Reject multiple @⁠HttpExchange declarations in HTTP interface clients

This commit updates HttpServiceMethod so that multiple @⁠HttpExchange
declarations on the same element (class or method) are rejected.

Closes gh-32049

spring-web/src/test/java/org/springframework/web/service/invoker/HttpServiceMethodTests.java

@@ -16,6 +16,11 @@
 
 package org.springframework.web.service.invoker;
 
+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 java.util.List;
 import java.util.Optional;
 
@@ -37,8 +42,10 @@ import org.springframework.lang.Nullable;
 import org.springframework.web.service.annotation.GetExchange;
 import org.springframework.web.service.annotation.HttpExchange;
 import org.springframework.web.service.annotation.PostExchange;
+import org.springframework.web.service.annotation.PutExchange;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 import static org.springframework.http.MediaType.APPLICATION_CBOR_VALUE;
 import static org.springframework.http.MediaType.APPLICATION_JSON_VALUE;
 
@@ -52,6 +59,7 @@ import static org.springframework.http.MediaType.APPLICATION_JSON_VALUE;
  *
  * @author Rossen Stoyanchev
  * @author Olga Maciaszek-Sharma
+ * @author Sam Brannen
  */
 class HttpServiceMethodTests {
 
@@ -204,6 +212,33 @@ class HttpServiceMethodTests {
 		assertThat(requestValues.getHeaders().getAccept()).containsExactly(MediaType.APPLICATION_JSON);
 	}
 
+	@Test  // gh-32049
+	void multipleAnnotationsAtClassLevel() {
+		Class<?> serviceInterface = MultipleClassLevelAnnotationsService.class;
+
+		assertThatIllegalStateException()
+				.isThrownBy(() -> this.proxyFactory.createClient(serviceInterface))
+				.withMessageContainingAll(
+					"Multiple @HttpExchange annotations found on " + serviceInterface,
+					"@" + HttpExchange.class.getName(),
+					"@" + ExtraHttpExchange.class.getName()
+				);
+	}
+
+	@Test  // gh-32049
+	void multipleAnnotationsAtMethodLevel() throws NoSuchMethodException {
+		Class<?> serviceInterface = MultipleMethodLevelAnnotationsService.class;
+		Method method = serviceInterface.getMethod("post");
+
+		assertThatIllegalStateException()
+				.isThrownBy(() -> this.proxyFactory.createClient(serviceInterface))
+				.withMessageContainingAll(
+					"Multiple @HttpExchange annotations found on method " + method,
+					"@" + PostExchange.class.getName(),
+					"@" + PutExchange.class.getName()
+				);
+	}
+
 	protected void verifyReactorClientInvocation(String methodName, @Nullable ParameterizedTypeReference<?> expectedBodyType) {
 		assertThat(this.reactorClient.getInvokedMethodName()).isEqualTo(methodName);
 		assertThat(this.reactorClient.getBodyType()).isEqualTo(expectedBodyType);
@@ -305,9 +340,34 @@ class HttpServiceMethodTests {
 
 	}
 
+
 	@SuppressWarnings("unused")
 	@HttpExchange(url = "${baseUrl}", contentType = APPLICATION_CBOR_VALUE, accept = APPLICATION_CBOR_VALUE)
 	private interface TypeAndMethodLevelAnnotatedService extends MethodLevelAnnotatedService {
 	}
 
+
+	@HttpExchange("/exchange")
+	@ExtraHttpExchange
+	private interface MultipleClassLevelAnnotationsService {
+
+		@PostExchange("/post")
+		void post();
+	}
+
+
+	private interface MultipleMethodLevelAnnotationsService {
+
+		@PostExchange("/post")
+		@PutExchange("/post")
+		void post();
+	}
+
+
+	@HttpExchange
+	@Target(ElementType.TYPE)
+	@Retention(RetentionPolicy.RUNTIME)
+	private @interface ExtraHttpExchange {
+	}
+
 }