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/test/java/org/springframework/core/MethodParameterTests.java

@@ -1,5 +1,5 @@
 /*
- * 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());
 
-	public int method(String p1, long p2) {
+		//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(@DummyAnnotation String p1, long p2) {
 		return 42;
 	}
 
+	@Target(ElementType.PARAMETER)
+	@Retention(RetentionPolicy.RUNTIME)
+	public @interface DummyAnnotation {
+
+	}
 }