The question why Grails has GSP when there is JSP is a natural one. Here are a few substantial differences:

  1. A GSP allows the same ${…} expressions as in a Groovy GString. JSP EL expressions are restricted to object navigation, which is generally a good idea but can also make it difficult to access anything that isn’t a getter (e.g. String length()). JSTL functions provide some help but the more general case requires creating static helper methods, registering them through a taglib descriptor, adding a taglib declaration, and finally using the function.
  2. Using Groovy in logical and iterative tags comes with major perks such as the safe navigation operator: ${customer.phones?.size()} or the Elvis operator: ${totalCount ?: 10}.
  3. The ability to invoke Grails dynamic tags as methods makes it easier to produce well-formed markup:
    <!-- With a regular tag -->
    <a href="<g:createLink action="list" />">A dynamic link</a>
    <!-- As a method call -->
    <a href="${createLink(action:'list')}">A dynamic link</a>
  4. GSP provides a much simpler mechanism for creating and testing custom tag libraries in Groovy that does not require tld files and taglib declarations and of course uses Groovy. Here is a sample test case for a Grails tag library:
    import grails.test.*
    class CustomerTagLibTests extends TagLibUnitTestCase {
      void testRepeat() {
        tagLib.repeat(times: '2') {
        assertEquals 'output<br/>output<br/>', tagLib.out.toString()
  5. The Grails paginate tag. It is such a common need for web applications. In comparison to the Displaytag library I think the Grails paginate tag is more lightweight and more usable.
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4 Responses to GSP and JSP

  1. juhu says:

    But Displaytag does more then paginate. It also groups, format and export the lists to csv, pdf, excel an xml.

  2. Administrator says:

    You’re right juhu. Displaytag is a very feature-rich tag library (perhaps a little bit to the detriment of clarity) whereas the Grails paginate tag is more narrowly focused on pagination as its name indicates. What I had in mind was that displaytag wraps the generation of the entire table, which in turn requires you to know how to customize its style, links, query parameters, etc.

  3. Pingback: Getting started with Grails and Groovy - Java4Developers

  4. Pingback: Getting started with Grails and Groovy « hop2croft's software development Blog

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