HttpServlet

1）是一個Servlet，繼承自GenericServlet，針對於HTTP協議所定製
2）在service（）方法中直接把ServletRequest和ServletResponse轉爲HTTPServletRequest和HTTPServletResponse
並調用了重載的service（HttpServletRequest , HttpServletResponse）
在service（HttpServletRequest , HttpServletResponse）獲取了請求方式：request.getMethod().根據請求方式創建了
doXxx（）方法（Xxx爲具體的請求方式，比如doGet和doPost）
public class MyHttpServlet extends MyGenericServlet {
3）實際開發中，直接繼承HTTPServlet，並根據請求方式複寫doXxx（）方法即可
4）好處：直接有針對性的覆蓋doXxx（）方法，直接 使用HttpServletRequest 和 HttpServletResponse，不再需要強轉


@Override
public void service(ServletRequest arg0, ServletResponse arg1) throws ServletException, IOException {
  
if (arg0  instanceof HttpServletRequest) {
HttpServletRequest request=(HttpServletRequest) arg0;

if (arg1 instanceof HttpServletResponse) {
HttpServletResponse response=(HttpServletResponse) arg1;
  
service(request, response);

}
}


}

public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1獲取請求方式
String method=request.getMethod();
//2根據請求方式再調用對應的處理方法
if ("GET".equalsIgnoreCase(method)) {
doGet(request,response);

}else if ("POST".equalsIgnoreCase(method)) {
doPost(request,response);

}

}


public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
// TODO Auto-generated method stub

}


public  void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub

}
}