Disable Tomcat’s reference clearing

Closes gh-15101

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/tomcat/DisableReferenceClearingContextCustomizer.java

+/*
+ * Copyright 2012-2019 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.web.embedded.tomcat;
+
+import org.apache.catalina.Context;
+import org.apache.catalina.core.StandardContext;
+
+/**
+ * A {@link TomcatContextCustomizer} that disables Tomcat's reflective reference clearing
+ * to avoid reflective access warnings on Java 9 and later JVMs.
+ *
+ * @author Andy Wilkinson
+ */
+class DisableReferenceClearingContextCustomizer implements TomcatContextCustomizer {
+
+	@Override
+	public void customize(Context context) {
+		if (!(context instanceof StandardContext)) {
+			return;
+		}
+		StandardContext standardContext = (StandardContext) context;
+		try {
+			standardContext.setClearReferencesObjectStreamClassCaches(false);
+			standardContext.setClearReferencesRmiTargets(false);
+			standardContext.setClearReferencesThreadLocals(false);
+		}
+		catch (NoSuchMethodError ex) {
+			// Earlier version of Tomcat (probably without
+			// setClearReferencesThreadLocals). Continue.
+		}
+	}
+
+}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/tomcat/TomcatReactiveWebServerFactory.java

 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.
@@ -149,6 +149,7 @@ public class TomcatReactiveWebServerFactory extends AbstractReactiveWebServerFac
 	 */
 	protected void configureContext(Context context) {
 		this.contextLifecycleListeners.forEach(context::addLifecycleListener);
+		new DisableReferenceClearingContextCustomizer().customize(context);
 		this.tomcatContextCustomizers
 				.forEach((customizer) -> customizer.customize(context));
 	}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/tomcat/TomcatServletWebServerFactory.java

 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.
@@ -347,6 +347,7 @@ public class TomcatServletWebServerFactory extends AbstractServletWebServerFacto
 			context.addMimeMapping(mapping.getExtension(), mapping.getMimeType());
 		}
 		configureSession(context);
+		new DisableReferenceClearingContextCustomizer().customize(context);
 		for (TomcatContextCustomizer customizer : this.tomcatContextCustomizers) {
 			customizer.customize(context);
 		}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/embedded/tomcat/TomcatReactiveWebServerFactoryTests.java

 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.
@@ -23,6 +23,8 @@ import org.apache.catalina.LifecycleEvent;
 import org.apache.catalina.LifecycleListener;
 import org.apache.catalina.connector.Connector;
 import org.apache.catalina.core.AprLifecycleListener;
+import org.apache.catalina.core.StandardContext;
+import org.apache.catalina.startup.Tomcat;
 import org.apache.catalina.valves.RemoteIpValve;
 import org.junit.Test;
 import org.mockito.ArgumentCaptor;
@@ -138,4 +140,16 @@ public class TomcatReactiveWebServerFactoryTests
 		assertForwardHeaderIsUsed(factory);
 	}
 
+	@Test
+	public void referenceClearingIsDisabled() {
+		TomcatReactiveWebServerFactory factory = getFactory();
+		this.webServer = factory.getWebServer(mock(HttpHandler.class));
+		this.webServer.start();
+		Tomcat tomcat = ((TomcatWebServer) this.webServer).getTomcat();
+		StandardContext context = (StandardContext) tomcat.getHost().findChildren()[0];
+		assertThat(context.getClearReferencesObjectStreamClassCaches()).isFalse();
+		assertThat(context.getClearReferencesRmiTargets()).isFalse();
+		assertThat(context.getClearReferencesThreadLocals()).isFalse();
+	}
+
 }

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/embedded/tomcat/TomcatServletWebServerFactoryTests.java

 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.
@@ -451,6 +451,18 @@ public class TomcatServletWebServerFactoryTests
 		this.webServer.start();
 	}
 
+	@Test
+	public void referenceClearingIsDisabled() {
+		TomcatServletWebServerFactory factory = getFactory();
+		this.webServer = factory.getWebServer();
+		this.webServer.start();
+		Tomcat tomcat = ((TomcatWebServer) this.webServer).getTomcat();
+		StandardContext context = (StandardContext) tomcat.getHost().findChildren()[0];
+		assertThat(context.getClearReferencesObjectStreamClassCaches()).isFalse();
+		assertThat(context.getClearReferencesRmiTargets()).isFalse();
+		assertThat(context.getClearReferencesThreadLocals()).isFalse();
+	}
+
 	@Override
 	protected JspServlet getJspServlet() throws ServletException {
 		Tomcat tomcat = ((TomcatWebServer) this.webServer).getTomcat();