Question

public static String getPortableFilePath(String target)    
{
Pattern ptr=Pattern.compile("[\\|/]+");
Matcher mtr=ptr.matcher(target);
return mtr.replaceAll(File.separator);  
}

public static void main(String[] args)
{
   System.out.println(getPortableFilePath("C:///Program Files////Java\\jdk1.6.0_23/bin"));  
}

In the above code I am trying to replace all the Forward and Backward slashes with the current systems File Separator. Code compiles fine when put into a class, but when executed it gives an array index out of bounds exception. Any guesses why?

The Exception:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 1

at java.lang.String.charAt(Unknown Source)
at java.util.regex.Matcher.appendReplacement(Unknown Source)
at java.util.regex.Matcher.replaceAll(Unknown Source)
at Files.getPortableFilePath
at Files.main

Answer 1

You need to get two backslashes through to the regex engine. Otherwise it will think you are escaping the next character. So use

"[\\\\/]+"

for the pattern string. That way it resolves to the pattern

[\\/]+

This is the problem with the string and the regex notation both using backslashes, and there being no way to skip the string interpolation stage.

And don’t use a vertical pipe in a square-bracket charclass: it is a literal there.