登陸提交表單使用 POST 請求進行驗證及轉發;
輸入用戶名(是否正確)及密碼(是否爲空) 使用 GET 請求進行驗證;javascript
<!--login.jsp-->
<form action="login" method="POST">
<div>
<input type="text" name="username" id="userId" placeholder="用戶名">
<span class="info"></span>
</div>
<div>
<input type="password" name="password" id="passwd" placeholder="密碼">
</div>
<input type="submit" value="登 錄" >
${error}
</form>
<!--index.jsp-->
<h3 style='color:#00f'>親愛的${user.name},歡迎您!</h3>
<p>如今的時間是:<% out.println(new java.util.Date()); %></p>
//javascript
var xmlHttp;
var userId = document.getElementById("userId");
var passwd = document.getElementById("passwd");
var info = document.getElementsByClassName("info");
userId.onblur = checkUser;
passwd.onblur = checkPwd;
function createXMLHttpRequest() {
//檢查是否支持 ActiveXObject 控件(IE瀏覽器)
if(window.ActiveXObject) {
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
} else if(window.XMLHttpRequest) {
xmlHttp = new XMLHttpRequest();
}
}
function checkUser() {
createXMLHttpRequest();
var url = "login?username="+userId.value;
xmlHttp.open("GET", url, true);
xmlHttp.send(null);
xmlHttp.onreadystatechange = function() {
if(xmlHttp.readyState == 4 && xmlHttp.status == 200) {
info[0].innerHTML = xmlHttp.responseText;
}
};
}
function checkPwd() {
createXMLHttpRequest();
var url = "login?password="+passwd.value;
xmlHttp.open("GET", url, true);
xmlHttp.send(null);
xmlHttp.onreadystatechange = function() {
if(xmlHttp.readyState == 4 && xmlHttp.status == 200) {
info[1].innerHTML = xmlHttp.responseText;
}
};
}
當 username 爲空時,按 tab 鍵使用戶名輸入框失去焦點,此時觸發GET請求,url 後綴爲: ?username=
,
即:username=="", password==null
html
當 username 不爲空,按 tab 鍵使用戶名輸入框失去焦點,並觸發GET請求,url 後綴爲: ?username=xxx
,
即:username=="xxx", password==null
java
若再按 tab 鍵使密碼輸入框又失去焦點,這時繼續GET請求,url 後綴爲: ?password=
,
即:username==null, password==""
ajax
//LoginServlet.java
@WebServlet("/login")
public class LoginServlet extends HttpServlet {
......
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
// username、password 可能爲null, 可能不爲null
if(request.getParameter("username") == "") {
//?username=
if(request.getParameter("password") == null) {
out.print("用戶名不能爲空!");
}
} else if(request.getParameter("username") == null) {
if(request.getParameter("password") == ""){
//?password=
out.print("密碼不能爲空!");
}
} else {
//?username=xxx
String name = request.getParameter("username");
if(!name.equals("admin")) {
if(request.getParameter("password") == null) {
out.print("用戶名不存在!");
}
}
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
String name = request.getParameter("username");
String pwd = request.getParameter("password");
if(name.equals("admin") && pwd.equals("admin")) {
User user = new User(name,pwd);
HttpSession session = request.getSession();
session.setAttribute("user", user);
RequestDispatcher rd = request.getRequestDispatcher("/");
rd.forward(request, response);
} else {
request.setAttribute("error", "用戶名或密碼錯誤,請從新登陸!");
RequestDispatcher rd = request.getRequestDispatcher("login.jsp");
rd.forward(request, response);
}
}
}
待續 …瀏覽器