RegEx in Java: how to deal with newline

RegEx in Java: how to deal with newline

In Java, regular expressions can handle newlines in a couple of different ways, depending on what you're trying to achieve. If you want to match a pattern that includes newline characters, or if you want to match across multiple lines, you'll need to use specific regex constructs and flags. Here are some common scenarios and solutions:

Matching Newline Characters

If you want to include newline characters (\n) in your match, you can use the . character in your regex pattern along with the Pattern.DOTALL flag. By default, . does not match newline characters, but Pattern.DOTALL changes this behavior.

Example:

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class RegexExample {
    public static void main(String[] args) {
        String text = "Hello\nWorld";
        Pattern pattern = Pattern.compile("Hello.World", Pattern.DOTALL);
        Matcher matcher = pattern.matcher(text);

        if (matcher.find()) {
            System.out.println("Match found: " + matcher.group());
        } else {
            System.out.println("No match found.");
        }
    }
}

In this example, Hello.World will match the string "Hello\nWorld" because Pattern.DOTALL makes . match newline characters.

Matching Patterns Across Multiple Lines

If your goal is to apply a regex to each line individually in a multiline string, you can use the Pattern.MULTILINE flag. This flag changes the behavior of ^ and $ from matching at the start and end of the entire input string to matching at the start and end of each line within the string.

Example:

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class RegexExample {
    public static void main(String[] args) {
        String text = "First line\nSecond line\nThird line";
        Pattern pattern = Pattern.compile("^Second.*", Pattern.MULTILINE);
        Matcher matcher = pattern.matcher(text);

        while (matcher.find()) {
            System.out.println("Match found: " + matcher.group());
        }
    }
}

Here, ^Second.* will match "Second line" even though it is not at the start of the entire string, because Pattern.MULTILINE makes ^ match the start of any line.

Escaping Newline Characters in a Pattern

If you need to include a literal newline character in your pattern (for example, if you're looking for a specific line break in the text), you can insert \n (and \r for a carriage return if needed) directly into your pattern.

Example:

Pattern pattern = Pattern.compile("line\nSecond");

In this case, the pattern matches "line" followed by a newline character followed by "Second".

Handling System-Dependent Line Separators

Remember that some systems use \r\n (carriage return and line feed) for newlines. If you are working with text from different sources or want to make your regex system-independent, you might need to account for both \n and \r\n in your patterns. You can use something like \r?\n to match both.

In summary, handling newlines in Java regular expressions depends on whether you want to match newline characters themselves or handle multiline strings. You can use the Pattern.DOTALL and Pattern.MULTILINE flags and the \n and \r\n sequences in your patterns to achieve the desired behavior.

More Tags

powerpoint html5-video addeventlistener drive android-support-library azure-servicebus-topics offline uiviewcontroller parseexception self-signed

More Java Questions

More Animal pregnancy Calculators

More Auto Calculators

More Everyday Utility Calculators

More Livestock Calculators