7017446: (fs) Updates to file system API (3/2011)

[Alan Bateman]

This webrev contains a couple of small API updates:

1. Files.getAttribute and readAttributes currently return null (or an 
empty map) when invoked with invalid attribute names. The proposed 
change here fixes this so that IllegalArgumentException is thrown when 
invalid names are used. UOE will continue to be throw if an unsupported 
view is specified.

2. A method is added to WatchKey to return the the object for which the 
watch key was created. This has come up several times, and the 
implementation changes for this were actually included in the last round 
of updates. For now the methods the Watchable and so must be cast to the 
specific type when used. Not ideal but the alternative propagates a type 
parameter and would require restricting the WatchService so that it only 
watches objects of one type.

3. The Files.createTempFile and createTemptDirectory methods that 
specify the temporary file directory are restricted to the default file 
system. The rational for this is that it may not be possible to generate 
a file name suitable for use with a custom file system. In the future we 
can extend the provider interface to support this if needed.

4. A couple of questions/inconsistencies were observed with the zip 
provider when comparing paths in different zip file systems. To address 
this, Path.equals is changed so that it returns false if the given 
object is a Path associated with a different FileSystem (used to return 
false if associated with a different provider). The startsWith/endsWith 
methods also return false if the given path is associated with a 
different FileSystem. This also addressed another concern that came up 
no this mailing list some time ago where ProviderMismatchException is 
thrown.

The webrev with the changes is here:
  http://cr.openjdk.java.net/~alanb/7017446/webrev/

Thanks,
Alan