通过ServletConfig对象来解析访问，web.xml配置的servlet类参数

web.xml中配置：
<servlet>
  		<servlet-name>myServlet</servlet-name>
  		<servlet-class>com.cancique.dao.LoginServlet</servlet-class>
  		<init-param>
  			<param-name>driver</param-name>
  			<param-value>com.mysql.jdbc.Driver</param-value>
  		</init-param>
  		<init-param>
  			<param-name>url</param-name>
  			<param-value>jdbc:mysql://localhost:3306/test_db</param-value>
  		</init-param>
  		<init-param>
  			<param-name>user</param-name>
  			<param-value>root</param-value>
  		</init-param>
  		<init-param>
  			<param-name>pass</param-name>
  			<param-value>900622</param-value>
  		</init-param>
  </servlet>
  
  <servlet-mapping>
  		<servlet-name>myServlet</servlet-name>
  		<url-pattern>/login</url-pattern>
  </servlet-mapping>

在需要用到这些参数的servlet类中，我们可以通过ServletConfig对象来解析：

			

public class LoginServlet extends HttpServlet{
	public void service(HttpServletRequest request,
			HttpServletResponse response)
	{

			ServletConfig config = getServletConfig();
			String driver = config.getInitParameter("driver");
			String url = config.getInitParameter("url");
			String user = config.getInitParameter("user");
			String pass = config.getInitParameter("pass");
			DbDao dao = DbDao.instance(driver,url,user,pass);
			................................................
	}
}

 ServletConfig config = getServletConfig();     getServletConfig()在servlet.java代码中得到web.xml中的配置的参数，然后使用它们。