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From HiuKwok <...@git.apache.org>
Subject [GitHub] commons-lang issue #340: [LANG-1406] StringIndexOutOfBoundsException in Stri...
Date Wed, 05 Sep 2018 15:32:50 GMT
Github user HiuKwok commented on the issue:

    https://github.com/apache/commons-lang/pull/340
  
    To whom who interested in this issue, here is some founding that I discovered throughout
this month of issue solving. 
    
    Problem:
     - The exception would happened when any String object passed in with unicode character.
In order to achieve ignore case replacement, the internal logic would first transform both
`text` and `SearchString` to lowerCase( ) for comparaition.   
    
    - However if anyone passion enough to digger deeper into the src logic of `.toLowerCase(
)`. Certain unicode character would be denormalized. In this way the result String length
would tend to longer than original length().  Example like:  ![image](https://user-images.githubusercontent.com/37996731/45103213-efec8780-b161-11e8-8370-88a7edacfc42.png)
    So making use of the transformed String, Out bound exception would happen when trying
to access the index that doesn't access at all (3 in this case vs 2 in length before lowerCase).
    
    Flow:
    
     - So the first thought into my mind is, why dun just normalize both `text` and `searchString`
before performing ignore case comparation? In this way the String length would always stay
consistence no matter `toLowerCase( )` or `toUpperCase( )` 3 -> 3.  However the another
problem would emerged, as you may noticed, while the String mentioned above denormalize, it
would turn into a UpperCase I and a dot sign. 
    
    - But what happen if the search pattern emerge into searchText in decompose form. In this
case let say I am trying to match a upper [I]. Then mismatch would happen and this is certain
not the desire behavior of this method I believe. 
    
    BTW I Drafted a simple main method to demonstrate how mismatch would happen in here.
    
    https://github.com/HiuKwok/commons-lang/blob/master/src/main/java/com/hiukwok/test.java#L10-L20
    



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