Allow adding additional tld skip patterns

This commit improves `TomcatEmbeddedServletContainerFactory` so that tld
skip patterns can be set or added to an existing set. An additional
`server.tomcat.additional-tld-skip-patterns` is now being exposed to
easily add patterns via configuration.

Closes gh-5010

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

@@ -19,8 +19,10 @@ package org.springframework.boot.autoconfigure.web;
 import java.io.File;
 import java.net.InetAddress;
 import java.nio.charset.Charset;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
@@ -72,6 +74,7 @@ import org.springframework.boot.web.servlet.ServletContextInitializer;
 import org.springframework.context.EnvironmentAware;
 import org.springframework.core.Ordered;
 import org.springframework.core.env.Environment;
+import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -671,6 +674,13 @@ public class ServerProperties
 		 */
 		private int acceptCount = 0;
 
+		/**
+		 * Comma-separated list of additional patterns that match jars to ignore for
+		 * TLD scanning. The special '?' and '*' characters can be used in the pattern
+		 * to match one and only one character and zero or more characters respectively.
+		 */
+		private List<String> additionalTldSkipPatterns = new ArrayList<String>();
+
 		public int getMaxThreads() {
 			return this.maxThreads;
 		}
@@ -779,6 +789,14 @@ public class ServerProperties
 			this.acceptCount = acceptCount;
 		}
 
+		public List<String> getAdditionalTldSkipPatterns() {
+			return this.additionalTldSkipPatterns;
+		}
+
+		public void setAdditionalTldSkipPatterns(List<String> additionalTldSkipPatterns) {
+			this.additionalTldSkipPatterns = additionalTldSkipPatterns;
+		}
+
 		void customizeTomcat(ServerProperties serverProperties,
 				TomcatEmbeddedServletContainerFactory factory) {
 			if (getBasedir() != null) {
@@ -819,6 +837,9 @@ public class ServerProperties
 			if (this.acceptCount > 0) {
 				customizeAcceptCount(factory);
 			}
+			if (!ObjectUtils.isEmpty(this.additionalTldSkipPatterns)) {
+				factory.getTldSkipPatterns().addAll(this.additionalTldSkipPatterns);
+			}
 		}
 
 		private void customizeAcceptCount(TomcatEmbeddedServletContainerFactory factory) {

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

@@ -488,6 +488,32 @@ public class ServerPropertiesTests {
 		verify(container).setAccessLogRotate(false);
 	}
 
+	@Test
+	public void customTomcatTldSkip() {
+		Map<String, String> map = new HashMap<String, String>();
+		map.put("server.tomcat.additional-tld-skip-patterns", "foo.jar,bar.jar");
+		bindProperties(map);
+
+		testCustomTomcatTldSkip("foo.jar", "bar.jar");
+	}
+
+	@Test
+	public void customTomcatTldSkipAsList() {
+		Map<String, String> map = new HashMap<String, String>();
+		map.put("server.tomcat.additional-tld-skip-patterns[0]", "biz.jar");
+		map.put("server.tomcat.additional-tld-skip-patterns[1]", "bah.jar");
+		bindProperties(map);
+
+		testCustomTomcatTldSkip("biz.jar", "bah.jar");
+	}
+
+	private void testCustomTomcatTldSkip(String... expectedJars) {
+		TomcatEmbeddedServletContainerFactory container = new TomcatEmbeddedServletContainerFactory();
+		this.properties.customize(container);
+		assertThat(container.getTldSkipPatterns()).contains(expectedJars);
+		assertThat(container.getTldSkipPatterns()).contains("junit-*.jar", "spring-boot-*.jar");
+	}
+
 	@Test
 	public void defaultUseForwardHeadersUndertow() throws Exception {
 		UndertowEmbeddedServletContainerFactory container = spy(