloadType) {
+		Set<Class<?>> expectedTypes = this.methodMap.keySet();
+		int minTypeDiffWeight = Integer.MAX_VALUE;
+		Method matchingMethod = null;
+		for (Class<?> expectedType : expectedTypes) {
+			int typeDiffWeight = getTypeDifferenceWeight(expectedType, payloadType);
+			if (typeDiffWeight < minTypeDiffWeight) {
+				minTypeDiffWeight = typeDiffWeight;
+				matchingMethod = this.methodMap.get(expectedType);
+			}
+		}
+		if (matchingMethod != null) {
+			this.methodMap.put(payloadType, matchingMethod);
+		}
+		return matchingMethod;
+	}
+
+	private int getTypeDifferenceWeight(Class<?> expectedType, Class<?> payloadType) {
+		int result = 0;
+		if (!ClassUtils.isAssignable(expectedType, payloadType)) {
+			return Integer.MAX_VALUE;
+		}
+		Class<?> superClass = payloadType.getSuperclass();
+		while (superClass != null) {
+			if (expectedType.equals(superClass)) {
+				result = result + 2;
+				superClass = null;
+			}
+			else if (ClassUtils.isAssignable(expectedType, superClass)) {
+				result = result + 2;
+				superClass = superClass.getSuperclass();
+			}
+			else {
+				superClass = null;
+			}
+		}
+		if (expectedType.isInterface()) {
+			result = result + 1;
+		}
+		return result;
+	}
+
+}