| <!doctype html> |
| <!-- Generated by FreeMarker/Docgen from DocBook --> |
| <html lang="en" class="page-type-section"> |
| <head prefix="og: http://ogp.me/ns#"> |
| <meta charset="utf-8"> |
| <title>Basics - FreeMarker Manual</title> |
| <meta http-equiv="X-UA-Compatible" content="IE=edge"> |
| <meta name="viewport" content="width=device-width,initial-scale=1"> |
| <meta name="format-detection" content="telephone=no"> |
| <meta property="og:site_name" content="FreeMarker Manual"> |
| <meta property="og:title" content="Basics"> |
| <meta property="og:locale" content="en_US"> |
| <meta property="og:url" content="http://example.com/pgui_datamodel_basics.html"> |
| <link rel="canonical" href="http://example.com/pgui_datamodel_basics.html"> |
| <link rel="icon" href="favicon.png" type="image/png"> |
| <link rel="stylesheet" type="text/css" href="docgen-resources/docgen.min.css?1594338519184"> |
| </head> |
| <body itemscope itemtype="https://schema.org/Code"> |
| <meta itemprop="url" content="http://example.com/"> |
| <meta itemprop="name" content="FreeMarker Manual"> |
| |
| <!--[if lte IE 9]> |
| <div style="background-color: #C00; color: #fff; padding: 12px 24px;">Please use a modern browser to view this website.</div> |
| <![endif]--><div class="header-top-bg"><div class="site-width header-top"><a class="logo" href="http://example.com" role="banner"> <img itemprop="image" src="logo.png" alt="My Logo"> |
| </a></div></div><div class="header-bottom-bg"><div class="site-width search-row"><a href="index.html" class="navigation-header">FreeMarker Manual</a><div class="navigation-header"></div></div><div class="site-width breadcrumb-row"><ul class="breadcrumb" itemscope itemtype="http://schema.org/BreadcrumbList"><li class="step-0" itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a class="label" itemprop="item" href="index.html"><span itemprop="name">FreeMarker Manual</span></a></li><li class="step-1" itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a class="label" itemprop="item" href="pgui.html"><span itemprop="name">Programmer's Guide</span></a></li><li class="step-2" itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a class="label" itemprop="item" href="pgui_datamodel.html"><span itemprop="name">The Data Model</span></a></li><li class="step-3" itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a class="label" itemprop="item" href="pgui_datamodel_basics.html"><span itemprop="name">Basics</span></a></li></ul><div class="bookmarks" title="Bookmarks"><span class="sr-only">Bookmarks:</span><ul class="bookmark-list"><li><a href="alphaidx.html">Index</a></li><li><a href="gloss.html">Glossary</a></li><li><a href="ref.html">Reference</a></li><li><a href="app_faq.html">FAQ</a></li><li><a href="preface.html#test_target">Bőregér</a></li><li><a href="api/index.html">API</a></li><li><a href="../index.html">Home</a></li></ul></div></div></div> <div class="main-content site-width"> |
| <div class="content-wrapper"> |
| <div id="table-of-contents-wrapper" class="col-left"> |
| <script>var breadcrumb = ["FreeMarker Manual","Programmer\'s Guide","The Data Model","Basics"];</script> |
| <script src="toc.js?1594338519184"></script> |
| <script src="docgen-resources/main.min.js?1594338519184"></script> |
| </div> |
| <div class="col-right"><div class="page-content"><div class="page-title"><div class="pagers top"><a class="paging-arrow previous" href="pgui_datamodel.html"><span>Previous</span></a><a class="paging-arrow next" href="pgui_datamodel_scalar.html"><span>Next</span></a></div><div class="title-wrapper"> |
| <h1 class="content-header header-section1" id="pgui_datamodel_basics" itemprop="headline">Basics</h1> |
| </div></div><p>You have seen how to build a data-model in the <a href="pgui_quickstart.html">Getting Started</a> using the standard |
| Java classes (<code class="inline-code">Map</code>, <code class="inline-code">String</code>, |
| etc.). Internally, the variables available in the template are java |
| objects that implement the |
| <code class="inline-code">freemarker.template.TemplateModel</code> interface. But |
| you could use standard java collections as variables in your |
| data-model, because these were replaced with the appropriate |
| <code class="inline-code">TemplateModel</code> instances behind the scenes. This |
| facility is called <strong>object wrapping</strong>. |
| The object wrapping facility can convert <em>any</em> kind |
| of object transparently to the instances of classes that implement |
| <code class="inline-code">TemplateModel</code> interface. This makes it possible, |
| for example, to access <code class="inline-code">java.sql.ResultSet</code> as |
| sequence variable in templates, or to access |
| <code class="inline-code">javax.servlet.ServletRequest</code> objects as a hash |
| variable that contains the request attributes, or even to traverse XML |
| documents as FTL variables (<a href="xgui.html">see here</a>). To |
| wrap (convert) these objects, however, you need to plug the proper, so |
| called, object wrapper implementation (possibly your custom |
| implementation); this will be discussed <a href="pgui_datamodel_objectWrapper.html">later</a>. The meat for now |
| is that any object that you want to access from the templates, sooner |
| or later must be converted to an object that implements |
| <code class="inline-code">TemplateModel</code> interface. So first you should |
| familiarize yourself with writing of <code class="inline-code">TemplateModel</code> |
| implementations.</p><p>There is roughly one |
| <code class="inline-code">freemarker.template.TemplateModel</code> descendant |
| interface corresponding to each basic type of variable |
| (<code class="inline-code">TemplateHashModel</code> for hashes, |
| <code class="inline-code">TemplateSequenceModel</code> sequences, |
| <code class="inline-code">TemplateNumberModel</code> for numbers, etc.). For |
| example, if you want to expose a <code class="inline-code">java.sql.ResultSet</code> |
| as a sequence for the templates, then you have to write a |
| <code class="inline-code">TemplateSequenceModel</code> implementation that can read |
| <code class="inline-code">java.sql.ResultSet</code>-s. We used to say on this, that |
| you <em>wrap</em> the |
| <code class="inline-code">java.sql.ResultSet</code> with your |
| <code class="inline-code">TemplateModel</code> implementation, as basically you just |
| encapsulate the <code class="inline-code">java.sql.ResultSet</code> to provide |
| access to it with the common <code class="inline-code">TemplateSequenceModel</code> |
| interface. Note that a class can implement multiple |
| <code class="inline-code">TemplateModel</code> interfaces; this is why FTL variables |
| can have multiple types (see: <a href="dgui_datamodel_basics.html">Template Author's Guide/Values, Types/Basics</a>)</p><p>Note that a trivial implementation of these interfaces is |
| provided with the <code class="inline-code">freemarker.template</code> package. For |
| example, to convert a <code class="inline-code">String</code> to FTL string |
| variable, you can use <code class="inline-code">SimpleScalar</code>, to convert a |
| <code class="inline-code">java.util.Map</code> to FTL hash variable, you can use |
| <code class="inline-code">SimpleHash</code>, etc.</p><p>An easy way to try your own <code class="inline-code">TemplateModel</code> |
| implementation, is to create an instance of that, and drop it directly |
| into the data-model (as <code class="inline-code">put</code> it into the root hash). |
| The object wrapper will expose it untouched for the template, as it |
| already implements <code class="inline-code">TemplateModel</code>, so no conversion |
| (wrapping) needed. (This trick is also useful in cases when you do not |
| want the object wrapper to try to wrap (convert) a certain |
| object.)</p><div class="bottom-pagers-wrapper"><div class="pagers bottom"><a class="paging-arrow previous" href="pgui_datamodel.html"><span>Previous</span></a><a class="paging-arrow next" href="pgui_datamodel_scalar.html"><span>Next</span></a></div></div></div></div> </div> |
| </div> |
| <div class="site-footer"><div class="site-width"><div class="footer-top"><div class="col-left sitemap"></div><div class="col-right"><a class="xxe" href="http://www.xmlmind.com/xmleditor/" rel="nofollow" title="Edited with XMLMind XML Editor"><span>Edited with XMLMind XML Editor</span></a></div></div><div class="footer-bottom"> <p class="last-generated"> |
| Last generated: |
| <time itemprop="dateModified" datetime="2020-07-09T23:48:39Z" title="Thursday, July 9, 2020 11:48:39 PM GMT">2020-07-09 23:48:39 GMT</time> </p> |
| <p class="copyright"> |
| © <span itemprop="copyrightYear">1999</span>–2020 |
| <a itemtype="http://schema.org/Organization" itemprop="copyrightHolder" href="https://apache.org/">The Apache Software Foundation</a> </p> |
| </div></div></div></body> |
| </html> |