Java正则表达式验证

Question

I want to validate a string which allows only alpha numeric values and only one dot character and only underscore character in java .

String fileName = (String) request.getParameter("read");

I need to validate the fileName retrieving from the request and should satisfy the above criteria

I tried in "^[a-zA-Z0-9_'.']*$" , but this allows more than one dot character

I need to validate my string in the given scenarios ,

1 . Filename contains only alpha numeric values . 2 . It allows only one dot character (.) , example : fileRead.pdf , fileWrite.txt etc 3 . it allows only underscore characters . All the other symbols should be declined

Can any one help me on this ?

Answer 1

You should use String.matches() method :

System.out.println("My_File_Name.txt".matches("\\w+\\.\\w+"));

You can also use java.util.regex package.

java.util.regex.Pattern pattern = 
java.util.regex.Pattern.compile("\\w+\\.\\w+");

java.util.regex.Matcher matcher = pattern.matcher("My_File_Name.txt");

System.out.println(matcher.matches());

For more information about REGEX and JAVA , look at this page : https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html

Answer 2

You could use two negative lookaheads here:

^((?!.*\..*\.)(?!.*_.*_)[A-Za-z0-9_.])*$

Each lookahead asserts that either a dot or an underscore does not occur two times, implying that it can occur at most once.

It wasn't completely clear whether you require one dot and/or underscore. I assumed not, but my regex could be easily modified to this requirement.

Demo

Answer 3

You can first check the special characters which have the number limits. Here is the code:

int occurance = StringUtils.countOccurrencesOf("123123..32131.3", ".");

or

int count = StringUtils.countMatches("123123..32131.3", ".");

If it does not match your request you can discard it before regex check. If there is no problem you can now put your String to alphanumeric value check.