之前學習過一種模板渲染技術是Thymleaf,今天講解下另一種模板渲染技術Velocity!
知識點預習:
- 使用Properties封裝Velocity的各種屬性
- VelocityEngine根據Properties封裝屬性實例化模板引擎對象
- 實例化VelocityContext並在其中封裝渲染數據
- VelocityEngine將上下文中的數據渲染至指定的模板中並將渲染後的頁面數據寫入StringWriter
- 通過HttpServletResponse的輸出流將StringWriter中頁面數據響應至前端
下面通過案例來展示!
一.案例展示
1.測試準備
項目工程(maven中選擇webapp工程)
2.代碼展示
***index.jsp
<%-- Created by IntelliJ IDEA. --%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title></title>
</head>
<body>
<%
out.print("Hello,EveryBody!");
%>
</body>
</html>
***pom.xml
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.apache.tomcat</groupId>
<artifactId>servlet-api</artifactId>
<version>6.0.37</version>
</dependency>
<dependency>
<groupId>org.apache.velocity</groupId>
<artifactId>velocity</artifactId>
<version>1.7</version>
</dependency>
<dependency>
<groupId>org.apache.velocity</groupId>
<artifactId>velocity-tools</artifactId>
<version>2.0</version>
</dependency>
</dependencies>
***test.vm
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
##字符串變量
<fieldset>
$article
</fieldset>
##list集合
<fieldset>
#foreach($area in $areas)
$area <br/>
#end
</fieldset>
##數組
<fieldset>
#foreach($name in $names)
$name <br/>
#end
</fieldset>
##map集合
<fieldset>
#foreach($person in $personMap.entrySet())
${person.key} ::: ${person.value} <br/>
#end
</fieldset>
</body>
</html>
***VelocityServlet.java
package com.howie;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.Velocity;
import org.apache.velocity.app.VelocityEngine;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.*;
/**
* @Author weihuanwen
* @Date 2019/8/23 7:30
* @Version 1.0
*/
@WebServlet("/vs")
public class VelocityServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("UTF-8");
resp.setContentType("text/html;charset=UTF-8");
//獲取輸出流
PrintWriter out = resp.getWriter();
//設定velocity屬性
Properties prop=new Properties();
//設置velocity資源加載方式爲class
prop.setProperty("resource.loader", "class");
//設置velocity資源加載方式爲class時的處理類
prop.setProperty("class.resource.loader.class",
"org.apache.velocity.runtime.resource.loader.ClasspathResourceLoader");
//設置模板的默認編碼格式
prop.setProperty(Velocity.ENCODING_DEFAULT, "UTF-8");
//設置模板的輸入編碼格式
prop.setProperty(Velocity.INPUT_ENCODING, "UTF-8");
//設置模板的輸出編碼格式
prop.setProperty(Velocity.OUTPUT_ENCODING, "UTF-8");
//實例化一個VelocityEngine對象
VelocityEngine velocityEngine = new VelocityEngine(prop);
//獲取Velocity上下文
VelocityContext context=new VelocityContext();
String article = "how to learn velocity?";
context.put("article",article);
//list集合
List<String> areas = new ArrayList<>();
areas.add("北京");
areas.add("上海");
context.put("areas",areas);
//數組
String[] names = {"Jhon","Lily"};
context.put("names",names);
//map集合
Map<String,Integer> personMap = new HashMap<>();
personMap.put("Jhon",20);
personMap.put("Lily",26);
context.put("personMap", personMap);
//在字符串緩衝區中收集輸出的字符流，可用於構造字符串， 關閉流無效，關閉後調用其他方法不會報異常
StringWriter sw = new StringWriter();
//加載指定路徑下的vm模板
velocityEngine.mergeTemplate("templates/test.vm", "utf-8", context, sw);
out.println(sw.toString());
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
3.測試
①啓動項目,頁面展示如下:
②訪問請求地址:http://localhost:8080/vs,頁面展示如下:
