Optimize JarLauncher when used with exploded jar

- Previously, we would create a JarFileArchive for all nested jars.
This was an additional overhead. We only need to create a JarFileArchive
for jars that can have nested jars in them. For all other jars we only need
the URL to build the classpath.
- While iterating over nested entries in the exploded jar, we only need to
look at BOOT-INF and we can skip any entry that does not match that.

Closes gh-16655

Co-authored-by: Phillip Webb <[email protected]>

Author: mbhave

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/ExecutableArchiveLauncher.java

@@ -17,8 +17,8 @@
 package org.springframework.boot.loader;
 
 import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.List;
-import java.util.jar.JarEntry;
 import java.util.jar.Manifest;
 
 import org.springframework.boot.loader.archive.Archive;
@@ -65,27 +65,64 @@ protected String getMainClass() throws Exception {
 	}
 
 	@Override
-	protected List<Archive> getClassPathArchives() throws Exception {
-		List<Archive> archives = new ArrayList<>(this.archive.getNestedArchives(this::isNestedArchive));
-		postProcessClassPathArchives(archives);
+	protected Iterator<Archive> getClassPathArchivesIterator() throws Exception {
+		Iterator<Archive> archives = this.archive.getNestedArchives(this::isSearchCandidate, this::isNestedArchive);
+		if (isPostProcessingClassPathArchives()) {
+			archives = applyClassPathArchivePostProcessing(archives);
+		}
 		return archives;
 	}
 
+	private Iterator<Archive> applyClassPathArchivePostProcessing(Iterator<Archive> archives) throws Exception {
+		List<Archive> list = new ArrayList<Archive>();
+		while (archives.hasNext()) {
+			list.add(archives.next());
+		}
+		postProcessClassPathArchives(list);
+		return list.iterator();
+	}
+
+	/**
+	 * Determine if the specified entry is a a candidate for further searching.
+	 * @param entry the entry to check
+	 * @return {@code true} if the entry is a candidate for further searching
+	 */
+	protected boolean isSearchCandidate(Archive.Entry entry) {
+		return true;
+	}
+
 	/**
-	 * Determine if the specified {@link JarEntry} is a nested item that should be added
-	 * to the classpath. The method is called once for each entry.
-	 * @param entry the jar entry
+	 * Determine if the specified entry is a nested item that should be added to the
+	 * classpath.
+	 * @param entry the entry to check
 	 * @return {@code true} if the entry is a nested item (jar or folder)
 	 */
 	protected abstract boolean isNestedArchive(Archive.Entry entry);
 
+	/**
+	 * Return if post processing needs to be applied to the archives. For back
+	 * compatibility this method returns {@true}, but subclasses that don't override
+	 * {@link #postProcessClassPathArchives(List)} should provide an implementation that
+	 * returns {@code false}.
+	 * @return if the {@link #postProcessClassPathArchives(List)} method is implemented
+	 */
+	protected boolean isPostProcessingClassPathArchives() {
+		return true;
+	}
+
 	/**
 	 * Called to post-process archive entries before they are used. Implementations can
 	 * add and remove entries.
 	 * @param archives the archives
 	 * @throws Exception if the post processing fails
+	 * @see #isPostProcessingClassPathArchives()
 	 */
 	protected void postProcessClassPathArchives(List<Archive> archives) throws Exception {
 	}
 
+	@Override
+	protected boolean supportsNestedJars() {
+		return this.archive.supportsNestedJars();
+	}
+
 }

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/JarLauncher.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.loader;
 
 import org.springframework.boot.loader.archive.Archive;
+import org.springframework.boot.loader.archive.Archive.EntryFilter;
 
 /**
  * {@link Launcher} for JAR based archives. This launcher assumes that dependency jars are
@@ -29,9 +30,12 @@
  */
 public class JarLauncher extends ExecutableArchiveLauncher {
 
-	static final String BOOT_INF_CLASSES = "BOOT-INF/classes/";
-
-	static final String BOOT_INF_LIB = "BOOT-INF/lib/";
+	static final EntryFilter NESTED_ARCHIVE_ENTRY_FILTER = (entry) -> {
+		if (entry.isDirectory()) {
+			return entry.getName().equals("BOOT-INF/classes/");
+		}
+		return entry.getName().startsWith("BOOT-INF/lib/");
+	};
 
 	public JarLauncher() {
 	}
@@ -40,12 +44,19 @@ protected JarLauncher(Archive archive) {
 		super(archive);
 	}
 
+	@Override
+	protected boolean isPostProcessingClassPathArchives() {
+		return false;
+	}
+
+	@Override
+	protected boolean isSearchCandidate(Archive.Entry entry) {
+		return entry.getName().startsWith("BOOT-INF/");
+	}
+
 	@Override
 	protected boolean isNestedArchive(Archive.Entry entry) {
-		if (entry.isDirectory()) {
-			return entry.getName().equals(BOOT_INF_CLASSES);
-		}
-		return entry.getName().startsWith(BOOT_INF_LIB);
+		return NESTED_ARCHIVE_ENTRY_FILTER.matches(entry);
 	}
 
 	public static void main(String[] args) throws Exception {

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/Launcher.java

@@ -19,9 +19,11 @@
 import java.io.File;
 import java.net.URI;
 import java.net.URL;
+import java.net.URLClassLoader;
 import java.security.CodeSource;
 import java.security.ProtectionDomain;
 import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.List;
 
 import org.springframework.boot.loader.archive.Archive;
@@ -46,8 +48,10 @@ public abstract class Launcher {
 	 * @throws Exception if the application fails to launch
 	 */
 	protected void launch(String[] args) throws Exception {
-		JarFile.registerUrlProtocolHandler();
-		ClassLoader classLoader = createClassLoader(getClassPathArchives());
+		if (supportsNestedJars()) {
+			JarFile.registerUrlProtocolHandler();
+		}
+		ClassLoader classLoader = createClassLoader(getClassPathArchivesIterator());
 		launch(args, getMainClass(), classLoader);
 	}
 
@@ -56,11 +60,24 @@ protected void launch(String[] args) throws Exception {
 	 * @param archives the archives
 	 * @return the classloader
 	 * @throws Exception if the classloader cannot be created
+	 * @deprecated since 2.3.0 in favor of {@link #createClassLoader(Iterator)}
 	 */
+	@Deprecated
 	protected ClassLoader createClassLoader(List<Archive> archives) throws Exception {
-		List<URL> urls = new ArrayList<>(archives.size());
-		for (Archive archive : archives) {
-			urls.add(archive.getUrl());
+		return createClassLoader(archives.iterator());
+	}
+
+	/**
+	 * Create a classloader for the specified archives.
+	 * @param archives the archives
+	 * @return the classloader
+	 * @throws Exception if the classloader cannot be created
+	 * @since 2.3.0
+	 */
+	protected ClassLoader createClassLoader(Iterator<Archive> archives) throws Exception {
+		List<URL> urls = new ArrayList<>(50);
+		while (archives.hasNext()) {
+			urls.add(archives.next().getUrl());
 		}
 		return createClassLoader(urls.toArray(new URL[0]));
 	}
@@ -72,7 +89,10 @@ protected ClassLoader createClassLoader(List<Archive> archives) throws Exception
 	 * @throws Exception if the classloader cannot be created
 	 */
 	protected ClassLoader createClassLoader(URL[] urls) throws Exception {
-		return new LaunchedURLClassLoader(urls, getClass().getClassLoader());
+		if (supportsNestedJars()) {
+			return new LaunchedURLClassLoader(urls, getClass().getClassLoader());
+		}
+		return new URLClassLoader(urls, getClass().getClassLoader());
 	}
 
 	/**
@@ -109,8 +129,23 @@ protected MainMethodRunner createMainMethodRunner(String mainClass, String[] arg
 	 * Returns the archives that will be used to construct the class path.
 	 * @return the class path archives
 	 * @throws Exception if the class path archives cannot be obtained
+	 * @since 2.3.0
+	 */
+	protected Iterator<Archive> getClassPathArchivesIterator() throws Exception {
+		return getClassPathArchives().iterator();
+	}
+
+	/**
+	 * Returns the archives that will be used to construct the class path.
+	 * @return the class path archives
+	 * @throws Exception if the class path archives cannot be obtained
+	 * @deprecated since 2.3.0 in favor of implementing
+	 * {@link #getClassPathArchivesIterator()}.
 	 */
-	protected abstract List<Archive> getClassPathArchives() throws Exception;
+	@Deprecated
+	protected List<Archive> getClassPathArchives() throws Exception {
+		throw new IllegalStateException("Unexpected call to getClassPathArchives()");
+	}
 
 	protected final Archive createArchive() throws Exception {
 		ProtectionDomain protectionDomain = getClass().getProtectionDomain();
@@ -127,4 +162,14 @@ protected final Archive createArchive() throws Exception {
 		return (root.isDirectory() ? new ExplodedArchive(root) : new JarFileArchive(root));
 	}
 
+	/**
+	 * Returns if the launcher needs to support fully nested JARs. If this method returns
+	 * {@code false} then only regular JARs are supported and the additional URL and
+	 * ClassLoader support infrastructure will not be installed.
+	 * @return if nested JARs are supported
+	 */
+	protected boolean supportsNestedJars() {
+		return true;
+	}
+
 }

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/PropertiesLauncher.java

@@ -28,6 +28,7 @@
 import java.net.URLDecoder;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Locale;
@@ -447,12 +448,12 @@ private String getProperty(String propertyKey, String manifestKey, String defaul
 	}
 
 	@Override
-	protected List<Archive> getClassPathArchives() throws Exception {
+	protected Iterator<Archive> getClassPathArchivesIterator() throws Exception {
 		List<Archive> lib = new ArrayList<>();
 		for (String path : this.paths) {
 			for (Archive archive : getClassPathArchives(path)) {
 				if (archive instanceof ExplodedArchive) {
-					List<Archive> nested = new ArrayList<>(archive.getNestedArchives(new ArchiveEntryFilter()));
+					List<Archive> nested = asList(archive.getNestedArchives(null, new ArchiveEntryFilter()));
 					nested.add(0, archive);
 					lib.addAll(nested);
 				}
@@ -462,7 +463,7 @@ protected List<Archive> getClassPathArchives() throws Exception {
 			}
 		}
 		addNestedEntries(lib);
-		return lib;
+		return lib.iterator();
 	}
 
 	private List<Archive> getClassPathArchives(String path) throws Exception {
@@ -543,7 +544,7 @@ private List<Archive> getNestedArchives(String path) throws Exception {
 			root = "";
 		}
 		EntryFilter filter = new PrefixMatchingArchiveFilter(root);
-		List<Archive> archives = new ArrayList<>(parent.getNestedArchives(filter));
+		List<Archive> archives = asList(parent.getNestedArchives(null, filter));
 		if (("".equals(root) || ".".equals(root)) && !path.endsWith(".jar") && parent != this.parent) {
 			// You can't find the root with an entry filter so it has to be added
 			// explicitly. But don't add the root of the parent archive.
@@ -557,12 +558,10 @@ private void addNestedEntries(List<Archive> lib) {
 		// directories, meaning we are running from an executable JAR. We add nested
 		// entries from there with low priority (i.e. at end).
 		try {
-			lib.addAll(this.parent.getNestedArchives((entry) -> {
-				if (entry.isDirectory()) {
-					return entry.getName().equals(JarLauncher.BOOT_INF_CLASSES);
-				}
-				return entry.getName().startsWith(JarLauncher.BOOT_INF_LIB);
-			}));
+			Iterator<Archive> archives = this.parent.getNestedArchives(null, JarLauncher.NESTED_ARCHIVE_ENTRY_FILTER);
+			while (archives.hasNext()) {
+				lib.add(archives.next());
+			}
 		}
 		catch (IOException ex) {
 			// Ignore
@@ -591,6 +590,14 @@ private String cleanupPath(String path) {
 		return path;
 	}
 
+	private List<Archive> asList(Iterator<Archive> iterator) {
+		List<Archive> list = new ArrayList<Archive>();
+		while (iterator.hasNext()) {
+			list.add(iterator.next());
+		}
+		return list;
+	}
+
 	public static void main(String[] args) throws Exception {
 		PropertiesLauncher launcher = new PropertiesLauncher();
 		args = launcher.getArgs(args);

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/WarLauncher.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.loader;
 
 import org.springframework.boot.loader.archive.Archive;
+import org.springframework.boot.loader.archive.Archive.Entry;
 
 /**
  * {@link Launcher} for WAR based archives. This launcher for standard WAR archives.
@@ -29,29 +30,29 @@
  */
 public class WarLauncher extends ExecutableArchiveLauncher {
 
-	private static final String WEB_INF = "WEB-INF/";
-
-	private static final String WEB_INF_CLASSES = WEB_INF + "classes/";
-
-	private static final String WEB_INF_LIB = WEB_INF + "lib/";
-
-	private static final String WEB_INF_LIB_PROVIDED = WEB_INF + "lib-provided/";
-
 	public WarLauncher() {
 	}
 
 	protected WarLauncher(Archive archive) {
 		super(archive);
 	}
 
+	@Override
+	protected boolean isPostProcessingClassPathArchives() {
+		return false;
+	}
+
+	@Override
+	protected boolean isSearchCandidate(Entry entry) {
+		return entry.getName().startsWith("WEB-INF/");
+	}
+
 	@Override
 	public boolean isNestedArchive(Archive.Entry entry) {
 		if (entry.isDirectory()) {
-			return entry.getName().equals(WEB_INF_CLASSES);
-		}
-		else {
-			return entry.getName().startsWith(WEB_INF_LIB) || entry.getName().startsWith(WEB_INF_LIB_PROVIDED);
+			return entry.getName().equals("WEB-INF/classes/");
 		}
+		return entry.getName().startsWith("WEB-INF/lib/") || entry.getName().startsWith("WEB-INF/lib-provided/");
 	}
 
 	public static void main(String[] args) throws Exception {