Attempt to reduce JarFileWrapper heap consumption

Update `JarURLConnection` to use a single shared wrapper per
jar file rather than creating a new one each time. This update
should help to reduce GC pressure.

Fixes gh-28042

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

@@ -91,6 +91,8 @@ public class JarFile extends AbstractJarFile implements Iterable<java.util.jar.J
 
 	private volatile boolean closed;
 
+	private volatile JarFileWrapper wrapper;
+
 	/**
 	 * Create a new {@link JarFile} backed by the specified file.
 	 * @param file the root jar file
@@ -183,6 +185,15 @@ public class JarFile extends AbstractJarFile implements Iterable<java.util.jar.J
 		};
 	}
 
+	JarFileWrapper getWrapper() throws IOException {
+		JarFileWrapper wrapper = this.wrapper;
+		if (wrapper == null) {
+			wrapper = new JarFileWrapper(this);
+			this.wrapper = wrapper;
+		}
+		return wrapper;
+	}
+
 	@Override
 	Permission getPermission() {
 		return new FilePermission(this.rootFile.getFile().getPath(), READ_ACTION);

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -263,7 +263,7 @@ final class JarURLConnection extends java.net.JarURLConnection {
 				&& !jarFile.containsEntry(jarEntryName.toString())) {
 			return NOT_FOUND_CONNECTION;
 		}
-		return new JarURLConnection(url, new JarFileWrapper(jarFile), jarEntryName);
+		return new JarURLConnection(url, jarFile.getWrapper(), jarEntryName);
 	}
 
 	private static int indexOfRootSpec(StringSequence file, String pathFromRoot) {