RFR - 8132734: java.util.jar.* changes to support multi-release jar files

[Steve Drach]

I think the following is a reasonable solution.

If the JarFile is constructed with any of the 5 constructors that do not contain a Release argument, then entries()/stream() returns the set of all entries in the jar file including those under the META-INF/versions/directory.  The base entries are “raw”, they are not aliases for versioned entries.

If the JarFile is constructed with the 1 constructor that does include a Release argument, then entries()/stream() returns the set of appropriately versioned entries that would result from invoking getEntry()/getJarEntry() with the name of each base entry.  The entries in the tree rooted at the directory META-INF/versions/ are not returned.

> On Feb 1, 2016, at 12:29 PM, Steve Drach <steve.drach at oracle.com> wrote:
> 
> I’m sorry, I didn’t look at the code close enough before I started talking ;-)  Right now entries()/stream() returns all entries and if the JarFile is constructed with a Release object != Release.BASE, the base entries that are returned are the versioned entries.  I think this behavior is a bit confusing and we should just return all entries without regard to versioning.  Then create the two new methods for specific versioned entries.
> 
>> On Feb 1, 2016, at 12:18 PM, Steve Drach <steve.drach at oracle.com> wrote:
>> 
>>>>>> Alan’s point is that traversing using entries()/stream() always returns the versioned entries (if any) rather than all entries, thus in a sense filters.
>>>>>> 
>>>>>> My assumption was the traversal should by default be consistent with a calls to getEntry, thus:
>>>>>> 
>>>>>> jarFile.stream().forEach(e ->  {
>>>>>>   JarEntry je = jarFile.getJarEntry(e.getName());
>>>>>>   assert e.equals(je);
>>>>>> });
>>>>>> 
>>>>>> There might need to be another stream method that returns all entries.
>>>>>> 
>>>>> Right, I'm mostly just wondering if entries()/streams() should override the entries in the stream with versioned entries and filter out the META-INF/versions/ tree.
>>>> I don’t think so.  That kind of behavior might be difficult to understand.  Returning all the entries provides some flexibility.  One can write code like this:
>>>> 
>>>> jarfile.stream().map(JarEntry::getName).filter(s ->  !s.startsWith(“META-INF”)).map(JarFile::getJarEntry).etc
>>>> 
>>>> to get the versioned results for any version you specify when constructing the JarFile.
>>> 
>>> The current specification treats those class files under meta-inf/releases like
>>> kind of "metadata" of those base entries. Ideally those files should not even
>>> be individual "files", but part of their corresponding entries. The consumer of
>>> the MR-Jar should not need to be aware of these version-ed entries at all to use
>>> this MR-jar file to load classes/resources. From this point of view, these entries
>>> probably should be "invisible" from entries()/stream(), when the jar file is opened
>>> with "version-enabled". And all returned entries should have all their "data"
>>> (size, csize, timestamps, crc ...) pointed to the corresponding version-ed entries,
>>> withe the only exception is the "name".
>>> 
>>> On the other hand it might be desired to keep JarFile.entries()/stream() asis to
>>> match their "zip file" perspective, to return "all" raw entries. Then it might also
>>> be desired to have an alternative "versioned streamVersion()" …
>> 
>> It seems to that we have two reasonable alternatives: (1) return all entries, and (2) return all entries except those under the “META-INF/versions/“ directory and for any entries returned, return their versioned equivalent if it exists.  If we choose alternative 2, we can still get alternative 1 by asking for JarFile.super.entries() and JarFile.super.stream().
>> 
>> Or we can do it both ways, leaving entries()/stream() as is and adding two new methods, versionedEntries() and versionedStream().
>> 
>>> 
>>> something like
>>> 
>>>  public Stream<JarEntry> stream(Release r); ?
>> 
>> We should not parametrize the methods with a Release, because what does it mean if we construct the JarFile with one Release but specify a different Release for the stream argument.  Parameterizing methods with a Release object feels like we’re starting to slide down a slippery slope.
>> 
>> I think adding the two new methods is the “right” solution, but I’d like some consensus here.
>> 
>>> 
>>> -sherman
>>> 
>>> 
>>> 
>>> 
>>>>> If I've gone to trouble of specifying the a Release then it seems the right thing to do. On the other hand, it comes at a cost and there will be use-cases like "get the names of all entries" that would be more efficient to just build on the current entries()/stream(). I'm loath to suggest this might need a new method but it might be one of the options to consider here. Minimally there is a javadoc to specify on how these methods behave when the JAR is multi-release and opened by specifying a release.
>>>> How’s this?
>>>> 
>>>> diff -r 68867430065b src/java.base/share/classes/java/util/jar/JarFile.java
>>>> --- a/src/java.base/share/classes/java/util/jar/JarFile.java	Fri Jan 29 12:34:44 2016 -0800
>>>> +++ b/src/java.base/share/classes/java/util/jar/JarFile.java	Mon Feb 01 09:48:05 2016 -0800
>>>> @@ -576,9 +576,11 @@
>>>>    }
>>>> 
>>>>    /**
>>>> -     * Returns an enumeration of the jar file entries.
>>>> +     * Returns an enumeration of all the jar file entries.  Constructing this
>>>> +     * JarFile with the {@link JarFile#JarFile(File, boolean, int, Release)}
>>>> +     * constructor does not modify the behavior of this method.
>>>>     *
>>>> -     * @return an enumeration of the jar file entries
>>>> +     * @return an enumeration of the all jar file entries
>>>>     * @throws IllegalStateException
>>>>     *         may be thrown if the jar file has been closed
>>>>     */
>>>> @@ -587,11 +589,13 @@
>>>>    }
>>>> 
>>>>    /**
>>>> -     * Returns an ordered {@code Stream} over the jar file entries.
>>>> +     * Returns an ordered {@code Stream} over all the jar file entries.
>>>>     * Entries appear in the {@code Stream} in the order they appear in
>>>> -     * the central directory of the jar file.
>>>> +     * the central directory of the jar file.  Constructing this
>>>> +     * JarFile with the {@link JarFile#JarFile(File, boolean, int, Release)}
>>>> +     * constructor does not modify the behavior of this method.
>>>>     *
>>>> -     * @return an ordered {@code Stream} of entries in this jar file
>>>> +     * @return an ordered {@code Stream} of all entries in this jar file
>>>>     * @throws IllegalStateException if the jar file has been closed
>>>>     * @since 1.8
>>>>     */
>