Improve Tomcat performance when using nested jars

Add `NestedJarResourceSet` which can be used for nested jar URLs
and unlike the standard Tomcat implementation does not assume that
the JAR is backed by a single file.

Closes gh-37452

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

@@ -0,0 +1,161 @@
+/*
+ * Copyright 2012-2023 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
+ *
+ *      https://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 java.io.IOException;
+import java.net.JarURLConnection;
+import java.net.URL;
+import java.net.URLConnection;
+import java.util.jar.Attributes;
+import java.util.jar.Attributes.Name;
+import java.util.jar.JarEntry;
+import java.util.jar.JarFile;
+import java.util.jar.Manifest;
+
+import org.apache.catalina.LifecycleException;
+import org.apache.catalina.WebResource;
+import org.apache.catalina.WebResourceRoot;
+import org.apache.catalina.WebResourceSet;
+import org.apache.catalina.webresources.AbstractSingleArchiveResourceSet;
+import org.apache.catalina.webresources.JarResource;
+
+import org.springframework.util.Assert;
+import org.springframework.util.ResourceUtils;
+
+/**
+ * A {@link WebResourceSet} for a resource in a nested JAR.
+ *
+ * @author Phillip Webb
+ */
+class NestedJarResourceSet extends AbstractSingleArchiveResourceSet {
+
+	private static final Name MULTI_RELEASE = new Name("Multi-Release");
+
+	private final URL url;
+
+	private JarFile archive = null;
+
+	private long archiveUseCount = 0;
+
+	private boolean useCaches;
+
+	private volatile Boolean multiRelease;
+
+	NestedJarResourceSet(URL url, WebResourceRoot root, String webAppMount, String internalPath)
+			throws IllegalArgumentException {
+		this.url = url;
+		setRoot(root);
+		setWebAppMount(webAppMount);
+		setInternalPath(internalPath);
+		setStaticOnly(true);
+		if (getRoot().getState().isAvailable()) {
+			try {
+				start();
+			}
+			catch (LifecycleException ex) {
+				throw new IllegalStateException(ex);
+			}
+		}
+	}
+
+	@Override
+	protected WebResource createArchiveResource(JarEntry jarEntry, String webAppPath, Manifest manifest) {
+		return new JarResource(this, webAppPath, getBaseUrlString(), jarEntry);
+	}
+
+	@Override
+	protected void initInternal() throws LifecycleException {
+		try {
+			JarURLConnection connection = connect();
+			try {
+				setManifest(connection.getManifest());
+				setBaseUrl(connection.getJarFileURL());
+			}
+			finally {
+				if (!connection.getUseCaches()) {
+					connection.getJarFile().close();
+				}
+			}
+		}
+		catch (IOException ex) {
+			throw new IllegalStateException(ex);
+		}
+	}
+
+	@Override
+	protected JarFile openJarFile() throws IOException {
+		synchronized (this.archiveLock) {
+			if (this.archive == null) {
+				JarURLConnection connection = connect();
+				this.useCaches = connection.getUseCaches();
+				this.archive = connection.getJarFile();
+			}
+			this.archiveUseCount++;
+			return this.archive;
+		}
+	}
+
+	@Override
+	protected void closeJarFile() {
+		synchronized (this.archiveLock) {
+			this.archiveUseCount--;
+		}
+	}
+
+	@Override
+	protected boolean isMultiRelease() {
+		if (this.multiRelease == null) {
+			synchronized (this.archiveLock) {
+				if (this.multiRelease == null) {
+					// JarFile.isMultiRelease() is final so we must go to the manifest
+					Manifest manifest = getManifest();
+					Attributes attributes = (manifest != null) ? manifest.getMainAttributes() : null;
+					this.multiRelease = (attributes != null) ? attributes.containsKey(MULTI_RELEASE) : false;
+				}
+			}
+		}
+		return this.multiRelease.booleanValue();
+	}
+
+	@Override
+	public void gc() {
+		synchronized (this.archiveLock) {
+			if (this.archive != null && this.archiveUseCount == 0) {
+				try {
+					if (!this.useCaches) {
+						this.archive.close();
+					}
+				}
+				catch (IOException ex) {
+					// Ignore
+				}
+				this.archive = null;
+				this.archiveEntries = null;
+			}
+		}
+	}
+
+	private JarURLConnection connect() throws IOException {
+		URLConnection connection = this.url.openConnection();
+		ResourceUtils.useCachesIfNecessary(connection);
+		Assert.state(connection instanceof JarURLConnection,
+				() -> "URL '%s' did not return a JAR connection".formatted(this.url));
+		connection.connect();
+		return (JarURLConnection) connection;
+	}
+
+}

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

@@ -19,6 +19,7 @@ package org.springframework.boot.web.embedded.tomcat;
 import java.io.File;
 import java.io.InputStream;
 import java.lang.reflect.Method;
+import java.net.MalformedURLException;
 import java.net.URL;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
@@ -46,6 +47,7 @@ import org.apache.catalina.LifecycleListener;
 import org.apache.catalina.Manager;
 import org.apache.catalina.Valve;
 import org.apache.catalina.WebResource;
+import org.apache.catalina.WebResourceRoot;
 import org.apache.catalina.WebResourceRoot.ResourceSetType;
 import org.apache.catalina.WebResourceSet;
 import org.apache.catalina.Wrapper;
@@ -772,6 +774,10 @@ public class TomcatServletWebServerFactory extends AbstractServletWebServerFacto
 
 	private final class StaticResourceConfigurer implements LifecycleListener {
 
+		private static final String WEB_APP_MOUNT = "/";
+
+		private static final String INTERNAL_PATH = "/META-INF/resources";
+
 		private final Context context;
 
 		private StaticResourceConfigurer(Context context) {
@@ -804,23 +810,39 @@ public class TomcatServletWebServerFactory extends AbstractServletWebServerFacto
 
 		private void addResourceSet(String resource) {
 			try {
-				if (isInsideNestedJar(resource)) {
-					// It's a nested jar but we now don't want the suffix because Tomcat
-					// is going to try and locate it as a root URL (not the resource
-					// inside it)
-					resource = resource.substring(0, resource.length() - 2);
+				if (isInsideClassicNestedJar(resource)) {
+					addClassicNestedResourceSet(resource);
+					return;
 				}
+				WebResourceRoot root = this.context.getResources();
 				URL url = new URL(resource);
-				String path = "/META-INF/resources";
-				this.context.getResources().createWebResourceSet(ResourceSetType.RESOURCE_JAR, "/", url, path);
+				if (isInsideNestedJar(resource)) {
+					root.addJarResources(new NestedJarResourceSet(url, root, WEB_APP_MOUNT, INTERNAL_PATH));
+				}
+				else {
+					root.createWebResourceSet(ResourceSetType.RESOURCE_JAR, WEB_APP_MOUNT, url, INTERNAL_PATH);
+				}
 			}
 			catch (Exception ex) {
 				// Ignore (probably not a directory)
 			}
 		}
 
-		private boolean isInsideNestedJar(String dir) {
-			return dir.indexOf("!/") < dir.lastIndexOf("!/");
+		private void addClassicNestedResourceSet(String resource) throws MalformedURLException {
+			// It's a nested jar but we now don't want the suffix because Tomcat
+			// is going to try and locate it as a root URL (not the resource
+			// inside it)
+			URL url = new URL(resource.substring(0, resource.length() - 2));
+			this.context.getResources()
+				.createWebResourceSet(ResourceSetType.RESOURCE_JAR, WEB_APP_MOUNT, url, INTERNAL_PATH);
+		}
+
+		private boolean isInsideClassicNestedJar(String resource) {
+			return !isInsideNestedJar(resource) && resource.indexOf("!/") < resource.lastIndexOf("!/");
+		}
+
+		private boolean isInsideNestedJar(String resource) {
+			return resource.startsWith("jar:nested:");
 		}
 
 	}