Provide Reactor 3 auto-configuration

This commit provides auto-configuration for the Reactor Core 3 library.
A new configuration namespace, "spring.reactor" allows to configure
hooks on operators, like "spring.reactor.stacktrace-mode.enabled".

This property is enabled automatically by devtools, since it improves
the developer experience and provides full stacktrace information when
exceptions occur (but at a performance cost).

Fixes gh-7302

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/reactor/core/ReactorCoreAutoConfiguration.java

+/*
+ * Copyright 2012-2017 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.autoconfigure.reactor.core;
+
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Hooks;
+import reactor.core.publisher.Mono;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * {@link EnableAutoConfiguration Auto-configuration} for Reactor Core.
+ *
+ * @author Brian Clozel
+ */
+@Configuration
+@ConditionalOnClass({Mono.class, Flux.class})
+@EnableConfigurationProperties(ReactorCoreProperties.class)
+public class ReactorCoreAutoConfiguration {
+
+	@Autowired
+	protected void initialize(ReactorCoreProperties properties) {
+		if (properties.getStacktraceMode().isEnabled()) {
+			Hooks.onOperator(h -> h.operatorStacktrace());
+		}
+	}
+
+}

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/reactor/core/ReactorCoreProperties.java

+/*
+ * Copyright 2012-2017 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.autoconfigure.reactor.core;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+
+/**
+ * Properties for Reactor Core.
+ *
+ * @author Brian Clozel
+ * @since 2.0.0
+ */
+@ConfigurationProperties(prefix = "spring.reactor")
+public class ReactorCoreProperties {
+
+	private final StacktraceMode stacktraceMode = new StacktraceMode();
+
+	public StacktraceMode getStacktraceMode() {
+		return this.stacktraceMode;
+	}
+
+	public static class StacktraceMode {
+
+		/**
+		 * Set whether Reactor should collect stacktrace information at runtime.
+		 */
+		private boolean enabled;
+
+		public boolean isEnabled() {
+			return this.enabled;
+		}
+
+		public void setEnabled(boolean enabled) {
+			this.enabled = enabled;
+		}
+	}
+}

spring-boot-autoconfigure/src/main/resources/META-INF/spring.factories

@@ -85,6 +85,7 @@ org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfigura
 org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
 org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
 org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
+org.springframework.boot.autoconfigure.reactor.core.ReactorCoreAutoConfiguration,\
 org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration,\
 org.springframework.boot.autoconfigure.security.SecurityFilterAutoConfiguration,\
 org.springframework.boot.autoconfigure.security.FallbackWebSecurityAutoConfiguration,\

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/env/DevToolsPropertyDefaultsPostProcessor.java

 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 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.
@@ -57,6 +57,7 @@ public class DevToolsPropertyDefaultsPostProcessor implements EnvironmentPostPro
 		properties.put("spring.template.provider.cache", "false");
 		properties.put("spring.mvc.log-resolved-exception", "true");
 		properties.put("server.jsp-servlet.init-parameters.development", "true");
+		properties.put("spring.reactor.stacktrace-mode.enabled", "true");
 		PROPERTIES = Collections.unmodifiableMap(properties);
 	}
 

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -119,6 +119,9 @@ content into your application; rather pick only the properties that you need.
 	spring.messages.encoding=UTF-8 # Message bundles encoding.
 	spring.messages.fallback-to-system-locale=true # Set whether to fall back to the system Locale if no files for a specific Locale have been found.
 
+	# REACTOR
+	spring.reactor.stacktrace-mode.enabled=true # Set whether Reactor should collect stacktrace information at runtime.
+
 	# OUTPUT
 	spring.output.ansi.enabled=detect # Configure the ANSI output.