Apache Velocity

<h2 id="uses">Uses</h2>
<p>Some common types of applications that use Velocity are:
</p>
<ul><li><a href="/facts/Web_application/BLkF3BIN">Web applications</a>: <a href="/facts/Web_developer/Cd0mJftL">Web developers</a> render <a href="/facts/HTML/sSc3fT78">HTML</a> page structures.  The content is populated with dynamic information. The page is processed with <i>VelocityViewServlet</i> or any of a number of frameworks that support Velocity.</li>
<li><a href="/facts/Source_code/o9J6Jv23">Source code</a> generation: Velocity can be used to generate <a href="/facts/Java_(programming_language)/9ScgFyAL">Java</a>, <a href="/facts/SQL/UjQLJcYm">SQL</a>, or <a href="/facts/PostScript/h2XwbcmC">PostScript</a> source code, based on <a href="/facts/Web_template/zWstHsCF">templates</a>. A number of <a href="/facts/Open-source_software/HzTaB8E9">open source</a> and commercial development <a href="/facts/Software_package_(installation)/kEX4kx7g">software packages</a> use Velocity in this manner.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a></li>
<li>Automatic <a href="/facts/Email/6pD9GLtI">emails</a>: Many applications generate automatic emails for account signup, <a href="/facts/Password/WEoul230">password</a> reminders, or automatically sent reports. Using Velocity, the email <a href="/facts/Web_template/zWstHsCF">template</a> can be stored in a <a href="/facts/Text_file/zYW4JmES">text file</a>, rather than directly embedded in Java code.</li>
<li><a href="/facts/XML/clNgUfWk">XML</a> transformation: Velocity provides an <a href="/facts/Apache_Ant/CT6ABXEx">Ant</a> task, called Anakia, which reads an XML file and makes it available to a Velocity template. A common application is to convert <a href="/facts/Software_documentation/cSXDUPPg">software documentation</a> stored in a generic "xdoc" format into a styled HTML document.</li>
<li>AWS API Gateway uses Apache Velocity engine for body mapping templates - <a href="/facts/JSON/bs1rUAhd">JSON</a> is output.</li></ul>
<h2 id="code-examples">Code examples</h2>
<p>The following <a href="/facts/Web_template/zWstHsCF">template</a>:
</p>
## Velocity Hello World
<html>
    <body>
        #set( $foo = "Velocity" )
        ## followed by
        Hello $foo World!
    </body>
</html>

<p>processed by Velocity produces the following HTML:
</p>
<html>
    <body>
        Hello Velocity World!
    </body>
</html>
<p>
Another example using conditions:</p>#if( $foo < 10 )
    **Go North**
#elseif( $foo == 10 )
    **Go East**
#elseif( $bar == 6 )
    **Go South**
#else
    **Go West**
#end
<p>AWS API Gateway body mapping template, for <a href="/facts/Amazon_DynamoDB/UPbk0ydN">DynamoDB</a> HTTP:</p>{
    "TableName": "happy-marketer",
    "KeyConditionExpression": "pk = :pk AND begins_with(sk, :sk)",
    #if ($input.params('projectStatus') == 'archived')
    "FilterExpression": "projectStatus = :Archived",
    #else
    "FilterExpression": "projectStatus = :InProgress OR projectStatus = :Completed",
    #end
    "ExpressionAttributeValues": {
        ":pk": {
            "S": "project"
        },
        ":sk": {
            "S": "$context.authorizer.claims.email"
        },
        #if ($input.params('projectStatus') == 'archived')
        ":Archived": {
            "S": "Archived"
        }
        #else
        ":InProgress": {
            "S": "In Progress"
        },
        ":Completed": {
            "S": "Completed"
        }
        #end
    }
}
<p>Another example with <a href="https://stackoverflow.com/questions/38647604/api-gateway-body-mapping-template-optional-body-parameters">optional array</a>; without condition will fail because of invalid resulting JSON:</p>{
    "email": "$context.authorizer.claims.email"
    #if ($input.params('countries') != "")
    , "countries": $input.params('countries')
    #end
}
<p>The syntax and overall concept of the Apache Velocity templates is similar to the syntax of the older <a href="/facts/WebMacro/y4a94bQn">WebMacro</a> template engine, which is now also an open source project. 
</p><h2 id="see-also">See also</h2>
<ul>
<li>Free and open-source software portal</li></ul>
<ul><li>Apache Torque</li>
<li><a href="/facts/FreeMarker/FvP4jVza">FreeMarker</a></li>
<li><a href="/facts/Jakarta_Server_Pages/LAr4ALkb">Jakarta Server Pages</a></li>
<li><a href="/facts/Thymeleaf/yuuyLXSz">Thymeleaf</a></li></ul>

<h2 id="bibliography">Bibliography</h2>

<ul><li>Harrop, Rob; Darwin, Ian (August 30, 2004), <a href="https://web.archive.org/web/20090705091506/http://www.apress.com/book/view/9781590594100"><i>Pro Jakarta Velocity: From Professional to Expert</i></a> (1st ed.), <a href="/facts/Apress/pxdyEeD3">Apress</a>, p. 370, <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-1-59059-410-0, archived from <a href="http://www.apress.com/book/view/9781590594100">the original</a> on July 5, 2009, retrieved September 4, 2009</li>
<li>Cole, Jim; D. Gradecki, Joseph (July 16, 2003), <a href="https://web.archive.org/web/20121007002812/http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471457949.html"><i>Mastering Apache Velocity</i></a> (1st ed.), <a href="/facts/John_Wiley_%26_Sons/53g3LqJc">Wiley</a>, p. 372, <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-471-45794-7, archived from <a href="http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471457949.html">the original</a> on October 7, 2012, retrieved September 4, 2009</li></ul>

<h2 id="external-links">External links</h2>
<ul><li><a href="https://velocity.apache.org/">Velocity at Apache</a></li>
<li><a href="https://velocity.apache.org/engine/1.7/user-guide.html">User guide</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"PoweredByVelocity". Velocity Wiki. Wiki.apache.org. 2009-12-30. Archived from the original on 23 March 2010. Retrieved 2010-03-29. <a href="https://wiki.apache.org/velocity/PoweredByVelocity" target="_blank">https://wiki.apache.org/velocity/PoweredByVelocity</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
</ol>

Apache Velocity open-in-new

Apache Velocity