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<% //获取session中的登录状态 String user = (String)session.getAttribute("user"); %> <% if(user == null || "".equals(user)){//用户没有登录 %> 欢迎光临!游客! <a href="${pageContext.request.contextPath }/loginout/login.jsp">登录</a> <a href="#">注册</a> <% }else{//用户登录过 %> 欢迎回来!<%=user %>! <a href="${pageContext.request.contextPath }/servlet/LogoutServlet">注销</a> <% } %>
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1.杀死session if(request.getSession(false)!=null && request.getSession().getAttribute("user")!=null){ request.getSession().invalidate(); } //2.重定向到主页 response.sendRedirect(request.getContextPath()+"/loginout/index.jsp"); }
<form action="${pageContext.request.contextPath }/servlet/LoginServlet" method="POST"> 用户名:<input type="text" name="username"/> 密码:<input type="password" name="password"/> <input type="submit" value="登录"/> </form>
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("utf-8"); response.setContentType("text/html;charset=utf-8"); //1.获取用户名密码 String username = request.getParameter("username"); String password = request.getParameter("password"); //2.查询数据库检查用户名密码 if(UserDao.valiNamePsw(username, password)){ //3.如果正确登录后重定向到主页 request.getSession().setAttribute("user", username); response.sendRedirect(request.getContextPath()+"/loginout/index.jsp"); return; }else{ //4.如果错误提示 response.getWriter().write("用户名密码不正确!"); } }
public class UserDao { private UserDao() { } private static Map <String,String>map = new HashMap<String, String>(); static{ map.put("111", "111"); map.put("222", "222"); map.put("333", "222"); } public static boolean valiNamePsw(String username,String password){ return map.containsKey(username) && map.get(username).equals(password); } }
<script type="text/javascript"> var isNotSub = true;//表单是否已经提交标识,默认为false function canSub(){ if(isNotSub){ isNotSub = false;//提交表单后,将表单是否已经提交标识设置为true return true;//返回true让表单正常提交 }else{ alert("请不要重复提交!!!"); return false;//返回false那么表单将不提交 } } </script> <% Random r = new Random(); int valinum = r.nextInt(); session.setAttribute("valinum",valinum+""); %> <form action="${pageContext.request.contextPath }/servlet/ResubServlet" method="POST" onsubmit="return canSub()"> 用户名:<input type="text" name="username"/> <input type="hidden" name="valinum" value="<%=valinum %>"/> <input type="submit" value="注册"/> </form>
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("utf-8"); try { Thread.sleep(4*1000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } String username = request.getParameter("username"); String valinum = request.getParameter("valinum"); String valinum2 = (String) request.getSession().getAttribute("valinum"); if(valinum2!=null && !"".equals(valinum2) && valinum.equals(valinum2)){ request.getSession().removeAttribute("valinum"); System.out.println("向数据库中注册一次:"+username); }else{ response.getWriter().write("from web:不要重复提交!!"); } }