● 请说明一下web.xml文件中可以配置哪些内容？
web.xml用于配置Web应用的相关信息，如：监听器（listener）、过滤器（filter）、 Servlet、相关参数、会话超时时间、安全验证方式、错误页面等，下面是一些开发中常见的配置：
①配置Spring上下文加载监听器加载Spring配置文件并创建IOC容器：
<context-param><param-name>contextConfigLocation</param-name><param-value>classpath:applicationContext.xml</param-value></context-param><listener><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class></listener>
②配置Spring的OpenSessionInView过滤器来解决延迟加载和Hibernate会话关闭的矛盾：
<filter><filter-name>openSessionInView</filter-name><filter-class>org.springframework.orm.hibernate3.support.OpenSessionInViewFilter</filter-class></filter><filter-mapping><filter-name>openSessionInView</filter-name><url-pattern>/*</url-pattern></filter-mapping>
③配置会话超时时间为10分钟：
<session-config><session-timeout>10</session-timeout></session-config>
④配置404和Exception的错误页面：
<error-page><error-code>404</error-code><location>/error.jsp</location></error-page><error-page><exception-type>java.lang.Exception</exception-type><location>/error.jsp</location></error-page>
⑤配置安全认证方式：
<security-constraint><web-resource-collection><web-resource-name>ProtectedArea</web-resource-name><url-pattern>/admin/*</url-pattern><http-method>GET</http-method><http-method>POST</http-method></web-resource-collection><auth-constraint><role-name>admin</role-name></auth-constraint></security-constraint><login-config><auth-method>BASIC</auth-method></login-config><security-role><role-name>admin</role-name></security-role>
