jsp几种方法

1.必须继承自HttpServlet
  2.必须实现doGet()或者doPost()
  3.必须在web.xml中配置Servlet
  <servlet>
  <servlet-name> </servlet-name>
  <servlet-class> </servlet-class>
  </servlet>
  <servlet-mapping>
  <servlet-name> </servlet-name>
  <url-pattern> </url-pattern>
  </servelt-mapping>
  
  HttpServeltRrequest:请求对象
  getParameter():获得表单元素的值
  getAttribute():获得request范围中的属性值
  setAttribute():设置reqeust范围中的属性值
  setCharacterEncoding():设置字符编码
  
  HttpSerletResponse:相应对象
  sendRedirect():外部跳转
  getWriter():获得输出流对象
  setContentType("text/html; charset=utf-8"):设置相应内容格式和编码
  
  四种会话跟踪方式:
  1.Session
  HttpSession session = request.getSession();
  session.setAttribute("name", "zhangsan");
  session.setAttribute("pwd", "aaa");
  String name = (String) session.getAttribute("name");
  
  2.cookie:
  //创建Cookie
  Cookie cookie = new Cookie("name", "zhangsan");
  //设置Cookie的超时时间
  cookie.setMaxAge(24 * 60 * 60 *60);
  //把Cookie发送到客户端
  response.addCookie(cookie);
  
  //得到客户端发送的Cookie
  Cookie [] cookies = request.getCookies();
  for(int i=0; i <cookies.length; i++) {
   Cookie temp = cookies[i];
   String key = temp.getName();
   String value = temp.getValue();
  }
  
  3.隐藏表单域
  <input type="hidden" name="name" value="zhangsan" />
  request.getParameter("name");
  
  4.Url重写
  问号传参
  LoginServlet?username=zhangsan&pwd=123
  String name = request.getParameter("username");