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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>â2017 -<a itemtype="http://schema.org/Organization"; itemprop="copyrightHolder
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