RFR 8136831 : Undefined null behavior in Class[Loader].getResourceXXXX()

[Brent Christian]

Hi,

Please review my fix for 8136831 - Undefined null behavior in 
Class[Loader].getResourceXXXX().

Bug:
https://bugs.openjdk.java.net/browse/JDK-8136831
Webrev:
http://cr.openjdk.java.net/~bchristi/8136831/webrev.00/


Class and ClassLoader have the following public methods for locating 
resources by name:

Class.getResource(String name)
Class.getResourceAsStream(String name)
ClassLoader.getResource(String name)
ClassLoader.getResourceAsStream(String name)
ClassLoader.getResources(String name)

Of these, only Class.getResourceAsStream() specifies the behavior when 
passed a null 'name' argument - throw a NullPointerException.

All methods throw an NPE in this case (going back at least to JDK 7u), 
with ClassLoader.getResources() being something of an exception.  As 
described in the bug report, it returns an Enumeration object with a 
buggy implementation which throws an NPE from hasMoreElements().

As of the module system going into JDK9b111, these methods no longer 
throw an NPE, but return null (again, with the exception of 
ClassLoader.getResources(), which now returns a non-buggy Enumeration 
with working hasMoreElements() method).

I believe this issue should be resolved as follows:

1. Restore the historical NPE behavior by adding code to ensure this 
behavior (instead of relying on it happening incidentally deeper in the 
code - see the stack traces in the bug report).

2. Specify @throws NPE in the JavaDoc for these methods.

For ClassLoader.getResources() this is a change in behavior, though the 
old behavior of returning a buggy Enumeration is not worth keeping. 
Better to fail fast, and behave like other related methods.

Thanks,
-Brent