Always initialize stompWebSocketHandlerMapping eagerly

Previously, when lazy initialization was enabled, STOMP-based WebSocket
messaging would not work as the stompWebSocketHandlerMapping bean was
not initialized and CONNECT requests would go unanswered.

This commit adds a LazyInitializationExcludeFilter that causes the
stompWebSocketHandlerMapping bean to always be initialized eagerly.
This triggers initialization of the WebSocket transport allowing
requests to be received and processed.

Fixes gh-19611

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/websocket/servlet/WebSocketMessagingAutoConfiguration.java

 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -20,6 +20,7 @@ import java.util.List;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 
+import org.springframework.boot.LazyInitializationExcludeFilter;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
@@ -27,6 +28,7 @@ import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication.Type;
 import org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration;
+import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.messaging.converter.ByteArrayMessageConverter;
 import org.springframework.messaging.converter.DefaultContentTypeResolver;
@@ -74,6 +76,11 @@ public class WebSocketMessagingAutoConfiguration {
 			return false;
 		}
 
+		@Bean
+		static LazyInitializationExcludeFilter eagerStompWebSocketHandlerMapping() {
+			return (name, definition, type) -> name.equals("stompWebSocketHandlerMapping");
+		}
+
 	}
 
 }

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/websocket/servlet/WebSocketMessagingAutoConfigurationTests.java

 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -31,6 +31,7 @@ import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+import org.springframework.boot.LazyInitializationBeanFactoryPostProcessor;
 import org.springframework.boot.autoconfigure.ImportAutoConfiguration;
 import org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration;
 import org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration;
@@ -108,6 +109,13 @@ class WebSocketMessagingAutoConfigurationTests {
 		assertThat(new String((byte[]) result)).isEqualTo("string data");
 	}
 
+	@Test
+	void whenLazyInitializationIsEnabledThenBasicMessagingWorks() throws Throwable {
+		this.context.register(LazyInitializationBeanFactoryPostProcessor.class);
+		Object result = performStompSubscription("/app/string");
+		assertThat(new String((byte[]) result)).isEqualTo("string data");
+	}
+
 	@Test
 	void customizedConverterTypesMatchDefaultConverterTypes() {
 		List<MessageConverter> customizedConverters = getCustomizedConverters();
@@ -190,7 +198,7 @@ class WebSocketMessagingAutoConfigurationTests {
 		stompClient.connect("ws://localhost:{port}/messaging", handler,
 				this.context.getEnvironment().getProperty("local.server.port"));
 
-		if (!latch.await(30000, TimeUnit.SECONDS)) {
+		if (!latch.await(30, TimeUnit.SECONDS)) {
 			if (failure.get() != null) {
 				throw failure.get();
 			}