URLClassloader.close() does not close JAR files whose resources have been loaded via getResource()

SYNOPSIS
--------
URLClassloader.close() does not close JAR files whose resources have been loaded via getResource()

OPERATING SYSTEM
----------------
All

FULL JDK VERSION
----------------
Java 7 onwards
Reproducible with latest Java 8 build (b46)

PROBLEM DESCRIPTION
-------------------
Closeables is a new feature introduced in Java7. The documentation states that all JAR files and other Closeable resources opened by a class loader will be closed when the class loader is itself closed. However, when a resource is loaded from a JAR file using getResource(), the JAR file is NOT closed when the class loader is closed.

The attached testcase does the following:

1. Creates a JAR file
2. Places a resource (a small text file) inside the JAR
3. Creates a URLClassloader and uses it to load the resource from the JAR
4. Calls close() on the URLClassloader
5. Attempts to delete the JAR file

Step 5 should be successful, as all references to it should have been closed by the call to URLClassLoader.close(), but it fails.

REPRODUCTION INSTRUCTIONS
-------------------------
1. Compile and run the testcase
2. Observe the output

Expected output:
Test PASSED

Observed output:
Test FAILED: Closeables failed to close

WORKAROUND
----------
Close the JAR file manually. One strategy can be seen in the testcase, which uses a workaround after the initial attempt to delete the file fails.

TESTCASE
--------
import java.io.*;
import java.net.*;
import java.util.zip.*;

public class TestURLClassLoader {
    public static void main(String[] args) throws Exception {
        // Create a JAR file
        File f = new File("urlcl" + 1 + ".jar");
        ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(f));

        // add a file
        zos.putNextEntry(new ZipEntry("TestResource"));
        byte[] b = new String("This is a test resource").getBytes();
        zos.write(b, 0, b.length);
        zos.close();

        // Load the file using cl.getResource()
        URLClassLoader cl = new URLClassLoader(new URL[] { new URL("jar:" + f.toURI().toURL() + "!/")}, null);
        cl.getResource("TestResource");

        // Close the class loader - this should free up all of its Closeables, including the JAR file
        cl.close();

        // Try to delete the JAR file
        f.delete();

        // Check to see if the file was deleted
        if (f.exists()) {
            System.out.println("Test FAILED: Closeables failed to close");
            // Delete the jar using a workaround
            for (URL u : cl.getURLs()) {
                if (u.getProtocol().equals("jar")) {
                    ((JarURLConnection)u.openConnection()).getJarFile().close();
                }
                f.delete();
            }
        } else {
            System.out.println("Test PASSED");
        }
    }
}

SUGGESTED FIX
-------------
These diffs are relative to the 7u6 codebase.

--- 7u6\URLClassLoader.java 2012-06-26 22:08:54.000000000 +0100
+++ new\URLClassLoader.java 2012-07-11 13:00:00.205574000 +0100
@@ -552,6 +552,21 @@
                 }
             }, acc);

+ if (url != null) {
+ if (url.getProtocol().equals("jar")) {
+ try {
+ JarFile jar = ((JarURLConnection)url.openConnection()).getJarFile();
+ synchronized (closeables) {
+ if (!closeables.containsKey(jar)) {
+ closeables.put(jar, null);
+ }
+ }
+ } catch (java.io.IOException ioe) {
+ ioe.printStackTrace();
+ }
+ }
+ }
+
         return url != null ? ucp.checkURL(url) : null;
     }