📄 jsp-velocity.xtp
字号:
<document> <header> <product>resin</product> <title>Velocity-Style Syntax</title> <keywords> <keyword>velocity</keyword> </keywords> <description> <p>The Apache <a href="http://jakarta.apache.org/velocity">Velocity</a> project introduces an alternative syntax to the familiar JSP expressions and scriptlets. Resin's extension allows the use of Velocity-style syntax in JSP files. The Velocity-style syntax is transformed into JSTL standard tags. </p> </description> </header> <body> <summary/><s1 title="Velocity"><p>The syntax is based on expressions like <var>${'${'}foo}</var>and scriptlets with <var>#\{...}#</var>. Because thealternative syntax avoids the brackets which fill JSP pages, it can makepages more readable and therefore more maintainable.</p><p>Because Resin's Velocity-style syntax is transformed to the JSTLtag library, all JSTL expressions are allowed.</p><example title='JSP style'><%int count;%><h3>A sample <%= count %></h3><% if ("foo".equals(request.getParameter("a"))) { %> <h3>Foo!</h3><% } else { %> <h3>Bar!</h3><% } %></example><p>The same JSP file could be written in Velocity-style as follows. Thejsp:directive is required because JSP pages use strict JSP syntaxby default.</p><example title='Velocity style'><jsp:directive.page velocity='true'/>\#{int count;}#<h3>A sample ${'${'}count}</h3>#if ("foo" == params.a) <h3>Foo!</h3>#else <h3>Bar!</h3>#end</example><p>The choice between the two is a matter of preferences. An advantageof the velocity style is that expressions and scriptlets avoid usingbrackets. In large pages, sorting out the HTML or XML from the JSP syntaxcan become confusing.</p></s1><s1 title="Enabling velocity-style syntax"><p>Velocity-style syntax can either be enabled on a per-JSP page with<var/velocity='true'/> or in the web-app with the <jsp> tag:</p><example title='Enabling velocity for a page'><jsp:directive.page isVelocityEnabled='true'/> ...</example><example title='Enabling velocity for a web-app'><web-app xmlns="http://caucho.com/ns/resin"> <jsp velocity-enabled='true'/> ...</web-app></example><s2 title="Older web applications and JSTL"><p>Resin uses the format of the web.xml to determine the specification version forthe web application. Older versions of the specification did not support JSTLsyntax, which is also used for Velocity syntax (see <a href="#expressions">expressions</a>, below).It is important when using velocity syntax that the WEB-INF/web.xml and/orWEB-INF/resin-web.xml files indicate the proper specification version. Theeasiest way to do this is to specify the top level element as <code><web-app xmlns="http://caucho.com/ns/resin"></code></p></s2></s1><s1 title='expressions'><p>Expressions are enclosed between "${'${'}" and "}", for example'${'${'}count}' and '${'${'}count + 15}'.</p><p>The '${'${'}...}' syntax is equivalent to '<var><c:out value="..."/></var>'.</p><def>${'${'}<var/expression/>}</def></s1><s1 title='scriptlets'><p>Scriptlets use the '\#{ ... }#' syntax. This is entirely equivalent to'<% ... %>'. (Note, Velocity does not have this syntax because itcreates its own language instead of escaping to Java.)</p><def>\#{ <var/statements/>}#</def><example>\#{String key = request.getParameter("key");if (key.equals("")) { response.sendError(500, "Bad key"); return;}}#...</example></s1><s1 title='if statements'><p>The velocity-style syntax directly supports if statements. The syntax is</p><def>#if (expr1) ...#elseif (expr1) ...#else ...#end</def><p>The expressions can be any JSTL expression. The if statement is transformed into:</p><example><c:choose><c:when test="${'${'}<var/expr1/>}"> ...</c:when><c:when test="${'${'}<var/expr2/>}"> ...</c:when><c:otherwise> ...</c:otherwise></c:choose></example></s1><s1 title='foreach statements'><p>The velocity-style syntax directly supports iteration with a foreachstatements.</p><def>#foreach (var in expr) ...#end</def><p>This style of foreach is transformed into the following:</p><example><c:forEach items="${'${'}<var/expr/>}" var="<var/var/>"> ...</c:forEach></example><p>An example use might be the following:</p><example title='foreach in Java'><jsp:page.directive velocity='true' import='java.lang.*'/>\#{ ArrayList list = new ArrayList(); list.add("foo"); list.add("foobar"); pageContext.setAttribute("list", list);}##foreach (value in list) <li>${'${'}value}#end</example><p>The velocity-style syntax also supports integer iteration.</p> <!--<def>#foreach (var in [begin .. end])#end</def><p>The range is transformed into the following:</p><example><c:forEach begin="<var/${'${'}begin}/>" end="<var/${'${'}end/>" var="<var/var/>"> </c:forEach></example>--><p>An example might be the following:</p><example title='foreach in Java'><jsp:page.directive velocity='true'/>#foreach (value in [3..9]) <li>$value#end</example></s1></body></document>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -