velocity实践——初识velocity

在项目开发中为了减少代码书写量，需要学习模板引擎，自动生成代码，今天第一天开始学习，做了一个简单的例子，运行成功，记录学习过程

1、新建web工程，命名为velocity。

2、下载velocity-1.5.jar，velocity-dep-1.5.jar 放在本工程/WE-INF/lib/ 目录下。

3、编写hello.vm

public $tableName{
/**
*@parm id  
*@return
*/
public java.util.Vector findById(String id){
String sql="select * from $tableName where $id='"+id+"'";
}
}

 4、新建类VelocityServletTest.java

 

package com.twb;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.FileNotFoundException;
import java.io.StringWriter;
import java.util.Properties;

import javax.servlet.ServletConfig;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.velocity.Template;
import org.apache.velocity.context.Context;
import org.apache.velocity.servlet.VelocityServlet;
import org.apache.velocity.app.Velocity;
import org.apache.velocity.app.VelocityEngine;

import org.apache.velocity.VelocityContext;

public class VelocityServletTest extends VelocityServlet {
	
	//重写父类方法
    protected Properties loadConfiguration(ServletConfig config)
            throws IOException, FileNotFoundException {

        VelocityEngine engine = new VelocityEngine();

        Properties p = new Properties();

        String path = config.getServletContext().getRealPath("/");

        if (path == null) {
            path = "/";
        }

        p.setProperty(Velocity.FILE_RESOURCE_LOADER_PATH, path);

        p.setProperty("runtime.log", path + "velocity.log");

        try {
            engine.init(p); // 载入模板的路径path ,即上下文路径
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        return p;
    }
    
    //重写父类方法
    public Template handleRequest(HttpServletRequest request,
            HttpServletResponse response, Context ctx) {
    	
        Template template = null;

        Template template2 = null;
        
        try {//页面显示代码
            Velocity.init();
            VelocityContext context = new VelocityContext();
            ctx.put("tableName", "User");
            template = Velocity.getTemplate("/web/hello.vm");
        } catch (Exception e) {
            e.printStackTrace();
        }
        
        
        try {// 获得模板的内容
        	//加载模板
            template2 = Velocity.getTemplate("/web/hello.vm");
            
            VelocityContext context = new VelocityContext();
            
            //设置模板中变量的值
            context.put("tableName", "User");
            context.put("id", "userId");
            StringWriter writer = new StringWriter();

            template2.merge(context, writer);
            
            //将模板内容写入twb.java
            File file=new File("D:\\twb.java");
            FileOutputStream f=new FileOutputStream(file);
            f.write(writer.toString().getBytes());
            f.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

        return template;
    }
}

 

5、配置web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
  <servlet-name>vilocity</servlet-name>
  <servlet-class>com.twb.VelocityServletTest</servlet-class>
  <init-param>
      <param-name>org.apache.velocity.properties</param-name>
      <param-value>/WEB-INF/classes/velocity.properties</param-value>
    </init-param>
 </servlet>
 <servlet-mapping>
  <servlet-name>vilocity</servlet-name>
  <url-pattern>/velocity/*</url-pattern>
 </servlet-mapping>
</web-app>

 

工程建立基本完成，打开浏览器，输入：http://localhost:8080/velocity/velocity/hello.vm

可以看到页面显示

public User{ /** *@parm id *@return */ public java.util.Vector findById(String id){ String sql="select * from User where $id='"+id+"'"; } }

 

同时在d:\\下生成twb.java

public User{
/**
*@parm id  
*@return
*/
public java.util.Vector findById(String id){
String sql="select * from User where userId='"+id+"'";
}
}

 ok,第一个velocity实例成功。