Velocity模板引擎详解-优快云博客

本文链接：https://blog.youkuaiyun.com/clq9761/article/details/84114839

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。

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。

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

准备工作：导入相关依赖包，在下面附件中。

例1：应用程序事例

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!
#else
Welcome 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)- $element.
	#end
outer:This is ($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.

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context
		VelocityContext 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

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>

2.在web-inf目录下建立velocity.properties属性文件

resource.loader = file
file.resource.loader.path = /WEB-INF/velocity
file.resource.loader.cache = true
file.resource.loader.modificationCheckInterval = 300

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>

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

Velocity模板应用