mirror of https://github.com/apache/lucene.git
40 lines
1.7 KiB
Plaintext
40 lines
1.7 KiB
Plaintext
# JRE Version Migration Guide
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If possible, use the same JRE major version at both index and search time.
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When upgrading to a different JRE major version, consider re-indexing.
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Different JRE major versions may implement different versions of Unicode,
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which will change the way some parts of Lucene treat your text.
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For example: with Java 1.4, `LetterTokenizer` will split around the character U+02C6,
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but with Java 5 it will not.
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This is because Java 1.4 implements Unicode 3, but Java 5 implements Unicode 4.
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For reference, JRE major versions with their corresponding Unicode versions:
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* Java 1.4, Unicode 3.0
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* Java 5, Unicode 4.0
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* Java 6, Unicode 4.0
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* Java 7, Unicode 6.0
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* Java 8, Unicode 6.2
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* Java 9 (not yet released / offcially supported by Lucene), Unicode 8.0
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In general, whether or not you need to re-index largely depends upon the data that
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you are searching, and what was changed in any given Unicode version. For example,
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if you are completely sure that your content is limited to the "Basic Latin" range
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of Unicode, you can safely ignore this.
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## Special Notes: LUCENE 2.9 TO 3.0, JAVA 1.4 TO JAVA 5 TRANSITION
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* `StandardAnalyzer` will return the same results under Java 5 as it did under
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Java 1.4. This is because it is largely independent of the runtime JRE for
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Unicode support, (with the exception of lowercasing). However, no changes to
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casing have occurred in Unicode 4.0 that affect StandardAnalyzer, so if you are
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using this Analyzer you are NOT affected.
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* `SimpleAnalyzer`, `StopAnalyzer`, `LetterTokenizer`, `LowerCaseFilter`, and
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`LowerCaseTokenizer` may return different results, along with many other `Analyzer`s
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and `TokenStream`s in Lucene's analysis modules. If you are using one of these
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components, you may be affected.
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