[jira] [Updated] (LUCENE-6879) Allow to define custom CharTokenizer using Java 8 Lambdas/Method references

["Uwe Schindler (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LUCENE-6879?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Uwe Schindler updated LUCENE-6879:
----------------------------------
    Attachment: LUCENE-6879.patch

Patch using Java 8s new functional APIs. Very cool and simple to define a new Tokenizer.

I only don't like that CharTokenizer is in oal.analysis.util package. Maybe we should move the factories to a separate class in the oal.analysis,core pkg.

The patch also has some tests showing how you would use them.

> Allow to define custom CharTokenizer using Java 8 Lambdas/Method references
> ---------------------------------------------------------------------------
>
>                 Key: LUCENE-6879
>                 URL: https://issues.apache.org/jira/browse/LUCENE-6879
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: modules/analysis
>    Affects Versions: Trunk
>            Reporter: Uwe Schindler
>             Fix For: Trunk
>
>         Attachments: LUCENE-6879.patch
>
>
> As a followup from LUCENE-6874, I thought about how to generate custom CharTokenizers wthout subclassing. I had this quite often and I was a bit annoyed, that you had to create a subclass every time.
> This issue is using the pattern like ThreadLocal or many collection methods in Java 8: You have the (abstract) base class and you define a factory method named {{fromXxxPredicate}} (like {{ThreadLocal.fromInitial(() -> value}}).
> {code:java}
> public static CharTokenizer fromPredicate(java.util.function.IntPredicate predicate)
> {code}
> This would allow to define a new CharTokenizer with a single line statement using any predicate:
> {code:java}
> // long variant with lambda:
> Tokenizer tok = CharTokenizer.fromTokenCharPredicate(c -> !UCharacter.isUWhiteSpace(c));
> // method reference for separator char predicate + normalization by uppercasing:
> Tokenizer tok = CharTokenizer.fromSeparatorCharPredicate(UCharacter::isUWhiteSpace, Character::toUpperCase);
> // method reference to custom function:
> private boolean myTestFunction(int c) {
>  return (cracy condition);
> }
> Tokenizer tok = CharTokenizer.fromTokenCharPredicate(this::myTestFunction);
> {code}
> I know this would not help Solr users that want to define the Tokenizer in a config file, but for real Lucene users the Java 8-like way would be the following static method on CharTokenizer without subclassing. It is fast as hell, as it is just a reference to a method and Java 8 is optimized for that.
> The inverted factories {{fromSeparatorCharPredicate()}} are provided to allow quick definition without lambdas using method references. In lots of cases, like WhitespaceTokenizer, predicates are on the separator chars ({{isWhitespace(int)}}, so using the 2nd set of factories you can define them without the counter-intuitive negation. Internally it just uses {{Predicate#negate()}}.
> The factories also allow to give the normalization function, e.g. to Lowercase, you may just give {{Character::toLowerCase}} as {{IntUnaryOperator}} reference.



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