关于velocity与SpringMVC的配置请参考前一篇文章，此处不再介绍。velocity作为Java模版引擎的主要目的是为了允许任何人使用简单而强大的模板语言来引用定义在Java代码中的对象。在velocity文件中可以给该页面指定模版布局，从而节省了大量的时间去写通用的模版布局。可以定义变量，与Java方法进行交互。
class="html plain">#set($layout='layout/yourlayout.vm')
那么如何定义一个layout，看下面的例子：
? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17<!DOCTYPE?html?PUBLIC?"-//W3C//DTD?XHTML?1.0?Transitional//EN"?"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html?xmlns="http://www.w3.org/1999/xhtml">
<HEAD>
????<TITLE>$!page_title?测试layout页面</TITLE>
????<meta?http-equiv="Content-Type"?content="text/html;?charset=UTF-8"/>
????<meta?http-equiv="Content-Language"?content="zh-CN"/>
????<meta?http-equiv="Content-Type"?content="text/html;?charset=UTF-8"/>
????<meta?http-equiv="Content-Language"?content="zh-CN"/>
????<link?href="/resources/lib/font-awesome/css/font-awesome.min.css"?tppabs="/resources/lib/font-awesome/css/font-awesome.min.css"?rel="stylesheet"?type="text/css"/>
????<link?href="/resources/lib/bootstrap/css/bootstrap.min.css"?tppabs="/resources/lib/bootstrap/css/bootstrap.min.css"?rel="stylesheet"?type="text/css"/>
</HEAD>
<BODY>
????$screen_content
<script?src="/resources/lib/jquery-1.10.2.min.js"?tppabs="/resources/lib/jquery-1.10.2.min.js"?type="text/javascript"></script>
<script?src="/resources/lib/jquery-migrate-1.2.1.min.js"?tppabs="/resources/lib/jquery-migrate-1.2.1.min.js"?type="text/javascript"></script>
</BODY>
</HTML>
那么$screen_content所在的位置即是你所打开页面将要占用的位置。
#set($var='xxxx')
?
##输出上面的变量直接使用$var
#foreach($ele?in?$list)
<span>output?element:$ele</span>
#end
#if($var=='xxxx')
<span>it?is?right</span>
#elseif($var=='')
<span>sorry</span>
#else
<span>it?is?wrong</span>
#end
类似于JSP，velocity也有自己的内置对象，如$request,$response,$session这样以来我们就可以将Java对象request和response以及session里的东西轻而易举的展现在web页面里。
velocity同时也支持自定义标签，或者称为指令。如果查看velocity的源码就会发现有个directive.properties
? 1 2 3 4 5 6 7 8 9directive.1=org.apache.velocity.runtime.directive.Foreach
directive.2=org.apache.velocity.runtime.directive.Include
directive.3=org.apache.velocity.runtime.directive.Parse
directive.4=org.apache.velocity.runtime.directive.Macro
directive.5=org.apache.velocity.runtime.directive.Literal
directive.6=org.apache.velocity.runtime.directive.Evaluate
directive.7=org.apache.velocity.runtime.directive.Break
directive.8=org.apache.velocity.runtime.directive.Define
directive.9=org.apache.velocity.runtime.directive.Stop
这里正是velocity当前所提供的9个标签（指令），下面我们新添加一个指令say
? 1 2 3<body>
??#say("hello")
</body>
java代码实现
? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48import?java.io.IOException;
import?java.io.Serializable;
import?java.io.StringWriter;
import?java.io.Writer;
import?java.util.HashMap;
import?java.util.Map;
?
import?org.apache.velocity.VelocityContext;
import?org.apache.velocity.app.VelocityEngine;
import?org.apache.velocity.context.InternalContextAdapter;
import?org.apache.velocity.exception.MethodInvocationException;
import?org.apache.velocity.exception.ParseErrorException;
import?org.apache.velocity.exception.ResourceNotFoundException;
import?org.apache.velocity.runtime.directive.Directive;
import?org.apache.velocity.runtime.parser.node.Node;
import?org.apache.velocity.runtime.parser.node.SimpleNode;
import?org.springframework.beans.factory.annotation.Autowired;
?
import?com.alibaba.citrus.service.template.TemplateService;
import?com.alibaba.click.util.HostUtil;
?
public?class?Say?extends?Directive{
?????
????@Autowired
????TemplateService?templateService;
?????
????private?static?final?VelocityEngine?velocityEngine?=?new?VelocityEngine();
?
????@Override
????public?String?getName()?{
????????return?"say";
????}
?
????@Override
????public?int?getType()?{
????????return?LINE;
????}
?
????@Override
????public?boolean?render(InternalContextAdapter?context,?Writer?writer,
????????????Node?node)?throws?IOException,?ResourceNotFoundException,
????????????ParseErrorException,?MethodInvocationException?{
????????SimpleNode?sn?=?(SimpleNode)?node.jjtGetChild(0);???
????????writer.write((String)sn.value(context));
????????return?true;
????}
?????
}
接下来就可以在velocity.properties文件里添加上
? 1say=cn.buglife.demo.msv.directive.Say
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