如何在java中编写和使用正则表达式

Question

I want to write a regular expression in java which will accept the String having alphabets, numbers, - and space any number of times any where.

The string should only contain above mentioned and no other special characters. How to code the regular expression in java?

I tried the following, It works when I run it as a java application.

But the same code when I run in web application and accept the values through XML, It accepts '/'.

 String test1 = null;

 Scanner scan = new Scanner(System.in);
 test1 = scan.nextLine();

 String alphaExp = "^[a-zA-Z0-9-]*$";

 Pattern r = Pattern.compile(alphaExp);
 Matcher m = r.matcher(test1);

 boolean flag = m.lookingAt();

 System.out.println(flag);

Can anyone help me on this please?

Answer 1

You can try to use POSIX character classes (see here ):

Pattern p = Pattern.compile("^[\\p{Alnum}\\p{Space}-]*$");
Matcher m = p.matcher("asfsdf 1212sdfsd-gf121sdg5 4s");
boolean b = m.lookingAt();

With this regular expression if the string you pass contain anything else than alphanumeric or space characters it will be a no match result.

Answer 2

I think you're just missing a space from the character class - since you mentioned it in your text ^[a-zA-Z0-9 -]*$

You can add the Pattern.MULTILINE flag too so you can specify how the pattern handles the lines:

     String alphaExp = "^[a-zA-Z0-9 -]*$";

     Pattern r = Pattern.compile(alphaExp, Pattern.MULTILINE);
     Matcher m = r.matcher(test1);

     boolean flag = m.lookingAt();

Answer 3

Pay attention to the fact that * quantifier will make it match to everything including no matches (0 or more times, like empty lines or blank tokens "" , infinitely.

If you instead use + " [\\w\\d\\s-\\]+ " it will match one or more (consider using \\\\ for each \\ in your Java Regex code as follow: " [\\\\w\\\\d\\\\s-]+ "

Consider that * is a quantity operator that works as {0, } and + works like {1, }