Reduce memory consumption of fat/exploded jars

Refactor `spring-boot-loader` to reduce the amount of memory required
to load fat & exploded jars. Jar files now no longer store a full list
of entry data records, but instead use an array of entry name hashes.

Since ClassLoaders often ask each JAR if they contain a particular
entry (and mostly they do not), the hash array provides a quick way to
deal with misses. Only when a hash does exist is data actually loaded
from the underlying file.

In addition to the JarFile changes, the Archive abstraction has also
been updated to reduce memory consumption.

See gh-4882

Author: philwebb

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

@@ -24,6 +24,7 @@
 import java.util.List;
 import java.util.Set;
 import java.util.jar.JarEntry;
+import java.util.jar.Manifest;
 
 import org.springframework.boot.loader.archive.Archive;
 import org.springframework.boot.loader.archive.Archive.Entry;
@@ -66,7 +67,16 @@ protected final Archive getArchive() {
 
 	@Override
 	protected String getMainClass() throws Exception {
-		return this.archive.getMainClass();
+		Manifest manifest = this.archive.getManifest();
+		String mainClass = null;
+		if (manifest != null) {
+			mainClass = manifest.getMainAttributes().getValue("Start-Class");
+		}
+		if (mainClass == null) {
+			throw new IllegalStateException(
+					"No 'Start-Class' manifest entry specified in " + this);
+		}
+		return mainClass;
 	}
 
 	@Override

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

@@ -19,7 +19,6 @@
 import java.util.List;
 
 import org.springframework.boot.loader.archive.Archive;
-import org.springframework.boot.loader.util.AsciiBytes;
 
 /**
  * {@link Launcher} for JAR based archives. This launcher assumes that dependency jars are
@@ -29,7 +28,7 @@
  */
 public class JarLauncher extends ExecutableArchiveLauncher {
 
-	private static final AsciiBytes LIB = new AsciiBytes("lib/");
+	private static final String LIB = "lib/";
 
 	public JarLauncher() {
 	}

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

@@ -204,20 +204,15 @@ private void definePackageForFindClass(final String name, final String packageNa
 			AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
 				@Override
 				public Object run() throws ClassNotFoundException {
-					String path = name.replace('.', '/').concat(".class");
 					for (URL url : getURLs()) {
 						try {
 							if (url.getContent() instanceof JarFile) {
 								JarFile jarFile = (JarFile) url.getContent();
-								// Check the jar entry data before needlessly creating the
-								// manifest
-								if (jarFile.getJarEntryData(path) != null
-										&& jarFile.getManifest() != null) {
+								if (jarFile.getManifest() != null) {
 									definePackage(packageName, jarFile.getManifest(),
 											url);
 									return null;
 								}
-
 							}
 						}
 						catch (IOException ex) {

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

@@ -21,14 +21,15 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.HttpURLConnection;
+import java.net.MalformedURLException;
 import java.net.URISyntaxException;
 import java.net.URL;
 import java.net.URLClassLoader;
 import java.net.URLConnection;
 import java.net.URLDecoder;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collections;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Properties;
 import java.util.jar.Manifest;
@@ -39,9 +40,7 @@
 import org.springframework.boot.loader.archive.Archive.Entry;
 import org.springframework.boot.loader.archive.Archive.EntryFilter;
 import org.springframework.boot.loader.archive.ExplodedArchive;
-import org.springframework.boot.loader.archive.FilteredArchive;
 import org.springframework.boot.loader.archive.JarFileArchive;
-import org.springframework.boot.loader.util.AsciiBytes;
 import org.springframework.boot.loader.util.SystemPropertyUtils;
 
 /**
@@ -122,8 +121,6 @@ public class PropertiesLauncher extends Launcher {
 	 */
 	public static final String SET_SYSTEM_PROPERTIES = "loader.system";
 
-	private static final List<String> DEFAULT_PATHS = Arrays.asList();
-
 	private static final Pattern WORD_SEPARATOR = Pattern.compile("\\W+");
 
 	private static final URL[] EMPTY_URLS = {};
@@ -132,7 +129,7 @@ public class PropertiesLauncher extends Launcher {
 
 	private final JavaAgentDetector javaAgentDetector;
 
-	private List<String> paths = new ArrayList<String>(DEFAULT_PATHS);
+	private List<String> paths = new ArrayList<String>();
 
 	private final Properties properties = new Properties();
 
@@ -168,7 +165,6 @@ private void initializeProperties(File home) throws Exception, IOException {
 		config = SystemPropertyUtils.resolvePlaceholders(
 				SystemPropertyUtils.getProperty(CONFIG_LOCATION, config));
 		InputStream resource = getResource(config);
-
 		if (resource != null) {
 			log("Found: " + config);
 			try {
@@ -353,7 +349,6 @@ protected ClassLoader createClassLoader(List<Archive> archives) throws Exception
 	@SuppressWarnings("unchecked")
 	private ClassLoader wrapWithCustomClassLoader(ClassLoader parent,
 			String loaderClassName) throws Exception {
-
 		Class<ClassLoader> loaderClass = (Class<ClassLoader>) Class
 				.forName(loaderClassName, true, parent);
 
@@ -363,15 +358,13 @@ private ClassLoader wrapWithCustomClassLoader(ClassLoader parent,
 		catch (NoSuchMethodException ex) {
 			// Ignore and try with URLs
 		}
-
 		try {
 			return loaderClass.getConstructor(URL[].class, ClassLoader.class)
 					.newInstance(new URL[0], parent);
 		}
 		catch (NoSuchMethodException ex) {
 			// Ignore and try without any arguments
 		}
-
 		return loaderClass.newInstance();
 	}
 
@@ -384,21 +377,18 @@ private String getProperty(String propertyKey, String manifestKey) throws Except
 			manifestKey = propertyKey.replace(".", "-");
 			manifestKey = toCamelCase(manifestKey);
 		}
-
 		String property = SystemPropertyUtils.getProperty(propertyKey);
 		if (property != null) {
 			String value = SystemPropertyUtils.resolvePlaceholders(property);
 			log("Property '" + propertyKey + "' from environment: " + value);
 			return value;
 		}
-
 		if (this.properties.containsKey(propertyKey)) {
 			String value = SystemPropertyUtils
 					.resolvePlaceholders(this.properties.getProperty(propertyKey));
 			log("Property '" + propertyKey + "' from properties: " + value);
 			return value;
 		}
-
 		try {
 			// Prefer home dir for MANIFEST if there is one
 			Manifest manifest = new ExplodedArchive(this.home, false).getManifest();
@@ -412,7 +402,6 @@ private String getProperty(String propertyKey, String manifestKey) throws Except
 		catch (IllegalStateException ex) {
 			// Ignore
 		}
-
 		// Otherwise try the parent archive
 		Manifest manifest = createArchive().getManifest();
 		if (manifest != null) {
@@ -478,7 +467,7 @@ private Archive getArchive(File file) throws IOException {
 		return null;
 	}
 
-	private Archive getNestedArchive(final String root) throws Exception {
+	private Archive getNestedArchive(String root) throws Exception {
 		if (root.startsWith("/")
 				|| this.parent.getUrl().equals(this.home.toURI().toURL())) {
 			// If home dir is same as parent archive, no need to add it twice.
@@ -628,40 +617,84 @@ private void log(String message) {
 		}
 	}
 
+	/**
+	 * Convenience class for finding nested archives that have a prefix in their file path
+	 * (e.g. "lib/").
+	 */
+	private static final class PrefixMatchingArchiveFilter implements EntryFilter {
+
+		private final String prefix;
+
+		private final ArchiveEntryFilter filter = new ArchiveEntryFilter();
+
+		private PrefixMatchingArchiveFilter(String prefix) {
+			this.prefix = prefix;
+		}
+
+		@Override
+		public boolean matches(Entry entry) {
+			return entry.getName().startsWith(this.prefix) && this.filter.matches(entry);
+		}
+
+	}
+
 	/**
 	 * Convenience class for finding nested archives (archive entries that can be
 	 * classpath entries).
 	 */
 	private static final class ArchiveEntryFilter implements EntryFilter {
 
-		private static final AsciiBytes DOT_JAR = new AsciiBytes(".jar");
+		private static final String DOT_JAR = ".jar";
 
-		private static final AsciiBytes DOT_ZIP = new AsciiBytes(".zip");
+		private static final String DOT_ZIP = ".zip";
 
 		@Override
 		public boolean matches(Entry entry) {
 			return entry.getName().endsWith(DOT_JAR) || entry.getName().endsWith(DOT_ZIP);
 		}
+
 	}
 
 	/**
-	 * Convenience class for finding nested archives that have a prefix in their file path
-	 * (e.g. "lib/").
+	 * Decorator to apply an {@link Archive.EntryFilter} to an existing {@link Archive}.
 	 */
-	private static final class PrefixMatchingArchiveFilter implements EntryFilter {
+	private static class FilteredArchive implements Archive {
 
-		private final AsciiBytes prefix;
+		private final Archive parent;
 
-		private final ArchiveEntryFilter filter = new ArchiveEntryFilter();
+		private final EntryFilter filter;
 
-		private PrefixMatchingArchiveFilter(String prefix) {
-			this.prefix = new AsciiBytes(prefix);
+		FilteredArchive(Archive parent, EntryFilter filter) {
+			this.parent = parent;
+			this.filter = filter;
 		}
 
 		@Override
-		public boolean matches(Entry entry) {
-			return entry.getName().startsWith(this.prefix) && this.filter.matches(entry);
+		public URL getUrl() throws MalformedURLException {
+			return this.parent.getUrl();
+		}
+
+		@Override
+		public Manifest getManifest() throws IOException {
+			return this.parent.getManifest();
+		}
+
+		@Override
+		public Iterator<Entry> iterator() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public List<Archive> getNestedArchives(final EntryFilter filter)
+				throws IOException {
+			return this.parent.getNestedArchives(new EntryFilter() {
+				@Override
+				public boolean matches(Entry entry) {
+					return FilteredArchive.this.filter.matches(entry)
+							&& filter.matches(entry);
+				}
+			});
 		}
-	}
 
+	}
 }

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

@@ -17,7 +17,6 @@
 package org.springframework.boot.loader;
 
 import org.springframework.boot.loader.archive.Archive;
-import org.springframework.boot.loader.util.AsciiBytes;
 
 /**
  * {@link Launcher} for WAR based archives. This launcher for standard WAR archives.
@@ -29,14 +28,13 @@
  */
 public class WarLauncher extends ExecutableArchiveLauncher {
 
-	private static final AsciiBytes WEB_INF = new AsciiBytes("WEB-INF/");
+	private static final String WEB_INF = "WEB-INF/";
 
-	private static final AsciiBytes WEB_INF_CLASSES = WEB_INF.append("classes/");
+	private static final String WEB_INF_CLASSES = WEB_INF + "classes/";
 
-	private static final AsciiBytes WEB_INF_LIB = WEB_INF.append("lib/");
+	private static final String WEB_INF_LIB = WEB_INF + "lib/";
 
-	private static final AsciiBytes WEB_INF_LIB_PROVIDED = WEB_INF
-			.append("lib-provided/");
+	private static final String WEB_INF_LIB_PROVIDED = WEB_INF + "lib-provided/";
 
 	public WarLauncher() {
 		super();