Optimized access to resolved bean type (avoiding BeanFactory locks)

Revised HandlerMethod.getBeanType() impl for both web and messaging.
In addition, HandlerMethods get created with the internal BeanFactory now.

Issue: SPR-12832

spring-messaging/src/main/java/org/springframework/messaging/handler/HandlerMethod.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -30,26 +30,30 @@ import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 
 /**
- * Encapsulates information about a bean method consisting of a {@link #getMethod() method}
- * and a {@link #getBean() bean}. Provides convenient access to method parameters,
- * method return value, method annotations.
+ * Encapsulates information about a handler method consisting of a
+ * {@linkplain #getMethod() method} and a {@linkplain #getBean() bean}.
+ * Provides convenient access to method parameters, method return value, method annotations.
  *
- * <p>The class may be created with a bean instance or with a bean name (e.g. lazy bean,
- * prototype bean). Use {@link #createWithResolvedBean()} to obtain an {@link HandlerMethod}
- * instance with a bean instance initialized through the bean factory.
+ * <p>The class may be created with a bean instance or with a bean name (e.g. lazy-init bean,
+ * prototype bean). Use {@link #createWithResolvedBean()} to obtain a {@link HandlerMethod}
+ * instance with a bean instance resolved through the associated {@link BeanFactory}.
  *
  * @author Arjen Poutsma
  * @author Rossen Stoyanchev
+ * @author Juergen Hoeller
  * @since 4.0
  */
 public class HandlerMethod {
 
-	protected final Log logger = LogFactory.getLog(HandlerMethod.class);
+	/** Logger that is available to subclasses */
+	protected final Log logger = LogFactory.getLog(getClass());
 
 	private final Object bean;
 
 	private final BeanFactory beanFactory;
 
+	private final Class<?> beanType;
+
 	private final Method method;
 
 	private final Method bridgedMethod;
@@ -65,6 +69,7 @@ public class HandlerMethod {
 		Assert.notNull(method, "Method is required");
 		this.bean = bean;
 		this.beanFactory = null;
+		this.beanType = ClassUtils.getUserClass(bean);
 		this.method = method;
 		this.bridgedMethod = BridgeMethodResolver.findBridgedMethod(method);
 		this.parameters = initMethodParameters();
@@ -79,6 +84,7 @@ public class HandlerMethod {
 		Assert.notNull(methodName, "Method name is required");
 		this.bean = bean;
 		this.beanFactory = null;
+		this.beanType = ClassUtils.getUserClass(bean);
 		this.method = bean.getClass().getMethod(methodName, parameterTypes);
 		this.bridgedMethod = BridgeMethodResolver.findBridgedMethod(this.method);
 		this.parameters = initMethodParameters();
@@ -93,22 +99,22 @@ public class HandlerMethod {
 		Assert.hasText(beanName, "Bean name is required");
 		Assert.notNull(beanFactory, "BeanFactory is required");
 		Assert.notNull(method, "Method is required");
-		Assert.isTrue(beanFactory.containsBean(beanName),
-				"BeanFactory [" + beanFactory + "] does not contain bean [" + beanName + "]");
 		this.bean = beanName;
 		this.beanFactory = beanFactory;
+		this.beanType = ClassUtils.getUserClass(beanFactory.getType(beanName));
 		this.method = method;
 		this.bridgedMethod = BridgeMethodResolver.findBridgedMethod(method);
 		this.parameters = initMethodParameters();
 	}
 
 	/**
-	 * Copy constructor for use in sub-classes.
+	 * Copy constructor for use in subclasses.
 	 */
 	protected HandlerMethod(HandlerMethod handlerMethod) {
 		Assert.notNull(handlerMethod, "HandlerMethod is required");
 		this.bean = handlerMethod.bean;
 		this.beanFactory = handlerMethod.beanFactory;
+		this.beanType = handlerMethod.beanType;
 		this.method = handlerMethod.method;
 		this.bridgedMethod = handlerMethod.bridgedMethod;
 		this.parameters = handlerMethod.parameters;
@@ -122,6 +128,7 @@ public class HandlerMethod {
 		Assert.notNull(handler, "Handler object is required");
 		this.bean = handler;
 		this.beanFactory = handlerMethod.beanFactory;
+		this.beanType = handlerMethod.beanType;
 		this.method = handlerMethod.method;
 		this.bridgedMethod = handlerMethod.bridgedMethod;
 		this.parameters = handlerMethod.parameters;
@@ -152,18 +159,17 @@ public class HandlerMethod {
 	}
 
 	/**
-	 * Returns the type of the handler for this handler method.
-	 * Note that if the bean type is a CGLIB-generated class, the original, user-defined class is returned.
+	 * This method returns the type of the handler for this handler method.
+	 * <p>Note that if the bean type is a CGLIB-generated class, the original
+	 * user-defined class is returned.
 	 */
 	public Class<?> getBeanType() {
-		Class<?> clazz = (this.bean instanceof String ?
-				this.beanFactory.getType((String) this.bean) : this.bean.getClass());
-		return ClassUtils.getUserClass(clazz);
+		return this.beanType;
 	}
 
 	/**
-	 * If the bean method is a bridge method, this method returns the bridged (user-defined) method.
-	 * Otherwise it returns the same method as {@link #getMethod()}.
+	 * If the bean method is a bridge method, this method returns the bridged
+	 * (user-defined) method. Otherwise it returns the same method as {@link #getMethod()}.
 	 */
 	protected Method getBridgedMethod() {
 		return this.bridgedMethod;
@@ -198,8 +204,8 @@ public class HandlerMethod {
 	}
 
 	/**
-	 * Returns a single annotation on the underlying method traversing its super methods if no
-	 * annotation can be found on the given method itself.
+	 * Returns a single annotation on the underlying method traversing its super methods
+	 * if no annotation can be found on the given method itself.
 	 * @param annotationType the type of annotation to introspect the method for.
 	 * @return the annotation, or {@code null} if none found
 	 */
@@ -208,8 +214,8 @@ public class HandlerMethod {
 	}
 
 	/**
-	 * If the provided instance contains a bean name rather than an object instance, the bean name is resolved
-	 * before a {@link HandlerMethod} is created and returned.
+	 * If the provided instance contains a bean name rather than an object instance,
+	 * the bean name is resolved before a {@link HandlerMethod} is created and returned.
 	 */
 	public HandlerMethod createWithResolvedBean() {
 		Object handler = this.bean;
@@ -220,26 +226,27 @@ public class HandlerMethod {
 		return new HandlerMethod(this, handler);
 	}
 
+	public String getShortLogMessage() {
+		int args = this.method.getParameterTypes().length;
+		return getBeanType().getName() + "#" + this.method.getName() + "[" + args + " args]";
+	}
+
+
 	@Override
-	public boolean equals(Object obj) {
-		if (this == obj) {
+	public boolean equals(Object other) {
+		if (this == other) {
 			return true;
 		}
-		if (obj != null && obj instanceof HandlerMethod) {
-			HandlerMethod other = (HandlerMethod) obj;
-			return this.bean.equals(other.bean) && this.method.equals(other.method);
+		if (!(other instanceof HandlerMethod)) {
+			return false;
 		}
-		return false;
+		HandlerMethod otherMethod = (HandlerMethod) other;
+		return (this.bean.equals(otherMethod.bean) && this.method.equals(otherMethod.method));
 	}
 
 	@Override
 	public int hashCode() {
-		return this.bean.hashCode() * 31 + this.method.hashCode();
-	}
-
-	public String getShortLogMessage() {
-		int args = method.getParameterTypes().length;
-		return getBeanType().getName() + "#" + this.method.getName() + "[" + args + " args]";
+		return (this.bean.hashCode() * 31 + this.method.hashCode());
 	}
 
 	@Override

spring-messaging/src/main/java/org/springframework/messaging/handler/invocation/AbstractMethodMessageHandler.java

@@ -30,7 +30,6 @@ import java.util.concurrent.ConcurrentHashMap;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
-import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.InitializingBean;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextAware;
@@ -159,7 +158,7 @@ public abstract class AbstractMethodMessageHandler<T>
 	/**
 	 * Configure the complete list of supported argument types effectively overriding
 	 * the ones configured by default. This is an advanced option. For most use cases
-	 * it should be sufficient to use {@link #setCustomArgumentResolvers(java.util.List)}.
+	 * it should be sufficient to use {@link #setCustomArgumentResolvers}.
 	 */
 	public void setArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
 		if (argumentResolvers == null) {
@@ -176,7 +175,7 @@ public abstract class AbstractMethodMessageHandler<T>
 	/**
 	 * Configure the complete list of supported return value types effectively overriding
 	 * the ones configured by default. This is an advanced option. For most use cases
-	 * it should be sufficient to use {@link #setCustomReturnValueHandlers(java.util.List)}
+	 * it should be sufficient to use {@link #setCustomReturnValueHandlers}.
 	 */
 	public void setReturnValueHandlers(List<HandlerMethodReturnValueHandler> returnValueHandlers) {
 		if (returnValueHandlers == null) {
@@ -198,7 +197,7 @@ public abstract class AbstractMethodMessageHandler<T>
 	}
 
 	@Override
-	public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
+	public void setApplicationContext(ApplicationContext applicationContext) {
 		this.applicationContext = applicationContext;
 	}
 
@@ -209,7 +208,6 @@ public abstract class AbstractMethodMessageHandler<T>
 
 	@Override
 	public void afterPropertiesSet() {
-
 		if (this.argumentResolvers.getResolvers().isEmpty()) {
 			this.argumentResolvers.addResolvers(initArgumentResolvers());
 		}
@@ -227,17 +225,17 @@ public abstract class AbstractMethodMessageHandler<T>
 
 	/**
 	 * Return the list of argument resolvers to use. Invoked only if the resolvers
-	 * have not already been set via {@link #setArgumentResolvers(java.util.List)}.
-	 * <p>Sub-classes should also take into account custom argument types configured via
-	 * {@link #setCustomArgumentResolvers(java.util.List)}.
+	 * have not already been set via {@link #setArgumentResolvers}.
+	 * <p>Subclasses should also take into account custom argument types configured via
+	 * {@link #setCustomArgumentResolvers}.
 	 */
 	protected abstract List<? extends HandlerMethodArgumentResolver> initArgumentResolvers();
 
 	/**
 	 * Return the list of return value handlers to use. Invoked only if the return
-	 * value handlers have not already been set via {@link #setReturnValueHandlers(java.util.List)}.
-	 * <p>Sub-classes should also take into account custom return value types configured
-	 * via {@link #setCustomReturnValueHandlers(java.util.List)}.
+	 * value handlers have not already been set via {@link #setReturnValueHandlers}.
+	 * <p>Subclasses should also take into account custom return value types configured
+	 * via {@link #setCustomReturnValueHandlers}.
 	 */
 	protected abstract List<? extends HandlerMethodReturnValueHandler> initReturnValueHandlers();
 
@@ -253,9 +251,8 @@ public abstract class AbstractMethodMessageHandler<T>
 	 * @param handler the handler to check, either an instance of a Spring bean name
 	 */
 	protected final void detectHandlerMethods(Object handler) {
-
-		Class<?> handlerType = (handler instanceof String) ?
-				this.applicationContext.getType((String) handler) : handler.getClass();
+		Class<?> handlerType = (handler instanceof String ?
+				this.applicationContext.getType((String) handler) : handler.getClass());
 
 		final Class<?> userType = ClassUtils.getUserClass(handlerType);
 
@@ -290,14 +287,13 @@ public abstract class AbstractMethodMessageHandler<T>
 	 * under the same mapping
 	 */
 	protected void registerHandlerMethod(Object handler, Method method, T mapping) {
-
 		HandlerMethod newHandlerMethod = createHandlerMethod(handler, method);
-		HandlerMethod oldHandlerMethod = handlerMethods.get(mapping);
+		HandlerMethod oldHandlerMethod = this.handlerMethods.get(mapping);
 
 		if (oldHandlerMethod != null && !oldHandlerMethod.equals(newHandlerMethod)) {
-			throw new IllegalStateException("Ambiguous mapping found. Cannot map '" + newHandlerMethod.getBean()
-					+ "' bean method \n" + newHandlerMethod + "\nto " + mapping + ": There is already '"
-					+ oldHandlerMethod.getBean() + "' bean method\n" + oldHandlerMethod + " mapped.");
+			throw new IllegalStateException("Ambiguous mapping found. Cannot map '" + newHandlerMethod.getBean() +
+					"' bean method \n" + newHandlerMethod + "\nto " + mapping + ": There is already '" +
+					oldHandlerMethod.getBean() + "' bean method\n" + oldHandlerMethod + " mapped.");
 		}
 
 		this.handlerMethods.put(mapping, newHandlerMethod);
@@ -318,7 +314,8 @@ public abstract class AbstractMethodMessageHandler<T>
 		HandlerMethod handlerMethod;
 		if (handler instanceof String) {
 			String beanName = (String) handler;
-			handlerMethod = new HandlerMethod(beanName, this.applicationContext, method);
+			handlerMethod = new HandlerMethod(beanName,
+					this.applicationContext.getAutowireCapableBeanFactory(), method);
 		}
 		else {
 			handlerMethod = new HandlerMethod(handler, method);
@@ -333,7 +330,7 @@ public abstract class AbstractMethodMessageHandler<T>
 	protected abstract Set<String> getDirectLookupDestinations(T mapping);
 
 	/**
-	 * Sub-classes can invoke this method to populate the MessagingAdviceBean cache
+	 * Subclasses can invoke this method to populate the MessagingAdviceBean cache
 	 * (e.g. to support "global" {@code @MessageExceptionHandler}).
 	 * @since 4.2
 	 */
@@ -505,9 +502,8 @@ public abstract class AbstractMethodMessageHandler<T>
 			}
 			this.returnValueHandlers.handleReturnValue(returnValue, returnType, message);
 		}
-		catch (Throwable t) {
-			logger.error("Error while handling exception", t);
-			return;
+		catch (Throwable ex2) {
+			logger.error("Error while processing handler method exception", ex2);
 		}
 	}
 

spring-web/src/main/java/org/springframework/web/method/HandlerMethod.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -30,9 +30,9 @@ import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 
 /**
- * Encapsulates information about a handler method consisting of a {@linkplain #getMethod() method}
- * and a {@linkplain #getBean() bean}. Provides convenient access to method parameters,
- * method return value, method annotations.
+ * Encapsulates information about a handler method consisting of a
+ * {@linkplain #getMethod() method} and a {@linkplain #getBean() bean}.
+ * Provides convenient access to method parameters, method return value, method annotations.
  *
  * <p>The class may be created with a bean instance or with a bean name (e.g. lazy-init bean,
  * prototype bean). Use {@link #createWithResolvedBean()} to obtain a {@link HandlerMethod}
@@ -40,17 +40,20 @@ import org.springframework.util.ClassUtils;
  *
  * @author Arjen Poutsma
  * @author Rossen Stoyanchev
+ * @author Juergen Hoeller
  * @since 3.1
  */
 public class HandlerMethod {
 
 	/** Logger that is available to subclasses */
-	protected final Log logger = LogFactory.getLog(HandlerMethod.class);
+	protected final Log logger = LogFactory.getLog(getClass());
 
 	private final Object bean;
 
 	private final BeanFactory beanFactory;
 
+	private final Class<?> beanType;
+
 	private final Method method;
 
 	private final Method bridgedMethod;
@@ -66,6 +69,7 @@ public class HandlerMethod {
 		Assert.notNull(method, "Method is required");
 		this.bean = bean;
 		this.beanFactory = null;
+		this.beanType = ClassUtils.getUserClass(bean);
 		this.method = method;
 		this.bridgedMethod = BridgeMethodResolver.findBridgedMethod(method);
 		this.parameters = initMethodParameters();
@@ -80,6 +84,7 @@ public class HandlerMethod {
 		Assert.notNull(methodName, "Method name is required");
 		this.bean = bean;
 		this.beanFactory = null;
+		this.beanType = ClassUtils.getUserClass(bean);
 		this.method = bean.getClass().getMethod(methodName, parameterTypes);
 		this.bridgedMethod = BridgeMethodResolver.findBridgedMethod(this.method);
 		this.parameters = initMethodParameters();
@@ -94,22 +99,22 @@ public class HandlerMethod {
 		Assert.hasText(beanName, "Bean name is required");
 		Assert.notNull(beanFactory, "BeanFactory is required");
 		Assert.notNull(method, "Method is required");
-		Assert.isTrue(beanFactory.containsBean(beanName),
-				"BeanFactory [" + beanFactory + "] does not contain bean [" + beanName + "]");
 		this.bean = beanName;
 		this.beanFactory = beanFactory;
+		this.beanType = ClassUtils.getUserClass(beanFactory.getType(beanName));
 		this.method = method;
 		this.bridgedMethod = BridgeMethodResolver.findBridgedMethod(method);
 		this.parameters = initMethodParameters();
 	}
 
 	/**
-	 * Copy constructor for use in sub-classes.
+	 * Copy constructor for use in subclasses.
 	 */
 	protected HandlerMethod(HandlerMethod handlerMethod) {
 		Assert.notNull(handlerMethod, "HandlerMethod is required");
 		this.bean = handlerMethod.bean;
 		this.beanFactory = handlerMethod.beanFactory;
+		this.beanType = handlerMethod.beanType;
 		this.method = handlerMethod.method;
 		this.bridgedMethod = handlerMethod.bridgedMethod;
 		this.parameters = handlerMethod.parameters;
@@ -123,6 +128,7 @@ public class HandlerMethod {
 		Assert.notNull(handler, "Handler object is required");
 		this.bean = handler;
 		this.beanFactory = handlerMethod.beanFactory;
+		this.beanType = handlerMethod.beanType;
 		this.method = handlerMethod.method;
 		this.bridgedMethod = handlerMethod.bridgedMethod;
 		this.parameters = handlerMethod.parameters;
@@ -153,18 +159,17 @@ public class HandlerMethod {
 	}
 
 	/**
-	 * Returns the type of the handler for this handler method.
-	 * Note that if the bean type is a CGLIB-generated class, the original, user-defined class is returned.
+	 * This method returns the type of the handler for this handler method.
+	 * <p>Note that if the bean type is a CGLIB-generated class, the original
+	 * user-defined class is returned.
 	 */
 	public Class<?> getBeanType() {
-		Class<?> clazz = (this.bean instanceof String ?
-				this.beanFactory.getType((String) this.bean) : this.bean.getClass());
-		return ClassUtils.getUserClass(clazz);
+		return this.beanType;
 	}
 
 	/**
-	 * If the bean method is a bridge method, this method returns the bridged (user-defined) method.
-	 * Otherwise it returns the same method as {@link #getMethod()}.
+	 * If the bean method is a bridge method, this method returns the bridged
+	 * (user-defined) method. Otherwise it returns the same method as {@link #getMethod()}.
 	 */
 	protected Method getBridgedMethod() {
 		return this.bridgedMethod;
@@ -199,8 +204,8 @@ public class HandlerMethod {
 	}
 
 	/**
-	 * Returns a single annotation on the underlying method traversing its super methods if no
-	 * annotation can be found on the given method itself.
+	 * Returns a single annotation on the underlying method traversing its super methods
+	 * if no annotation can be found on the given method itself.
 	 * @param annotationType the type of annotation to introspect the method for.
 	 * @return the annotation, or {@code null} if none found
 	 */
@@ -209,8 +214,8 @@ public class HandlerMethod {
 	}
 
 	/**
-	 * If the provided instance contains a bean name rather than an object instance, the bean name is resolved
-	 * before a {@link HandlerMethod} is created and returned.
+	 * If the provided instance contains a bean name rather than an object instance,
+	 * the bean name is resolved before a {@link HandlerMethod} is created and returned.
 	 */
 	public HandlerMethod createWithResolvedBean() {
 		Object handler = this.bean;
@@ -221,21 +226,22 @@ public class HandlerMethod {
 		return new HandlerMethod(this, handler);
 	}
 
+
 	@Override
-	public boolean equals(Object obj) {
-		if (this == obj) {
+	public boolean equals(Object other) {
+		if (this == other) {
 			return true;
 		}
-		if (obj != null && obj instanceof HandlerMethod) {
-			HandlerMethod other = (HandlerMethod) obj;
-			return (this.bean.equals(other.bean) && this.method.equals(other.method));
+		if (!(other instanceof HandlerMethod)) {
+			return false;
 		}
-		return false;
+		HandlerMethod otherMethod = (HandlerMethod) other;
+		return (this.bean.equals(otherMethod.bean) && this.method.equals(otherMethod.method));
 	}
 
 	@Override
 	public int hashCode() {
-		return this.bean.hashCode() * 31 + this.method.hashCode();
+		return (this.bean.hashCode() * 31 + this.method.hashCode());
 	}
 
 	@Override

spring-webmvc/src/main/java/org/springframework/web/servlet/handler/AbstractHandlerMethodMapping.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -40,8 +40,8 @@ import org.springframework.web.method.HandlerMethodSelector;
 import org.springframework.web.servlet.HandlerMapping;
 
 /**
- * Abstract base class for {@link HandlerMapping} implementations that define a
- * mapping between a request and a {@link HandlerMethod}.
+ * Abstract base class for {@link HandlerMapping} implementations that define
+ * a mapping between a request and a {@link HandlerMethod}.
  *
  * <p>For each registered handler method, a unique mapping is maintained with
  * subclasses defining the details of the mapping type {@code <T>}.
@@ -73,7 +73,6 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 
 	private HandlerMethodMappingNamingStrategy<T> namingStrategy;
 
-
 	private final Map<T, HandlerMethod> handlerMethods = new LinkedHashMap<T, HandlerMethod>();
 
 	private final MultiValueMap<String, T> urlMap = new LinkedMultiValueMap<String, T>();
@@ -96,8 +95,6 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 	/**
 	 * Configure the naming strategy to use for assigning a default name to every
 	 * mapped handler method.
-	 *
-	 * @param namingStrategy strategy to use.
 	 */
 	public void setHandlerMethodMappingNamingStrategy(HandlerMethodMappingNamingStrategy<T> namingStrategy) {
 		this.namingStrategy = namingStrategy;
@@ -118,6 +115,7 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 		return this.nameMap.get(mappingName);
 	}
 
+
 	/**
 	 * Detects handler methods at initialization.
 	 */
@@ -234,7 +232,6 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 	}
 
 	private void updateNameMap(String name, HandlerMethod newHandlerMethod) {
-
 		List<HandlerMethod> handlerMethods = this.nameMap.get(name);
 		if (handlerMethods != null) {
 			for (HandlerMethod handlerMethod : handlerMethods) {
@@ -266,7 +263,8 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 		HandlerMethod handlerMethod;
 		if (handler instanceof String) {
 			String beanName = (String) handler;
-			handlerMethod = new HandlerMethod(beanName, getApplicationContext(), method);
+			handlerMethod = new HandlerMethod(beanName,
+					getApplicationContext().getAutowireCapableBeanFactory(), method);
 		}
 		else {
 			handlerMethod = new HandlerMethod(handler, method);
@@ -375,7 +373,7 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 	 * Return a comparator for sorting matching mappings.
 	 * The returned comparator should sort 'better' matches higher.
 	 * @param request the current request
-	 * @return the comparator, never {@code null}
+	 * @return the comparator (never {@code null})
 	 */
 	protected abstract Comparator<T> getMappingComparator(HttpServletRequest request);