You are viewing a plain text version of this content. The canonical link for it is here.
Posted to notifications@freemarker.apache.org by dd...@apache.org on 2017/03/15 21:19:45 UTC
[48/51] [partial] incubator-freemarker-site git commit: 2.3.26-voting
docs, removed nightly
http://git-wip-us.apache.org/repos/asf/incubator-freemarker-site/blob/a4004324/builds/2.3.26-nightly/app_faq.html
----------------------------------------------------------------------
diff --git a/builds/2.3.26-nightly/app_faq.html b/builds/2.3.26-nightly/app_faq.html
deleted file mode 100644
index fda425b..0000000
--- a/builds/2.3.26-nightly/app_faq.html
+++ /dev/null
@@ -1,1797 +0,0 @@
-<!doctype html>
-<!-- Generated by FreeMarker/Docgen from DocBook -->
-<html lang="en" class="page-type-appendix">
-<head prefix="og: http://ogp.me/ns#">
-<meta charset="utf-8">
-<title>FAQ - Apache 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="Apache FreeMarker Manual">
-<meta property="og:title" content="FAQ">
-<meta property="og:locale" content="en_US">
-<meta property="og:url" content="http://freemarker.org/docs/app_faq.html">
-<link rel="canonical" href="http://freemarker.org/docs/app_faq.html">
-<link rel="icon" href="favicon.png" type="image/png">
-<link rel="stylesheet" type="text/css" href="http://fonts.googleapis.com/css?family=Roboto:500,700,400,300|Droid+Sans+Mono">
-<link rel="stylesheet" type="text/css" href="docgen-resources/docgen.min.css?1489402528979">
-<script>
-(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
-(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
-m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
-})(window,document,'script','//www.google-analytics.com/analytics.js','ga');
-ga('create', 'UA-55420501-1', 'auto');
-ga('send', 'pageview');
-</script>
-</head>
-<body itemscope itemtype="https://schema.org/Code">
- <meta itemprop="url" content="http://freemarker.org/docs/">
- <meta itemprop="name" content="Apache 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://freemarker.org" role="banner"> <img itemprop="image" src="logo.png" alt="FreeMarker">
-</a><ul class="tabs"><li><a href="http://freemarker.org/">Home</a></li><li class="current"><a href="index.html">Manual</a></li><li><a class="external" href="api/index.html">Java API</a></li></ul><ul class="secondary-tabs"><li><a class="tab icon-heart" href="http://freemarker.org/contribute.html" title="Contribute"><span>Contribute</span></a></li><li><a class="tab icon-bug" href="https://issues.apache.org/jira/browse/FREEMARKER/" title="Report a Bug"><span>Report a Bug</span></a></li><li><a class="tab icon-download" href="http://freemarker.org/freemarkerdownload.html" title="Download"><span>Download</span></a></li></ul></div></div><div class="header-bottom-bg"><div class="site-width search-row"><a href="index.html" class="navigation-header">Manual</a><div class="navigation-header"></div><form method="get" class="search-form" action="search-results.html"><fieldset><legend class="sr-only">Search form</legend><label for="search-field" class="sr-only">Search query</label><input id="searc
h-field" name="q" type="search" class="search-input" placeholder="Search" spellcheck="false" autocorrect="off" autocomplete="off"><button type="submit" class="search-btn"><span class="sr-only">Search</span></button></fieldset></form></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">Apache FreeMarker Manual</span></a></li><li class="step-1" itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a class="label" itemprop="item" href="app.html"><span itemprop="name">Appendixes</span></a></li><li class="step-2" itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a class="label" itemprop="item" href="app_faq.html"><span itemprop="name">FAQ</span></a></li></ul><div class="bookmarks" title="Bookmarks"><span clas
s="sr-only">Bookmarks:</span><ul class="bookmark-list"><li><a href="alphaidx.html">Alpha. index</a></li><li><a href="gloss.html">Glossary</a></li><li><a href="dgui_template_exp.html#exp_cheatsheet">Expressions</a></li><li><a href="ref_builtins_alphaidx.html">?builtins</a></li><li><a href="ref_directive_alphaidx.html">#directives</a></li><li><a href="ref_specvar.html">.spec_vars</a></li><li>FAQ</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 = ["Apache FreeMarker Manual","Appendixes","FAQ"];</script>
- <script src="toc.js?1489402528979"></script>
- <script src="docgen-resources/main.min.js?1489402528979"></script>
- </div>
-<div class="col-right"><div class="page-content"><div class="page-title"><div class="pagers top"><a class="paging-arrow previous" href="app.html"><span>Previous</span></a><a class="paging-arrow next" href="app_versions.html"><span>Next</span></a></div><div class="title-wrapper">
-<h1 class="content-header header-chapter" id="app_faq" itemprop="headline">FAQ</h1>
-</div></div> <div class="qandaset">
-
- <ol>
- <li>
- <a href="#faq_jsp_vs_freemarker">
-
- JSP versus FreeMarker?
-
-
- </a>
- </li>
- <li>
- <a href="#faq_picky_about_missing_vars">
-
- Why is FreeMarker so picky about <code class="inline-code">null</code>-s
- and missing variables, and what to do with it?
- </a>
- </li>
- <li>
- <a href="#faq_number_grouping">
-
- Why does FreeMarker print the numbers with strange
- formatting (as 1,000,000 or 1�000�000 instead of 1000000)?
- </a>
- </li>
- <li>
- <a href="#faq_number_decimal_point">
-
- Why does FreeMarker print bad decimal and/or grouping
- separator symbol (as 3.14 instead of 3,14)?
- </a>
- </li>
- <li>
- <a href="#faq_number_boolean_formatting">
-
- Why does FreeMarker give an error when I try to print a
- boolean like <code class="inline-code">${aBoolean}</code>, and how to fix
- it?
- </a>
- </li>
- <li>
- <a href="#faq_template_not_found">
-
- FreeMarker can't find my templates
- (<code class="inline-code">TemplateNotFoundException</code> or
- <code class="inline-code">FileNotFoundException</code>, "Template not
- found" error message)
- </a>
- </li>
- <li>
- <a href="#faq_check_version">
-
- The documentation writes about feature
- <em>X</em>, but it seems that FreeMarker doesn't
- know that, or it behaves in a different way as documented, or a
- bug that was supposedly fixed is still present.
- </a>
- </li>
- <li>
- <a href="#faq_alternative_syntax">
-
- The <code class="inline-code"><</code> and <code class="inline-code">></code> of
- FreeMarker tags confuses my editor or the XML parser. What to
- do?
- </a>
- </li>
- <li>
- <a href="#faq_legal_variable_names">
-
- What are the legal variable names?
-
-
- </a>
- </li>
- <li>
- <a href="#faq_strange_variable_name">
-
- How can I use variable names (macro name, parameter name)
- that contain minus sign (<code class="inline-code">-</code>), colon
- (<code class="inline-code">:</code>), dot (<code class="inline-code">.</code>), or or other
- special characters?
- </a>
- </li>
- <li>
- <a href="#faq_jsp_custom_tag_syntax">
-
- Why do I get "java.lang.IllegalArgumentException: argument
- type mismatch" when I try to use <em>X</em> JSP
- custom tag?
- </a>
- </li>
- <li>
- <a href="#faq_servlet_include">
-
- How to include other resources in a way as
- <code class="inline-code">jsp:include</code> does it?
- </a>
- </li>
- <li>
- <a href="#faq_parameter_unwrapping">
-
- How can I get the parameters to my
- plain-Java-method/<code class="inline-code">TemplateMethodModelEx</code>/<code class="inline-code">TemplateTransformModel</code>/<code class="inline-code">TemplateDirectiveModel</code>
- implementation as plain
- <code class="inline-code">java.lang.*</code>/<code class="inline-code">java.util.*</code>
- objects?
- </a>
- </li>
- <li>
- <a href="#faq_nonstring_keys">
-
- Why I can't use non-string key in the
- <code class="inline-code">myMap[myKey]</code> expression? And what to do
- now?
-
-
- </a>
- </li>
- <li>
- <a href="#faq_simple_map">
-
- When I list the contents of a map (a hash) with
- <code class="inline-code">?keys</code>/<code class="inline-code">?values</code>, I get the
- <code class="inline-code">java.util.Map</code> methods mixed with the real map
- entries. Of course, I only want to get the map entries.
- </a>
- </li>
- <li>
- <a href="#faq_modify_seq_and_map">
-
- How can I modify sequences (lists) and hashes (maps) in
- FreeMarker templates?
-
-
-
-
-
-
-
-
- </a>
- </li>
- <li>
- <a href="#faq_null">
-
- What about <code class="inline-code">null</code> and the FreeMarker
- template language?
- </a>
- </li>
- <li>
- <a href="#faq_capture">
-
- How can I use the output of a directive (macro) in
- expressions (as a parameter to another directive)?
- </a>
- </li>
- <li>
- <a href="#faq_questionmark">
-
- Why do I have "?"-s in the output instead of
- character <em>X</em>?
- </a>
- </li>
- <li>
- <a href="#faq_retrieve_calculated_values">
-
- How to retrieve values calculated in templates after
- template execution done?
- </a>
- </li>
- <li>
- <a href="#faq_assign_to_dynamic_variable_name">
-
- How to assign to (or <code class="inline-code">#import</code> into) a
- dynamically constructed variable name (like to name that's stored
- in another variable)?
- </a>
- </li>
- <li>
- <a href="#faq_template_uploading_security">
-
-
-
- Can I allow users to upload templates and what are the
- security implications?
- </a>
- </li>
- <li>
- <a href="#faq_implement_function_or_macro_in_java">
-
- How to implement a function or macro in Java Language
- instead of in the template language?
- </a>
- </li>
- <li>
- <a href="#faq_nice_error_page">
-
- In my Servlet
- based application, how do I show a nice error page instead of a
- stack trace when error occurs during template processing?
- </a>
- </li>
- <li>
- <a href="#faq_html_editor_mangles">
-
- I'm using a visual HTML editor that mangles template tags.
- Will you change the template language syntax to accommodate my
- editor?
- </a>
- </li>
- </ol>
- <dl>
-
-
-
- <dt class="question" id="faq_jsp_vs_freemarker">
- 1.
- JSP versus FreeMarker?
-
-
-
- </dt>
-
-
- <dd class="answer">
-
- <p>We compare FreeMarker with the JSP 2.0 + JSTL combo
- here.</p>
-
- <p>FreeMarker Pros:</p>
-
- <ul>
- <li>
- <p>FreeMarker is not tied to Servlets or networking/Web; it
- is just a class library to generate text output by merging a
- template with Java objects (the data-model). You can execute
- templates anywhere and anytime; no HTTP request forwarding or
- similar tricks needed, no Servlet environment needed at all.
- Because of this you can easily integrate it into any
- system.</p>
- </li>
-
- <li>
- <p>Terser syntax. Consider this JSP (assuming
- <code class="inline-code"><%@ taglib prefix="c"
- uri="http://java.sun.com/jsp/jstl/core"
- %></code>):</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><c:if test="${t}">
- True
-</c:if>
-
-<c:choose>
- <c:when test="${n == 123}">
- Do this
- </c:when>
- <c:otherwise>
- Do that
- </c:otherwise>
-</c:choose>
-
-<c:forEach var="i" items="${ls}">
-- ${i}
-</c:forEach></pre></div>
-
- <p>and the equivalent FTL:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><#if t>
- True
-</#if>
-
-<#if n == 123>
- Do this
-<#else>
- Do that
-</#if>
-
-<#list ls as i>
-- ${i}
-</#list></pre></div>
- </li>
-
- <li>
- <p>No servlet specific scopes and other highly technical
- things in templates (unless, of course, you expose them into
- the data-model deliberately). It was made for MVC from the
- beginning, it focuses only on the presentation.</p>
- </li>
-
- <li>
- <p>You can load the templates from anywhere; from the class
- path, from a data-base, etc.</p>
- </li>
-
- <li>
- <p>Locale-sensitive number and date formatting by default.
- When you output for a human audience, all you need to do is
- just write <code class="inline-code">${x}</code> rather than
- <code class="inline-code"><fmt:formatNumber value="${x}"
- /></code>.</p>
- </li>
-
- <li>
- <p>Easier to define ad-hoc macros and functions.</p>
- </li>
-
- <li>
- <p>No sweeping errors under the carpet. Missing variables
- and <code class="inline-code">null</code>-s will not silently default to
- <code class="inline-code">0</code>/<code class="inline-code">false</code>/empty-string,
- but cause error. <a href="#faq_picky_about_missing_vars">See more about this
- here...</a></p>
- </li>
-
- <li>
- <p>"Object wrapping". This lets you show the
- objects to templates in a customized, presentation oriented
- way (e.g. <a href="xgui_imperative_learn.html">see
- here</a> how a W3C DOM nodes can be seen by templates using
- this technology.)</p>
- </li>
-
- <li>
- <p>Macros and functions are just variables, so they can be
- easily passed around as parameter values, put into the
- data-model, etc., just like any other values.</p>
- </li>
-
- <li>
- <p>Virtually unnoticeable delay when visiting a page for
- the first time (or after it was changed), because no expensive
- compilation happens.</p>
- </li>
- </ul>
-
- <p>FreeMarker Cons:</p>
-
- <ul>
- <li>
- <p>Not a "standard". There are fewer tools and
- IDE integrations, fewer developers knows it and there's much
- less industry support in general. (However, most JSP tag
- libraries can work in FreeMarker templates with the proper
- setup, unless they are base on <code class="inline-code">.tag</code>
- files.)</p>
- </li>
-
- <li>
- <p>Its syntax doesn't follow the HTML/XML rules apart from
- some visual similarity, which is confusing for new users (it's
- the price of the terseness). JSP doesn't follow it either, but
- it's closer to it.</p>
- </li>
-
- <li>
- <p>Since macros and functions are just variables, incorrect
- directive and parameter names and missing required parameters
- can be detected only on runtime.</p>
- </li>
-
- <li>
- <p>Doesn't work with JSF. (It could work technically, but
- nobody has implemented that yet.)</p>
- </li>
- </ul>
-
- <p>You may read this if you are considering replacing JSP with
- FreeMarker in an existing application or in a legacy framework
- that only supports JSP: <a href="pgui_misc_servlet.html#pgui_misc_servlet_model2">Programmer's Guide/Miscellaneous/Using FreeMarker with servlets/Using FreeMarker for "Model 2"</a></p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_picky_about_missing_vars">
- 2.
- Why is FreeMarker so picky about <code class="inline-code">null</code>-s
- and missing variables, and what to do with it?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>To recapitulate what's this entry is about: FreeMarker by
- default treats an attempt to access a non-existent variable or a
- <code class="inline-code">null</code> value (<a href="#faq_null">this two
- is the same for FreeMarker</a>) as error, which aborts the
- template execution.</p>
-
- <p>First of all, you should understand the reason of being
- picky. Most scripting languages and template languages are rather
- forgiving with missing variables (and with
- <code class="inline-code">null</code>-s), and they usually treat them as empty
- string and/or 0 and/or logical false. This behavior has several
- problems:</p>
-
- <ul>
- <li>
- <p>It potentially hides accidental mistakes, like a typo in
- a variable name, or when the template author refers to a
- variable that the programmer doesn't put into the data-model
- for that template, or for which the programmer uses a
- different name. Humans are prone to do such mistakes, while
- computers are not, so missing this opportunity that the
- template engine can show these errors is a bad business. Even
- if you very carefully check the output of the templates during
- development, it is easy to look over mistakes like
- <code class="inline-code"><#if hasWarnigs><em class="code-color">print warnings
- here...</em></#if></code>, which would then
- silently never print the warnings, since you have mistyped the
- variable name (have you noticed it?). Also think about
- maintenance, when you later modify your application; probably
- you will not re-check templates (many applications has
- hundreds of them) that carefully each time, for all possible
- scenarios. Unit tests typically doesn't cover web page content
- very good either (if you have them at all...); they mostly
- only check certain manually set patterns in the web page, so
- they will often gloss though changes that are actually bugs.
- But if the page fails with exception, that's something human
- testers will notice and unit test will notice (as the whole
- page will fail), and in production the maintainers will notice
- (assuming somebody check error logs).</p>
- </li>
-
- <li>
- <p>Makes dangerous assumptions. The script language or
- template engine knows nothing about the application domain, so
- when it decides the value of something that it doesn't know to
- be 0/false, it is a quite irresponsible and arbitrary thing.
- Just because it's not know what's your current balance at your
- bank, can we just say it's $0? Just because it is not known if
- a patient has penicillin allergy, can we just say he/she
- doesn't have it? Just consider the implications of such
- mistakes. Showing an error page is often better than showing
- incorrect information that looks good, leading to bad
- decisions on the user side.</p>
- </li>
- </ul>
-
- <p>Being not picky is mostly sweeping under the carpet in this
- case (not facing the problems), which of course most people feels
- more convenient, but still, we believe that in most cases being
- strict will save your time and increase your software quality on
- the long run.</p>
-
- <p>On the other hand, we recognize that there are cases where
- you don't want FreeMarker to be that picky for good reason, and
- there is solution for them:</p>
-
- <ul>
- <li>
- <p>It's often normal that your data-model contains
- <code class="inline-code">null</code>-s or have optional variables. In such
- cases use <a href="dgui_template_exp.html#dgui_template_exp_missing">these
- operators</a>. If you use them too often, try to rethink
- your data-model, because depending on them too much won't just
- make the templates too verbose, but increases the probability
- of hiding errors and printing arbitrary incorrect output (for
- the reasons described earlier).</p>
- </li>
-
- <li>
- <p>In some application you may rather want to show an
- incomplete/damaged page than an error page. In this case you
- can <a href="pgui_config_errorhandling.html">use another
- error handler</a> than the default one. A custom error
- handler can skip the problematic part, or show an error
- indicator there, instead of aborting the whole page rendering.
- Note, however, that although the error handlers don't give
- arbitrary default values to variables, for pages that show
- critical information it's maybe still better to show an error
- page.</p>
- </li>
-
- <li>
- <p>If the pages contain parts that aren't critically
- important (like some side bars), another feature you may
- interested in is <a href="ref_directive_attempt.html">the
- <code>attempt</code>/<code>recover</code>
- directives</a>.</p>
- </li>
- </ul>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_number_grouping">
- 3.
- Why does FreeMarker print the numbers with strange
- formatting (as 1,000,000 or 1�000�000 instead of 1000000)?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>FreeMarker uses the locale-sensitive number formatting
- capability of the Java platform. The default number format for
- your locale may uses grouping or other formatting. If you don't
- want that, you have to override the number format suggested by the
- Java platform with the <code class="inline-code">number_format</code> <a href="pgui_config_settings.html">FreeMarker setting</a>. For
- example:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-unspecified">cfg.setNumberFormat("0.######"); // now it will print 1000000
-// where cfg is a freemarker.template.Configuration object</pre></div>
-
- <p>Note however than humans often find it hard to read big
- numbers without grouping separator. So in general it is
- recommended to keep them, and in cases where the numbers are for
- ''computer audience'' (which is confused on the grouping
- separators), use the <a href="ref_builtins_number.html#ref_builtin_c"><code>c</code> built-in</a>. For
- example:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><a href="/shop/productdetails?id=${<strong>product.id?c</strong>}">Details...</a></pre></div>
-
- <p>For computer audience you need <code class="inline-code">?c</code> anyway,
- as the decimal separators can also wary depending on the
- locale.</p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_number_decimal_point">
- 4.
- Why does FreeMarker print bad decimal and/or grouping
- separator symbol (as 3.14 instead of 3,14)?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>Different countries use different decimal/grouping separator
- symbols. If you see incorrect symbols, then probably your locale
- is not set properly. Set the default locale of the JVM or override
- the default locale with the <code class="inline-code">locale</code> <a href="pgui_config_settings.html">FreeMarker setting</a>. For
- example:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-unspecified">cfg.setLocale(java.util.Locale.ITALY);
-// where cfg is a freemarker.template.Configuration object</pre></div>
-
- <p>However, sometimes you want to output a number not for human
- audience, but for "computer audience" (like you want
- to print a size in CSS), in which case you must use dot as decimal
- separator, regardless of the locale (language) of the page. For
- that use the <a href="ref_builtins_number.html#ref_builtin_c"><code>c</code>
- built-in</a>, for example:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template">font-size: ${<strong>fontSize?c</strong>}pt;</pre></div>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_number_boolean_formatting">
- 5.
- Why does FreeMarker give an error when I try to print a
- boolean like <code class="inline-code">${aBoolean}</code>, and how to fix
- it?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>Unlike numbers, booleans has no commonly accepted format,
- not even a common format within the same page. Like when you show
- on a HTML page if a product is washable, you will hardly want to
- show for the visitor "Washable: true", but rather "Washable: yes".
- So we force the template author (by <code class="inline-code">${washable}</code>
- causing error) to find out with his human knowledge how the
- boolean value should be shown at the given place. The common way
- of formatting a boolean is like <code class="inline-code">${washable?string("yes",
- "no")}</code>, <code class="inline-code">${caching?string("Enabled",
- "Disabled")}</code>, <code class="inline-code">${heating?string("on",
- "off")}</code>, etc.</p>
-
- <p>However, there are two cases where this gets
- impractical:</p>
-
- <ul>
- <li>
- <p>When printing boolean to generate computer language
- output, and hence you want
- <code class="inline-code">true</code>/<code class="inline-code">false</code>, use
- <code class="inline-code">${<em class="code-color">someBoolean</em>?c}</code>.
- (This requires at least FreeMarker 2.3.20. Before that, the
- common practice was writing
- <code class="inline-code">${<em class="code-color">someBoolean</em>?string}</code>,
- however that's dangerous because its output depends on the
- current boolean format setting, whose default is
- <code class="inline-code">"true"</code>/<code class="inline-code">"false"</code>.)</p>
- </li>
-
- <li>
- <p>When you have format most of the booleans on the same
- way. In this case you can set the
- <code class="inline-code">boolean_format</code> setting
- (<code class="inline-code">Configuration.setBooleanFormat</code>) to reflect
- that, and then since FreeMarker 2.3.20 you can just write
- <code class="inline-code">${<em class="code-color">someBoolean</em>}</code>.
- (Note that this doesn't work for
- <code class="inline-code">true</code>/<code class="inline-code">false</code> though - you
- have to use <code class="inline-code">?c</code> there.)</p>
- </li>
- </ul>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_template_not_found">
- 6.
- FreeMarker can't find my templates
- (<code class="inline-code">TemplateNotFoundException</code> or
- <code class="inline-code">FileNotFoundException</code>, "Template not
- found" error message)
-
- </dt>
-
-
- <dd class="answer">
-
- <p>First of all, you should know that FreeMarker doesn't load
- templates from file system paths directly. Instead, it uses a
- simple virtual file system that might reads non-filesystem
- resources (templates from inside jar-s, from inside a database
- table, etc.). What that virtual file is decided by a configuration
- setting,
- <code class="inline-code">Configuration.setTemplateLoader(TemplateLoader)</code>.
- Even if the <code class="inline-code">TemplateLoader</code> your are using maps
- to the file system, it will have a base directory that contains
- all the templates, and that will be the root of your virtual file
- system that you can't reach out from (i.e., absolute paths will be
- still relative to the virtual file system root).</p>
-
- <p>Tips to solve the problem:</p>
-
- <ul>
- <li>
- <p>If you are the one who configure FreeMarker, be sure
- that you set a proper
- <code class="inline-code">TemplateLoader</code>.</p>
- </li>
-
- <li>
- <p>Otherwise see if the template-not-found error's message
- contains the description of the
- <code class="inline-code">TemplateLoader</code> used. If it doesn't, you are
- using an old FreeMarker version, so update it. Getting
- <code class="inline-code">FileNotFoundException</code> instead of
- <code class="inline-code">TemplateNotFoundException</code> is also a sign of
- that, and so you will get less helpful error messages. (If the
- <code class="inline-code">TemplateLoader</code> in the error message is like
- <code class="inline-code">foo.SomeTemplateLoader@64f6106c</code> and so
- doesn't show some relevant parameters, you may should ask the
- author to define a nicer
- <code class="inline-code">toString()</code>.)</p>
- </li>
-
- <li>
- <p>A frequent mistake is using a
- <code class="inline-code">FileTemplateLoader</code> for a Servlet-based web
- application, instead of a
- <code class="inline-code">WebappTemplateLoader</code>. It may works in one
- environment, but not in another, as the Servlet specification
- makes no promises about your resources being accessible as
- plain files, not even when the <code class="inline-code">war</code> file is
- extracted.</p>
- </li>
-
- <li>
- <p>Know that when you are including/importing a template
- from another template, if you don't start the template name
- with <code class="inline-code">/</code>, it will be interpreted relatively
- to the directory of the including template. The error message
- contains the full (resolved) name, so you should notice this
- there.</p>
- </li>
-
- <li>
- <p>Check that you aren't using <code class="inline-code">\</code>
- (backslash) instead of <code class="inline-code">/</code> (slash).
- (FreeMarker 2.3.22 and later will warn you about that in the
- error message.)</p>
- </li>
-
- <li>
- <p>As a last resort, turn on debug level logging (in the
- logging framework that you are using) for the category
- <code class="inline-code">freemarker.cache</code>, to see more of what's
- going on.</p>
- </li>
- </ul>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_check_version">
- 7.
- The documentation writes about feature
- <em>X</em>, but it seems that FreeMarker doesn't
- know that, or it behaves in a different way as documented, or a
- bug that was supposedly fixed is still present.
-
- </dt>
-
-
- <dd class="answer">
-
- <p>Are you sure that you are using the documentation written
- for the same version of FreeMarker that you actually use?
- Especially, note that our online documentation is for the latest
- stable FreeMarker release. You may use an older release; update
- it.</p>
-
- <p>Are you sure that the Java class loader finds the same
- <code class="inline-code">freemarker.jar</code> that you expect to use? Maybe
- there is an older version of <code class="inline-code">freemarker.jar</code>
- around, which shadows the never. To check this, try to print the
- version number in a template with <code class="inline-code">${.version}</code>.
- (If it dies with "Unknown built-in variable: version"
- error message, then you use a very, very old release.).</p>
-
- <p>If you suspect that the problem is that you have multiple
- <code class="inline-code">freemarker.jar</code>-s, the typical culprit is that
- some module has a Maven or Ivy dependency with the old
- <code class="inline-code">freemarker</code> group ID, as opposed to the more
- modern <code class="inline-code">org.freemarker</code> group ID. Because of the
- different group ID-s these aren't seen as conflicting artifacts by
- Maven or Ivy, and so both version gets in. In this case you have
- to exclude the <code class="inline-code">freemarker</code> dependency.</p>
-
- <p>If you think that the documentation or FreeMarker is wrong,
- please report it using the bug tracker, or the mailing list. Thank
- you!</p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_alternative_syntax">
- 8.
- The <code class="inline-code"><</code> and <code class="inline-code">></code> of
- FreeMarker tags confuses my editor or the XML parser. What to
- do?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>Starting from FreeMarker 2.3.4 you can use
- <code class="inline-code">[</code> and <code class="inline-code">]</code> instead of
- <code class="inline-code"><</code> and <code class="inline-code">></code>. For more
- details <a href="dgui_misc_alternativesyntax.html">read
- this...</a></p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_legal_variable_names">
- 9.
- What are the legal variable names?
-
-
-
- </dt>
-
-
- <dd class="answer">
-
- <p>FreeMarker has no limitations regarding the characters used
- in variable names, nor regarding the length of the variable names,
- but for your convenience try to chose variable names that can be
- used with the simple variable reference expressions (see it <a href="dgui_template_exp.html#dgui_template_exp_var_toplevel">here</a>). If you have
- to choose a more extreme variable name, that's not a big problem
- either: <a href="#faq_strange_variable_name">see
- here</a>.</p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_strange_variable_name">
- 10.
- How can I use variable names (macro name, parameter name)
- that contain minus sign (<code class="inline-code">-</code>), colon
- (<code class="inline-code">:</code>), dot (<code class="inline-code">.</code>), or or other
- special characters?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>If you have a variable with strange name like
- "foo-bar", FreeMarker will misunderstand what you
- mean if you just use it like in <code class="inline-code">${foo-bar}</code>. In
- this case, it will believe that you want to subtract the value of
- <code class="inline-code">bar</code> from <code class="inline-code">foo</code>. This FAQ entry
- explains how to handle situations like this.</p>
-
- <p>First of all it should be clear that these are just
- syntactical problems, as otherwise FreeMarker has no limitations
- regarding the characters used in variable names, nor regarding the
- length of them.</p>
-
- <p>If the special character is one of minus sign
- (<code class="inline-code">-</code>, UCS 0x2D) or dot (<code class="inline-code">.</code>, UCS
- 0x2E) or colon (<code class="inline-code">:</code>, UCS 0x3A), then all you have
- to do is putting a backslash (<code class="inline-code">\</code>) before these
- characters, like in <code class="inline-code">foo\-bar</code> (since FreeMarker
- 2.3.22). Then FreeMarker will know that you didn't mean the
- operator with the same symbol. This works everywhere where you
- specify unquoted identifiers, like for macro and function names,
- parameter names, and all kind of variable references in general.
- (Note that these escapes only work in identifiers, not in string
- literals.)</p>
-
- <p>When the special character is not one of minus sign, dot, or
- colon, then it gets trickier. Let's say the problematic variable
- name is "a+b". Then:</p>
-
- <ul>
- <li>
- <p>If you want to read the variable: If it's a subvariable
- of something, you can write
- <code class="inline-code">something["a+b"]</code> (remember,
- <code class="inline-code">something.x</code> is equivalent to
- <code class="inline-code">something["x"])</code>. If it's a top-level
- variable, those are accessible through the special hash
- variable ,<code class="inline-code">.vars</code>, so you can write
- <code class="inline-code">.vars["a+b"]</code>. Naturally, this trick works
- with macro and function invocations too:
- <code class="inline-code"><@.vars["a+b"]/></code>,
- <code class="inline-code">.vars["a+b"](1, 2)</code>.</p>
- </li>
-
- <li>
- <p>If you want to create or modify the variable: All
- directives that let you create or modify a variable (such as
- <code class="inline-code">assign</code>, <code class="inline-code">local</code>,
- <code class="inline-code">global</code>, <code class="inline-code">macro</code>,
- <code class="inline-code">function</code>, etc.) allows the quotation of the
- destination variable name. For example, <code class="inline-code"><#assign
- foo = 1></code> is the same as <code class="inline-code"><#assign
- "foo" = 1></code>. So you can write things like
- <code class="inline-code"><#assign "a+b" = 1></code> and
- <code class="inline-code"><#macro "a+b"></code>.</p>
- </li>
-
- <li>
- <p>Unfortunately, you can't use such a variable name (that
- contains special characters other than <code class="inline-code">-</code>,
- <code class="inline-code">.</code> and <code class="inline-code">:</code>) as macro
- parameter name.</p>
- </li>
- </ul>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_jsp_custom_tag_syntax">
- 11.
- Why do I get "java.lang.IllegalArgumentException: argument
- type mismatch" when I try to use <em>X</em> JSP
- custom tag?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>Fist of all, update FreeMarker, because 2.3.22 and later
- gives a much more helpful error message, that pretty much answers
- the question. Anyway, the reason is as follows. On JSP pages you
- quote all parameter (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 plain user-defined
- FTL directives, you have to use the FTL syntax rules inside the
- custom tags, not the JSP rules. Thus, according to FTL rules, you
- must not quote boolean and numerical parameter values, 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.</p>
-
- <p>For example, the <code class="inline-code">flush</code> parameter to
- Struts Tiles <code class="inline-code">insert</code> tag is boolean. In JSP the
- correct syntax was:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><tiles:insert page="/layout.jsp" <strong>flush="true"</strong>/>
-<em>...</em></pre></div>
-
- <p>but in FTL you should write:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><@tiles.insert page="/layout.ftl" <strong>flush=true</strong>/>
-<em>...</em></pre></div>
-
- <p>Also, for similar reasons, this is wrong:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><tiles:insert page="/layout.jsp" <strong>flush="${needFlushing}"</strong>/>
-<em>...</em></pre></div>
-
- <p>and you should write:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><tiles:insert page="/layout.jsp" <strong>flush=needFlushing</strong>/>
-<em>...</em></pre></div>
-
- <p>(Not <code class="inline-code">flush=${needFlushing}</code>!)</p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_servlet_include">
- 12.
- How to include other resources in a way as
- <code class="inline-code">jsp:include</code> does it?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>Not with <code class="inline-code"><#include ...></code>, as that
- just includes another FreeMarker template without involving the
- Servlet container.</p>
-
- <p>Since the inclusion method you look for is Servlet-related,
- and pure FreeMarker is unaware of Servlets or even HTTP, it's the
- Web Application Framework that decides if you can do this and if
- so how. For example, in Struts 2 you can do this like this:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><@s.include value="/WEB-INF/just-an-example.jspf" /></pre></div>
-
- <p>If the FreeMarker support of the Web Application Framework
- is based on
- <code class="inline-code">freemarker.ext.servlet.FreemarkerServlet</code>, then
- you can also do this (since FreeMarker 2.3.15):</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><@include_page path="/WEB-INF/just-an-example.jspf" /></pre></div>
-
- <p>but if the Web Application Framework provides its own
- solution, then you may prefer that, after all it may does
- something special.</p>
-
- <p>For more information about <code class="inline-code">include_page</code>
- <a href="pgui_misc_servlet.html#pgui_misc_servlet_include">read
- this...</a></p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_parameter_unwrapping">
- 13.
- How can I get the parameters to my
- plain-Java-method/<code class="inline-code">TemplateMethodModelEx</code>/<code class="inline-code">TemplateTransformModel</code>/<code class="inline-code">TemplateDirectiveModel</code>
- implementation as plain
- <code class="inline-code">java.lang.*</code>/<code class="inline-code">java.util.*</code>
- objects?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>Unfortunately, there is no simple general-purpose solution
- for this problem. The problem is that FreeMarker object wrapping
- is very flexible, which is good when you access variables from
- templates, but makes unwrapping on the Java side a tricky
- question. For example, it is possible to wrap a
- non-<code class="inline-code">java.util.Map</code> object as
- <code class="inline-code">TemplateHashModel</code> (FTL hash variable). But
- then, it can't be unwrapped to <code class="inline-code">java.util.Map</code>,
- since there is no wrapped <code class="inline-code">java.util.Map</code> around
- at all.</p>
-
- <p>So what to do then? Basically there are two cases:</p>
-
- <ul>
- <li>
- <p>Directives and methods that are written for presentation
- purposes (like kind of "tools" for helping
- FreeMarker templates) should declare their arguments as
- <code class="inline-code">TemplateModel</code>-s and the more specific sub
- interfaces of that. After all, the object wrapping is about
- transforming the data-model to something that serves the
- purpose of the presentation layer, and these methods are part
- of the presentation layer. If you still need a plain Java type
- there, you may turn to the
- <code class="inline-code">ObjectWrapperAndUnwrapper</code> interface of the
- current <code class="inline-code">ObjectWrapper</code> (can be get with
- <code class="inline-code">Environment.getObjectWrapper()</code>).</p>
- </li>
-
- <li>
- <p>Methods that are not for presentation related tasks (but
- for business logic and like) should be implemented as plain
- Java methods, and should not use any FreeMarker specific
- classes at all, since according the MVC paradigm they must be
- independent of the presentation technology (FreeMarker). If
- such a method is called from a template, then it is the
- responsibility of the <a href="pgui_datamodel_objectWrapper.html">object wrapper</a>
- to ensure the conversion of the arguments to the proper type.
- If you use the <a href="pgui_datamodel_objectWrapper.html#pgui_datamodel_defaultObjectWrapper"><code>DefaultObjectWrapper</code></a>
- or the <a href="pgui_misc_beanwrapper.html"><code>BeansWrapper</code></a>
- then this will happen automatically. For
- <code class="inline-code">DefaultObjectWrapper</code>, this mechanism works
- much better, if you <a href="pgui_datamodel_objectWrapper.html#topic.defaultObjectWrapperIcI">set its
- <code>incompatibleImprovements</code> to
- 2.3.22</a>.</p>
- </li>
- </ul>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_nonstring_keys">
- 14.
- Why I can't use non-string key in the
- <code class="inline-code">myMap[myKey]</code> expression? And what to do
- now?
-
-
-
- </dt>
-
-
- <dd class="answer">
-
- <p>The "hash" type of the FreeMarker Template
- Language (FTL) is not the same as Java's <code class="inline-code">Map</code>.
- FTL's hash is an associative array too, but it uses string keys
- exclusively. This is because it was introduced for sub variables
- (as <code class="inline-code">password</code> in
- <code class="inline-code">user.password</code>, which is the same as
- <code class="inline-code">user["password"]</code>), and variable names are
- strings.</p>
-
- <p>If you only need to list the key-value pairs of a
- <code class="inline-code">Map</code>, you can just write something like
- <code class="inline-code"><#list myMap as k, v>${k}:
- ${v}</#list></code> (see more about <a href="ref_directive_list.html#ref.directive.list">the <code>list directive</code>
- here</a>). This enumerates the <code class="inline-code">Map</code> entries,
- and supports non-string keys. This requires FreeMarker 2.3.25 or
- later. (If for some reason you can't upgrade to 2.3.25, you can
- use the Java API of <code class="inline-code">Map</code> instead, like
- <code class="inline-code"><#list myMap?api.entrySet() as kvp>${kvp.key}:
- ${kvp.value}</#list></code>.)</p>
-
- <p>If you need to do more than listing, you will have to turn
- to the Java API of the <code class="inline-code">Map</code>. You can do it like
- this: <code class="inline-code">myMap?api.get(nonStringKey)</code>. However, for
- <code class="inline-code">?api</code> to be enabled, you may need to configure
- FreeMarker a bit (<a href="ref_builtins_expert.html#ref_buitin_api_and_has_api">see
- more here</a>).</p>
-
- <p>Note that as Java's <code class="inline-code">Map</code> is particular
- about the exact class of the key, at least for numerical keys
- calculated inside the templates you will have to cast them to the
- proper Java type, otherwise the item will not be found. For
- example if you use <code class="inline-code">Integer</code> keys in a Map, then
- you should write <code class="inline-code">${myMap.get(numKey?int)}</code>. This
- is because of FTL's deliberately simplified type system has only a
- single numerical type, while Java distinguishes a lot of numerical
- types. Note that the casting is not needed when the key value
- comes directly from the data-model (i.e., you didn't modified its
- value with arithmetical calculations in the template), including
- the case when it's the return value of a method, and it was of the
- proper class before wrapping, because then the result of the
- unwrapping will be of the original type.</p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_simple_map">
- 15.
- When I list the contents of a map (a hash) with
- <code class="inline-code">?keys</code>/<code class="inline-code">?values</code>, I get the
- <code class="inline-code">java.util.Map</code> methods mixed with the real map
- entries. Of course, I only want to get the map entries.
-
- </dt>
-
-
- <dd class="answer">
-
- <p>Certainly you are using pure <code class="inline-code">BeansWrapper</code>
- as your object wrapper (instead of the default,
- <code class="inline-code">DefaultObjectWrapper</code>), or a custom subclass of
- it, and the <code class="inline-code">simpleMapWrapper</code> property of that
- is left to <code class="inline-code">false</code>. Unfortunately, that's the
- default of <code class="inline-code">BeansWrapper</code> (for backward
- compatibility), so you have to explicitly set it to
- <code class="inline-code">true</code> where you instantiate it. Also, at least
- since 2.3.22, applications should just use
- <code class="inline-code">DefaultObjectWrapper</code> (with <a href="pgui_datamodel_objectWrapper.html#topic.defaultObjectWrapperIcI">its
- <code>incompatibleImprovements</code> set to at least
- 2.3.22</a> - that's especially important if you are switching
- from pure <code class="inline-code">BeansWrapper</code>), which never had this
- problem.</p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_modify_seq_and_map">
- 16.
- How can I modify sequences (lists) and hashes (maps) in
- FreeMarker templates?
-
-
-
-
-
-
-
-
-
- </dt>
-
-
- <dd class="answer">
-
- <p>First of all, you may don't want to modify the
- sequence/hash, just concatenate (add) two or more of them, which
- results in a new sequence/hash, rather than modifying an existing
- one. In this case use the <a href="dgui_template_exp.html#dgui_template_exp_sequenceop_cat">sequence
- concatenation</a> and <a href="dgui_template_exp.html#dgui_template_exp_hashop_cat">hash concatenation
- operators</a>. Also, you may use the <a href="dgui_template_exp.html#dgui_template_exp_seqenceop_slice">subsequence
- operator</a> instead of removing sequence items. However, be
- aware of the performance implications: these operations are fast,
- but the hashes/sequences that are the result of many subsequent
- applications of these operations (i.e., when you use the result of
- the operation as the input of yet another operation, and so on)
- will be slow to read.</p>
-
- <p>Now if you still want to modify sequences/hashes, then read
- on...</p>
-
- <p>The FreeMarkes Template Language doesn't support the
- modification of sequences/hashes. It's for displaying already
- calculated things, not for calculating data. Keep templates
- simple. But don't give it up, you will see some advices and tricks
- bellow.</p>
-
- <p>The best is if you can divide the work between the
- data-model builder program and the template so that the template
- doesn't need to modify sequences/hashes. Maybe if you rethink your
- data-model, you will realize this is possible. But, seldom there
- are cases where you need to modify sequences/hashes for some
- complex but purely presentation related algorithms. It seldom
- happens, so think twice whether that calculation (or parts of it)
- rather belongs to the data-model domain than to the presentation
- domain. Let's assume you are sure it belongs to the presentation
- domain. For example, you want to display a keyword index on some
- very smart way, whose algorithm need you to create and write some
- sequence variables. Then you should do something like this (ugly
- situations has ugly solutions...):</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><#assign caculatedResults =
- 'com.example.foo.SmartKeywordIndexHelper'?new().calculate(keywords)>
-<#-- some simple algorithms comes here, like: -->
-<ul>
- <#list caculatedResults as kw>
- <li><a href="${kw.link}">${kw.word}</a>
- </#list>
-</ul></pre></div>
-
- <p>That is, you move out the complex part of the presentation
- task from the template into Java code. Note that it doesn't affect
- the data-model, so the presentation is still kept separated from
- other the other application logic. Of course the drawback is that
- for this the template author will need the help of a Java
- programmer, but for complex algorithms that's probably needed
- anyway.</p>
-
- <p>Now, if you still say you need to modify sequences/hashes
- directly with the FreeMarker template, here are some solutions,
- but please read the warning after them:</p>
-
- <ul>
- <li>
- <p>You can access the Java API of a
- <code class="inline-code">java.util.Map</code> with the help of the
- <code class="inline-code">api</code> built-in, like
- <code class="inline-code">myMap?api.put(11, "eleven")</code>. You will need
- to get a <code class="inline-code">Map</code> from somewhere though (an FTL
- hash literal like <code class="inline-code">{}</code> won't suffice, as it's
- read only and doesn't support <code class="inline-code">api</code> either).
- For example, you could expose a Java method or
- <code class="inline-code">TemplateMethodModelEx</code> to the template that
- returns a <code class="inline-code">new LinkeHashMap()</code>, so you can do
- <code class="inline-code"><#assign myMap =
- utils.newLinkedHashMap()></code>.</p>
- </li>
-
- <li>
- <p>You can write a <code class="inline-code">TemplateMethodModelEx</code>
- and <code class="inline-code">TemplateDirectiveModel</code> implementation
- that can modify certain types of sequences/hashes. Just
- certain types, because
- <code class="inline-code">TemplateSequenceModel</code> and
- <code class="inline-code">TemplateHashModel</code> doesn't have methods for
- modification, so you will need the sequence or hash to
- implement some additional methods. An example of this solution
- can be seen in FMPP. It allows you to do things like this
- (<code class="inline-code">pp</code> stores the services provided by FMPP
- for templates):</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><#assign a = pp.newWritableSequence()>
-<@pp.add seq=a value="red" /></pre></div>
-
- <p>The <code class="inline-code">pp.add</code> directive works only with
- sequences that were created with
- <code class="inline-code">pp.newWritableSequence()</code>. So for example
- the template author can't modify a sequence that comes from
- the data-model with this.</p>
- </li>
-
- <li>
- <p>A sequence can have some methods/directives if you use a
- customized wrapper (so you can write something like
- <code class="inline-code"><@myList.append foo /></code>).</p>
- </li>
- </ul>
-
- <p>But beware, these solutions have a problem: The <a href="dgui_template_exp.html#dgui_template_exp_sequenceop_cat">sequence
- concatenation</a>, <a href="dgui_template_exp.html#dgui_template_exp_seqenceop_slice">sequence slice</a>
- operator (like <code class="inline-code">seq[5..10]</code>) and
- <code class="inline-code">?reverse</code> do not copy the original sequence,
- just wraps it (for efficiency), so the resulting sequence will
- change if the original sequence is changed later (an abnormal
- aliasing effect). The same problem exists with the result of <a href="dgui_template_exp.html#dgui_template_exp_hashop_cat">hash concatenation</a>;
- it just wraps the two hashes, so the resulting hash will magically
- change if you modify the hashes you have added earlier. As a
- work-around, after you did the above problematic operations,
- either be sure you will not modify the objects that were used as
- input, or create a copy of the result with a method provided by
- the solution described in above two points (e.g. in FMPP you could
- do <code class="inline-code"><#assign b =
- pp.newWritableSequence(a[5..10])></code> and
- <code class="inline-code"><#assign c = pp.newWritableHash(hashA +
- hashB)></code>). Of course this is easy to miss... so again,
- rather try to build the data-model so you will not need to modify
- collections, or use a presentation task helper class as was shown
- earlier.</p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_null">
- 17.
- What about <code class="inline-code">null</code> and the FreeMarker
- template language?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>The FreeMarker template language doesn't know the Java
- language <code class="inline-code">null</code> at all. It doesn't have
- <code class="inline-code">null</code> keyword, and it can't test if something is
- <code class="inline-code">null</code> or not. When it technically faces with a
- <code class="inline-code">null</code>, it treats it exactly as a missing
- variable. For example, both if <code class="inline-code">x</code> is
- <code class="inline-code">null</code> in the data-model and if it's not present
- at all, <code class="inline-code">${x!'missing'}</code> will print
- "missing", you can't tell the difference. Also, if
- for example you want to test if a Java method has returned
- <code class="inline-code">null</code>, just write something like
- <code class="inline-code"><#if foo.bar()??></code>.</p>
-
- <p>You may interested in the rationale behind this. From the
- viewpoint of the presentation layer a <code class="inline-code">null</code> and
- non-existent thing is almost always the same. The difference
- between this two is usually just a technical detail, which is
- rather the result of implementation details than of the
- application logic. That you can't compare something to
- <code class="inline-code">null</code> (unlike in Java); it doesn't make sense to
- compare something with <code class="inline-code">null</code> in a template,
- since the template language doesn't do identity comparison (like
- the Java <code class="inline-code">==</code> operator when you compare two
- objects) but the more common sense value comparison (like Java's
- <code class="inline-code">Object.equals(Object)</code>; that doesn't work with
- <code class="inline-code">null</code> either). And how could FreeMarker tell if
- something concrete equals with something that is missing and thus
- unknown? Or if two missing (unknown) things are equal? Of course
- these questions can't be answered.</p>
-
- <p>There is at least one problem with this
- <code class="inline-code">null</code>-unaware approach. When you call a Java
- method from a template, you may want to pass a
- <code class="inline-code">null</code> value as argument (since the method was
- designed to be used in Java language, where the concept of
- <code class="inline-code">null</code> is known). In this case you can exploit a
- bug of FreeMarker (that we will not fix until we provide a correct
- solution for passing <code class="inline-code">null</code> values to a method):
- if you specify a missing variable as the argument, then it will
- not cause an error, but a <code class="inline-code">null</code> will be passed
- to the method instead. Like <code class="inline-code">foo.bar(nullArg)</code>
- will call the <code class="inline-code">bar</code> method with
- <code class="inline-code">null</code> as argument, assuming that there is no
- variable exists with "nullArg" name.</p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_capture">
- 18.
- How can I use the output of a directive (macro) in
- expressions (as a parameter to another directive)?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>Capture the output into a variable with the
- <code class="inline-code">assign</code> or <code class="inline-code">local</code> directive.
- For example:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><#assign capturedOutput><@outputSomething /></#assign>
-<@otherDirective someParam=capturedOutput /></pre></div>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_questionmark">
- 19.
- Why do I have "?"-s in the output instead of
- character <em>X</em>?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>This is because the character that you want to print can't
- be represented with the <a href="gloss.html#gloss.charset">charset</a> (encoding) used for the
- output stream, so the Java platform (not FreeMarker) substitutes
- the problematic character with question mark. In general you
- should use the same charset for the output as for the template
- (use the <code class="inline-code">getEncoding()</code> method of the template
- object), or which is even safer, you should always use UTF-8
- charset for the output. The charset used for the output stream is
- not decided by FreeMarker, but by you, when you create the
- <code class="inline-code">Writer</code> that you pass to the
- <code class="inline-code">process</code> method of the template.</p>
-
- <p>Example: Here I use UTF-8 charset in a servlet:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-unspecified">...
-resp.setContentType("text/html; charset=utf-8");
-Writer out = resp.getWriter();
-...
-t.process(root, out);
-...</pre></div>
-
- <p>Note that the question marks (or other substitution
- characters) may be produced outside FreeMarker, in which case the
- above obviously will not help. For example a bad/missconfigured
- database connection or JDBC driver may bring the text already with
- substitution characters in it. HTML forms are another potential
- source of encoding problems. It's a good idea to print the
- numerical code of the characters of the string on various places,
- to see where the problem occurs first.</p>
-
- <p>You can read more about charsets and FreeMarker <a href="pgui_misc_charset.html">here...</a></p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_retrieve_calculated_values">
- 20.
- How to retrieve values calculated in templates after
- template execution done?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>First of all, be sure your application is designed well:
- templates should display data, and almost never calculate data. If
- you are still sure you want to do it, read on...</p>
-
- <p>When you use <code class="inline-code"><#assign x = "foo"></code>,
- then you do not actually modify the data-model (since that is
- read-only, see: <a href="pgui_misc_multithreading.html">Programmer's Guide/Miscellaneous/Multithreading</a>), but
- create the <code class="inline-code">x</code> variable in the runtime <a href="gloss.html#gloss.environment">environment</a> of the processing
- (see <a href="pgui_misc_var.html">Programmer's Guide/Miscellaneous/Variables, scopes</a>). The problem is that this
- runtime environment will be discarded when
- <code class="inline-code">Template.process</code> returns, as it was created for
- a single <code class="inline-code">Template.process</code> call:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-unspecified">// internally an Environment will be created, and then discarded
-myTemplate.process(root, out);</pre></div>
-
- <p>To prevent this, you can do the below, which is equivalent
- with the above, except that you have chance to return the
- variables created in the template:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-unspecified">Environment env = myTemplate.createProcessingEnvironment(root, out);
-env.process(); // process the template
-TemplateModel x = env.getVariable("x"); // get variable x</pre></div>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_assign_to_dynamic_variable_name">
- 21.
- How to assign to (or <code class="inline-code">#import</code> into) a
- dynamically constructed variable name (like to name that's stored
- in another variable)?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>If you really can't avoid doing that (you should, as it's
- confusing), you can solve that with constructing the appropriate
- FTL source code dynamically in a string, then using the <a href="ref_builtins_expert.html#ref_builtin_interpret"><code>interpret</code>
- built-in</a>. For example, if you want to assign to the
- variable whose name is stored in the <code class="inline-code">varName</code>
- variable:</p>
-
-
-
-<div class="code-wrapper"><pre class="code-block code-template"><@"<#assign ${varName}='example'>"?interpret /></pre></div>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_template_uploading_security">
- 22.
-
-
- Can I allow users to upload templates and what are the
- security implications?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>In general you shouldn't allow that, unless those users are
- system administrators or other trusted personnel. Consider
- templates as part of the source code just like
- <code class="inline-code">*.java</code> files are. If you still want to allow
- users to upload templates, here are what to consider:</p>
-
- <ul>
- <li>
- <p>Denial-of-Service (DoS) attacks: It's trivial to create
- templates that run practically forever (with a loop), or
- exhaust memory (by concatenating to a string in a loop).
- FreeMarker can't enforce CPU or memory usage limits, so this
- is something that has no solution on the
- FreeMarker-level.</p>
- </li>
-
- <li>
- <p>Data-model and wrapping
- (<code class="inline-code">Configuration.setObjectWrapper</code>): The
- data-model might gives access to the public Java API of some
- objects that you have put into the data-model. By default, for
- objects that aren't instances of a the bunch of specially
- handler types (<code class="inline-code">String</code>,
- <code class="inline-code">Number</code>, <code class="inline-code">Boolean</code>,
- <code class="inline-code">Date</code>, <code class="inline-code">Map</code>,
- <code class="inline-code">List</code>, array, and a few others), their
- public Java API will be exposed. To avoid that, you have to
- construct the data-model so that it only exposes the things
- that are really necessary for the template. For that, you may
- want to use <code class="inline-code">SimpleObjectWrapper</code> (via
- <code class="inline-code">Configuration.setObjectWrapper</code> or the
- <code class="inline-code">object_wrapper</code> setting) and then create the
- data-model purely from <code class="inline-code">Map</code>-s,
- <code class="inline-code">List</code>-s, <code class="inline-code">Array</code>-s,
- <code class="inline-code">String</code>-s, <code class="inline-code">Number</code>-s,
- <code class="inline-code">Boolean</code>-s and <code class="inline-code">Date</code>-s.
- Or, you can implement your own extremely restrictive
- <code class="inline-code">ObjectWrapper</code>, which for example could
- expose your POJO-s safely.</p>
- </li>
-
- <li>
- <p>Template-loader
- (<code class="inline-code">Configuration.setTemplateLoader</code>):
- Templates may load other templates by name (by path), like
- <code class="inline-code"><#include "../secret.txt"></code>. To avoid
- loading sensitive data, you have to use a
- <code class="inline-code">TemplateLoader</code> that double-checks that the
- file to load is something that should be exposed. FreeMarker
- tries to prevent the loading of files outside the template
- root directory regardless of template loader, but depending on
- the underlying storage mechanism, exploits may exist that
- FreeMarker can't consider (like, just as an example,
- <code class="inline-code">~</code> jumps to the current user's home
- directory). Note that
- <code class="inline-code">freemarker.cache.FileTemplateLoader</code> checks
- the canonical paths, so that's maybe a good candidate for this
- task, yet, adding a file extension check (file must be
- <code class="inline-code">*.ftl</code>) is maybe a good idea.</p>
- </li>
-
- <li>
- <p>The <code class="inline-code">new</code> built-in
- (<code class="inline-code">Configuration.setNewBuiltinClassResolver</code>,
- <code class="inline-code">Environment.setNewBuiltinClassResolver</code>):
- It's used in templates like
- <code class="inline-code">"com.example.SomeClass"?new()</code>, and is
- important for FTL libraries that are partially implemented in
- Java, but shouldn't be needed in normal templates. While
- <code class="inline-code">new</code> will not instantiate classes that are
- not <code class="inline-code">TemplateModel</code>-s, FreeMarker contains a
- <code class="inline-code">TemplateModel</code> class that can be used to
- create arbitrary Java objects. Other "dangerous"
- <code class="inline-code">TemplateModel</code>-s can exist in you
- class-path. Plus, even if a class doesn't implement
- <code class="inline-code">TemplateModel</code>, its static initialization
- will be run. To avoid these, you should use a
- <code class="inline-code">TemplateClassResolver</code> that restricts the
- accessible classes (possibly based on which template asks for
- them), such as
- <code class="inline-code">TemplateClassResolver.ALLOWS_NOTHING_RESOLVER</code>.</p>
- </li>
- </ul>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_implement_function_or_macro_in_java">
- 23.
- How to implement a function or macro in Java Language
- instead of in the template language?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>It's not possible (yet), but something very similar is
- possible if you write a class that implements
- <code class="inline-code">freemarker.template.TemplateMethodModelEx</code> or
- <code class="inline-code">freemarker.template.TemplateDirectiveModel</code>
- respectively, and then where you were write <code class="inline-code"><#function
- my
- <em class="code-color">...</em>><em class="code-color">...</em></#function></code>
- or <code class="inline-code"><#macro my
- <em class="code-color">...</em>><em class="code-color">...</em></#macro></code>
- you write <code class="inline-code"><#assign my = "your.package.YourClass
- "?</code><a href="ref_builtins_expert.html#ref_builtin_new"><code>new</code></a><code class="inline-code">()></code>
- instead. Note that using the <code class="inline-code">assign</code> directive
- for this works because functions (and methods) and macros are just
- plain variables in FreeMarker. (For the same reason you could also
- put <code class="inline-code">TemplateMethodModelEx</code> or
- <code class="inline-code">TemplateDirectiveModel</code> instances into the
- data-model before calling the template, or into the shared
- variable map (see:
- <code class="inline-code">freemarker.template.Configuration.setSharedVariable(String,
- TemplateModel)</code>) when you initialize the
- application.)</p>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_nice_error_page">
- 24.
- <a name="misc.faq.niceErrorPage"></a> In my Servlet
- based application, how do I show a nice error page instead of a
- stack trace when error occurs during template processing?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>First of all, use <code class="inline-code">RETHROW_HANDLER</code> instead
- of the default <code class="inline-code">DEBUG_HANDLER</code> (for more
- information about template exception handlers <a href="pgui_config_errorhandling.html">read this...</a>). Now
- FreeMarker will not print anything to the output when an error
- occurs, so the control is in your hands. After you have caught the
- exception of
- <code class="inline-code">Template.process(<em class="code-color">...</em>)</code>
- basically you can follow two strategies:</p>
-
- <ul>
- <li>
- <p>Call <code class="inline-code">httpResp.isCommitted()</code>, and if
- that returns <code class="inline-code">false</code>, then you call
- <code class="inline-code">httpResp.reset()</code> and print a "nice
- error page" for the visitor. If the return value was
- <code class="inline-code">true</code>, then try to finish the page be
- printing something that makes clear for the visitor that the
- page generation was abruptly interrupted because of an error
- on the Web server. You may have to print a lot of redundant
- HTML end-tags and set colors and font size to ensure that the
- error message will be actually readable in the browser window
- (check the source code of the
- <code class="inline-code">HTML_DEBUG_HANDLER</code> in
- <code class="inline-code">src\freemarker\template\TemplateException.java</code>
- to see an example).</p>
- </li>
-
- <li>
- <p>Use full page buffering. This means that the
- <code class="inline-code">Writer</code> doesn't send the output to the
- client progressively, but buffers the whole page in the
- memory. Since you provide the <code class="inline-code">Writer</code>
- instance for the
- <code class="inline-code">Template.process(<em class="code-color">...</em>)</code>
- method, this is your responsibility, FreeMarker has nothing to
- do with it. For example, you may use a
- <code class="inline-code">StringWriter</code>, and if
- <code class="inline-code">Template.process(<em class="code-color">...</em>)</code>
- returns by throwing an exception, then ignore the content
- accumulated by the <code class="inline-code">StringWriter</code>, and send
- an error page instead, otherwise you print the content of
- <code class="inline-code">StringWriter</code> to the output. With this
- method you surely don't have to deal with partially sent
- pages, but it can have negative performance implications
- depending on the characteristic of the pages (for example, the
- user will experience more response delay for a long page that
- is generated slowly, also the server will consume more RAM).
- Note that using a <code class="inline-code">StringWriter</code> is surely
- not the most efficient solution, as it often reallocates its
- buffer as the accumulated content grows.</p>
- </li>
- </ul>
- </dd>
-
-
-
-
-
- <dt class="question" id="faq_html_editor_mangles">
- 25.
- I'm using a visual HTML editor that mangles template tags.
- Will you change the template language syntax to accommodate my
- editor?
-
- </dt>
-
-
- <dd class="answer">
-
- <p>We won't change the standard version, because a lot of
- templates depend on it.</p>
-
- <p>Our view is that the editors that break template code are
- themselves broken. A good editor should ignore, not mangle, what
- it doesn't understand.</p>
-
- <p>You maybe interested in that starting from FreeMarker 2.3.4
- you can use <code class="inline-code">[</code> and <code class="inline-code">]</code> instead
- of <code class="inline-code"><</code> and <code class="inline-code">></code>. For more
- details <a href="dgui_misc_alternativesyntax.html">read
- this...</a></p>
- </dd>
-
-
- </dl>
-
- </div>
-<div class="bottom-pagers-wrapper"><div class="pagers bottom"><a class="paging-arrow previous" href="app.html"><span>Previous</span></a><a class="paging-arrow next" href="app_versions.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 class="column"><h3 class="column-header">Overview</h3><ul><li><a href="http://freemarker.org/">What is FreeMarker?</a></li><li><a href="http://freemarker.org/freemarkerdownload.html">Download</a></li><li><a href="app_versions.html">Version history</a></li><li><a href="http://freemarker.org/history.html">About us</a></li><li><a itemprop="license" href="app_license.html">License</a></li></ul></div><div class="column"><h3 class="column-header">Handy stuff</h3><ul><li><a href="http://freemarker-online.kenshoo.com/">Try template online</a></li><li><a href="dgui_template_exp.html#exp_cheatsheet">Expressions cheatsheet</a></li><li><a href="ref_directive_alphaidx.html">#directives</a></li><li><a href="ref_builtins_alphaidx.html">?built_ins</a></li><li><a href="ref_specvar.html">.special_vars</a></li></ul></div><div class="column"><h3 class="column-header">Community</h3><ul><li><a href
="https://github.com/freemarker/freemarker">FreeMarker on Github</a></li><li><a href="https://twitter.com/freemarker">Follow us on Twitter</a></li><li><a href="https://issues.apache.org/jira/browse/FREEMARKER/">Report a bug</a></li><li><a href="http://stackoverflow.com/questions/ask?tags=freemarker">Ask a question</a></li><li><a href="http://freemarker.org/mailing-lists.html">Mailing lists</a></li></ul></div></div><div class="col-right"><ul class="social-icons"><li><a class="github" href="https://github.com/freemarker/freemarker">Github</a></li><li><a class="twitter" href="https://twitter.com/freemarker">Twitter</a></li><li><a class="stack-overflow" href="http://stackoverflow.com/questions/ask?tags=freemarker">Stack Overflow</a></li></ul><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="2017-03-13T10:55:28Z" title="Monday, March 13, 2017 10:55:28 AM GMT">2017-03-13 10:55:28 GMT</time>, for Freemarker 2.3.26 </p>
-<p class="copyright">
-� <span itemprop="copyrightYear">1999</span>\u20132017
-<a itemtype="http://schema.org/Organization" itemprop="copyrightHolder
<TRUNCATED>