<p>I'm trying to come up with a Java regex that will match a filename only if it has a valid extension. For example it should match "foo.bar" and "foo.b", but neither "foo." nor "foo".</p>

<p>I've written the following test program</p>

<pre><code>public static void main(String[] args) {
  Pattern fileExtensionPattern = Pattern.compile("\\.\\w+\\z");

  boolean one = fileExtensionPattern.matcher("foo.bar").matches();
  boolean two = fileExtensionPattern.matcher("foo.b").matches();
  boolean three = fileExtensionPattern.matcher("foo.").matches();
  boolean four = fileExtensionPattern.matcher("foo").matches();

  System.out.println(one + " " + two + " " + three + " " + four);
}
</code></pre>

<p>I expect this to print "true true false false", but instead it prints false for all 4 cases. Where am I going wrong?</p>

<p>Cheers,
Don</p>

The
Matcher.matches()
function tries to match the pattern against the entire input.  Thus, you have to add
```
.*
```
to the beginning of your regex (and the
```
\\Z
```
at the end is superfluous, too), or use the
find()
method.