regex and backslash..

[pradeep selvaraj]

Hi,

I have a regex pattern matching code like this.

/****************CODE***********************************************
public static boolean isValidProjectFile(String fileName)
{
Pattern p = Pattern.compile("([a-z,A-Z,0-9,_, ,/,\\,-,.])+[.]+ jar|class|txt)",Pattern.CASE_INSENSITIVE);
Matcher m = p.matcher(fileName);
return m.matches();
}
/******************************************************************

When i call this method as shown below

boolean test = isValidProjectFile("test\testdata\hibernate3.jar");

It returns false. I am expecting it to return true.

Where am i going wrong?

Thanks
Pradeep

[Ajay A Patil]

Try,

Pattern p = Pattern.compile("([a-z,A-Z,0-9,_, ,/,\\\,-,.])+[.]+ jar|class|txt)",Pattern.CASE_INSENSITIVE);

In Java regular expressions, when you have to use DOUBLE BACKSLASH
as escape character. Java eats up one BACKSLASH, and the regular
expression engine eats the other BACKSLASH.

[Ajay A Patil]

Actually, you will also have to escape the '.' character.

Pattern p = Pattern.compile("([a-z,A-Z,0-9,_, ,/,\\\,-,.])+[\\.]+ jar|class|txt)",Pattern.CASE_INSENSITIVE);

[Alan Moore]

In fact, you need four backslashes in the regex string to match one in the target string. And as for the dot, if you put it in a character class, it just matches a dot. So you can either put brackets around it, or put a backslash in front of it, but doing both is overkill (although it still works). The comma also has no special meaning, Pradeep; your character class will match a comma as well as all those other characters. And you don't need the parentheses around the character class, but you do need a matched pair of them around the final alternation (I'm sure that's just a typo).

Pattern p = Pattern.compile("[\\w /-.\\\\]+\\.(jar|class|txt)", Pattern.CASE_INSENSITIVE);

(\w is the same as [A-Za-z0-9_])

[pradeep selvaraj]

Thanks you very much guys.I was on this problem.