Velocity模板应用
Velocity是一个基于java的模板引擎(模板引擎的作用就是取得数据并加以处理，最后显示出数据)。
???? 它允许任何人仅仅简单的使用模板语言来引用由java代码定义的对象。
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主要应用在：
??1.Web应用的开发。
??2.作为模板产生SQL,XML或代码等。
??3.作为其他系统的集成组件使用。
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当Velocity应用于application program或 a servlet,主要工作流程如下：
??1.初始化Velocity．
??2.创建Context对象
??3.添加数据到Context
??4.选择模板
??5.合并模板和数据产生输出页面
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准备工作：导入相关依赖包，在下面附件中。
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例1：应用程序事例
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1.模板文件hellovelocity.vm文件
##这是一行注释，不会输出#*这是多行注释，不会输出 多行注释*#// ---------- 1.变量赋值输出------------Welcome $name to Javayou.com!today is $date.tdday is $mydae.//未被定义的变量将当成字符串// -----------2.设置变量值,所有变量都以$开头----------------#set( $iAmVariable = "good!" )Welcome $name to Javayou.com!today is $date.$iAmVariable//-------------3.if,else判断--------------------------#set ($admin = "admin")#set ($user = "user")#if ($admin == $user)Welcome admin!#elseWelcome user!#end//--------------4.迭代数据List---------------------#foreach( $product in $list )$product#end// ------------5.迭代数据HashSet-----------------#foreach($key in $hashVariable.keySet() ) $key ‘s value: $ hashVariable.get($key)#end//-----------6.迭代数据List Bean($velocityCount为列举序号，默认从1开始，可调整)#foreach ($s in $listBean)<$velocityCount> Address: $s.address#end//-------------7.模板嵌套---------------------#foreach ($element in $list)#foreach ($element in $list)inner:This is ($velocityCount)- $element.#endouter:This is ($velocityCount)- $element.#end//-----------8.导入其它文件,多个文件用逗号隔开--------------#include("com/test2/test.txt")?
2.其它非模板文件text.txt
======text.txt==================== this is test's content.yeah.
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3.客户端应用测试代码：
package com.test2;import java.io.FileOutputStream;import java.io.StringWriter;import java.util.*;import org.apache.velocity.app.Velocity;import org.apache.velocity.app.VelocityEngine;import org.apache.velocity.Template;import org.apache.velocity.VelocityContext;public class HelloVelocity {public static void main(String[] args) throws Exception {// 初始化并取得Velocity引擎VelocityEngine ve = new VelocityEngine();// 取得velocity的模版Properties p =new Properties();p.put(Velocity.FILE_RESOURCE_LOADER_PATH, "D:/myspace/VelocityTest/src");ve.init(p);//取得velocity的模版 Template t = ve.getTemplate("com/test2/hellovelocity.vm","utf-8"); // 取得velocity的上下文contextVelocityContext context = new VelocityContext();// 把数据填入上下文context.put("name", "Liang");context.put("date", (new Date()).toString());// 为后面的展示，提前输入List数值List temp = new ArrayList();temp.add("item1");temp.add("item2");context.put("list", temp);List tempBean = new ArrayList();tempBean.add(new UserInfo("1","张三","福建"));tempBean.add(new UserInfo("2","李四","湖南"));context.put("listBean", tempBean);// 输出流StringWriter writer = new StringWriter();// 转换输出t.merge(context, writer);// 输出信息System.out.println(writer.toString());// 输出到文件FileOutputStream of = new FileOutputStream("d:/velocity.txt"); of.write(writer.toString().getBytes("GBK")); of.flush(); of.close();}}?
4.UserInfo实体类
package com.test2;public class UserInfo {private String userId;private String userName;private String address;public UserInfo(String userId, String userName, String address) {super();this.userId = userId;this.userName = userName;this.address = address;}public String getUserId() {return userId;}public void setUserId(String userId) {this.userId = userId;}public String getUserName() {return userName;}public void setUserName(String userName) {this.userName = userName;}public String getAddress() {return address;}public void setAddress(String address) {this.address = address;}}?
例2：Web应用事例
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1.在web-inf目录下建立velocity目录，建立一模板文件velocity.vm。
<html><title>hello！Lizhiwo_wo！</title><body>#set($foo = "Velocity")Hello $foo World! 欢迎您~~~~~~~~~~~~<table><tr><td>ID</td><td>姓名</td><td>地址</td></tr>#foreach ($s in $listBean)<tr><td>$s.userId</td><td>$s.userName</td><td>$s.address</td></tr>#end</table></body></html>
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2.在web-inf目录下建立velocity.properties属性文件
resource.loader = filefile.resource.loader.path = /WEB-INF/velocityfile.resource.loader.cache = truefile.resource.loader.modificationCheckInterval = 300
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3.建立Servlet文件VelocityServletTest.java
package servlet;import java.io.IOException;import java.io.StringWriter;import java.util.ArrayList;import java.util.List;import javax.servlet.ServletConfig;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.apache.commons.collections.ExtendedProperties;import org.apache.velocity.Template;import org.apache.velocity.app.Velocity;import org.apache.velocity.context.Context;import org.apache.velocity.tools.view.servlet.VelocityViewServlet;import com.test2.UserInfo;public class VelocityServletTest extends VelocityViewServlet{private static final long serialVersionUID = 1L;//第一步 加载配置文件这个方法会在VelocityServlet的初始化方法init()中被调用 protected ExtendedProperties loadConfiguration(ServletConfig config) throws IOException { ExtendedProperties p = super.loadConfiguration(config); // 获取velocity.properties中配置的velocity模板路径 String velocityLoadPath = p.getString(Velocity.FILE_RESOURCE_LOADER_PATH); if (velocityLoadPath != null) { // 获取模板路径的绝对路径 velocityLoadPath = getServletContext().getRealPath(velocityLoadPath); if (velocityLoadPath != null) { //重新设置模板路径 System.out.println("vMPath2:"+velocityLoadPath); p.setProperty(Velocity.FILE_RESOURCE_LOADER_PATH, velocityLoadPath); } } return p; }protected Template handleRequest(HttpServletRequest req, HttpServletResponse res, Context context) throws Exception{//字符编码 req.setCharacterEncoding("gb2312"); res.setCharacterEncoding("gb2312"); //页面输出 res.setContentType("text/html;charset=" + "gb2312");List tempBean = new ArrayList();tempBean.add(new UserInfo("1","张三","福建"));tempBean.add(new UserInfo("2","李四","湖南"));context.put("listBean", tempBean); String templateName = "velocity.vm"; // 测试信息输出 Template t= getTemplate(templateName, "utf-8"); StringWriter writer = new StringWriter();// 转换输出t.merge(context, writer);// 输出信息System.out.println(writer.toString()); // 获取模板页面展示 return templateName != null ? getTemplate(templateName, "utf-8") : null;}}?
?4.在web.xml文件中进行配置
<?xml version="1.0" encoding="UTF-8"?><web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"><servlet> <servlet-name>velocityServletTest</servlet-name> <servlet-class>servlet.VelocityServletTest</servlet-class> <init-param> <param-name>org.apache.velocity.properties</param-name> <param-value>/WEB-INF/velocity.properties</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>velocityServletTest</servlet-name> <url-pattern>/velocityServletTest</url-pattern> </servlet-mapping></web-app>
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5.将其部署到tomcat下，页面访问
? http://localhost:8080/VelocityTest/velocityServletTest，
? 输出页面如下：
Hello Velocity World! 欢迎您~~~~~~~~~~~~ ID姓名地址 1张三福建 2李四湖南
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