Cache MethodParameter annotation lookup results

Prior to this change, Spring's MethodParameter#getParameterAnnotations
called java.lang.Method#getParameterAnnotations on every invocation.
The latter ends up contending for a monitor inside (Sun) JDK code. This
is problematic when dealing with the high number of @RequestMapping
invocations that can occur in a Spring MVC @Controller.

This commit eliminates this contention by caching values returned by
java.lang.Method#getParameterAnnotations in a static ConcurrentMap.

Note that only Method parameter annotations are cached, while
Constructor parameter annotations are not. This is because the
issue of primary concern is, as mentioned above, @RequestMapping
methods. By nature, constructors are called much more infrequently, and
in most cases in a single-threaded fashion.

Issue: SPR-9298

spring-core/src/main/java/org/springframework/core/MethodParameter.java

 /*
- * Copyright 2002-2011 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -26,6 +26,8 @@ import java.lang.reflect.Type;
 import java.lang.reflect.TypeVariable;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 
 import org.springframework.util.Assert;
 
@@ -37,11 +39,21 @@ import org.springframework.util.Assert;
  * @author Juergen Hoeller
  * @author Rob Harrop
  * @author Andy Clement
+ * @author Nikita Tovstoles
+ * @author Chris Beams
  * @since 2.0
  * @see GenericCollectionTypeResolver
  */
 public class MethodParameter {
 
+
+	private static final Annotation[][] EMPTY_ANNOTATION_MATRIX = new Annotation[0][0];
+
+	private static final Annotation[] EMPTY_ANNOTATION_ARRAY = new Annotation[0];
+
+	static final ConcurrentMap<Method, Annotation[][]> methodParamAnnotationsCache =
+			new ConcurrentHashMap<Method, Annotation[][]>();
+
 	private final Method method;
 
 	private final Constructor constructor;
@@ -280,7 +292,7 @@ public class MethodParameter {
 	public Annotation[] getParameterAnnotations() {
 		if (this.parameterAnnotations == null) {
 			Annotation[][] annotationArray = (this.method != null ?
-					this.method.getParameterAnnotations() : this.constructor.getParameterAnnotations());
+					getMethodParameterAnnotations(this.method) : this.constructor.getParameterAnnotations());
 			if (this.parameterIndex >= 0 && this.parameterIndex < annotationArray.length) {
 				this.parameterAnnotations = annotationArray[this.parameterIndex];
 			}
@@ -439,6 +451,41 @@ public class MethodParameter {
 		}
 	}
 
+	/**
+	 * Return the parameter annotations for the given method, retrieving cached values
+	 * if a lookup has already been performed for this method, otherwise perform a fresh
+	 * lookup and populate the cache with the result before returning. <strong>For
+	 * internal use only.</strong>
+	 * @param method the method to introspect for parameter annotations
+	 */
+	static Annotation[][] getMethodParameterAnnotations(Method method) {
+		Assert.notNull(method);
+
+		Annotation[][] result = methodParamAnnotationsCache.get(method);
+		if (result == null) {
+			result = method.getParameterAnnotations();
+
+			if(result.length == 0) {
+				result = EMPTY_ANNOTATION_MATRIX;
+			}
+			else {
+				for (int i = 0; i < result.length; i++) {
+					if (result[i].length == 0) {
+						result[i] = EMPTY_ANNOTATION_ARRAY;
+					}
+				}
+			}
+			methodParamAnnotationsCache.put(method, result);
+		}
+
+		//always return deep copy to prevent caller from modifying cache state
+		Annotation[][] resultCopy = new Annotation[result.length][0];
+		for(int i = 0; i < result.length; i++) {
+			resultCopy[i] = result[i].clone();
+		}
+		return resultCopy;
+	}
+
 	@Override
 	public boolean equals(Object obj) {
 		if (this == obj) {
@@ -460,7 +507,6 @@ public class MethodParameter {
 		return false;
 	}
 
-
 	@Override
 	public int hashCode() {
 		int result = this.hash;

spring-core/src/test/java/org/springframework/core/MethodParameterTests.java

 /*
- * Copyright 2002-2011 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -16,6 +16,11 @@
 
 package org.springframework.core;
 
+import java.lang.annotation.Annotation;
+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.Before;
@@ -25,6 +30,7 @@ import static org.junit.Assert.*;
 
 /**
  * @author Arjen Poutsma
+ * @author Nikita Tovstoles
  */
 public class MethodParameterTests {
 
@@ -43,7 +49,6 @@ public class MethodParameterTests {
 	}
 
 
-	
 	@Test
 	public void testEquals() throws NoSuchMethodException {
 		assertEquals(stringParameter, stringParameter);
@@ -77,9 +82,30 @@ public class MethodParameterTests {
 		assertTrue(longParameter.hashCode() != methodParameter.hashCode());
 	}
 
+	@Test
+	public void testGetMethodParamaterAnnotations() {
+		Method method = stringParameter.getMethod();
+		Annotation[][] expectedAnnotations = method.getParameterAnnotations();
+		assertEquals(2, expectedAnnotations.length);
+		assertEquals(DummyAnnotation.class, expectedAnnotations[0][0].annotationType());
+
+		//start with empty cache
+		MethodParameter.methodParamAnnotationsCache.clear();
+
+		//check correctness
+		assertArrayEquals(expectedAnnotations, MethodParameter.getMethodParameterAnnotations(method));
+		//check that return value's been cached
+		assertArrayEquals(expectedAnnotations, MethodParameter.methodParamAnnotationsCache.get(method));
+	}
+
 
-	public int method(String p1, long p2) {
+	public int method(@DummyAnnotation String p1, long p2) {
 		return 42;
 	}
 
+	@Target(ElementType.PARAMETER)
+	@Retention(RetentionPolicy.RUNTIME)
+	public @interface DummyAnnotation {
+
+	}
 }