Make Tomcat Access Log's buffering configurable via the environment

Closes gh-7456

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ServerProperties.java

@@ -1005,6 +1005,7 @@ public class ServerProperties
 			valve.setRequestAttributesEnabled(
 					this.accesslog.isRequestAttributesEnabled());
 			valve.setRotatable(this.accesslog.isRotate());
+			valve.setBuffered(this.accesslog.isBuffered());
 			factory.addEngineValves(valve);
 		}
 
@@ -1065,6 +1066,11 @@ public class ServerProperties
 			 */
 			private boolean requestAttributesEnabled;
 
+			/**
+			 * Buffer output such that it is only flushed periodically.
+			 */
+			private boolean buffered = true;
+
 			public boolean isEnabled() {
 				return this.enabled;
 			}
@@ -1129,6 +1135,14 @@ public class ServerProperties
 				this.requestAttributesEnabled = requestAttributesEnabled;
 			}
 
+			public boolean isBuffered() {
+				return this.buffered;
+			}
+
+			public void setBuffered(boolean buffered) {
+				this.buffered = buffered;
+			}
+
 		}
 
 	}

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/ServerPropertiesTests.java

@@ -31,6 +31,7 @@ import javax.servlet.SessionTrackingMode;
 
 import org.apache.catalina.Context;
 import org.apache.catalina.Valve;
+import org.apache.catalina.valves.AccessLogValve;
 import org.apache.catalina.valves.RemoteIpValve;
 import org.apache.coyote.AbstractProtocol;
 import org.junit.Before;
@@ -140,6 +141,48 @@ public class ServerPropertiesTests {
 		assertThat(this.properties.getServletPrefix()).isEqualTo("/foo");
 	}
 
+	@Test
+	public void tomcatAccessLogIsDisabledByDefault() {
+		TomcatEmbeddedServletContainerFactory tomcatContainer = new TomcatEmbeddedServletContainerFactory();
+		this.properties.customize(tomcatContainer);
+		assertThat(tomcatContainer.getEngineValves()).isEmpty();
+	}
+
+	@Test
+	public void tomcatAccessLogCanBeEnabled() {
+		TomcatEmbeddedServletContainerFactory tomcatContainer = new TomcatEmbeddedServletContainerFactory();
+		Map<String, String> map = new HashMap<String, String>();
+		map.put("server.tomcat.accesslog.enabled", "true");
+		bindProperties(map);
+		this.properties.customize(tomcatContainer);
+		assertThat(tomcatContainer.getEngineValves()).hasSize(1);
+		assertThat(tomcatContainer.getEngineValves()).first()
+				.isInstanceOf(AccessLogValve.class);
+	}
+
+	@Test
+	public void tomcatAccessLogIsBufferedByDefault() {
+		TomcatEmbeddedServletContainerFactory tomcatContainer = new TomcatEmbeddedServletContainerFactory();
+		Map<String, String> map = new HashMap<String, String>();
+		map.put("server.tomcat.accesslog.enabled", "true");
+		bindProperties(map);
+		this.properties.customize(tomcatContainer);
+		assertThat(((AccessLogValve) tomcatContainer.getEngineValves().iterator().next())
+				.isBuffered()).isTrue();
+	}
+
+	@Test
+	public void tomcatAccessLogBufferingCanBeDisabled() {
+		TomcatEmbeddedServletContainerFactory tomcatContainer = new TomcatEmbeddedServletContainerFactory();
+		Map<String, String> map = new HashMap<String, String>();
+		map.put("server.tomcat.accesslog.enabled", "true");
+		map.put("server.tomcat.accesslog.buffered", "false");
+		bindProperties(map);
+		this.properties.customize(tomcatContainer);
+		assertThat(((AccessLogValve) tomcatContainer.getEngineValves().iterator().next())
+				.isBuffered()).isFalse();
+	}
+
 	@Test
 	public void testTomcatBinding() throws Exception {
 		Map<String, String> map = new HashMap<String, String>();