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velocity是一个基于java的模板引擎，通过特定的语法，可以获取到在java中定义的对象，从而实现页面与java代码的分离。由于JSP需要先转换为Servlet，然后编译为class执行，导致效率较低。在访问量较大时表现较差，velocity则可以作为JSP的替代。
velocity的介绍、语法等可以参考：https://www.jianshu.com/p/5913903324ff。
这里是一个springmvc集成velocity的显示用户列表和修改用户信息的例子，备忘。
maven依赖
添加velocity的相关依赖。（注：spring相关的依赖未给出）
<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>
注意：必须引入spring-context-support依赖，否则velocityConfig配置中configLocation和resourceLoaderPath属性找不到。
springmvc配置
<!-- 自动扫描controller包下的所有类，如果@Controller注入为bean -->
<context:component-scan base-package="com.tommy.velocity.controller"/>
<!-- 注解驱动 -->
<mvc:annotation-driven />
<!-- velocity环境配置 -->
<bean id="velocityConfig" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer">
<!-- velocity配置文件路径 或者直接用velocityProperties属性 -->
<property name="configLocation" value="classpath:velocity.properties"/>
<!-- velocity模板路径 -->
<property name="resourceLoaderPath" value="/WEB-INF/view/"/>
</bean>
<!-- velocity视图解析器 -->
<bean id="velocityViewResolver" class="org.springframework.web.servlet.view.velocity.VelocityLayoutViewResolver">
<property name="order" value="0"/>
<property name="contentType" value="text/html;charset=UTF-8"/>
<property name="cache" value="true"/>
<property name="suffix" value=".vm"/>
<property name="layoutUrl" value="layout/layout.vm"/>
<property name="exposeSpringMacroHelpers" value="true"/>
<!--是否使用spring对宏定义的支持-->
<property name="exposeSessionAttributes" value="true"/>
<!--是否开放request属性-->
<property name="requestContextAttribute" value="request"/>
<!--request属性引用名称-->
<property name="dateToolAttribute" value="dateTool"/>
<property name="numberToolAttribute" value="numberTool"/>
</bean>
velocity.properties：
#设置字符集
#encoding
input.encoding=UTF-8
output.encoding=UTF-8
contentType=text/html;charset=UTF-8
#autoreload when vm changed
file.resource.loader.cache=false
file.resource.loader.modificationCheckInterval =1
velocimacro.library.autoreload=false
web.xml配置
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:spring.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<!-- 防止spring内存溢出监听器 -->
<listener>
<listener-class>org.springframework.web.util.IntrospectorCleanupListener</listener-class>
</listener>
<filter>
<filter-name>encodingFilter</filter-name>
<filter-class>
org.springframework.web.filter.CharacterEncodingFilter
</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>UTF-8</param-value>
</init-param>
<init-param>
<param-name>forceEncoding</param-name>
<param-value>true</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>encodingFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<servlet>
<servlet-name>rest</servlet-name>
<description>spring mvc servlet</description>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>
/WEB-INF/spring-mvc.xml
</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>rest</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
注意配置Spring的字符集过滤器，否则向后台提交数据时中文乱码。
模板文件
布局模板：
<html>
<head>
<title>$!page_title</title>
#parse("default/header.vm")
</head>
<body>
<div>
$screen_content
</div>
</body>
</html>
header.vm:
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<meta http-equiv="Cache-Control" content="no-store"/>
<meta http-equiv="Pragma" content="no-cache"/>
<meta http-equiv="Expires" content="3600"/>
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no" name="viewport">
展示用户列表的模板：
<html>
<head>
<title>Spring MVC and Velocity</title>
</head>
<body>
<h1>Spring MVC and Velocity</h1>
<table>
<tr>
<td>id</td>
<td>姓名</td>
<td>age</td>
<td>操作</td>
</tr>
#foreach($user in $users)
<tr>
<td>$!{user.id}</td>
<td>$!{user.name}</td>
<td>$!{user.age}</td>
<td><a href="/preEdit?userId=${user.id}">修改</a></td>
</tr>
#end
</table>
</body>
</html>
修改的模板：
<html>
<head>
<title>Spring MVC and Velocity</title>
</head>
<body>
<h1>Spring MVC and Velocity</h1>
<form action="/edit" method="post">
<input type="hidden" name="id" value="${user.id}" />
姓名：<input type="text" name="name" value="$!{user.name}" /><br>
年龄：<input type="text" name="age" value="$!{user.age}" />
<input type="submit" value="提交" />
</form>
</body>
</html>
controller
@Controller
public class HelloController {
private final static Map<Integer,User> users = new HashMap<>(8);
static {
initData();
}
@RequestMapping(value = "/list")
public String showList(ModelMap map) {
map.put("users",users);
return "/list";
}
@RequestMapping(value = "/preEdit")
public String preEdit(ModelMap map, Integer userId) {
User user = users.get(userId);
map.put("user",user);
return "/edit";
}
@RequestMapping(value = "/edit")
public String edit(ModelMap map, User user) {
users.put(user.getId(),user);
return showList(map);
}
private static void initData() {
for (int i=0;i<8;i++) {
User user = new User();
user.setId(i);
user.setName("测试用户" + i);
user.setAge((int) (Math.random()*100+10));
users.put(i, user);
}
}
}
User:
public class User {
private int id;
private String name;
private int age;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
演示：
列表页面
修改一个用户名称
再次回到列表页面
本文示例代码：https://gitee.com/tommy88/my-test-projects下的spring-velocity模块。