使用正则表达式在Java中进行模式匹配

Question

I am looking for a pattern to match this "LA5@10.232.140.133@Po6" and one more "LA5@10.232.140.133@Port-channel7" expression in Java using regular expression.

Like we have \\d{1,3}.\\d{1,3}.\\d{1,3}.\\d{1,3} for IP address validation.

Can we have the pattern like below? Please suggest--

[a-zA-Z0-9][a-zA-Z0-9][a-zA-Z0-9]@\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}@Po\d[1-9]
[a-zA-Z0-9][a-zA-Z0-9][a-zA-Z0-9]@\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}@Port-channel\d[1-9]

Thanks in advance.

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In my program i have,

import java.util.regex.*;
class ptternmatch {
    public static void main(String [] args) {
        Pattern p = Pattern.compile("\\w\\w\\w@\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3}@*");
        Matcher m = p.matcher("LA5@10.232.140.133@Port-channel7");
        boolean b = false;
        System.out.println("Pattern is " + m.pattern());
        while(b = m.find()) {
            System.out.println(m.start() + " " + m.group());
    }
    }
}

But i am getting compilation error with the pattern.--> Invalid escape sequence The sequence will be like a ->a 3 character word of digit n letter@ipaddress@some text..

Answer 1

Well, if you want to validate the IP address, then you need something a little bit more involved than \\d{1,3} . Also, keep in mind that for Java string literals, you need to escape the \\ with \\\\ so you end up with a single backslash in the actual regex to escape a character such as a period ( . ).

Assuming the LA5@ bit is static and that you're fine with either Po or Port-channel followed by a digit on the end, then you probably need a regex along these lines:

LA5@(((2((5[0-5])|([0-4][0-9])))|(1[0-9]{2})|([1-9][0-9]?)\\.){3}(2(5[0-5]|[0-4][0-9]))|(1[0-9]{2})|([1-9][0-9]?)@Po(rt-channel)?[1-9]

(Bracketing may be wonky, my apologies)

Answer 2

You can do something like matcher.find() and, if it is true, the groups to capture the information. Take a look a the tutorial here:

• http://download.oracle.com/javase/tutorial/essential/regex/

You would need to wrap the necessary parts int parentheses - eg (\\d{1,3}) . If you wrap all 4, you will have 4 groups to access.

Also, take a look at this tutorial

• http://www.javaworld.com/javaworld/jw-07-2001/jw-0713-regex.html?page=3

It's a very good tutorial, I think this one would explain most of your questions.

To match the second of your strings:

• LA5@10.232.140.133@Port-channel7

you can use something like:

\w{2}\d@\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3}@[a-zA-Z\-]+\d

This depends on what you want to do, so the regex might change.