Consistently use DefaultParameterNameDiscoverer.getSharedInstance()

This includes MethodParameter resolving getParameterName() by default now.
initParameterNameDiscovery(null) can be used to suppress such resolution.

Closes gh-36024

spring-aop/src/main/java/org/springframework/aop/aspectj/MethodInvocationProceedingJoinPoint.java

@@ -29,7 +29,6 @@ import org.jspecify.annotations.Nullable;
 
 import org.springframework.aop.ProxyMethodInvocation;
 import org.springframework.core.DefaultParameterNameDiscoverer;
-import org.springframework.core.ParameterNameDiscoverer;
 import org.springframework.util.Assert;
 
 /**
@@ -51,8 +50,6 @@ import org.springframework.util.Assert;
  */
 public class MethodInvocationProceedingJoinPoint implements ProceedingJoinPoint, JoinPoint.StaticPart {
 
-	private static final ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
-
 	private final ProxyMethodInvocation methodInvocation;
 
 	private @Nullable Object @Nullable [] args;
@@ -217,7 +214,7 @@ public class MethodInvocationProceedingJoinPoint implements ProceedingJoinPoint,
 		public @Nullable String @Nullable [] getParameterNames() {
 			@Nullable String[] parameterNames = this.parameterNames;
 			if (parameterNames == null) {
-				parameterNames = parameterNameDiscoverer.getParameterNames(getMethod());
+				parameterNames = DefaultParameterNameDiscoverer.getSharedInstance().getParameterNames(getMethod());
 				this.parameterNames = parameterNames;
 			}
 			return parameterNames;

spring-beans/src/main/java/org/springframework/beans/BeanUtils.java

@@ -45,7 +45,6 @@ import org.jspecify.annotations.Nullable;
 import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.KotlinDetector;
 import org.springframework.core.MethodParameter;
-import org.springframework.core.ParameterNameDiscoverer;
 import org.springframework.core.ResolvableType;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
@@ -72,9 +71,6 @@ import org.springframework.util.StringUtils;
  */
 public abstract class BeanUtils {
 
-	private static final ParameterNameDiscoverer parameterNameDiscoverer =
-			new DefaultParameterNameDiscoverer();
-
 	private static final Set<Class<?>> unknownEditorTypes =
 			Collections.newSetFromMap(new ConcurrentReferenceHashMap<>(64));
 
@@ -659,7 +655,8 @@ public abstract class BeanUtils {
 	@SuppressWarnings("NullAway") // Dataflow analysis limitation
 	public static @Nullable String[] getParameterNames(Constructor<?> ctor) {
 		ConstructorProperties cp = ctor.getAnnotation(ConstructorProperties.class);
-		@Nullable String[] paramNames = (cp != null ? cp.value() : parameterNameDiscoverer.getParameterNames(ctor));
+		@Nullable String[] paramNames = (cp != null ? cp.value() :
+				DefaultParameterNameDiscoverer.getSharedInstance().getParameterNames(ctor));
 		Assert.state(paramNames != null, () -> "Cannot resolve parameter names for constructor " + ctor);
 		int parameterCount = (KOTLIN_REFLECT_PRESENT && KotlinDelegate.hasDefaultConstructorMarker(ctor) ?
 				ctor.getParameterCount() - 1 : ctor.getParameterCount());

spring-context/src/main/java/org/springframework/cache/interceptor/CacheEvaluationContextFactory.java

@@ -39,21 +39,24 @@ class CacheEvaluationContextFactory {
 
 	private @Nullable Supplier<ParameterNameDiscoverer> parameterNameDiscoverer;
 
+
 	CacheEvaluationContextFactory(StandardEvaluationContext originalContext) {
 		this.originalContext = originalContext;
 	}
 
+
 	public void setParameterNameDiscoverer(Supplier<ParameterNameDiscoverer> parameterNameDiscoverer) {
 		this.parameterNameDiscoverer = parameterNameDiscoverer;
 	}
 
 	public ParameterNameDiscoverer getParameterNameDiscoverer() {
 		if (this.parameterNameDiscoverer == null) {
-			this.parameterNameDiscoverer = SingletonSupplier.of(new DefaultParameterNameDiscoverer());
+			this.parameterNameDiscoverer = SingletonSupplier.of(DefaultParameterNameDiscoverer.getSharedInstance());
 		}
 		return this.parameterNameDiscoverer.get();
 	}
 
+
 	/**
 	 * Creates a {@link CacheEvaluationContext} for the specified operation.
 	 * @param rootObject the {@code root} object to use for the context

spring-context/src/main/java/org/springframework/context/expression/CachedExpressionEvaluator.java

@@ -38,8 +38,6 @@ public abstract class CachedExpressionEvaluator {
 
 	private final SpelExpressionParser parser;
 
-	private final ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
-
 
 	/**
 	 * Create a new instance with the default {@link SpelExpressionParser}.
@@ -69,7 +67,7 @@ public abstract class CachedExpressionEvaluator {
 	 * @since 4.3
 	 */
 	protected ParameterNameDiscoverer getParameterNameDiscoverer() {
-		return this.parameterNameDiscoverer;
+		return DefaultParameterNameDiscoverer.getSharedInstance();
 	}
 
 	/**

spring-context/src/main/java/org/springframework/jmx/export/assembler/AbstractReflectiveMBeanInfoAssembler.java

@@ -183,7 +183,8 @@ public abstract class AbstractReflectiveMBeanInfoAssembler extends AbstractMBean
 
 	private boolean exposeClassDescriptor = false;
 
-	private @Nullable ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
+	private @Nullable ParameterNameDiscoverer parameterNameDiscoverer =
+			DefaultParameterNameDiscoverer.getSharedInstance();
 
 
 	/**
@@ -507,8 +508,8 @@ public abstract class AbstractReflectiveMBeanInfoAssembler extends AbstractMBean
 	 * @return the {@code MBeanParameterInfo} array
 	 */
 	protected MBeanParameterInfo[] getOperationParameters(Method method, String beanKey) {
-		ParameterNameDiscoverer paramNameDiscoverer = getParameterNameDiscoverer();
-		@Nullable String[] paramNames = (paramNameDiscoverer != null ? paramNameDiscoverer.getParameterNames(method) : null);
+		ParameterNameDiscoverer pnd = getParameterNameDiscoverer();
+		@Nullable String[] paramNames = (pnd != null ? pnd.getParameterNames(method) : null);
 		if (paramNames == null) {
 			return new MBeanParameterInfo[0];
 		}

spring-context/src/main/java/org/springframework/validation/beanvalidation/MethodValidationAdapter.java

@@ -87,7 +87,7 @@ public class MethodValidationAdapter implements MethodValidator {
 
 	private MessageCodesResolver messageCodesResolver = new DefaultMessageCodesResolver();
 
-	private ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
+	private ParameterNameDiscoverer parameterNameDiscoverer = DefaultParameterNameDiscoverer.getSharedInstance();
 
 	private ObjectNameResolver objectNameResolver = defaultObjectNameResolver;
 

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

@@ -16,6 +16,8 @@
 
 package org.springframework.core;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Default implementation of the {@link ParameterNameDiscoverer} strategy interface,
  * delegating to the Java 8 standard reflection mechanism.
@@ -37,6 +39,8 @@ public class DefaultParameterNameDiscoverer extends PrioritizedParameterNameDisc
 
 	private static final boolean KOTLIN_REFLECT_PRESENT = KotlinDetector.isKotlinReflectPresent();
 
+	private static volatile @Nullable DefaultParameterNameDiscoverer sharedInstance;
+
 
 	public DefaultParameterNameDiscoverer() {
 		if (KOTLIN_REFLECT_PRESENT) {
@@ -47,4 +51,25 @@ public class DefaultParameterNameDiscoverer extends PrioritizedParameterNameDisc
 		addDiscoverer(new StandardReflectionParameterNameDiscoverer());
 	}
 
+
+	/**
+	 * Return a shared default {@code ParameterNameDiscoverer} instance,
+	 * lazily building it once needed.
+	 * @return the shared {@code ParameterNameDiscoverer} instance
+	 * @since 7.0.3
+	 */
+	public static ParameterNameDiscoverer getSharedInstance() {
+		DefaultParameterNameDiscoverer pnd = sharedInstance;
+		if (pnd == null) {
+			synchronized (DefaultParameterNameDiscoverer.class) {
+				pnd = sharedInstance;
+				if (pnd == null) {
+					pnd = new DefaultParameterNameDiscoverer();
+					sharedInstance = pnd;
+				}
+			}
+		}
+		return pnd;
+	}
+
 }

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

@@ -89,7 +89,8 @@ public class MethodParameter {
 
 	private volatile Annotation @Nullable [] parameterAnnotations;
 
-	private volatile @Nullable ParameterNameDiscoverer parameterNameDiscoverer;
+	private volatile @Nullable ParameterNameDiscoverer parameterNameDiscoverer =
+			DefaultParameterNameDiscoverer.getSharedInstance();
 
 	volatile @Nullable String parameterName;
 
@@ -667,6 +668,10 @@ public class MethodParameter {
 	 * <p>This method does not actually try to retrieve the parameter name at
 	 * this point; it just allows discovery to happen when the application calls
 	 * {@link #getParameterName()} (if ever).
+	 * <p>Note: As of 7.0.3, a default parameter name discoverer is available.
+	 * This init method can be used to override the default discoverer or to
+	 * suppress discovery (passing {@code null}).
+	 * @see DefaultParameterNameDiscoverer#getSharedInstance()
 	 */
 	public void initParameterNameDiscovery(@Nullable ParameterNameDiscoverer parameterNameDiscoverer) {
 		this.parameterNameDiscoverer = parameterNameDiscoverer;

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

@@ -252,6 +252,12 @@ class MethodParameterTests {
 		assertThat(m3.getTypeIndexForCurrentLevel()).isEqualTo(3);
 	}
 
+	@Test
+	void parameterNames() {
+		assertThat(stringParameter.getParameterName()).isEqualTo("str");
+		assertThat(longParameter.getParameterName()).isEqualTo("lng");
+	}
+
 	@Test
 	void jspecifyNullableParameter() {
 		assertThat(jspecifyNullableParameter.isOptional()).isTrue();
@@ -272,7 +278,8 @@ class MethodParameterTests {
 		assertThat(springNonNullParameter.isOptional()).isFalse();
 	}
 
-	public int method(String p1, long p2) {
+
+	public int method(String str, long lng) {
 		return 42;
 	}
 

spring-core/src/test/kotlin/org/springframework/core/MethodParameterKotlinTests.kt

@@ -117,21 +117,18 @@ class MethodParameterKotlinTests {
 	@Test
 	fun `Parameter name for regular function`() {
 		val methodParameter = returnMethodParameter("nullable", 0)
-		methodParameter.initParameterNameDiscovery(KotlinReflectionParameterNameDiscoverer())
 		assertThat(methodParameter.getParameterName()).isEqualTo("nullable")
 	}
 
 	@Test
 	fun `Parameter name for suspending function`() {
 		val methodParameter = returnMethodParameter("suspendFun", 0)
-		methodParameter.initParameterNameDiscovery(KotlinReflectionParameterNameDiscoverer())
 		assertThat(methodParameter.getParameterName()).isEqualTo("p1")
 	}
 
 	@Test
 	fun `Continuation parameter name for suspending function`() {
 		val methodParameter = returnMethodParameter("suspendFun", 1)
-		methodParameter.initParameterNameDiscovery(KotlinReflectionParameterNameDiscoverer())
 		assertThat(methodParameter.getParameterName()).isNull()
 	}
 

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

@@ -47,7 +47,7 @@ public class InvocableHandlerMethod extends HandlerMethod {
 
 	private HandlerMethodArgumentResolverComposite resolvers = new HandlerMethodArgumentResolverComposite();
 
-	private ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
+	private ParameterNameDiscoverer parameterNameDiscoverer = DefaultParameterNameDiscoverer.getSharedInstance();
 
 
 	/**

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

@@ -55,7 +55,7 @@ public class InvocableHandlerMethod extends HandlerMethod {
 
 	private final HandlerMethodArgumentResolverComposite resolvers = new HandlerMethodArgumentResolverComposite();
 
-	private ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
+	private ParameterNameDiscoverer parameterNameDiscoverer = DefaultParameterNameDiscoverer.getSharedInstance();
 
 	private ReactiveAdapterRegistry reactiveAdapterRegistry = ReactiveAdapterRegistry.getSharedInstance();
 

spring-messaging/src/main/java/org/springframework/messaging/rsocket/service/RSocketServiceMethod.java

@@ -30,7 +30,6 @@ import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
-import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.KotlinDetector;
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ParameterizedTypeReference;
@@ -90,11 +89,9 @@ final class RSocketServiceMethod {
 			count -= 1;
 		}
 
-		DefaultParameterNameDiscoverer nameDiscoverer = new DefaultParameterNameDiscoverer();
 		MethodParameter[] parameters = new MethodParameter[count];
 		for (int i = 0; i < count; i++) {
 			parameters[i] = new SynthesizingMethodParameter(method, i);
-			parameters[i].initParameterNameDiscovery(nameDiscoverer);
 		}
 		return parameters;
 	}

spring-web/src/main/java/org/springframework/web/method/support/InvocableHandlerMethod.java

@@ -71,7 +71,7 @@ public class InvocableHandlerMethod extends HandlerMethod {
 
 	private HandlerMethodArgumentResolverComposite resolvers = new HandlerMethodArgumentResolverComposite();
 
-	private ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
+	private ParameterNameDiscoverer parameterNameDiscoverer = DefaultParameterNameDiscoverer.getSharedInstance();
 
 	private @Nullable WebDataBinderFactory dataBinderFactory;
 

spring-web/src/main/java/org/springframework/web/service/invoker/HttpServiceMethod.java

@@ -30,7 +30,6 @@ import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
-import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.KotlinDetector;
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ParameterizedTypeReference;
@@ -115,11 +114,9 @@ final class HttpServiceMethod {
 			count -= 1;
 		}
 
-		DefaultParameterNameDiscoverer nameDiscoverer = new DefaultParameterNameDiscoverer();
 		MethodParameter[] parameters = new MethodParameter[count];
 		for (int i = 0; i < count; i++) {
 			parameters[i] = new SynthesizingMethodParameter(method, i);
-			parameters[i].initParameterNameDiscovery(nameDiscoverer);
 		}
 		return parameters;
 	}

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java

@@ -90,7 +90,7 @@ public class InvocableHandlerMethod extends HandlerMethod {
 
 	private final HandlerMethodArgumentResolverComposite resolvers = new HandlerMethodArgumentResolverComposite();
 
-	private ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
+	private ParameterNameDiscoverer parameterNameDiscoverer = DefaultParameterNameDiscoverer.getSharedInstance();
 
 	private ReactiveAdapterRegistry reactiveAdapterRegistry = ReactiveAdapterRegistry.getSharedInstance();
 

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

@@ -605,14 +605,15 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 				HandlerMethod handlerMethod = createHandlerMethod(handler, method);
 				validateMethodMapping(handlerMethod, mapping);
 
-				Set<String> directPaths = AbstractHandlerMethodMapping.this.getDirectPaths(mapping);
+				Set<String> directPaths = getDirectPaths(mapping);
 				for (String path : directPaths) {
 					this.pathLookup.add(path, mapping);
 				}
 
 				String name = null;
-				if (getNamingStrategy() != null) {
-					name = getNamingStrategy().getName(handlerMethod, mapping);
+				HandlerMethodMappingNamingStrategy<T> namingStrategy = getNamingStrategy();
+				if (namingStrategy != null) {
+					name = namingStrategy.getName(handlerMethod, mapping);
 					addMappingName(name, handlerMethod);
 				}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/MvcUriComponentsBuilder.java

@@ -40,10 +40,8 @@ import org.springframework.cglib.proxy.Enhancer;
 import org.springframework.cglib.proxy.Factory;
 import org.springframework.cglib.proxy.MethodInterceptor;
 import org.springframework.cglib.proxy.MethodProxy;
-import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.MethodIntrospector;
 import org.springframework.core.MethodParameter;
-import org.springframework.core.ParameterNameDiscoverer;
 import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.core.annotation.AnnotatedMethod;
 import org.springframework.objenesis.ObjenesisException;
@@ -112,8 +110,6 @@ public class MvcUriComponentsBuilder {
 
 	private static final PathMatcher pathMatcher = new AntPathMatcher();
 
-	private static final ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
-
 	private static final CompositeUriComponentsContributor defaultUriComponentsContributor;
 
 	static {
@@ -608,7 +604,6 @@ public class MvcUriComponentsBuilder {
 		final Map<String, Object> uriVars = new HashMap<>();
 		for (int i = 0; i < paramCount; i++) {
 			MethodParameter param = annotatedMethod.getMethodParameters()[i];
-			param.initParameterNameDiscovery(parameterNameDiscoverer);
 			contributor.contributeMethodArgument(param, args[i], builder, uriVars);
 		}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerAdapter.java

@@ -187,7 +187,7 @@ public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
 
 	private SessionAttributeStore sessionAttributeStore = new DefaultSessionAttributeStore();
 
-	private ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
+	private ParameterNameDiscoverer parameterNameDiscoverer = DefaultParameterNameDiscoverer.getSharedInstance();
 
 	private @Nullable ConfigurableBeanFactory beanFactory;