一：分类
1、普通servlet
来自于tomcat-servlet-api.jar
2、filter
3、listener
二：获取参数
1、application参数：
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>
/WEB-INF/xfire-servlet.xml,classpath:applicationContext.xml,
/WEB-INF/conf/beans/**/*.xml
</param-value>
</context-param>
servletContext.getInitParameter......
上下文参数:
<init-param>
<param-name>forceEncoding</param-name>
<param-value>true</param-value>
</init-param>