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href="ref_specvar.html">.spec_vars</a></li><li><a href="app_faq.html">FAQ</a></li></ul></div></div></div> <div class="main-content site-width"> - <div class="content-wrapper"> - <div id="table-of-contents-wrapper" class="col-left"> - <script>var breadcrumb = ["Apache FreeMarker Manual","Template Author\'s Guide","The Template","Expressions"];</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="dgui_template_directives.html"><span>Previous</span></a><a class="paging-arrow next" href="dgui_template_valueinsertion.html"><span>Next</span></a></div><div class="title-wrapper"> -<h1 class="content-header header-section1" id="dgui_template_exp" itemprop="headline">Expressions</h1> -</div></div><div class="page-menu"> -<div class="page-menu-title">Page Contents</div> -<ul><li><a class="page-menu-link" href="#exp_cheatsheet" data-menu-target="exp_cheatsheet">Quick overview (cheat sheet)</a></li><li><a class="page-menu-link" href="#dgui_template_exp_direct" data-menu-target="dgui_template_exp_direct">Specify values directly</a><ul><li><a class="page-menu-link" href="#dgui_template_exp_direct_string" data-menu-target="dgui_template_exp_direct_string">Strings</a></li><li><a class="page-menu-link" href="#dgui_template_exp_direct_number" data-menu-target="dgui_template_exp_direct_number">Numbers</a></li><li><a class="page-menu-link" href="#dgui_template_exp_direct_boolean" data-menu-target="dgui_template_exp_direct_boolean">Booleans</a></li><li><a class="page-menu-link" href="#dgui_template_exp_direct_seuqence" data-menu-target="dgui_template_exp_direct_seuqence">Sequences</a></li><li><a class="page-menu-link" href="#dgui_template_exp_direct_ranges" data-menu-target="dgui_template_exp_direct_ranges">Ranges</a></li><li><a class="page-menu-link" href="#d gui_template_exp_direct_hash" data-menu-target="dgui_template_exp_direct_hash">Hashes</a></li></ul></li><li><a class="page-menu-link" href="#dgui_template_exp_var" data-menu-target="dgui_template_exp_var">Retrieving variables</a><ul><li><a class="page-menu-link" href="#dgui_template_exp_var_toplevel" data-menu-target="dgui_template_exp_var_toplevel">Top-level variables</a></li><li><a class="page-menu-link" href="#dgui_template_exp_var_hash" data-menu-target="dgui_template_exp_var_hash">Retrieving data from a hash</a></li><li><a class="page-menu-link" href="#dgui_template_exp_var_sequence" data-menu-target="dgui_template_exp_var_sequence">Retrieving data from a sequence</a></li><li><a class="page-menu-link" href="#dgui_template_exp_var_special" data-menu-target="dgui_template_exp_var_special">Special variables</a></li></ul></li><li><a class="page-menu-link" href="#dgui_template_exp_stringop" data-menu-target="dgui_template_exp_stringop">String operations</a><ul><li><a class="page-men u-link" href="#dgui_template_exp_stringop_interpolation" data-menu-target="dgui_template_exp_stringop_interpolation">Interpolation and concatenation</a></li><li><a class="page-menu-link" href="#dgui_template_exp_get_character" data-menu-target="dgui_template_exp_get_character">Getting a character</a></li><li><a class="page-menu-link" href="#dgui_template_exp_stringop_slice" data-menu-target="dgui_template_exp_stringop_slice">String slicing (substrings)</a></li></ul></li><li><a class="page-menu-link" href="#dgui_template_exp_sequenceop" data-menu-target="dgui_template_exp_sequenceop">Sequence operations</a><ul><li><a class="page-menu-link" href="#dgui_template_exp_sequenceop_cat" data-menu-target="dgui_template_exp_sequenceop_cat">Concatenation</a></li><li><a class="page-menu-link" href="#dgui_template_exp_seqenceop_slice" data-menu-target="dgui_template_exp_seqenceop_slice">Sequence slicing</a></li></ul></li><li><a class="page-menu-link" href="#dgui_template_exp_hashop" data-menu-ta rget="dgui_template_exp_hashop">Hash operations</a><ul><li><a class="page-menu-link" href="#dgui_template_exp_hashop_cat" data-menu-target="dgui_template_exp_hashop_cat">Concatenation</a></li></ul></li><li><a class="page-menu-link" href="#dgui_template_exp_arit" data-menu-target="dgui_template_exp_arit">Arithmetical calculations</a></li><li><a class="page-menu-link" href="#dgui_template_exp_comparison" data-menu-target="dgui_template_exp_comparison">Comparison</a></li><li><a class="page-menu-link" href="#dgui_template_exp_logicalop" data-menu-target="dgui_template_exp_logicalop">Logical operations</a></li><li><a class="page-menu-link" href="#dgui_template_exp_builtin" data-menu-target="dgui_template_exp_builtin">Built-ins</a></li><li><a class="page-menu-link" href="#dgui_template_exp_methodcall" data-menu-target="dgui_template_exp_methodcall">Method call</a></li><li><a class="page-menu-link" href="#dgui_template_exp_missing" data-menu-target="dgui_template_exp_missing">Handling miss ing values</a><ul><li><a class="page-menu-link" href="#dgui_template_exp_missing_default" data-menu-target="dgui_template_exp_missing_default">Default value operator</a></li><li><a class="page-menu-link" href="#dgui_template_exp_missing_test" data-menu-target="dgui_template_exp_missing_test">Missing value test operator</a></li></ul></li><li><a class="page-menu-link" href="#dgui_template_exp_assignment" data-menu-target="dgui_template_exp_assignment">Assignment Operators</a></li><li><a class="page-menu-link" href="#dgui_template_exp_parentheses" data-menu-target="dgui_template_exp_parentheses">Parentheses</a></li><li><a class="page-menu-link" href="#dgui_template_exp_whitespace" data-menu-target="dgui_template_exp_whitespace">White-space in expressions</a></li><li><a class="page-menu-link" href="#dgui_template_exp_precedence" data-menu-target="dgui_template_exp_precedence">Operator precedence</a></li></ul> </div><p>When you supply values for interpolations or directive - parameters you can use variables or more complex expressions. For - example, if x is the number 8 and y is 5, the value of <code class="inline-code">(x + - y)/2</code> resolves to the numerical value 6.5.</p><p>Before we go into details, let's see some concrete - examples:</p><ul> - <li> - <p>When you supply value for interpolations: The usage of - interpolations is - <code class="inline-code">${<em class="code-color">expression</em>}</code> where - expression gives the value you want to insert into the output as - text. So <code class="inline-code">${(5 + 8)/2}</code> prints "6.5" - to the output (or possibly "6,5" if the language of - your output is not US English).</p> - </li> - - <li> - <p>When you supply a value for the directive parameter: You - have already seen the <code class="inline-code">if</code> directive in the - Getting Started section. The syntax of this directive is: - <code class="inline-code"><#if - <em class="code-color">expression</em>><em class="code-color">...</em></#if></code>. - The expression here must evaluate to a boolean value. For example - in <code class="inline-code"><#if 2 < 3></code> the <code class="inline-code">2 < - 3</code> (2 is less than 3) is an expression which evaluates to - <code class="inline-code">true</code>.</p> - </li> - </ul> - - - - -<h2 class="content-header header-section2" id="exp_cheatsheet">Quick overview (cheat sheet)</h2> - - - <p>This is a reminder for those of you who already know - FreeMarker or are just experienced programmers:</p> - - <ul> - <li> - <a href="#dgui_template_exp_direct">Specify values - directly</a> - - <ul> - <li> - <a href="#dgui_template_exp_direct_string">Strings</a>: - <code class="inline-code">"Foo"</code> or <code class="inline-code">'Foo'</code> or - <code class="inline-code">"It's \"quoted\""</code> or <code class="inline-code">'It\'s - "quoted"'</code> or - <code class="inline-code">r"C:\raw\string"</code> - </li> - - <li> - <a href="#dgui_template_exp_direct_number">Numbers</a>: - <code class="inline-code">123.45</code> - </li> - - <li> - <a href="#dgui_template_exp_direct_boolean">Booleans</a>: - <code class="inline-code">true</code>, <code class="inline-code">false</code> - </li> - - <li> - <a href="#dgui_template_exp_direct_seuqence">Sequences</a>: - <code class="inline-code">["foo", "bar", 123.45]</code>; Ranges: - <code class="inline-code">0..9</code>, <code class="inline-code">0..<10</code> (or - <code class="inline-code">0..!10</code>), <code class="inline-code">0..</code> - </li> - - <li> - <a href="#dgui_template_exp_direct_hash">Hashes</a>: - <code class="inline-code">{"name":"green mouse", - "price":150}</code> - </li> - </ul> - </li> - - <li> - <a href="#dgui_template_exp_var">Retrieving - variables</a> - - <ul> - <li> - <a href="#dgui_template_exp_var_toplevel">Top-level - variables</a>: <code class="inline-code">user</code> - </li> - - <li> - <a href="#dgui_template_exp_var_hash">Retrieving - data from a hash</a>: <code class="inline-code">user.name</code>, - <code class="inline-code">user["name"]</code> - </li> - - <li> - <a href="#dgui_template_exp_var_sequence">Retrieving data - from a sequence</a>: - <code class="inline-code">products[5]</code> - </li> - - <li> - <a href="#dgui_template_exp_var_special">Special - variable</a>: <code class="inline-code">.main</code> - </li> - </ul> - </li> - - <li> - <a href="#dgui_template_exp_stringop">String - operations</a> - - <ul> - <li> - <a href="#dgui_template_exp_stringop_interpolation">Interpolation - and concatenation</a>: - <code class="inline-code">"Hello ${user}!"</code> (or <code class="inline-code">"Hello - " + user + "!"</code>) - </li> - - <li> - <a href="#dgui_template_exp_get_character">Getting a - character</a>: <code class="inline-code">name[0]</code> - </li> - - <li> - <a href="#dgui_template_exp_stringop_slice">String - slice:</a> Inclusive end: <code class="inline-code">name[0..4]</code>, - Exclusive end: <code class="inline-code">name[0..<5]</code>, - Length-based (lenient): <code class="inline-code">name[0..*5]</code>, - Remove starting: <code class="inline-code">name[5..]</code> - </li> - </ul> - </li> - - <li> - <a href="#dgui_template_exp_sequenceop">Sequence - operations</a> - - <ul> - <li> - <a href="#dgui_template_exp_sequenceop_cat">Concatenation</a>: - <code class="inline-code">users + ["guest"]</code> - </li> - - <li> - <a href="#dgui_template_exp_seqenceop_slice">Sequence - slice</a>: Inclusive end: - <code class="inline-code">products[20..29]</code>, Exclusive end: - <code class="inline-code">products[20..<30]</code>, Length-based - (lenient): <code class="inline-code">products[20..*10]</code>, Remove - starting: <code class="inline-code">products[20..]</code> - </li> - </ul> - </li> - - <li> - <a href="#dgui_template_exp_hashop">Hash - operations</a> - - <ul> - <li> - <a href="#dgui_template_exp_hashop_cat">Concatenation</a>: - <code class="inline-code">passwords + { "joe": "secret42" }</code> - </li> - </ul> - </li> - - <li> - <a href="#dgui_template_exp_arit">Arithmetical - calculations</a>: <code class="inline-code">(x * 1.5 + 10) / 2 - y % - 100</code> - </li> - - <li> - <a href="#dgui_template_exp_comparison">Comparison</a>: - <code class="inline-code">x == y</code>, <code class="inline-code">x != y</code>, - <code class="inline-code">x < y</code>, <code class="inline-code">x > y</code>, - <code class="inline-code">x >= y</code>, <code class="inline-code">x <= y</code>, - <code class="inline-code">x lt y</code>, <code class="inline-code">x lte y</code>, - <code class="inline-code">x gt y</code>, <code class="inline-code">x gte y</code>, - ...etc. - </li> - - <li> - <a href="#dgui_template_exp_logicalop">Logical - operations</a>: <code class="inline-code">!registered && (firstVisit - || fromEurope)</code> - </li> - - <li> - <a href="#dgui_template_exp_builtin">Built-ins</a>: - <code class="inline-code">name?upper_case</code>, - <code class="inline-code">path?ensure_starts_with('/')</code> - </li> - - <li> - <a href="#dgui_template_exp_methodcall">Method - call</a>: <code class="inline-code">repeat("What", 3)</code> - </li> - - <li> - <a href="#dgui_template_exp_missing">Missing value - handler operators</a>: - - <ul> - <li> - <a href="#dgui_template_exp_missing_default">Default - value</a>: <code class="inline-code">name!"unknown"</code> or - <code class="inline-code">(user.name)!"unknown"</code> or - <code class="inline-code">name!</code> or - <code class="inline-code">(user.name)!</code> - </li> - - <li> - <a href="#dgui_template_exp_missing_test">Missing - value test</a>: <code class="inline-code">name??</code> or - <code class="inline-code">(user.name)??</code> - </li> - </ul> - </li> - - <li> - <a href="#dgui_template_exp_assignment">Assignment - operators</a>: <code class="inline-code">=</code>, <code class="inline-code">+=</code>, - <code class="inline-code">-=</code>, <code class="inline-code">*=</code>, - <code class="inline-code">/=</code>, <code class="inline-code">%=</code>, - <code class="inline-code">++</code>, <code class="inline-code">--</code> - </li> - </ul> - - <p>See also: <a href="#dgui_template_exp_precedence">Operator - precedence</a></p> - - - - - -<h2 class="content-header header-section2" id="dgui_template_exp_direct">Specify values directly</h2> - - - - - - - <p>Often you want to specify a value directly and not as a result - of some calculations.</p> - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_direct_string">Strings</h3> - - - - - <p>To specify a string value directly you give the text in - quotation marks, e.g.: <code class="inline-code">"some text"</code> or in - apostrophe-quote, e.g. <code class="inline-code">'some text'</code>. The two - forms are equivalent. If the text itself contains the character - used for the quoting (either <code class="inline-code">"</code> or - <code class="inline-code">'</code>) or backslashes, you have to precede them - with a backslash; this is called escaping. You can type any other - character, including <a href="gloss.html#gloss.lineBreak">line - breaks</a>, in the text directly. Example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${"It's \"quoted\" and -this is a backslash: \\"} - -${'It\'s "quoted" and -this is a backslash: \\'}</pre></div> - - <p>will print:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">It's "quoted" and -this is a backslash: \ - -It's "quoted" and -this is a backslash: \</pre></div> - - <div class="callout note"> - <strong class="callout-label">Note:</strong> - - <p>Of course, you could simply type the above text into the - template, without using - <code class="inline-code">${<em class="code-color">...</em>}</code>. But we do - it here just for the sake of example, to demonstrate - expressions.</p> - </div> - - - <a name="topic.escapeSequence"></a> - - - - <p>This is the list of all supported escape sequences. All - other usage of backlash in string literals is an error and any - attempt to use the template will fail.</p> - - <div class="table-responsive"> - <table class="table"> - - <thead> - <tr> - <th>Escape sequence</th> - - - <th>Meaning</th> - - </tr> - - </thead> - - - <tbody> - <tr> - <td><code class="inline-code">\"</code></td> - - - <td>Quotation mark (u0022)</td> - - </tr> - - - <tr> - <td><code class="inline-code">\'</code></td> - - - <td>Apostrophe (a.k.a. apostrophe-quote) (u0027)</td> - - </tr> - - - <tr> - <td><code class="inline-code">\{</code></td> - - - <td>Opening curly brace: <code class="inline-code">{</code></td> - - </tr> - - - <tr> - <td><code class="inline-code">\\</code></td> - - - <td>Back slash (u005C)</td> - - </tr> - - - <tr> - <td><code class="inline-code">\n</code></td> - - - <td>Line feed (u000A)</td> - - </tr> - - - <tr> - <td><code class="inline-code">\r</code></td> - - - <td>Carriage return (u000D)</td> - - </tr> - - - <tr> - <td><code class="inline-code">\t</code></td> - - - <td>Horizontal tabulation (a.k.a. tab) (u0009)</td> - - </tr> - - - <tr> - <td><code class="inline-code">\b</code></td> - - - <td>Backspace (u0008)</td> - - </tr> - - - <tr> - <td><code class="inline-code">\f</code></td> - - - <td>Form feed (u000C)</td> - - </tr> - - - <tr> - <td><code class="inline-code">\l</code></td> - - - <td>Less-than sign: <code class="inline-code"><</code></td> - - </tr> - - - <tr> - <td><code class="inline-code">\g</code></td> - - - <td>Greater-than sign: <code class="inline-code">></code></td> - - </tr> - - - <tr> - <td><code class="inline-code">\a</code></td> - - - <td>Ampersand: <code class="inline-code">&</code></td> - - </tr> - - - <tr> - <td><code class="inline-code">\x<em class="code-color">Code</em></code></td> - - - <td>Character given with its hexadecimal <a href="gloss.html#gloss.unicode">Unicode</a> code (<a href="gloss.html#gloss.UCS">UCS</a> code)</td> - - </tr> - - </tbody> - - </table> - </div> - - - <p>The <code class="inline-code"><em class="code-color">Code</em></code> after - the <code class="inline-code">\x</code> is 1 to 4 hexadecimal digits. For - example this all put a copyright sign into the string: - <code class="inline-code">"\xA9 1999-2001"</code>, - <code class="inline-code">"\x0A9 1999-2001"</code>, - <code class="inline-code">"\x00A9 1999-2001"</code>. When the character directly - after the last hexadecimal digit can be interpreted as hexadecimal - digit, you must use all 4 digits or else FreeMarker will - misunderstand you.</p> - - <p>Note that the character sequence <code class="inline-code">${</code> (and - <code class="inline-code">#{</code>) has special meaning. It's used to insert - the value of expressions (typically: the value of variables, as in - <code class="inline-code">"Hello ${user}!"</code>). This will be explained <a href="#dgui_template_exp_stringop_interpolation">later</a>. - If you want to print <code class="inline-code">${</code> or - <code class="inline-code">#{</code>, you should either use raw string literals - as explained below, or escape the <code class="inline-code">{</code> like in - <code class="inline-code">"foo $\{bar}"</code>.</p> - - - - <p>A special kind of string literals is the raw string - literals. In raw string literals, backslash and - <code class="inline-code">${</code> have no special meaning, they are considered - as plain characters. To indicate that a string literal is a raw - string literal, you have to put an <code class="inline-code">r</code> directly - before the opening quotation mark or apostrophe-quote. - Example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${r"${foo}"} -${r"C:\foo\bar"}</pre></div> - - <p>will print:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">${foo} -C:\foo\bar</pre></div> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_direct_number">Numbers</h3> - - - - - <p>To specify a numerical value directly you type the number - without quotation marks. You have to use the dot as your decimal - separator and must not use any grouping separator symbols. You can - use <code class="inline-code">-</code> or <code class="inline-code">+</code> to indicate the - sign (<code class="inline-code">+</code> is redundant). Scientific notation is - not yet supported (so <code class="inline-code">1E3</code> is wrong). Also, you - cannot omit the 0 before the decimal separator (so - <code class="inline-code">.5</code> is wrong).</p> - - <p>Examples of valid number literals: <code class="inline-code">0.08</code>, - <code class="inline-code">-5.013</code>, <code class="inline-code">8</code>, - <code class="inline-code">008</code>, <code class="inline-code">11</code>, - <code class="inline-code">+11</code></p> - - <p>Note that numerical literals like <code class="inline-code">08</code>, - <code class="inline-code">+8</code>, <code class="inline-code">8.00</code> and - <code class="inline-code">8</code> are totally equivalent as they all symbolize - the number eight. Thus, <code class="inline-code">${08}</code>, - <code class="inline-code">${+8}</code>, <code class="inline-code">${8.00}</code> and - <code class="inline-code">${8}</code> will all print exactly same.</p> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_direct_boolean">Booleans</h3> - - - - - - - <p>To specify a boolean value you write <code class="inline-code">true</code> - or <code class="inline-code">false</code>. Don't use quotation marks.</p> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_direct_seuqence">Sequences</h3> - - - - - - - - - - - <p>To specify a literal sequence, you list the <a href="dgui_quickstart_datamodel.html#topic.dataModel.subVar">sub variables</a> separated by - commas, and put the whole list into square brackets. For - example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template"><#list <strong>["foo", "bar", "baz"]</strong> as x> -${x} -</#list></pre></div> - - <p>will print:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">foo -bar -baz - </pre></div> - - <p>The items in the list are expressions, so you can do this - for example: <code class="inline-code">[2 + 2, [1, 2, 3, 4], "foo"]</code>. Here - the first subvariable will be the number 4, the second will be - another sequence, and the third subvariable will be the string - "foo".</p> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_direct_ranges">Ranges</h3> - - - <p>Ranges are just sequences, but they are created by - specifying what range of whole numbers they contain, instead of - specifying their items one by one. For example, - <code class="inline-code">0..<m</code>, assuming the <code class="inline-code">m</code> - variable stores 5, will give a sequence that contains <code class="inline-code">[0, - 1, 2, 3, 4]</code>. Ranges are primarily used for iterating - over a range of numbers with <code class="inline-code"><#list - <em class="code-color">...</em>></code> and for <a href="#dgui_template_exp_seqenceop_slice">slicing - sequences</a> and <a href="#dgui_template_exp_stringop_slice">slicing - strings</a>.</p> - - <p>The generic forms of range expressions are (where - <code class="inline-code"><em class="code-color">start</em></code> and - <code class="inline-code"><em class="code-color">end</em></code> can be any - expression that evaluates to a number):</p> - - <ul> - <li> - <p><code class="inline-code"><em class="code-color">start</em>..<em class="code-color">end</em></code>: - Range with inclusive end. For example, <code class="inline-code">1..4</code> - gives <code class="inline-code">[1, 2, 3, 4]</code>, and - <code class="inline-code">4..1</code> gives <code class="inline-code">[4, 3, 2, 1]</code>. - Beware, ranges with inclusive end never give an empty - sequence, so <code class="inline-code">0..length-1</code> is - <em>WRONG</em>, because when length is - <code class="inline-code">0</code> it gives <code class="inline-code">[0, - -1]</code>.</p> - </li> - - <li> - <p><code class="inline-code"><em class="code-color">start</em>..<<em class="code-color">end</em></code> - or - <code class="inline-code"><em class="code-color">start</em>..!<em class="code-color">end</em></code>: - Range with exclusive end. For example, - <code class="inline-code">1..<4</code> gives <code class="inline-code">[1, 2, - 3]</code>, <code class="inline-code">4..<1</code> gives <code class="inline-code">[4, - 3, 2]</code>, and <code class="inline-code">1..<1</code> gives - <code class="inline-code">[]</code>. Note the last example; the result can - be an empty sequence. There's no difference between - <code class="inline-code">..<</code> and <code class="inline-code">..!</code>; the last - form is used in applications where using the - <code class="inline-code"><</code> character causes problems (for HTML - editors and such).</p> - </li> - - <li> - <p><code class="inline-code"><em class="code-color">start</em>..*<em class="code-color">length</em></code>: - Length limited range. For example, <code class="inline-code">10..*4</code> - gives <code class="inline-code">[10, 11, 12, 13]</code>, - <code class="inline-code">10..*-4</code> gives <code class="inline-code">[10, 9, 8, - 7]</code>, and <code class="inline-code">10..*0</code> gives - <code class="inline-code">[]</code>. When these kind of ranges are used for - slicing, the slice will end without error if the end of the - sliced sequence or string is reached before the specified - range length was reached; see <a href="#dgui_template_exp_seqenceop_slice">slicing - sequences</a> for more.</p> - - <div class="callout note"> - <strong class="callout-label">Note:</strong> - - <p>Length limited ranges were introduced in FreeMarker - 2.3.21.</p> - </div> - - </li> - - <li> - <p><code class="inline-code"><em class="code-color">start</em>..</code>: - Right-unbounded range. This are like length limited ranges - with infinite length. For example <code class="inline-code">1..</code> gives - <code class="inline-code">[1, 2, 3, 4, 5, 6, ... ]</code>, up to infinity. - Be careful when processing (like listing) such ranges, as - processing all items of it it would take forever or until the - application runs out of memory and crashes. Just like with - length limited ranges, when these kind of ranges are used for - slicing, the slice will end when the end of the sliced - sequence or string is reached.</p> - - <div class="callout warning"> - <strong class="callout-label">Warning!</strong> - - <p>Right-unbounded ranges before FreeMarker 2.3.21 were - only used for slicing, and behaved like an empty sequence - for other purposes. To activate the new behavior, it's not - enough to use FreeMarker 2.3.21, the programmer also have to - set the <code class="inline-code">incompatible_improvements</code> - configuration setting to at least 2.3.21.</p> - </div> - - </li> - </ul> - - <p>Further notes on ranges:</p> - - <ul> - <li> - <p>Range expressions themselves don't have square brackets, - for example, you write <code class="inline-code"><#assign myRange = - 0..<x</code>, NOT <code class="inline-code"><#assign myRange = - [0..<x]></code>. The last would create a sequence - that contains an item that's a range. The square brackets are - part of the slicing syntax, like - <code class="inline-code"><em class="code-color">seq</em>[<em class="code-color">myRange</em>]</code>.</p> - </li> - - <li> - <p>You can write arithmetical expression on the sides of - the <code class="inline-code">..</code> without parenthesis, like <code class="inline-code">n - + 1 ..< m / 2 - 1</code>.</p> - </li> - - <li> - <p><code class="inline-code">..</code>, <code class="inline-code">..<</code>, - <code class="inline-code">..!</code> and <code class="inline-code">..*</code> are - operators, so you can't have space inside them. Like - <code class="inline-code">n .. <m</code> is WRONG, but <code class="inline-code">n ..< - m</code> is good.</p> - </li> - - <li> - <p>The reported size of right-unbounded ranges is - 2147483647 (or 0 if - <code class="inline-code">incompatible_improvements</code> is less than - 2.3.21) due to a technical limitation (32 bits). However, when - listing them, their actual size is infinite.</p> - </li> - - <li> - <p>Ranges don't really store the numbers they consist of, - thus for example <code class="inline-code">0..1</code> and - <code class="inline-code">0..100000000</code> is equally fast to create and - takes the same amount of memory.</p> - </li> - </ul> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_direct_hash">Hashes</h3> - - - - - - - <p>To specify a hash in a template, you list the key/value - pairs separated by commas, and put the list into curly brackets. - The key and value within a key/value pair are separated with a - colon. Here is an example: <code class="inline-code">{ "name": "green mouse", - "price": 150 }</code>. Note that both the names and the values - are expressions. The keys must be strings. The values can be if - any type.</p> - - - - - - -<h2 class="content-header header-section2" id="dgui_template_exp_var">Retrieving variables</h2> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_var_toplevel">Top-level variables</h3> - - - - - <p>To access a top-level variable, you simply use the variable - name. For example, the expression <code class="inline-code">user</code> will - evaluate to the value of variable stored with name - "user" in the root. So this will print what you store - there:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${user}</pre></div> - - <p>If there is no such top-level variable, then an error will - result when FreeMarker tries to evaluate the expression, and it - aborts template processing (unless programmers has configured - FreeMarker differently).</p> - - <p>In this kind of expression, the variable name can only - contain letters (including non-Latin letters), digits (including - non-Latin digits), underline (<code class="inline-code">_</code>), dollar - (<code class="inline-code">$</code>), at sign (<code class="inline-code">@</code>). - Furthermore, the first character can't be a ASCII digit - (<code class="inline-code">0</code>-<code class="inline-code">9</code>). Starting from - FreeMarker 2.3.22, the variable name can also contain minus - (<code class="inline-code">-</code>), dot (<code class="inline-code">.</code>), and colon - (<code class="inline-code">:</code>) at any position, but these must be escaped - with a preceding backslash (<code class="inline-code">\</code>), or else they - would be interpreted as operators. For example, to read the - variable whose name is "data-id", the expression is - <code class="inline-code">data\-id</code>, as <code class="inline-code">data-id</code> would - be interpreted as "data minus id". (Note that these - escapes only work in identifiers, not in string literals.)</p> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_var_hash">Retrieving data from a hash</h3> - - - - - - - <p>If we already have a hash as a result of an expression, then - we can get its subvariable with a dot and the name of the - subvariable. Assume that we have this data-model:</p> - - - -<div class="code-wrapper"><pre class="code-block code-data-model">(root) - | - +- book - | | - | +- title = "Breeding green mouses" - | | - | +- author - | | - | +- name = "Julia Smith" - | | - | +- info = "Biologist, 1923-1985, Canada" - | - +- test = "title"</pre></div> - - <p>Now we can read the <code class="inline-code">title</code> with - <code class="inline-code">book.title</code>, since the book expression will - return a hash (as explained in the last chapter). Applying this - logic further, we can read the name of the author with this - expression: <code class="inline-code">book.author.name</code>.</p> - - <p>There is an alternative syntax if we want to specify the - subvariable name with an expression: - <code class="inline-code">book["title"]</code>. In the square brackets you can - give any expression as long as it evaluates to a string. So with - this data-model you can also read the title with - <code class="inline-code">book[test]</code>. More examples; these are all - equivalent: <code class="inline-code">book.author.name</code>, - <code class="inline-code">book["author"].name</code>, - <code class="inline-code">book.author.["name"]</code>, - <code class="inline-code">book["author"]["name"]</code>.</p> - - <p>When you use the dot syntax, the same restrictions apply - regarding the variable name as with top-level variables (name can - contain only letters, digits, <code class="inline-code">_</code>, - <code class="inline-code">$</code>, <code class="inline-code">@</code> but can't start with - <code class="inline-code">0</code>-<code class="inline-code">9</code>, also starting from - 2.3.22 you can also use <code class="inline-code">\-</code>, - <code class="inline-code">\.</code> and <code class="inline-code">\:</code>). There are no - such restrictions when you use the square bracket syntax, since - the name is the result of an arbitrary expression. (Note, that to - help the FreeMarker XML support, if the subvariable name is - <code class="inline-code">*</code> (asterisk) or <code class="inline-code">**</code>, then you - do not have to use square bracket syntax.)</p> - - <p>As with the top-level variables, trying to access a - non-existent subvariable causes an error and aborts the processing - of the template (unless programmers has configured FreeMarker - differently).</p> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_var_sequence">Retrieving data from a sequence</h3> - - - - - - - <p>This is the same as for hashes, but you can use the square - bracket syntax only, and the expression in the brackets must - evaluate to a number, not a string. For example to get the name of - the first animal of the <a href="dgui_datamodel_basics.html#example.stdDataModel">example data-model</a> (remember - that the number of the first item is 0, not 1): - <code class="inline-code">animals[0].name</code></p> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_var_special">Special variables</h3> - - - - - <p>Special variables are variables defined by the FreeMarker - engine itself. To access them, you use the - <code class="inline-code">.<em class="code-color">variable_name</em></code> - syntax.</p> - - <p>Normally you don't need to use special variables. They are - for expert users. The complete list of special variables can be - found in the <a href="ref_specvar.html">reference</a>.</p> - - - - - - -<h2 class="content-header header-section2" id="dgui_template_exp_stringop">String operations</h2> - - - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_stringop_interpolation">Interpolation and concatenation</h3> - - - - - - - - - - - - - - - <p>If you want to insert the value of an expression into a - string, you can use - <code class="inline-code">${<em class="code-color">...</em>}</code> (and the - deprecated <code class="inline-code">#{<em class="code-color">...</em>}</code>) - in string literals. - <code class="inline-code">${<em class="code-color">...</em>}</code> in string - literals <a href="dgui_template_valueinsertion.html">behaves - similarly as in <span class="marked-text">text</span> - sections</a> (so it goes through the same <em>locale - sensitive</em> number and date/time formatting).</p> - - <p>Example (assume that user is "Big Joe"):</p> - - - -<div class="code-wrapper"><pre class="code-block code-template"><#assign s = "Hello ${user}!"> -${s} <#-- Just to see what the value of s is --></pre></div> - - <p>This will print:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">Hello Big Joe!</pre></div> - - <div class="callout warning"> - <strong class="callout-label">Warning!</strong> - - <p>A frequent mistake of users is the usage of interpolations - in places where they needn't/shouldn't/can't be used. - Interpolations work <em>only</em> in <a href="dgui_template_overallstructure.html"><span class="marked-text">text</span> sections</a> (e.g. - <code class="inline-code"><h1>Hello ${name}!</h1></code>) and in - string literals (e.g. <code class="inline-code"><#include - "/footer/${company}.html"></code>). A typical - <em>WRONG</em> usage is <code class="inline-code"><#if - ${big}>...</#if></code>, which will cause a - syntactical error. You should simply write <code class="inline-code"><#if - big>...</#if></code>. Also, <code class="inline-code"><#if - "${big}">...</#if></code> is - <em>WRONG</em>, since it converts the parameter - value to string and the <code class="inline-code">if</code> directive wants a - boolean value, so it will cause a runtime error.</p> - </div> - - - <p><a name="dgui_template_exp_stringop_concatenation"></a>Alternatively, - you can use the <code class="inline-code">+</code> operator to achieve similar - result:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template"><#assign s = "Hello " + user + "!"></pre></div> - - <p>This gives the same result as the earlier example with the - <code class="inline-code">${<em class="code-color">...</em>}</code>.</p> - - <div class="callout warning"> - <strong class="callout-label">Warning!</strong> - - <p>Because <code class="inline-code">+</code> follows similar rules as - <code class="inline-code">${<em class="code-color">...</em>}</code>, the - appended string is influenced by the <code class="inline-code">locale</code>, - <code class="inline-code">number_format</code>, - <code class="inline-code">date_format</code>, <code class="inline-code">time_format</code>, - <code class="inline-code">datetime_format</code> and - <code class="inline-code">boolean_format</code>, etc. settings, and thus the - result targets humans and isn't in generally machine parseable. - This mostly leads to problems with numbers, as many locales use - grouping (thousands separators) by default, and so - <code class="inline-code">"someUrl?id=" + id</code> becomes to something like - <code class="inline-code">"someUrl?id=1 234"</code>. To prevent this, use the - <code class="inline-code">?c</code> (for Computer audience) built-in, like in - <code class="inline-code">"someUrl?id=" + id?c</code> or - <code class="inline-code">"someUrl?id=${id?c}"</code>, which will evaluate to - something like <code class="inline-code">"someUrl?id=1234"</code>, regardless - of locale and format settings.</p> - </div> - - - <p>As when <code class="inline-code">${<em class="code-color">...</em>}</code> - is used inside string <em>expressions</em> it's just a - shorthand of using the <code class="inline-code">+</code> operator, <a href="dgui_misc_autoescaping.html">auto-escaping</a> is not - applied on it.</p> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_get_character">Getting a character</h3> - - - - - - - <p>You can get a single character of a string at a given index - similarly as you can <a href="#dgui_template_exp_var_sequence">read the subvariable of a - sequence</a>, e.g. <code class="inline-code">user[0]</code>. The result will - be a string whose length is 1; FTL doesn't have a separate - character type. As with sequence sub variables, the index must be - a number that is at least 0 and less than the length of the - string, or else an error will abort the template - processing.</p> - - <p>Since the sequence subvariable syntax and the character - getter syntax clashes, you can use the character getter syntax - only if the variable is not a sequence as well (which is possible - because FTL supports multi-typed values), since in that case the - sequence behavior prevails. (To work this around, you can use - <a href="ref_builtins_string.html#ref_builtin_string_for_string">the - <code>string</code> built-in</a>, e.g. - <code class="inline-code">user?string[0]</code>. Don't worry if you don't - understand this yet; built-ins will be discussed later.)</p> - - <p>Example (assume that user is "Big Joe"):</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${user[0]} -${user[4]}</pre></div> - - <p>will print (note that the index of the first character is - 0):</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">B -J</pre></div> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_stringop_slice">String slicing (substrings)</h3> - - - - - - - - - - - <p>You can a slice a string in the same way as you <a href="#dgui_template_exp_seqenceop_slice">slice a - sequence</a> (see there), only here instead of sequence items - you work with characters. Some differences are:</p> - - <ul> - <li> - <p>Decreasing ranges aren't allowed for string slicing. - (That's because unlike sequences, you seldom if ever want to - show a string reversed, so if that happens, that's almost - always the result of an oversight.)</p> - </li> - - <li> - <p>If a value is both a string and a sequence (a - multi-typed value), then slicing will slice the sequence - instead of the string. When you are processing XML, such - values are common. In such cases you can use - <code class="inline-code"><em class="code-color">someXMLnode</em>?string[<em class="code-color">range</em>]</code>.</p> - </li> - - <li> - <p>There's a legacy bug where a range with - <em>inclusive</em> end that's one less than the - starting index and is non-negative (like in - <code class="inline-code">"abc"[1..0]</code>) will give an empty string - instead of an error. (It should be an error as it's a - decreasing range.) Currently this bug is emulated for backward - compatibility, but you shouldn't utilize it, as in the future - it will be certainly an error.</p> - </li> - </ul> - - <p>Example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template"><#assign s = "ABCDEF"> -${s[2..3]} -${s[2..<4]} -${s[2..*3]} -${s[2..*100]} -${s[2..]}</pre></div> - - <p>will print:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">CD -CD -CDE -CDEF -CDEF</pre></div> - - <div class="callout note"> - <strong class="callout-label">Note:</strong> - - <p>Some of the typical use-cases of string slicing is covered - by convenient built-ins: <a href="ref_builtins_string.html#ref_builtin_remove_beginning"><code>remove_beginning</code></a>, - <a href="ref_builtins_string.html#ref_builtin_remove_ending"><code>remove_ending</code></a>, - <a href="ref_builtins_string.html#ref_builtin_keep_before"><code>keep_before</code></a>, - <a href="ref_builtins_string.html#ref_builtin_keep_after"><code>keep_after</code></a>, - <a href="ref_builtins_string.html#ref_builtin_keep_before_last"><code>keep_before_last</code></a>, - <a href="ref_builtins_string.html#ref_builtin_keep_after_last"><code>keep_after_last</code></a></p> - </div> - - - - - - - -<h2 class="content-header header-section2" id="dgui_template_exp_sequenceop">Sequence operations</h2> - - - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_sequenceop_cat">Concatenation</h3> - - - - - - - - - - - <p>You can concatenate sequences in the same way as strings, - with <code class="inline-code">+</code>. Example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template"><#list ["Joe", "Fred"] + ["Julia", "Kate"] as user> -- ${user} -</#list></pre></div> - - <p>will print:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">- Joe -- Fred -- Julia -- Kate - </pre></div> - - <p>Note that sequence concatenation is not to be used for many - repeated concatenations, like for appending items to a sequence - inside a loop. It's just for things like <code class="inline-code"><#list users - + admins as person></code>. Although concatenating sequences - is fast and its speed is independently of the size of the - concatenated sequences, the resulting sequence will be always a - little bit slower to read than the original two sequences were. - This way the result of many repeated concatenations is a sequence - that is slow to read.</p> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_seqenceop_slice">Sequence slicing</h3> - - - - - - - - - <p>With - <code class="inline-code"><em class="code-color">seq</em>[<em class="code-color">range</em>]</code>, - were <code class="inline-code"><em class="code-color">range</em></code> is a - range value <a href="#dgui_template_exp_direct_ranges">as - described here</a>, you can take a slice of the sequence. The - resulting sequence will contain the items from the original - sequence (<code class="inline-code"><em class="code-color">seq</em></code>) whose - indexes are in the range. For example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template"><#assert seq = ["A", "B", "C", "D", "E"]> -<#list seq[1..3] as i>${i}</#list></pre></div> - - <p>will print</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">BCD </pre></div> - - <p>Furthermore, the items in the slice will be in the same - order as in the range. Thus for example the above example with the - <code class="inline-code">3..1</code> range would print - <code class="inline-code">DCB</code>.</p> - - <p>The numbers in the range must be valid indexes in the - sequence, or else the processing of the template will be aborted - with error. Like in the last example, - <code class="inline-code">seq[-1..0]</code> would be an error as - <code class="inline-code">seq[-1]</code> is invalid, also - <code class="inline-code">seq[1..5]</code> would be because - <code class="inline-code">seq[5]</code> is invalid. (Note that - <code class="inline-code">seq[100..<100]</code> or - <code class="inline-code">seq[100..*0]</code> would be valid despite that 100 is - out of bounds, because those ranges are empty.)</p> - - <p>Length limited ranges - (<code class="inline-code"><em class="code-color">start</em>..*<em class="code-color">length</em></code>) - and right-unbounded ranges - (<code class="inline-code"><em class="code-color">start</em>..</code>) adapt to - the length of the sliced sequence. They will slice out at most as - many items as there is available:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template"><#assign seq = ["A", "B", "C"]> - -Slicing with length limited ranges: -- <#list seq[0..*2] as i>${i}</#list> -- <#list seq[1..*2] as i>${i}</#list> -- <#list seq[2..*2] as i>${i}</#list> <#-- Not an error --> -- <#list seq[3..*2] as i>${i}</#list> <#-- Not an error --> - -Slicing with right-unlimited ranges: -- <#list seq[0..] as i>${i}</#list> -- <#list seq[1..] as i>${i}</#list> -- <#list seq[2..] as i>${i}</#list> -- <#list seq[3..] as i>${i}</#list></pre></div> - - <p>This will print:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">Slicing with length limited ranges: -- AB -- BC -- C -- - -Slicing with right-unlimited ranges: -- ABC -- BC -- C --</pre></div> - - <p>Note above that slicing with length limited and right - unbounded ranges allow the starting index to be past the last item - <em>by one</em> (but no more).</p> - - <div class="callout note"> - <strong class="callout-label">Note:</strong> - - <p>To split a sequence to slices of a given size, you should - use the <a href="ref_builtins_sequence.html#ref_builtin_chunk"><code>chunk</code></a> - built-in.</p> - </div> - - - - - - - -<h2 class="content-header header-section2" id="dgui_template_exp_hashop">Hash operations</h2> - - - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_hashop_cat">Concatenation</h3> - - - - - - - - - - - <p>You can concatenate hashes in the same way as strings, with - <code class="inline-code">+</code>. If both hashes contain the same key, the - hash on the right-hand side of the <code class="inline-code">+</code> takes - precedence. Example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template"><#assign ages = {"Joe":23, "Fred":25} + {"Joe":30, "Julia":18}> -- Joe is ${ages.Joe} -- Fred is ${ages.Fred} -- Julia is ${ages.Julia}</pre></div> - - <p>will print:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">- Joe is 30 -- Fred is 25 -- Julia is 18</pre></div> - - <p>Note that hash concatenation is not to be used for many - repeated concatenations, like for adding items to a hash inside a - loop. It's the same as with the <a href="#dgui_template_exp_sequenceop_cat">sequence - concatenation</a>.</p> - - - - - - -<h2 class="content-header header-section2" id="dgui_template_exp_arit">Arithmetical calculations</h2> - - - - - - - - - - - - - - - <p>This is the basic 4-function calculator arithmetic plus the - modulus operator. So the operators are:</p> - - <ul> - <li> - Addition: <code class="inline-code">+</code> - </li> - - <li> - Subtraction: <code class="inline-code">-</code> - </li> - - <li> - Multiplication: <code class="inline-code">*</code> - </li> - - <li> - Division: <code class="inline-code">/</code> - </li> - - <li> - Modulus (remainder) of integer operands: - <code class="inline-code">%</code> - </li> - </ul> - - - - <p>Example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${100 - x * x} -${x / 2} -${12 % 10}</pre></div> - - <p>Assuming that <code class="inline-code">x</code> is 5, it will print:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">75 -2.5 -2</pre></div> - - <p>Both operands must be expressions which evaluate to a - numerical value. So the example below will cause an error when - FreeMarker tries to evaluate it, since <code class="inline-code">"5"</code> is a - string and not the number 5:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${3 * "5"} <#-- WRONG! --></pre></div> - - <p>There is an exception to the above rule. The - <code class="inline-code">+</code> operator, is used to <a href="#dgui_template_exp_stringop_interpolation">concatenate - strings</a> as well. If on one side of <code class="inline-code">+</code> is a - string and on the other side of <code class="inline-code">+</code> is a numerical - value, then it will convert the numerical value to string (using the - format appropriate for language of the page) and then use the - <code class="inline-code">+</code> as string concatenation operator. - Example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${3 + "5"}</pre></div> - - - -<div class="code-wrapper"><pre class="code-block code-output">35</pre></div> - - <p>Generally, FreeMarker never converts a string to a number - automatically, but it may convert a number to a string - automatically.</p> - - <p> People often want only the integer part of the result - of a division (or of other calculations). This is possible with the - <code class="inline-code">int</code> built-in. (Built-ins are explained <a href="#dgui_template_exp_builtin">later</a>):</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${(x/2)?int} -${1.1?int} -${1.999?int} -${-1.1?int} -${-1.999?int}</pre></div> - - <p>Assuming that <code class="inline-code">x</code> is 5, it will print:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">2 -1 -1 --1 --1</pre></div> - - <p>Due to historical reasons, the <code class="inline-code">%</code> operator - works by first truncating the operands to an integer number, and - then returning the remainder of the division:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${12 % 5} <#-- Prints 2 --> -${12.9 % 5} <#-- Prints 2 --> -${12.1 % 5} <#-- Prints 2 --> - -${12 % 6} <#-- Prints 0 --> -${12 % 6.9} <#-- Prints 0 --></pre></div> - - <p>The sign of the result of <code class="inline-code">%</code> is the same as - the sign of the left hand operand, and its absolute value is the - same as if both operands where positive:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${-12 % -5} <#-- Prints -2 --> -${-12 % 5} <#-- Prints -2 --> -${12 % -5} <#-- Prints 2 --></pre></div> - - - - - -<h2 class="content-header header-section2" id="dgui_template_exp_comparison">Comparison</h2> - - - - - <p>Sometimes you want to know if two values are equal or not, or - which value is the greater.</p> - - <p>To show concrete examples I will use the <code class="inline-code">if</code> - directive here. The usage of <code class="inline-code">if</code> directive is: - <code class="inline-code"><#if - <em class="code-color">expression</em>>...</#if></code>, - where expression must evaluate to a boolean value or else an error - will abort the processing of the template. If the value of - expression is <code class="inline-code">true</code> then the things between the - begin and end-tag will be processed, otherwise they will be - skipped.</p> - - <p>To test two values for equality you use <code class="inline-code">==</code> - (or <code class="inline-code">=</code> as a <em>deprecated</em> - alternative) To test two values for inequality you use - <code class="inline-code">!=</code>. For example, assume that - <code class="inline-code">user</code> is "Big Joe":</p> - - - -<div class="code-wrapper"><pre class="code-block code-template"><#if <strong>user == "Big Joe"</strong>> - It is Big Joe -</#if> -<#if <strong>user != "Big Joe"</strong>> - It is not Big Joe -</#if></pre></div> - - <p>The <code class="inline-code">user == "Big Joe"</code> expression in the - <code class="inline-code"><#if ...></code> will evaluate to the boolean - <code class="inline-code">true</code>, so the above will say "It is Big - Joe".</p> - - <p>The expressions on both sides of the <code class="inline-code">==</code> or - <code class="inline-code">!=</code> must evaluate to a scalar (not a sequence or - hash). Furthermore, the two scalars must have the same type (i.e. - strings can only be compared to strings and numbers can only be - compared to numbers, etc.) or else an error will abort template - processing. For example <code class="inline-code"><#if 1 == "1"></code> will - cause an error. Note that FreeMarker does exact comparison, so - string comparisons are case and white-space sensitive: - <code class="inline-code">"x"</code> and <code class="inline-code">"x "</code> and - <code class="inline-code">"X"</code> are not equal values.</p> - - <p>For numerical and date, time and date-time values you can also - use <code class="inline-code"><</code>, <code class="inline-code"><=</code>, - <code class="inline-code">>=</code> and <code class="inline-code">></code>. You can't use - them for strings! Example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template"><#if x <strong><=</strong> 12> - x is less or equivalent with 12 -</#if></pre></div> - - <p>There's a problem with <code class="inline-code">>=</code> and - <code class="inline-code">></code>. FreeMarker interprets the - <code class="inline-code">></code> character as the closing character of the - FTL tag. To prevent this, you can use <code class="inline-code">lt</code> instead - of <code class="inline-code"><</code>, <code class="inline-code">lte</code> instead of - <code class="inline-code"><=</code>, <code class="inline-code">gt</code> instead of - <code class="inline-code">></code> and <code class="inline-code">gte</code> instead of - <code class="inline-code">>=</code>, like in <code class="inline-code"><#if x gt - y></code>. Another trick it to put the expression into <a href="#dgui_template_exp_parentheses">parentheses</a> like in - <code class="inline-code"><#if (x > y)></code>, although it's considered - to be less elegant.</p> - - <div class="callout note"> - <strong class="callout-label">Note:</strong> - - <p>FreeMarker supports some other alternatives too, but these - are deprecated:</p> - - <ul> - <li> - <p>Writing <code class="inline-code">&gt;</code> and - <code class="inline-code">&lt;</code> on the place of the problematic - relation marks, like in: <code class="inline-code"><#if x &gt; - y></code> or <code class="inline-code"><#if x &gt;= - y></code> . Note that in general FTL does not support - entity references (the - <code class="inline-code">&<em class="code-color">...</em>;</code> - things) in FTL tags; it's just an exception with the - arithmetical comparisons.</p> - </li> - - <li> - <p><code class="inline-code">\lt</code>, <code class="inline-code">\lte</code>, - <code class="inline-code">\gt</code> and <code class="inline-code">\gte</code> which are - the same as the ones without the backslash</p> - </li> - </ul> - </div> - - - - - - -<h2 class="content-header header-section2" id="dgui_template_exp_logicalop">Logical operations</h2> - - - - - - - - - - - - - <p>Just the usual logical operators:</p> - - <ul> - <li> - Logical or: <code class="inline-code">||</code> - </li> - - <li> - Logical and: <code class="inline-code">&&</code> - </li> - - <li> - Logical not: <code class="inline-code">!</code> - </li> - </ul> - - <p>The operators will work with boolean values only. Otherwise an - error will abort the template processing.</p> - - <p>Example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template"><#if x < 12 <strong>&&</strong> color == "green"> - We have less than 12 things, and they are green. -</#if> -<#if <strong>!</strong>hot> <#-- here hot must be a boolean --> - It's not hot. -</#if></pre></div> - - - - - -<h2 class="content-header header-section2" id="dgui_template_exp_builtin">Built-ins</h2> - - - - - <p>Built-ins are like methods that are added to the objects by - FreeMarker. To prevent name clashes with actual methods and other - sub-variables, instead of dot (<code class="inline-code">.</code>), you separate - them from the parent object with question mark - (<code class="inline-code">?</code>). For example, if you want to ensure that - <code class="inline-code">path</code> has an initial <code class="inline-code">/</code> then you - could write <code class="inline-code">path?ensure_starts_with('/')</code>. The - Java object behind <code class="inline-code">path</code> (a - <code class="inline-code">String</code> most certainly) doesn't have such method, - FreeMarker adds it. For brevity, if the method has no parameters, - you <em>must</em> omit the <code class="inline-code">()</code>, like, - to get the length of <code class="inline-code">path</code>, you have to write - <code class="inline-code">path?length</code>, <em>not</em> - <code class="inline-code">path?length()</code>.</p> - - <p>The other reason why built-ins are crucial is that normally - (though it depends on configuration settings), FreeMarker doesn't - expose the Java API of the objects. So despite that Java's - <code class="inline-code">String</code> has a <code class="inline-code">length()</code> method, - it's hidden from the template, you <em>have to</em> use - <code class="inline-code">path?length</code> instead. The advantage of that is - that thus the template doesn't depend on the exactly type of the - underlying Java objects. (Like <code class="inline-code">path</code> is maybe a - <code class="inline-code">java.nio.Path</code> behind the scenes, but if the - programmers has configure FreeMarker to expose - <code class="inline-code">Path</code> objects as FTL strings, the template won't - be aware of that, and <code class="inline-code">?length</code> will work, despite - that <code class="inline-code">java.nio.Path</code> has no similar method.)</p> - - <p>You can find some of the <a href="dgui_quickstart_template.html#topic.commonlyUsedBuiltIns">most commonly used built-ins - mentioned here</a>, and the <a href="ref_builtins.html">complete - list of built-ins in the Reference</a>. For now, just a few of - the more important ones:</p> - - <p>Example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${testString?upper_case} -${testString?html} -${testString?upper_case?html} - -${testSequence?size} -${testSequence?join(", ")}</pre></div> - - <p>Assuming that <code class="inline-code">testString</code> stores the string - "Tom & Jerry", and testSequnce stores the strings - "foo", "bar" and "baz", the - output will be:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">TOM & JERRY -Tom &amp; Jerry -TOM &amp; JERRY - -3 -foo, bar, baz</pre></div> - - <p>Note the <code class="inline-code">test?upper_case?html</code> above. Since - the result of <code class="inline-code">test?upper_case</code> is a string, you - can apply the <code class="inline-code">html</code> built-in on it.</p> - - <p>Naturally, the left side of the built-in can be arbitrary - expression, not just a variable name:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${testSeqence[1]?cap_first} -${"horse"?cap_first} -${(testString + " & Duck")?html}</pre></div> - - - -<div class="code-wrapper"><pre class="code-block code-output">Bar -Horse -Tom &amp; Jerry &amp; Duck</pre></div> - - - - - -<h2 class="content-header header-section2" id="dgui_template_exp_methodcall">Method call</h2> - - - - - - - <p>If you have a method then you can use the method call - operation on it. The method call operation is a comma-separated list - of expressions in parentheses. These values are called parameters. - The method call operation passes these values to the method which - will in turn return a result. This result will be the value of the - whole method call expression.</p> - - <p>For example, assume the programmers have made available a - method variable called <code class="inline-code">repeat</code>. You give a string - as the first parameter, and a number as the second parameter, and it - returns a string which repeats the first parameter the number of - times specified by the second parameter.</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${repeat("Foo", 3)}</pre></div> - - <p>will print:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">FooFooFoo</pre></div> - - <p>Here <code class="inline-code">repeat</code> was evaluated to the method - variable (according to how you <a href="#dgui_template_exp_var_toplevel">access top-level - variables</a>) and then <code class="inline-code">("What", 3)</code> invoked - that method.</p> - - <p>I would like to emphasize that method calls are just plain - expressions, like everything else. So this:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${repeat(repeat("x", 2), 3) + repeat("Foo", 4)?upper_case}</pre></div> - - <p>will print this:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">xxxxxxFOOFOOFOOFOO</pre></div> - - - - - -<h2 class="content-header header-section2" id="dgui_template_exp_missing">Handling missing values</h2> - - - <div class="callout note"> - <strong class="callout-label">Note:</strong> - - <p>These operators exist since FreeMarker 2.3.7 (replacing the - <code class="inline-code">default</code>, <code class="inline-code">exists</code> and - <code class="inline-code">if_exists</code> built-ins).</p> - </div> - - - - - - - - - - - - - <p>As we explained earlier, an error will occur and abort the - template processing if you try to access a missing variable. However - two special operators can suppress this error, and handle the - problematic situation. The handled variable can be top-level - variable, hash subvariable, or sequence subvariable as well. - Furthermore these operators handle the situation when a method call - doesn't return a value <span class="marked-for-programmers">(from the - viewpoint of Java programmers: it returns <code class="inline-code">null</code> or - it's return type is <code class="inline-code">void</code>)</span>, so it's more - correct to say that these operators handle missing values in - general, rather than just missing variables.</p> - - <p><span class="marked-for-programmers">For those who know what's Java - <code class="inline-code">null</code>, FreeMarker 2.3.<em>x</em> - treats them as missing values. Simply, the template language doesn't - know the concept of <code class="inline-code">null</code>. For example, if you - have a bean that has a <code class="inline-code">maidenName</code> property, and - the value of that property is <code class="inline-code">null</code>, then that's - the same as if there were no such property at all, as far as the - template is concerned (assuming you didn't configured FreeMarker to - use some extreme object wrapper, that is). The result of a method - call that returns <code class="inline-code">null</code> is also treated as a - missing variable (again, assuming that you use some usual object - wrapper). See more <a href="app_faq.html#faq_null">in the - FAQ</a>.</span></p> - - <div class="callout note"> - <strong class="callout-label">Note:</strong> - - <p>If you wonder why is FreeMarker so picky about missing - variables, <a href="app_faq.html#faq_picky_about_missing_vars">read this - FAQ entry</a>.</p> - </div> - - - - - - - -<h3 class="content-header header-section3" id="dgui_template_exp_missing_default">Default value operator</h3> - - - - - <p>Synopsis: - <code class="inline-code"><em class="code-color">unsafe_expr</em>!<em class="code-color">default_expr</em></code> - or <code class="inline-code"><em class="code-color">unsafe_expr</em>!</code> or - <code class="inline-code">(<em class="code-color">unsafe_expr</em>)!<em class="code-color">default_expr</em></code> - or - <code class="inline-code">(<em class="code-color">unsafe_expr</em>)!</code></p> - - <p>This operator allows you to specify a default value for the - case when the value is missing.</p> - - <p>Example. Assume no variable called <code class="inline-code">mouse</code> - is present:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">${mouse!"No mouse."} -<#assign mouse="Jerry"> -${mouse!"No mouse."}</pre></div> - - <p>The output will be:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">No mouse. -Jerry</pre></div> - - <p>The default value can be any kind of expression, so it - doesn't have to be a string. For example you can write - <code class="inline-code">hits!0</code> or <code class="inline-code">colors!["red", "green", - "blue"]</code>. There is no restriction regarding the - complexity of the expression that specifies the default value, for - example you can write: <code class="inline-code">cargo.weight!(item.weight * - itemCount + 10)</code>.</p> - - <div class="callout warning"> - <strong class="callout-label">Warning!</strong> - - <p>If you have a composite expression after the - <code class="inline-code">!</code>, like <code class="inline-code">1 + x</code>, - <em>always</em> use parenthesses, like - <code class="inline-code">${x!(1 + y)}</code> or <code class="inline-code">${(x!1) + - y)}</code>, depending on which interpretation you meant. - That's needed because due to a programming mistake in FreeMarker - 2.3.x, the precedence of <code class="inline-code">!</code> (when it's used as - default value operator) is very low at its right side. This - means that, for example, <code class="inline-code">${x!1 + y}</code> is - misinterpreted by FreeMarker as <code class="inline-code">${x!(1 + y)}</code> - while it should mean <code class="inline-code">${(x!1) + y}</code>. This - programming error will be fixed in FreeMarker 2.4, so you should - not utilize this wrong behavior, or else your templates will - break with FreeMarker 2.4!</p> - </div> - - - <p>If the default value is omitted, then it will be empty - string and empty sequence and empty hash at the same time. (This - is possible because FreeMarker allows multi-type values.) Note the - consequence that you can't omit the default value if you want it - to be <code class="inline-code">0</code> or <code class="inline-code">false</code>. - Example:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">(${mouse!}) -<#assign mouse = "Jerry"> -(${mouse!})</pre></div> - - <p>The output will be:</p> - - - -<div class="code-wrapper"><pre class="code-block code-output">() -(Jerry)</pre></div> - - <div class="callout warning"> - <strong class="callout-label">Warning!</strong> - - <p>Due to syntactical ambiguities <code class="inline-code"><@something - a=x! b=y /></code> will be interpreted as - <code class="inline-code"><@something a=x!(b=y) /></code>, that is, the - <code class="inline-code">b=y</code> will be interpreted as a comparison that - gives the default value for <code class="inline-code">x</code>, rather than - the specification of the <code class="inline-code">b</code> parameter. To - prevent this, write: <code class="inline-code"><@something a=(x!) b=y - /></code></p> - </div> - - - <p>You can use this operator in two ways with non-top-level - variables:</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">product.color!"red"</pre></div> - - <p>This will handle if <code class="inline-code">color</code> is missing - inside <code class="inline-code">product</code> (and returns - <code class="inline-code">"red"</code> if so), but will not handle if - <code class="inline-code">product</code> is missing. That is, the - <code class="inline-code">product</code> variable itself must exist, otherwise - the template processing will die with error.</p> - - - -<div class="code-wrapper"><pre class="code-block code-template">(product.color)!&
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