封裝了 Servlet的配置信息，並且可以獲取ServletContext對象
配置servlet的初始化參數
在web.xml文件中，<servlet></servlet節點裏，新增一個<init-param></init-param>節點，如
<servlet> <servlet-name></servlet-name> <servlet-class></servlet-class> <!--配置Servlet的初始化參數,*n，可以有多個init-param節點--> <init-param> <param-name>user</param-name> <param-value>fv</param-value> </init-param> <init-param> <param-name>password</param-name> <param-value>timewalkfv</param-value> </init-param> <!--可以指定Servlet被創建的時機，必須放在init-param節點的後面--> <load-on-startup>-1</load-on-startup> </servlet>
2.獲取初始化參數getInitParameter(String name)、getInitParameterNames() 獲取參數名組成的Enumeration
@Override
public void init(ServletConfig servletConfig) throws ServletException {
// TODO Auto-generated method stub
System.out.println("init");
String username = servletConfig.getInitParameter("username");
System.out.println("username: "+ username);
Enumeration<String> params = servletConfig.getInitParameterNames();
while(params.hasMoreElements()){
String name = params.nextElement();
String value = servletConfig.getInitParameter(name);
System.out.println(" name : " + name + "\n value : " + value );
}
String servletName = servletConfig.getServletName();
System.out.println("servletName : "+ servletName);
}