RFR: 8262277: java.net.URLClassLoader.getResource throws undocumented IllegalArgumentException

[Craig Andrews]

_NOTE_: I've reported this issue at https://bugreport.java.com/ (internal review ID : 9069151)

`java.net.URLClassLoader.getResource` can throw an undocumented `IllegalArgumentException`.

According to the javadoc for the `getResource` and `findResource` methods, neither should be throwing `IllegalArgumentException` - they should return null if the resource can't be resolved.

Quoting the javadoc for [`URLClassLoader.html#findResource`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/net/URLClassLoader.html#findResource(java.lang.String))
> Returns:
>     a URL for the resource, or null if the resource could not be found, or if the loader is closed.

And quoting the javadoc for [`ClassLoader.html#getResource`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/ClassLoader.html#getResource(java.lang.String))
> Returns:
>     URL object for reading the resource; null if the resource could not be found, a URL could not be constructed to locate the resource, the resource is in a package that is not opened unconditionally, or access to the resource is denied by the security manager.

Neither mentions throwing `IllegalArgumentException` and both are clear that when URL can't be constructed, `null` should be returned.

Here's a stack trace:
java.lang.IllegalArgumentException: name
        at java.base/jdk.internal.loader.URLClassPath$Loader.findResource(URLClassPath.java:600)
        at java.base/jdk.internal.loader.URLClassPath.findResource(URLClassPath.java:291)
        at java.base/java.net.URLClassLoader$2.run(URLClassLoader.java:655)
        at java.base/java.net.URLClassLoader$2.run(URLClassLoader.java:653)
        at java.base/java.security.AccessController.doPrivileged(Native Method)
        at java.base/java.net.URLClassLoader.findResource(URLClassLoader.java:652)

Looking at [`URLClassPath.findResource`](https://github.com/openjdk/jdk/blob/2b00367e1154feb2c05b84a11d62fb5750e46acf/src/java.base/share/classes/jdk/internal/loader/URLClassPath.java#L603)
        URL findResource(final String name, boolean check) {
            URL url;
            try {
                url = new URL(base, ParseUtil.encodePath(name, false));
            } catch (MalformedURLException e) {
                throw new IllegalArgumentException("name");
            }

Instead of throwing `IllegalArgumentException`, that line should simply return `null`.

A similar issue exists at [`URLClassPath.getResource`](https://github.com/openjdk/jdk/blob/2b00367e1154feb2c05b84a11d62fb5750e46acf/src/java.base/share/classes/jdk/internal/loader/URLClassPath.java#L639)
        URL findResource(final String name, boolean check) {
            URL url;
            try {
                url = new URL(base, ParseUtil.encodePath(name, false));
            } catch (MalformedURLException e) {
                throw new IllegalArgumentException("name");
            }

Instead of throwing `IllegalArgumentException`, that line should simply return `null`.

-------------

Commit messages:
 - 8262277: java.net.URLClassLoader.getResource throws undocumented IllegalArgumentException

Changes: https://git.openjdk.java.net/jdk/pull/2662/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2662&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262277
  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2662.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2662/head:pull/2662

PR: https://git.openjdk.java.net/jdk/pull/2662