在做我的作業時，第一個任務是嚴格關于 servlet，然后在 servlet 之間傳遞值時session.setAttribiute作業session.getAttribiute正常。但是自從使用 servlet 和 jsp 以來，我遇到了空值的問題。這是有問題的代碼。
小服務程式：
@WebServlet(name = "SubmitLoginServlet", value = "/submitLogin")
public class SubmitLogin extends HttpServlet {
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
PrintWriter out = response.getWriter();
response.setContentType("text/html;charset=UTF-8");
String username = request.getParameter("username");
String password = request.getParameter("password");
try {
Connection con = DatabaseConnection.initDatabase();
Statement statement = con.createStatement();
String sql = "SELECT * FROM users";
ResultSet resultSet = statement.executeQuery(sql);
while (resultSet.next()) {
String DBusername = resultSet.getString("name");
String DBpassword = resultSet.getString("password");
if(DBusername.equals(username) && DBpassword.equals(password)) {
request.getSession().setAttribute("username", "test");
// I USED "TEST" JUST FOR TESTING, STILL THE VALUE ON 'INDEX.JSP' IS EMPTY
request.getRequestDispatcher("/index.jsp").forward(request,response);
// response.sendRedirect("index.jsp");
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
// INDEX.JSP - pasted in this block because of bug with code formatting, sorry
// on top of the file I have <%@ page session = "false" %>
<div class="column is-one-fifth is-offset-two-fifths">
<%
HttpSession session = request.getSession(true);
if(session.getAttribute("username") == "" || session.getAttribute("username") == null) {
%>
<form action="register.jsp">
<button type="submit" class="button is-info is-fullwidth">Signup</button>
</form>
<form action="login.jsp" method="get">
<button type="submit" class="button is-success is-fullwidth">Login</button>
</form>
<% } else { %>
<h1 class="title"> Welcome <% request.getSession().getAttribute("username"); %></h1>
<button class="button is-danger">Logout</button>
<% } %>
</div>
然后在登錄并重定向到 index.jsp 后，我有Welcome和空白空間和注銷按鈕。有什么幫助嗎？
uj5u.com熱心網友回復：
抱歉，伙計們，我只是在 Java 方面很糟糕，僅此而已。我不知道當您想在 JSP 中輸出值時，您需要使用<%= %>標簽而不是<% %>用于邏輯的標簽。
轉載請註明出處，本文鏈接：https://www.uj5u.com/caozuo/425283.html
上一篇：添加活動類以鏈接到當前頁面