Tag Libraries.gdoc

h1. Tag Library Usage

A tag library fulfills role of "view helper" in the Model View Controller (MVC) pattern and helps with GSP rendering. In Grails a tag library is a class with a name that ends in the convention "TagLib" and lives in the @grails-app/taglib@ directory. Use the [create-tag-lib|commandLine] command create a tag library:

{code:java}
grails create-tag-lib format
{code}

or with your favourite IDE or text editor.

{code:java}
import java.text.SimpleDateFormat

class FormatTagLib {
    def dateFormat = { attrs, body ->
        out << new SimpleDateFormat(attrs.format).format(attrs.value)
    }
}
{code}

Each Closure property in a tag library that takes one or two arguments is considered a tag. The first argument (typically named @attrs@) will contain the attributes of the tag whilst the optional second argument (typically named @body@) is Closure that represents the inner HTML of the tag declaration from the GSP.

Refer to the user guide topic on [Tag Libraries|guide:taglibs] for more information.