RFR: 6957241: ClassLoader.getResources() returns only 1 instance when using jar indexing

[wxiang]

Using jarIndex for Hibench, there is an unexpected behavior with the exception "Exception in thread "main" org.apache.hadoop.fs.UnsupportedFileSystemException: No FileSystem for scheme "hdfs"".

After investigating it, it is related to the usage of ServiceLoader with JarIndex.
The below stack shows the issue with JDK11:

getResource:1016, URLClassPath$JarLoader (jdk.internal.loader)
getResource:937, URLClassPath$JarLoader (jdk.internal.loader)
findResource:912, URLClassPath$JarLoader (jdk.internal.loader)
next:341, URLClassPath$1 (jdk.internal.loader)
hasMoreElements:351, URLClassPath$1 (jdk.internal.loader)
hasNext:355, BuiltinClassLoader$1 (jdk.internal.loader)
hasMoreElements:363, BuiltinClassLoader$1 (jdk.internal.loader)
next:3032, CompoundEnumeration (java.lang)
hasMoreElements:3041, CompoundEnumeration (java.lang)
nextProviderClass:1203, ServiceLoader$LazyClassPathLookupIterator (java.util)
hasNextService:1221, ServiceLoader$LazyClassPathLookupIterator (java.util)
hasNext:1265, ServiceLoader$LazyClassPathLookupIterator (java.util)
hasNext:1300, ServiceLoader$2 (java.util)
hasNext:1385, ServiceLoader$3 (java.util)

The below API tries to get all the resources with the same name.

public Enumeration<URL> findResources(final String name,
                                     final boolean check) 
 ```
After using JarIndex, URLClassPath.findResources only returns 1 URL.
It is the same as the description in JDK-6957241.

The issue still exists in JDK18.

Root cause:

public Enumeration<URL> findResources(final String name,
                                     final boolean check) {
        return new Enumeration<>() {
            private int index = 0;
            private URL url = null;

            private boolean next() {
                if (url != null) {
                    return true;
                } else {
                    Loader loader;
                    while ((loader = getLoader(index++)) != null) {
                        url = loader.findResource(name, check);
                        if (url != null) {
                            return true;
                        }
                    }
                    return false;
                }
            }
...
        };
    }

With the JarIndex, there is only one loader which is corresponding to the jar with the index due to the implementation in JarLoader.getResource(final String name, boolean check, Set<String> visited).

Loaders corresponding to other jar packages will not appear in this while.
So it only returns 1 instance.

To solve the issue, I change the implementation "private boolean next()".
If the loader has index, traverse the index and get all the resource from the loader.

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

Commit messages:
 - solve Whitespace error
 - 6957241: ClassLoader.getResources() returns only 1 instance when using jar indexing

Changes: https://git.openjdk.java.net/jdk/pull/5316/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5316&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-6957241
  Stats: 769 lines in 8 files changed: 763 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5316.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5316/head:pull/5316

PR: https://git.openjdk.java.net/jdk/pull/5316