web.xml

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什么是web.xml?
在一个web项目中，往往需要一些初始化配置信息，如Welcome页面、servlet、servlet-mapping、filter、listener、启动加载级别等。
web.xml文件就是用来初始化这些配置信息。但不是所有的web项目都需要web.xml文件，如果配置不是很负责，可以将他们放到Application中。

##web.xml
web.xml也遵循Schema配置的规则，以<web-app>为根标签。文件配置信息为:

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<?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">

  #指定Web应用的大图标和小图标
  <icon>
    <small-icon>/images/app_small.gif</small-icon>
    <large-icon>/images/app_large.gif</large-icon>
  </icon>

  #Web应用的名称
  <display-name>Tomcat Example</display-name>

  #给出于此相关的说明性文本
  <disciption>Tomcat Example servlets and JSP pages.</disciption>

  <context-param>
    <param-name>ContextParameter</para-name>
    <param-value>test</param-value>
    <description>It is a test parameter.</description>
  </context-param>

  <!-- 过滤器配置 -->
  <filter>
    <filter-name>setCharacterEncoding</filter-name>
    <filter-class>com.myTest.setCharacterEncodingFilter</filter-class>
    <init-param>
        <param-name>encoding</param-name>
        <param-value>UTF-8</param-value>
    </init-param>
  </filter>
  <filter-mapping>
      <filter-name>setCharacterEncoding</filter-name>
      <url-pattern>/*</url-pattern>
  </filter-mapping>

  <!-- 监听器 -->
  <listener>
    <listerner-class>com.listener.SessionListener</listener-class>
  </listener>

  <!-- servlet -->
  <servlet>
    <servlet-name>servlet名称</servlet-name>
    <servlet-class>servlet类全路径</servlet-class>
    <init-param>
        <param-name>参数名</param-name>
        <param-value>参数值</param-value>
    </init-param>
    <run-as>
        <description>匿名访问的角色</description>
        <role-name>tomcat</role-name>
    </run-as>
  </servlet>
  <servlet-mapping>
      <servlet-name>servelet名称</servlet-name>
      <url-pattern>映射路径</url-pattern>
  </servlet-mapping>

  <!-- session超时时间（单位：分钟）-->
  <session-config>
    <session-timeout>120</session-timeout>
  </session-config>

  <!-- mime -->
  <mime-mapping>
    <extension>htm</extension>
    <mime-type>text/html</mime-type>
  </mime-mapping>

  <!-- 欢迎页 -->
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
  </welcome-file-list>

  <!-- 错误代码跳转页 -->
  <error-page>
      <error-code>404</error-code>
      <location>/NotFound.jsp</location>
  </error-page>
  <error-page>
      <exception-type>java.lang.NullException</exception-type>
      <location>/error.jsp</location>
  </error-page>

  <jsp-config>
    <taglib>
        <taglib-uri>Taglib</taglib-uri>
        <taglib-location>/WEB-INF/tlds/MyTaglib.tld</taglib-location>
    </taglib>
    <jsp-property-group>
        <description>Special property group for JSP Configuration JSP example.</description>
        <display-name>JSPConfiguration</display-name>
        <url-pattern>/jsp/* </url-pattern>
        <el-ignored>true</el-ignored>
        <page-encoding>GB2312</page-encoding>
        <scripting-invalid>true</scripting-invalid>
        <include-prelude>/include/prelude.jspf</include-prelude>
        <include-coda>/include/coda.jspf</include-coda>
    </jsp-property-group>
  </jsp-config>

</web-app>