Summary of what I learned in today's live coding stream at https://twitch.tv/jitterted.
Matching newlines in RegEx
For the text I'm working with, I want regex search and replace to work across newlines (by default matching stops at a new line). Today I learned that I need to pre-pend this: (?s) to the regex String, which turns on DOTALL mode and therefore the dot wildcard will match across new lines. For details, see the JavaDoc: https://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html#DOTALL
Example of matches() using DOTALL
I want to search for text that's surrounded by 3 equal signs (===)
both at the beginning and at the end. The text can span multiple lines.
For example:
Before text.
===
Text inside the equals signs.
===
Outside text.
To search for the text, I would use the String.matches() method, like this:
boolean found = text.matches("(?s)===(.*?)===");
Which returns true if the pattern is found, as it would be in the
above example.
Example of replaceAll using DOTALL
If I want to replace the triple backtick code block with a <pre> tag (as I do in my live stream), then I'd do this:
Which would output this:
<pre>
public class Stock {
}
</pre>
Scanner for Parsing
I used Scanner in a few places and forgot about it until I was reminded by one of my regular stream viewers (thanks flamaddidle84!). Today, I wanted to parse some text and split the lines whenever there was an empty line between two non-empty lines.
For example, given this text:
Block one.
Still part of block one.
Yep, still part of block one.
Block two here.
Still part of block two.
Last block here.
I want to end up with three pieces of text. Using the Scanner class and the fact that the delimiter can be specified, this is all I needed:
Scanner scanner = new Scanner(text).useDelimiter("\n\n");
Then, all I had to do was use the scanner.tokens() method (only available starting in Java 9) to give me a stream of these blocks, e.g.:
scanner.tokens()
.map(s -> "<p>" + s + "</p>\n")
.collect(Collectors.toList());
Which uses replaceAll on each block to surround it with the HTML <p> (paragraph) tag. Here's a full code example:
When run, it results in this output:
<p>Block one.
Still part of block one.
Yep, still part of block one.</p>
<p>Block two here.
Still part of block two.</p>
<p>Last block here.
</p>
Watch Me Live Code on Twitch
If you want to see how I use TDD to code in Java and Spring, and learn with me, tune in to my daily stream at Twitch.TV/JitterTed. I'm usually streaming from 12pm PDT (1900 UTC) for around 3 hours. You can also chat with me on my Discord.
Top comments (0)