= GEP-6: NIO2 Support for Groovy

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.Metadata
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*Number*:: GEP-6
*Title*:: NIO2 Support for Groovy
*Version*:: 2
*Type*:: Feature
*Status*:: Final
*Comment*:: Delivered in Groovy 2.3
*Leader*:: Merlyn Albery-Speyer/Hamlet D'Arcy
*Created*:: 2010-09-25
*Last modification*&#160;:: 2018-10-12
****

== Abstract

JDK 7 includes a new java.nio.file package and Path class.
These provide extended capabilities for filesystem tasks.
We should explore incorporation into Groovy.

== Approach

I propose:

* Create an openjdk7 build of Groovy
* Move NIO2 support to a Groovy Module for now
* Move NIO2 Groovy Module to Groovy-core when JDK7 is officially released

JDK7 is still in beta. It is subject to change. If we build NIO2 support into Groovy today and make a release,
then we risk having JDK7 make an API change, which would force us to support 2 different APIs. That would be bad.

=== Todo in Groovy NIO Module:

* Support new Path object
* All of the GDK File API needs to be on Path
* NIO2 contains a new WatchService API. We need to probably provide a GDK on WatchService to make it easy to work
with using closures, etc. This is the most interesting piece of work IMO.

=== Todo in Groovy Core:

Groovy has a FileNameFinder and FileNameRegExFinder. This stuff needs to work with Paths as well:
http://mrhaki.blogspot.com/2009/11/groovy-goodness-finding-files-with.html

I haven't looked at each file in this list yet, but we need to analyze these Groovy source files and see if
any parallel Path implementations are needed. The first 3 files look like the most important:

```
./groovy/util/IFileNameFinder.java
./groovy/io/FileType.java
./groovy/io/FileVisitResult.java
./org/codehaus/groovy/runtime/WritableFile.java
./org/codehaus/groovy/ant/FileIterator.java
./org/codehaus/groovy/ant/FileScanner.java
./org/codehaus/groovy/control/io/FileReaderSource.java
```

I couldn't find any instances of this in Groovy-core, but any `asType(File)` methods need a parallel
`asType(Path)` - I believe `asWritable(Path)` is the only change required. In NIO2, I believe `File.list`
and another method now return an iterator, which enables this method to work better over networks.
We need to update the File GDK to use this approach by default to also support network dir or ls style listings.
NIO2 has a new `FileVisitor` class. We need to unify this new `FileVisitor` JDK method with what Groovy does
today in with GDK with the `.eachFile` method. As well as the `.eachFileXXX` methods and the `.eachDirXXX`
methods we should include the `.traverse` method when looking through potential places for unification.
The `.traverse` method's primary role was to make some `FileVisitor` like functionality available in the pre-JDK 7
world but having NIO2 there might open up some more possibilities. There was also some thought at the time of having
additional overloaded traverse methods with a more statically typed flavor rather than just the current Map solution.
I guess now is a good time to also look at that option.

== References and useful links

=== Mailing-list discussions

* https://markmail.org/thread/osst6q4obk56fxqg[groovy-dev: OpenJDK 7 Groovy Build and NIO2 support]
* https://docs.oracle.com/javase/8/docs/technotes/guides/io/index.html[Java I/O, NIO and NIO.2]

=== JIRA issues

* https://issues.apache.org/jira/browse/GROOVY-4390[GROOVY-4390: Add GDK File methods to the NIO2 API]
* https://issues.apache.org/jira/browse/GROOVY-4391[GROOVY-4391: Groovy build fails test target using Java 1.7.0]

== Update history

1 (2010-02-16):: Version as extracted from Codehaus wiki
2 (2018-10-14):: Numerous minor tweaks