java.lang.ClassCastException: class jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to class java.io.Closeable

[ashishbhat]

I have created an Ant XJC task and I am using jaxb-xjc-4.0.4. While building I am seeing below error:
java.lang.ClassCastException: class jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to class java.io.Closeable (jdk.internal.loader.ClassLoaders$AppClassLoader and java.io.Closeable are in module java.base of loader 'bootstrap')

[bond4u]

I have this happening with ant 1.10.12 and jaxb-ri 4.0.3. Looking at ProtectedTask class, it seems that it tries to close classloader without checking that classloader implements Closeable.

[abcoates]

Repeating what I wrote in #107:

In com.sun.istack.tools.ProtectedTask, lines 87-94, the code is

    while (cl != null && !ccl.equals(cl)) {
        try {
            ((Closeable) cl).close();
        } catch (IOException ex) {
            throw new BuildException(ex);
        }
        cl = getParentClassLoader(cl);
    }

The problem is that on line 89 'cl' is cast to 'Closeable' without checking whether it is an instance of 'Closeable' or not. In JDK8, classloaders were invariably a type of URLClassLoader, which is 'Closeable', but in JDK9+ this is no longer a valid assumption, causing a ClassCastException at line 89.

This issue affects anyone using the XJC task in Apache Ant who is trying to move from JDK8 to JDK9+. The fix is to change the lines 87-89 from

    while (cl != null && !ccl.equals(cl)) {
        try {
            ((Closeable) cl).close();

to

    while (cl != null && !ccl.equals(cl) && (cl instanceof Closeable)) {
        try {
            ((Closeable) cl).close();

I'm personally held up on a project by this issue, so would be enormously grateful to see this fix released. Thanks very much in advance for your help.