Servlet中有哪些常见的API呢？

 servlet所有的API都位于javax.servlet和javax.servlet.http下面
 javax.servlet包：包含servlet或Web容器使用的许多接口和类
 javax.servlet.http包：包含仅用于负责http请求的接口和类

javax.servlet包中的接口信息

1. Servlet
2. ServletRequest
3. ServletResponse
4. RequestDispatcher
5. ServletConfig
6. ServletContext
7. SingleThreadModel
8. Filter
9. FilterConfig
10. FilterChain
11. ServletRequestlistener
12. ServletRequestAttributeListener
13. ServletContextListener
14. ServletContextAttributeListener

javax.servlet包中的类

1. GenericServlet
2. ServletInputStream
3. ServletOutputStream
4. ServletRequestWrapper
5. ServletResponseWrapper
6. ServletRequestEvent
7. ServletContextEvent
8. ServletRequestAttributeEvent
9. ServletContextAttributeEvent
10. ServletExceptionUnavailableException

javax.servlet.http包中的接口

1. HttpServletRequest
2. HttpServletResponse
3. HttpSessionHttpSessionListener
4. HttpSessionAttributeListener
5. HttpSessionBindingListener
6. HttpSessionActivationListener
7. HttpSessionContext (注：过时，已弃用)

javax.servlet.http包中的类

1. HttpServlet
2. Cookie
3. HttpServletRequestWrapper
4. HttpServletResponseWrapper
5. HttpSessionEvent
6. HttpSessionBindingEventHttpUtils(注：过时)