(Quick Reference)

8.2.2.3 Search and Filtering

Version: 3.2.6

8.2.2.3 Search and Filtering

If you have collections of objects you often need to sort and filter them. Use the findAll and grep tags for these tasks:

Stephen King's Books:
<g:findAll in="${books}" expr="it.author == 'Stephen King'">
     <p>Title: ${it.title}</p>
</g:findAll>

The expr attribute contains a Groovy expression that can be used as a filter. The grep tag does a similar job, for example filtering by class:

<g:grep in="${books}" filter="NonFictionBooks.class">
     <p>Title: ${it.title}</p>
</g:grep>

Or using a regular expression:

<g:grep in="${books.title}" filter="~/.*?Groovy.*?/">
     <p>Title: ${it}</p>
</g:grep>

The above example is also interesting due to its usage of GPath. GPath is an XPath-like language in Groovy. The books variable is a collection of Book instances. Since each Book has a title, you can obtain a list of Book titles using the expression books.title. Groovy will auto-magically iterate the collection, obtain each title, and return a new list!