velocity一些用法(不是uesrguide).doc

velocity一些用法(不是uesrguide)近期研究一下eclipse的代码生成.在两个模板中间决择.网上一查发现全是说FREEMARKER好的.而且还拿出来强有例的对比的表格.但是,对比的对象velocity基本上就是1.0的初初级版.这个对比.简直就好象是韦小宝学习韦陀掌的招式,来跟普通的少林弟子过招,就算是人家用长拳,韦小宝当然也打不过啦.有点扯远了呵呵Velocity还是一个不错的开源项目.其实,一般开源项目,只要持续的更新.那么就算开始的时候多么的垃圾多么的不完善.也终会成大器的.hibernate是这样,mysql 是这样.网上写的例子一般都是TVM的模板.而且还是有些例子完成不能运行的这些不说了.大家直接看velocity 官网的userguide就好了.比网上写的还全.而且主要是人家跟最新的velocity是对应的,是可以运行的.上来先来一个大家都常见的就是把一个list里的东西,转成aaa, bbb , ccc 注意最后的这个没有”,” 我记得我以前也是被这个问题困扰了好久. #foreach 会生成包含$products 中对象的一个列表. 每一次循环都会将列表中的一个对象赋与变量$product .$allProducts 或以是一个 Vector, a Hashtable or an Array 类型的容器. 指定给变量 $product 是一个引用到其中一个 java 对象的引用. For example, if $product 确实是一个 java 代码中的 Productclass i,它可以这样的方法访问$product.Name method (ie: $Product.getName().我们假设 $allProducts 是一个 Hashtable.看看取出其中的东东多么简单:#foreach( $key in $allProducts.keySet() )Key: $key - Value: $allProducts.get($key)#end通过引用变量$velocityCount 可以访问到 Velocity 提供的计数器:#foreach( $customer in $customerList )$velocityCount$customer.Name#end但是官网上的例子这样写道:Velocity provides an easy way to get the loop counter so that you can do something like the following: #foreach( $customer in $customerList ) $foreach.count$customer.Name#end这个小例子.真的是憋倒一堆人呀.还以为在freemarker里好实现在vm里不好写呢.结果,这么容易. Velocity also now provides an easy way to tell if you are on the last iteration of a loop: #foreach( $customer in $customerList ) $customer.Name#if( $foreach.hasNext ),#end#end为什么让这个有名的小例子全面运行.给一个完整的TEST吧./* * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * License); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * /licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, * software distributed under the License is distributed on an * AS IS BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * KIND, either express or implied. See the License for the * specific language governing permissions and limitations * under the License. */import org.apache.velocity.app.Velocity;import org.apache.velocity.VelocityContext;import org.apache.velocity.Template;import org.apache.velocity.exception.ParseErrorException;import org.apache.velocity.exception.ResourceNotFoundException;import java.io.*;import java.util.ArrayList;/* * This class is a simple demonstration of how the Velocity Template Engine * can be used in a standalone application. * * author Jason van Zyl * author Geir Magnusson Jr. * version $Id: Example.java 463298 2006-10-12 16:10:32Z henning $ */public class Example public Example(String templateFile) try Velocity.init(perties);/ 直接用Velocity.init() 也可以. VelocityContext context = new VelocityContext(); context.put(list, getNames(); Template template = null; try template = Velocity.getTemplate(templateFile); catch( ResourceNotFoundException rnfe ) System.out.println(Example : error : cannot find template + templateFile ); catch( ParseErrorException pee ) System.out.println(Example : Syntax error in template + templateFile + : + pee ); BufferedWriter writer = writer = new BufferedWriter( new OutputStreamWriter(System.out); if ( template != null) template.merge(context, writer); writer.flush(); writer.close(); catch( Exception e ) System.out.println(e); public ArrayList getNames() ArrayList list = new ArrayList(); list.add(ArrayList element 1); list.add(ArrayList element 2); list.add(ArrayList element 3); list.add(ArrayList element 4); return list; public static void main(String args) Example t = new Example(example.vm); VM.文件.#set( $this = Velocity)$this is great!#foreach( $name in $list ) $name #if( $foreach.hasNext ),#end#end#set( $condition = true)#if ($condition) The condition is true!#else The condition is false!#endvelocity还能变态的支持XML文件.SAXBuilder builder; Document root = null; try builder = new SAXBuilder(); root = builder.build(test.xml); catch( Exception ee) System.out.println(Exception building Document : + ee); return; /* * now, make a Context object and populate it. */ VelocityContext context = new VelocityContext(); context.put(root, root); /* * make a writer, and merge the template against the context */ Template template = Velocity.getTemplate(templateFile); writer = new BufferedWriter(new OutputStreamWriter(System.out); template.merge( context , writer);这样就可以了.#macro ( recursive $e $indent )#if( $e.getChildren().size() 0 )$indent #foreach ($child in $e.getChildren() )#recursive( $child $indent )#end$indent #else$indent $indent $e.getTextTrim()$indent #end#end#set($i = )First, we print out the document tree with arecursive Velocimacro :#recursive( $root.getRootElement() $i )Next, we access pieces of data directly :email : $root.getRootElement().getChild(properties).getChild(author).getChild(email).getText()last name : $root.getRootElement().getChild(properties).getChild(author).getChild(name).getChild(last).getChild(full).getText()这个写法.也挺疯的.附上XML文件. TeamT Velocity The Velocity Project I am the body 还支持breakIf you want to stop looping in a foreach from within your template, you can now use the #break directive to stop looping at any time: # list first 5 customers only#foreach( $customer in $customerList ) #if( $foreach.count 5 ) #break #end $customer.Name#endvelocity 必杀技.:The #evaluate directive can be used to dynamically evaluate VTL. This allows the template to evaluate a string that is created at render time. Such a string m