=== Regular Expressions

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String parameters can be checked to ensure that they match a regular expression.
There are three elements involved in this:

* The xref:refguide:applib:index/annotation/Parameter.adoc#regexPattern[regexPattern()] element validates the contents of any string parameter with respect to a regular expression pattern.
It is ignored if applied to parameters of any other type.

* The xref:refguide:applib:index/annotation/Parameter.adoc#regexPatternFlags[regexPatternFlags()] element specifies flags that modify the handling of the pattern.
The values are those that would normally be passed to `java.util.regex.Pattern#compile(String,int)`.

* The xref:refguide:applib:index/annotation/Parameter.adoc#regexPatternReplacement[regexPatternReplacement()] element specifies the error message to show if the provided argument does not match the regex pattern.

For example:

[source,java]
----
public class Customer {
    public void updateEmail(
            @Parameter(
                regexPattern = "(\\w+\\.)*\\w+@(\\w+\\.)+[A-Za-z]+",
                regexPatternFlags = Pattern.CASE_INSENSITIVE,
                regexPatternReplacement =
                    "Must be valid email address " +
                    "(containing a '@') symbol"                     // <.>
            )
            @ParameterLayout(named = "Email")
            final String email) {
        ...
    }
)
----
<.> Note that there is currently no i18n support for this phrase.

