web工程中web.xml元素加载顺序以及配置实例

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简介

web.xml是web工程的配置文件，容器加载web工程时，会首先从WEB-INF中查询web.xml，并加载其中的配置信息，可以将web.xml认为是web工程的入口。

web.xml中包含有welcome欢迎页面、servlet、servlet-mapping、filter、listener和启动加载级别等。

web.xml加载顺序

容器读取工程的配置文件web.xml，读取<listener>和<context-param>两个节点。
容器创建ServletContext，所有的web项目都将共享该ServletContext。
容器将<context-param>转换为键值对，并交给ServletContext。
容器创建<listener>中的类的实例，创建监听器

web.xml内容详解

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xmlns:web="http://java.sun.com/xml/ns/javaee" xmlns="http://java.sun.com/xml/ns/javaee"    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"    id="WebApp_ID" version="3.0">    <display-name>console</display-name>    <!--servletContext加载的属性信息 -->    <context-param>        <param-name>contextConfigLocation</param-name>        <param-value>classpath:spring.xml,classpath:spring-mybatis.xml,classpath:spring-shiro.xml</param-value>    </context-param>    <!-- 定义过滤器的名称，以及其初始化参数-->    <filter>        <filter-name>shiroFilter</filter-name>        <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>        <init-param>            <param-name>targetFilterLifecycle</param-name>            <param-value>true</param-value>        </init-param>    </filter>    <!-- 定义url被哪个filter过滤，下面的配置表示所有的请求都必须经过shiroFilter  -->    <filter-mapping>        <filter-name>shiroFilter</filter-name>        <url-pattern>/*</url-pattern>    </filter-mapping>    <filter>        <filter-name>ResponseCrossFilter</filter-name>        <filter-class>com.emcc.changedig.filter.ResponseCrossFilter</filter-class>    </filter>    <filter-mapping>        <filter-name>ResponseCrossFilter</filter-name>        <url-pattern>/*</url-pattern>    </filter-mapping>    <!--  定义监听器，控制容器在启动和停止时的行为 -->    <listener>        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>    </listener>    <filter>        <filter-name>encodingFilter</filter-name>        <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>        <init-param>            <description>字符集编码</description>            <param-name>encoding</param-name>            <param-value>UTF-8</param-value>        </init-param>    </filter>    <filter-mapping>        <filter-name>encodingFilter</filter-name>        <url-pattern>/*</url-pattern>    </filter-mapping>    <!--  清理监听器，当应用停止时，使用该listener释放资源 -->    <listener>        <listener-class>org.springframework.web.util.IntrospectorCleanupListener</listener-class>    </listener>    <! – 定义servlet，初始化参数以及启动顺序 -->    <servlet>        <description>spring mvc servlet</description>        <servlet-name>springMvc</servlet-name>        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>        <init-param>            <description>spring mvc 配置文件</description>            <param-name>contextConfigLocation</param-name>            <param-value>classpath:spring-mvc.xml</param-value>        </init-param>        <load-on-startup>1</load-on-startup>    </servlet>    <servlet>         <servlet-name>DruidStatView</servlet-name>         <servlet-class>com.alibaba.druid.support.http.StatViewServlet</servlet-class>         <init-param>             <!-- 允许清空统计数据 -->             <param-name>resetEnable</param-name>             <param-value>true</param-value>         </init-param>         <init-param>             <!-- 用户名 -->             <param-name>loginUsername</param-name>             <param-value>druid</param-value>         </init-param>         <init-param>             <!-- 密码 -->             <param-name>loginPassword</param-name>             <param-value>druid</param-value>         </init-param>     </servlet>     <!-- 定义servlet 映射规则 -->    <servlet-mapping>         <servlet-name>DruidStatView</servlet-name>         <url-pattern>/druid/*</url-pattern>     </servlet-mapping>    <servlet-mapping>        <servlet-name>springMvc</servlet-name>        <url-pattern>/</url-pattern>    </servlet-mapping>    <session-config>        <!-- 时间单位是分钟 -->        <session-timeout>360</session-timeout>    </session-config>    <!-- default表示，对客户端请求的静态资源，交由默认的servlet来处理 -->    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.css</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.js</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.ico</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.gif</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.jpg</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.png</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.bmp</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.jpeg</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.swf</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.flv</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.xml</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.txt</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.htm</url-pattern>    </servlet-mapping>    <servlet-mapping>        <servlet-name>default</servlet-name>        <url-pattern>*.html</url-pattern>    </servlet-mapping>    <!--  定义错误返回页面  -->    <error-page>        <error-code>404</error-code>        <location>/web/error/404.html</location>    </error-page></web-app>

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