Java Regex: Extract Emails

/* Write a program to extract all email addresses from given text.
 * The text comes at the first input line.
 * Print the emails in the output, each at a separate line.
 * Emails are considered to be in format <user>@<host>, where:
 * <user> is a sequence of letters and digits, where '.', '-' and '_' can appear between them.
 * Examples of valid users: "stephan", "mike03", "s.johnson", "st_steward", "softuni-bulgaria",
 * "12345". Examples of invalid users: ''--123", ".....", "nakov_-", "_steve", ".info".
 * <host> is a sequence of at least two words, separated by dots '.'.
 * Each word is sequence of letters and can have hyphens '-' between the letters.
 * Examples of hosts: "softuni.bg", "software-university.com", "intoprogramming.info",
 * "mail.softuni.org". Examples of invalid hosts: "helloworld", ".unknown.soft.",
 * "invalid-host-", "invalid-".
 * Example of valid emails: [email protected], [email protected],
 * [email protected], [email protected], [email protected]. */


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class ExtractEmails {
    public static void main(String[] args) {
        StringBuilder text = new StringBuilder();

        try (BufferedReader reader =
                     new BufferedReader(new InputStreamReader(System.in))) {

            String line = reader.readLine();
            while (!line.equals("end")) {
                text.append(line);

                line = reader.readLine();
            }

        } catch (IOException e) {
            e.printStackTrace();
        }

        Pattern pattern = Pattern
                .compile("(^|\\s)[a-z0-9][-._a-z0-9]*[a-z0-9]@[a-z0-9][-.a-z0-9]*[a-z0-9]\\.[a-z]{2,}");

        Matcher matcher = pattern.matcher(text);
        while (matcher.find()) {
            System.out.println(matcher.group().trim());
        }
    }
}