Prevent @Bean method overloading by default (with enforceUniqueMethods flag)

Closes gh-22609

spring-context/src/main/java/org/springframework/context/annotation/Configuration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -460,4 +460,16 @@ public @interface Configuration {
 	 */
 	boolean proxyBeanMethods() default true;
 
+	/**
+	 * Specify whether {@code @Bean} methods need to have unique method names,
+	 * raising an exception otherwise in order to prevent accidental overloading.
+	 * <p>The default is {@code true}, preventing accidental method overloads which
+	 * get interpreted as overloaded factory methods for the same bean definition
+	 * (as opposed to separate bean definitions with individual conditions etc).
+	 * Switch this flag to {@code false} in order to allow for method overloading
+	 * according to those semantics, accepting the risk for accidental overlaps.
+	 * @since 6.0
+	 */
+	boolean enforceUniqueMethods() default true;
+
 }

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClass.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -29,6 +29,7 @@ import org.springframework.beans.factory.support.BeanDefinitionReader;
 import org.springframework.core.io.DescriptiveResource;
 import org.springframework.core.io.Resource;
 import org.springframework.core.type.AnnotationMetadata;
+import org.springframework.core.type.MethodMetadata;
 import org.springframework.core.type.classreading.MetadataReader;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
@@ -210,8 +211,9 @@ final class ConfigurationClass {
 	}
 
 	void validate(ProblemReporter problemReporter) {
-		// A configuration class may not be final (CGLIB limitation) unless it declares proxyBeanMethods=false
 		Map<String, Object> attributes = this.metadata.getAnnotationAttributes(Configuration.class.getName());
+
+		// A configuration class may not be final (CGLIB limitation) unless it declares proxyBeanMethods=false
 		if (attributes != null && (Boolean) attributes.get("proxyBeanMethods")) {
 			if (this.metadata.isFinal()) {
 				problemReporter.error(new FinalConfigurationProblem());
@@ -220,6 +222,18 @@ final class ConfigurationClass {
 				beanMethod.validate(problemReporter);
 			}
 		}
+
+		// A configuration class may not contain overloaded bean methods unless it declares enforceUniqueMethods=false
+		if (attributes != null && (Boolean) attributes.get("enforceUniqueMethods")) {
+			Map<String, MethodMetadata> beanMethodsByName = new LinkedHashMap<>();
+			for (BeanMethod beanMethod : this.beanMethods) {
+				MethodMetadata current = beanMethod.getMetadata();
+				MethodMetadata existing = beanMethodsByName.put(current.getMethodName(), current);
+				if (existing != null && existing.getDeclaringClassName().equals(current.getDeclaringClassName())) {
+					problemReporter.error(new BeanMethodOverloadingProblem(existing.getMethodName()));
+				}
+			}
+		}
 	}
 
 	@Override
@@ -250,4 +264,19 @@ final class ConfigurationClass {
 		}
 	}
 
+
+	/**
+	 * Configuration classes are not allowed to contain overloaded bean methods
+	 * by default (as of 6.0).
+	 */
+	private class BeanMethodOverloadingProblem extends Problem {
+
+		BeanMethodOverloadingProblem(String methodName) {
+			super(String.format("@Configuration class '%s' contains overloaded @Bean methods with name '%s'. Use " +
+							"unique method names for separate bean definitions (with individual conditions etc) " +
+							"or switch '@Configuration.enforceUniqueMethods' to 'false'.",
+					getSimpleName(), methodName), new Location(getResource(), getMetadata()));
+		}
+	}
+
 }

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -967,8 +967,7 @@ class ConfigurationClassParser {
 
 		public Collection<SourceClass> getMemberClasses() throws IOException {
 			Object sourceToProcess = this.source;
-			if (sourceToProcess instanceof Class) {
+			if (sourceToProcess instanceof Class<?> sourceClass) {
-				Class<?> sourceClass = (Class<?>) sourceToProcess;
 				try {
 					Class<?>[] declaredClasses = sourceClass.getDeclaredClasses();
 					List<SourceClass> members = new ArrayList<>(declaredClasses.length);
@@ -1013,8 +1012,7 @@ class ConfigurationClassParser {
 
 		public Set<SourceClass> getInterfaces() throws IOException {
 			Set<SourceClass> result = new LinkedHashSet<>();
-			if (this.source instanceof Class) {
+			if (this.source instanceof Class<?> sourceClass) {
-				Class<?> sourceClass = (Class<?>) this.source;
 				for (Class<?> ifcClass : sourceClass.getInterfaces()) {
 					result.add(asSourceClass(ifcClass, DEFAULT_EXCLUSION_FILTER));
 				}
@@ -1029,8 +1027,7 @@ class ConfigurationClassParser {
 
 		public Set<SourceClass> getAnnotations() {
 			Set<SourceClass> result = new LinkedHashSet<>();
-			if (this.source instanceof Class) {
+			if (this.source instanceof Class<?> sourceClass) {
-				Class<?> sourceClass = (Class<?>) this.source;
 				for (Annotation ann : sourceClass.getDeclaredAnnotations()) {
 					Class<?> annType = ann.annotationType();
 					if (!annType.getName().startsWith("java")) {

spring-context/src/test/java/org/springframework/context/annotation/BeanMethodPolymorphismTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -41,7 +41,7 @@ public class BeanMethodPolymorphismTests {
 	@Test
 	public void beanMethodDetectedOnSuperClass() {
 		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(Config.class);
-		assertThat(ctx.getBean("testBean", TestBean.class)).isNotNull();
+		assertThat(ctx.getBean("testBean", BaseTestBean.class)).isNotNull();
 	}
 
 	@Test
@@ -51,7 +51,7 @@ public class BeanMethodPolymorphismTests {
 		ctx.setAllowBeanDefinitionOverriding(false);
 		ctx.refresh();
 		assertThat(ctx.getDefaultListableBeanFactory().containsSingleton("testBean")).isFalse();
-		assertThat(ctx.getBean("testBean", TestBean.class).toString()).isEqualTo("overridden");
+		assertThat(ctx.getBean("testBean", BaseTestBean.class).toString()).isEqualTo("overridden");
 		assertThat(ctx.getDefaultListableBeanFactory().containsSingleton("testBean")).isTrue();
 	}
 
@@ -62,7 +62,7 @@ public class BeanMethodPolymorphismTests {
 		ctx.setAllowBeanDefinitionOverriding(false);
 		ctx.refresh();
 		assertThat(ctx.getDefaultListableBeanFactory().containsSingleton("testBean")).isFalse();
-		assertThat(ctx.getBean("testBean", TestBean.class).toString()).isEqualTo("overridden");
+		assertThat(ctx.getBean("testBean", BaseTestBean.class).toString()).isEqualTo("overridden");
 		assertThat(ctx.getDefaultListableBeanFactory().containsSingleton("testBean")).isTrue();
 	}
 
@@ -73,7 +73,7 @@ public class BeanMethodPolymorphismTests {
 		ctx.setAllowBeanDefinitionOverriding(false);
 		ctx.refresh();
 		assertThat(ctx.getDefaultListableBeanFactory().containsSingleton("testBean")).isFalse();
-		assertThat(ctx.getBean("testBean", TestBean.class).toString()).isEqualTo("overridden");
+		assertThat(ctx.getBean("testBean", BaseTestBean.class).toString()).isEqualTo("overridden");
 		assertThat(ctx.getDefaultListableBeanFactory().containsSingleton("testBean")).isTrue();
 	}
 
@@ -84,7 +84,7 @@ public class BeanMethodPolymorphismTests {
 		ctx.setAllowBeanDefinitionOverriding(false);
 		ctx.refresh();
 		assertThat(ctx.getDefaultListableBeanFactory().containsSingleton("testBean")).isFalse();
-		assertThat(ctx.getBean("testBean", TestBean.class).toString()).isEqualTo("overridden");
+		assertThat(ctx.getBean("testBean", BaseTestBean.class).toString()).isEqualTo("overridden");
 		assertThat(ctx.getDefaultListableBeanFactory().containsSingleton("testBean")).isTrue();
 	}
 
@@ -171,7 +171,15 @@ public class BeanMethodPolymorphismTests {
 		ctx.register(AnnotationAwareAspectJAutoProxyCreator.class);
 		ctx.register(TestAdvisor.class);
 		ctx.refresh();
-		ctx.getBean("testBean", TestBean.class);
+		ctx.getBean("testBean", BaseTestBean.class);
+	}
+
+
+	static class BaseTestBean {
+	}
+
+
+	static class ExtendedTestBean extends BaseTestBean {
 	}
 
 
@@ -179,8 +187,8 @@ public class BeanMethodPolymorphismTests {
 	static class BaseConfig {
 
 		@Bean
-		public TestBean testBean() {
+		public BaseTestBean testBean() {
-			return new TestBean();
+			return new BaseTestBean();
 		}
 	}
 
@@ -195,8 +203,8 @@ public class BeanMethodPolymorphismTests {
 
 		@Bean @Lazy
 		@Override
-		public TestBean testBean() {
+		public BaseTestBean testBean() {
-			return new TestBean() {
+			return new BaseTestBean() {
 				@Override
 				public String toString() {
 					return "overridden";
@@ -206,10 +214,6 @@ public class BeanMethodPolymorphismTests {
 	}
 
 
-	static class ExtendedTestBean extends TestBean {
-	}
-
-
 	@Configuration
 	static class NarrowedOverridingConfig extends BaseConfig {
 
@@ -226,7 +230,7 @@ public class BeanMethodPolymorphismTests {
 	}
 
 
-	@Configuration
+	@Configuration(enforceUniqueMethods = false)
 	static class ConfigWithOverloading {
 
 		@Bean
@@ -241,7 +245,7 @@ public class BeanMethodPolymorphismTests {
 	}
 
 
-	@Configuration
+	@Configuration(enforceUniqueMethods = false)
 	static class ConfigWithOverloadingAndAdditionalMetadata {
 
 		@Bean @Lazy

spring-context/src/test/java/org/springframework/context/annotation/configuration/ConfigurationClassProcessingTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -626,7 +626,7 @@ public class ConfigurationClassProcessingTests {
 	}
 
 
-	@Configuration
+	@Configuration(enforceUniqueMethods = false)
 	public static class OverloadedBeanMismatch {
 
 		@Bean(name = "other")