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<div class="col-right"><div class="page-content"><div class="page-title"><div class="pagers top"><a class="paging-arrow previous" href="pgui_misc_logging.html"><span>Previous</span></a><a class="paging-arrow next" href="pgui_misc_secureenv.html"><span>Next</span></a></div><div class="title-wrapper">
<h1 class="content-header header-section1" id="pgui_misc_servlet" itemprop="headline">Using FreeMarker with servlets</h1>
</div></div><div class="page-menu">
<div class="page-menu-title">Page Contents</div>
<ul><li><a class="page-menu-link" href="#pgui_misc_servlet_model2" data-menu-target="pgui_misc_servlet_model2">Using FreeMarker for ``Model 2&#39;&#39;</a></li><li><a class="page-menu-link" href="#pgui_misc_servlet_include" data-menu-target="pgui_misc_servlet_include">Including content from other web application
resources</a></li><li><a class="page-menu-link" href="#autoid_55" data-menu-target="autoid_55">Using JSP custom tags in FTL</a></li><li><a class="page-menu-link" href="#autoid_56" data-menu-target="autoid_56">Embed FTL into JSP pages</a></li></ul> </div><a name="topic.servlet"></a><p>In a fundamental sense, using FreeMarker in the web application
space is no different from anywhere else; FreeMarker writes its output
to a <code class="inline-code">Writer</code> that you pass to the
<code class="inline-code">Template.process</code> method, and it does not care if
that <code class="inline-code">Writer</code> prints to the console or to a file or
to the output stream of <code class="inline-code">HttpServletResponse</code>.
FreeMarker knows nothing about servlets and Web; it just merges Java
object with template files and generates text output from them. From
here, it is up to you how to build a Web application around
this.</p><p>But, probably you want to user FreeMarker with some already
existing Web application framework. Many frameworks rely on the
``Model 2&#39;&#39; architecture, where JSP pages handle presentation. If you
use such a framework (for example, <a href="http://jakarta.apache.org/struts">Apache Struts</a>),
then read on. For other frameworks please refer to the documentation
of the framework.</p>
<h2 class="content-header header-section2" id="pgui_misc_servlet_model2">Using FreeMarker for ``Model 2&#39;&#39;</h2>
<p>Many frameworks follow the strategy that the HTTP request is
dispatched to user-defined ``action&#39;&#39; classes that put data into
<code class="inline-code">ServletContext</code>, <code class="inline-code">HttpSession</code>
and <code class="inline-code">HttpServletRequest</code> objects as attributes, and
then the request is forwarded by the framework to a JSP page (the
view) that will generate the HTML page using the data sent with the
attributes. This is often referred as Model 2.</p>
<p class="center-img"> <img src="figures/model2sketch.png" alt="Figure"> </p>
<p>With these frameworks you can simply use FTL files instead of
JSP files. But, since your servlet container (Web application
server), unlike with JSP files, does not know out-of-the-box what to
do with FTL files, a little extra configuring is needed for your Web
application:</p>
<div class="orderedlist"><ol type="1">
<li>
<p>Copy <code class="inline-code">freemarker.jar</code> (from the
<code class="inline-code">lib</code> directory of the FreeMarker distribution)
into the <code class="inline-code">WEB-INF/lib</code> directory of your Web
application.</p>
</li>
<li>
<p>Insert the following section to the
<code class="inline-code">WEB-INF/web.xml</code> file of your Web application
(and adjust it if required):</p>
</li>
</ol></div>
<div class="code-wrapper"><pre class="code-block code-unspecified">&lt;servlet&gt;
&lt;servlet-name&gt;freemarker&lt;/servlet-name&gt;
&lt;servlet-class&gt;<strong>freemarker.ext.servlet.FreemarkerServlet</strong>&lt;/servlet-class&gt;
&lt;!-- FreemarkerServlet settings: --&gt;
&lt;init-param&gt;
&lt;param-name&gt;TemplatePath&lt;/param-name&gt;
&lt;param-value&gt;/&lt;/param-value&gt;
&lt;/init-param&gt;
&lt;init-param&gt;
&lt;param-name&gt;NoCache&lt;/param-name&gt;
&lt;param-value&gt;true&lt;/param-value&gt;
&lt;/init-param&gt;
&lt;init-param&gt;
&lt;param-name&gt;ContentType&lt;/param-name&gt;
&lt;param-value&gt;text/html&lt;/param-value&gt;
&lt;/init-param&gt;
&lt;!-- FreeMarker settings: --&gt;
&lt;init-param&gt;
&lt;param-name&gt;template_update_delay&lt;/param-name&gt;
&lt;param-value&gt;0&lt;/param-value&gt; &lt;!-- 0 is for development only! Use higher value otherwise. --&gt;
&lt;/init-param&gt;
&lt;init-param&gt;
&lt;param-name&gt;default_encoding&lt;/param-name&gt;
&lt;param-value&gt;ISO-8859-1&lt;/param-value&gt;
&lt;/init-param&gt;
&lt;init-param&gt;
&lt;param-name&gt;number_format&lt;/param-name&gt;
&lt;param-value&gt;0.##########&lt;/param-value&gt;
&lt;/init-param&gt;
&lt;load-on-startup&gt;1&lt;/load-on-startup&gt;
&lt;/servlet&gt;
&lt;servlet-mapping&gt;
&lt;servlet-name&gt;freemarker&lt;/servlet-name&gt;
&lt;url-pattern&gt;<strong>*.ftl</strong>&lt;/url-pattern&gt;
&lt;/servlet-mapping&gt;</pre></div>
<p>That&#39;s all. After this, you can use FTL files
(<code class="inline-code">*.ftl</code>) in the same manner as JSP
(<code class="inline-code">*.jsp</code>) files. (Of course you can choose another
extension besides <code class="inline-code">ftl</code>; it is just the
convention)</p>
<div class="callout note">
<strong class="callout-label">Note:</strong>
<p>How does it work? Let&#39;s examine how JSP-s work. Many servlet
container handles JSP-s with a servlet that is mapped to the
<code class="inline-code">*.jsp</code> request URL pattern. That servlet will
receive all requests where the request URL ends with
<code class="inline-code">.jsp</code>, find the JSP file based on the request
URL, and internally compiles it to a <code class="inline-code">Servlet</code>,
and then call the generated servlet to generate the page. The
<code class="inline-code">FreemarkerServlet</code> mapped here to the
<code class="inline-code">*.ftl</code> URL pattern does the same, except that
FTL files are not compiled to <code class="inline-code">Servlet</code>-s, but to
<code class="inline-code">Template</code> objects, and then the
<code class="inline-code">process</code> method of <code class="inline-code">Template</code>
will be called to generate the page.</p>
</div>
<p><a name="topic.servlet.scopeAttr"></a>For example,
instead of this JSP file (note that it heavily uses Struts tag-libs
to save designers from embedded Java monsters):</p>
<div class="code-wrapper"><pre class="code-block code-template">&lt;%@ taglib uri=&quot;/WEB-INF/struts-bean.tld&quot; prefix=&quot;bean&quot; %&gt;
&lt;%@ taglib uri=&quot;/WEB-INF/struts-logic.tld&quot; prefix=&quot;logic&quot; %&gt;
&lt;html&gt;
&lt;head&gt;&lt;title&gt;Acmee Products International&lt;/title&gt;
&lt;body&gt;
&lt;h1&gt;Hello &lt;bean:write name=&quot;user&quot;/&gt;!&lt;/h1&gt;
&lt;p&gt;These are our latest offers:
&lt;ul&gt;
&lt;logic:iterate name=&quot;latestProducts&quot; id=&quot;prod&quot;&gt;
&lt;li&gt;&lt;bean:write name=&quot;prod&quot; property=&quot;name&quot;/&gt;
for &lt;bean:write name=&quot;prod&quot; property=&quot;price&quot;/&gt; Credits.
&lt;/logic:iterate&gt;
&lt;/ul&gt;
&lt;/body&gt;
&lt;/html&gt;</pre></div>
<p>you can use this FTL file (use <code class="inline-code">ftl</code> file
extension instead of <code class="inline-code">jsp</code>):</p>
<div class="code-wrapper"><pre class="code-block code-template">&lt;html&gt;
&lt;head&gt;&lt;title&gt;Acmee Products International&lt;/title&gt;
&lt;body&gt;
&lt;h1&gt;Hello ${user}!&lt;/h1&gt;
&lt;p&gt;These are our latest offers:
&lt;ul&gt;
&lt;#list latestProducts as prod&gt;
&lt;li&gt;${prod.name} for ${prod.price} Credits.
&lt;/#list&gt;
&lt;/ul&gt;
&lt;/body&gt;
&lt;/html&gt;</pre></div>
<div class="callout warning">
<strong class="callout-label">Warning!</strong>
<p>In FreeMarker <code class="inline-code">&lt;html:form
action=&quot;/query&quot;&gt;<em class="code-color">...</em>&lt;/html:form&gt;</code>
is just static text, so it is printed to the output as is, like
any other XML or HTML markup. JSP tags are just FreeMarker
directives, nothing special, so you <em>use FreeMarker
syntax</em> for calling them, not JSP syntax:
<code class="inline-code">&lt;@html.form
action=&quot;/query&quot;&gt;<em class="code-color">...</em>&lt;/@html.form&gt;</code>.
Note that in the FreeMarker syntax you <em>don&#39;t use
<code class="inline-code">${<em class="code-color">...</em>}</code> in
parameters</em> as in JSP, and you <em>don&#39;t quote the
parameter values</em>. So this is
<em>WRONG</em>:</p>
<div class="code-wrapper"><pre class="code-block code-template">&lt;#-- WRONG: --&gt;
&lt;@my.jspTag color=&quot;${aVariable}&quot; name=&quot;aStringLiteral&quot;
width=&quot;100&quot; height=${a+b} /&gt;</pre></div>
<p>and this is good:</p>
<div class="code-wrapper"><pre class="code-block code-template">&lt;#-- Good: --&gt;
&lt;@my.jspTag color=aVariable name=&quot;aStringLiteral&quot;
width=100 height=a+b /&gt;</pre></div>
</div>
<p>In both templates, when you refer to <code class="inline-code">user</code>
and <code class="inline-code">latestProduct</code>, it will first try to find a
variable with that name that was created in the template (like
<code class="inline-code">prod</code>; if you master JSP: a page scope attribute).
If that fails, it will try to look up an attribute with that name in
the <code class="inline-code">HttpServletRequest</code>, and if it is not there
then in the <code class="inline-code">HttpSession</code>, and if it still doesn&#39;t
find it then in the <code class="inline-code">ServletContext</code>. In the case
of FTL this works because <code class="inline-code">FreemarkerServlet</code>
builds the data-model from the attributes of the mentioned 3
objects. That is, in this case the root hash is not a
<code class="inline-code">java.util.Map</code> (as it was in some example codes in
this manual), but
<code class="inline-code">ServletContext</code>+<code class="inline-code">HttpSession</code>+<code class="inline-code">HttpServletRequest</code>;
FreeMarker is pretty flexible about what the data-model is. So if
you want to put variable <code class="inline-code">&quot;name&quot;</code> into the
data-model, then you call
<code class="inline-code">servletRequest.setAttribute(&quot;name&quot;, &quot;Fred&quot;)</code>; this
is the logic of Model 2, and FreeMarker adapts itself to it.</p>
<p><code class="inline-code">FreemarkerServlet</code> also puts 3 hashes into
the data-model, by which you can access the attributes of the 3
objects directly. The hash variables are:
<code class="inline-code">Request</code>, <code class="inline-code">Session</code>,
<code class="inline-code">Application</code> (corresponds to
<code class="inline-code">ServletContext</code>). It also exposes another hash
named <code class="inline-code">RequestParameters</code> that provides access to
the parameters of the HTTP request.</p>
<p><code class="inline-code">FreemarkerServlet</code> has various init-params.
It can be set up to load templates from an arbitrary directory, from
the classpath, or relative to the Web application directory. You can
set the charset used for templates. You can set up what object
wrapper do you want to use. Etc.</p>
<p><code class="inline-code">FreemarkerServlet</code> is easily tailored to
special needs through subclassing. Say, if you need to have
additional variables available in your data-model for all templates,
subclass the servlet and override the
<code class="inline-code">preTemplateProcess()</code> method to shove any
additional data you need into the model before the template gets
processed. Or subclass the servlet, and set these globally available
variables as <a href="pgui_config_sharedvariables.html">shared
variables</a> in the <code class="inline-code">Configuration</code>.</p>
<p>For more information please read the Java API documentation of
the class.</p>
<h2 class="content-header header-section2" id="pgui_misc_servlet_include">Including content from other web application
resources</h2>
<p>You can use the <code class="inline-code">&lt;@include_page
path=&quot;...&quot;/&gt;</code> custom directive provided by the
<code class="inline-code">FreemarkerServlet</code> (since 2.3.15) to include the
contents of another web application resource into the output; this
is often useful to integrate output of JSP pages (living alongside
the FreeMarker templates in the same web server) into the FreeMarker
template output. Using:</p>
<div class="code-wrapper"><pre class="code-block code-template">&lt;@include_page path=&quot;path/to/some.jsp&quot;/&gt;</pre></div>
<p>is identical to using this tag in JSP:</p>
<div class="code-wrapper"><pre class="code-block code-template">&lt;jsp:include page=&quot;path/to/some.jsp&quot;&gt;</pre></div>
<div class="callout note">
<strong class="callout-label">Note:</strong>
<p><code class="inline-code">&lt;@include_page ...&gt;</code> is not to be
confused with <code class="inline-code">&lt;#include ...&gt;</code>, as the last
is for including FreeMarker templates without involving the
Servlet container. An <code class="inline-code">&lt;#include ...&gt;</code>-ed
template shares the template processing state with the including
template, such as the data-model and the template-language
variables, while <code class="inline-code">&lt;@include_page ...&gt;</code>
starts an independent HTTP request processing.</p>
</div>
<div class="callout note">
<strong class="callout-label">Note:</strong>
<p>Some Web Application Frameworks provide their own solution
for this, in which case you possibly should use that instead. Also
some Web Application Frameworks don&#39;t use
<code class="inline-code">FreemarkerServlet</code>, so
<code class="inline-code">include_page</code> is not available.</p>
</div>
<p>The path can be relative or absolute. Relative paths are
interpreted relative to the URL of the current HTTP request (one
that triggered the template processing), while absolute paths are
absolute in the current servlet context (current web application).
You can not include pages from outside the current web application.
Note that you can include any page, not just a JSP page; we just
used page with path ending in <code class="inline-code">.jsp</code> as an
illustration.</p>
<p>In addition to the <code class="inline-code">path</code> parameter, you can
also specify an optional parameter named
<code class="inline-code">inherit_params</code> with a boolean value (defaults to
true when not specified) that specifies whether the included page
will see the HTTP request parameters of the current request or
not.</p>
<p>Finally, you can specify an optional parameter named
<code class="inline-code">params</code> that specifies new request parameters that
the included page will see. In case inherited parameters are passed
too, the values of specified parameters will get prepended to the
values of inherited parameters of the same name. The value of
<code class="inline-code">params</code> must be a hash, with each value in it
being either a string, or a sequence of strings (if you need
multivalued parameters). Here&#39;s a full example:</p>
<div class="code-wrapper"><pre class="code-block code-template">&lt;@include_page path=&quot;path/to/some.jsp&quot; inherit_params=true params={&quot;foo&quot;: &quot;99&quot;, &quot;bar&quot;: [&quot;a&quot;, &quot;b&quot;]}/&gt;</pre></div>
<p>This will include the page
<code class="inline-code">path/to/some.jsp</code>, pass it all request parameters
of the current request, except for &quot;foo&quot; and &quot;bar&quot;, which will be
set to &quot;99&quot; and multi-value of &quot;a&quot;, &quot;b&quot;, respectively. In case the
original request already had values for these parameters, the new
values will be prepended to the existing values. I.e. if &quot;foo&quot; had
values &quot;111&quot; and &quot;123&quot;, then it will now have values &quot;99&quot;, &quot;111&quot;,
&quot;123&quot;.</p>
<p><span class="marked-for-programmers">It is in fact possible to pass
non-string values for parameter values within
<code class="inline-code">params</code>. Such a value will be converted to a
suitable Java object first (i.e. a Number, a Boolean, a Date, etc.),
and then its Java <code class="inline-code">toString()</code> method will be used
to obtain the string value. It is better to not rely on this
mechanism, though, and instead explicitly ensure that parameter
values that aren&#39;t strings are converted to strings on the template
level where you have control over formatting using the
<code class="inline-code">?string</code> and <code class="inline-code">?c</code> built-ins.
</span></p>
<h2 class="content-header header-section2" id="autoid_55">Using JSP custom tags in FTL</h2>
<p><code class="inline-code">FreemarkerServlet</code> puts a hash
<code class="inline-code">JspTaglibs</code> into the data-model, what you can use
to access JSP taglibs. The JSP custom tags will be accessible as
plain user-defined directives. For example, this is a JSP file that
uses some Struts tags:</p>
<div class="code-wrapper"><pre class="code-block code-template">&lt;%@page contentType=&quot;text/html;charset=ISO-8859-2&quot; language=&quot;java&quot;%&gt;
&lt;%@taglib uri=&quot;/WEB-INF/struts-html.tld&quot; prefix=&quot;html&quot;%&gt;
&lt;%@taglib uri=&quot;/WEB-INF/struts-bean.tld&quot; prefix=&quot;bean&quot;%&gt;
&lt;html&gt;
&lt;body&gt;
&lt;h1&gt;&lt;bean:message key=&quot;welcome.title&quot;/&gt;&lt;/h1&gt;
&lt;html:errors/&gt;
&lt;html:form action=&quot;/query&quot;&gt;
Keyword: &lt;html:text property=&quot;keyword&quot;/&gt;&lt;br&gt;
Exclude: &lt;html:text property=&quot;exclude&quot;/&gt;&lt;br&gt;
&lt;html:submit value=&quot;Send&quot;/&gt;
&lt;/html:form&gt;
&lt;/body&gt;
&lt;/html&gt;</pre></div>
<p>And this is the (near) equivalent FTL:</p>
<div class="code-wrapper"><pre class="code-block code-template">&lt;#assign html=JspTaglibs[&quot;/WEB-INF/struts-html.tld&quot;]&gt;
&lt;#assign bean=JspTaglibs[&quot;/WEB-INF/struts-bean.tld&quot;]&gt;
&lt;html&gt;
&lt;body&gt;
&lt;h1&gt;&lt;@bean.message key=&quot;welcome.title&quot;/&gt;&lt;/h1&gt;
&lt;@html.errors/&gt;
&lt;@html.form action=&quot;/query&quot;&gt;
Keyword: &lt;@html.text property=&quot;keyword&quot;/&gt;&lt;br&gt;
Exclude: &lt;@html.text property=&quot;exclude&quot;/&gt;&lt;br&gt;
&lt;@html.submit value=&quot;Send&quot;/&gt;
&lt;/@html.form&gt;
&lt;/body&gt;
&lt;/html&gt;</pre></div>
<p>Since JSP custom tags are written to operate in JSP
environment, they assume that variables (often referred as ``beans&#39;&#39;
in JSP world) are stored in 4 scopes: page scope, request scope,
session scope and application scope. FTL has no such notation (the 4
scopes), but <code class="inline-code">FreemarkerServlet</code> provides emulated
JSP environment for the custom JSP tags, which maintains
correspondence between the ``beans&#39;&#39; of JSP scopes and FTL
variables. For the custom JSP tags, the request, session and
application scopes are exactly the same as with real JSP: the
attributes of the <code class="inline-code">javax.servlet.ServletContext</code>,
<code class="inline-code">HttpSession</code> and <code class="inline-code">ServerRequest</code>
objects. From the FTL side you see these 3 scopes together as the
data-model, as it was explained earlier. The page scope corresponds
to the FTL global variables (see the <a href="ref_directive_global.html#ref.directive.global"><code>global</code>
directive</a>). That is, if you create a variable with the
<code class="inline-code">global</code> directive, it will be visible for the
custom tags as page scope variable through the emulated JSP
environment. Also, if a JSP-tag creates a new page scope variable,
the result will be the same as if you create a variable with the
<code class="inline-code">global</code> directive. Note that the variables in the
data-model are not visible as page-scope attributes for the JSP
tags, despite that they are globally visible, since the data-model
corresponds to the request, session and application scopes, not the
page-scope.</p>
<p>On JSP pages you quote all attribute values, it does not mater
if the type of the parameter is string or boolean or number. But
since custom tags are accessible in FTL templates as user-defined
FTL directives, you have to use the FTL syntax rules inside the
custom tags, not the JSP rules. So when you specify the value of an
``attribute&#39;&#39;, then on the right side of the <code class="inline-code">=</code>
there is an <a href="dgui_template_exp.html">FTL expression</a>.
Thus, <em>you must not quote boolean and numerical parameter
values</em> (e.g. <code class="inline-code">&lt;@tiles.insert
page=&quot;/layout.ftl&quot; flush=true/&gt;</code>), or they are
interpreted as string values, and this will cause a type mismatch
error when FreeMarker tries to pass the value to the custom tag that
expects non-string value. Also note, that naturally, you can use any
FTL expression as attribute value, such as variables, calculated
values, etc. (e.g. <code class="inline-code">&lt;@tiles.insert page=layoutName
flush=foo &amp;&amp; bar/&gt;</code>).</p>
<p>FreeMarker does not rely on the JSP support of the servlet
container in which it is run when it uses JSP taglibs since it
implements its own lightweight JSP runtime environment. There is
only one small detail to pay attention to: to enable the FreeMarker
JSP runtime environment to dispatch events to JSP taglibs that
register event listeners in their TLD files, you should add this to
the <code class="inline-code">WEB-INF/web.xml</code> of your Web
application:</p>
<div class="code-wrapper"><pre class="code-block code-unspecified">&lt;listener&gt;
&lt;listener-class&gt;freemarker.ext.jsp.EventForwarding&lt;/listener-class&gt;
&lt;/listener&gt;</pre></div>
<p>Note that you can use JSP taglibs with FreeMarker even if the
servlet container has no native JSP support, just make sure that the
<code class="inline-code">javax.servlet.jsp.*</code> packages for JSP 1.2 (or
later) are available to your Web application. If your servlet
container comes with JSP 1.1, then you have to obtain the following
six classes (for example you can extract them from the jar-s of
Tomcat 5.x or Tomcat 4.x), and copy them into your webapp&#39;s
<code class="inline-code">WEB-INF/classes/<em class="code-color">...</em></code>
directory: <code class="inline-code">javax.servlet.jsp.tagext.IterationTag</code>,
<code class="inline-code">javax.servlet.jsp.tagext.TryCatchFinally</code>,
<code class="inline-code">javax.servlet.ServletContextListener</code>,
<code class="inline-code">javax.servlet.ServletContextAttributeListener</code>,
<code class="inline-code">javax.servlet.http.HttpSessionAttributeListener</code>,
<code class="inline-code">javax.servlet.http.HttpSessionListener</code>. But
beware, since containers that come with JSP 1.1 usually use earlier
Serlvet versions than 2.3, event listeners will not be supported,
and thus JSP 1.2 taglibs that register event listeners will not work
properly.</p>
<p>As of this writing, JSP features up to JSP 2.1 are
implemented, except the &quot;tag files&quot; feature of JSP 2 (i.e., custom
JSP tags <em>implemented</em> in JSP language). The tag
files had to be compiled to Java classes to be usable under
FreeMarker.</p>
<h2 class="content-header header-section2" id="autoid_56">Embed FTL into JSP pages</h2>
<p>There is a taglib that allows you to put FTL fragments into
JSP pages. The embedded FTL fragment can access the attributes
(Beans) of the 4 JSP scopes. You can find a working example and the
taglib in the FreeMarker distribution.</p>
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