Java Web應用程序中的登錄和注冊是非常重要的功能。通過這兩個功能，用戶可以注冊自己的帳戶并登錄，從而獲得訪問受保護內容的權限。下面將介紹如何使用Java Web技術實現這兩個功能。

登錄功能的實現：

public class LoginController extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String userName = request.getParameter("userName");
String password = request.getParameter("password");
if (userName == null || password == null) {
response.sendRedirect("login.jsp?error=1");
} else if (userName.equals("admin") && password.equals("123456")) {
HttpSession session = request.getSession();
session.setAttribute("userName", userName);
response.sendRedirect("welcome.jsp");
} else {
response.sendRedirect("login.jsp?error=2");
}
}
}

注冊功能的實現：

public class RegisterController extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String userName = request.getParameter("userName");
String password = request.getParameter("password");
String email = request.getParameter("email");
String phone = request.getParameter("phone");
if (userName == null || password == null || email == null || phone == null) {
response.sendRedirect("register.jsp?error=1");
} else {
// 執行注冊邏輯
response.sendRedirect("login.jsp?success=1");
}
}
}

以上兩段代碼分別是登錄和注冊的后臺代碼，需要與前端的登錄頁面和注冊頁面進行對接。具體的頁面代碼可以根據需要編寫，這里不再贅述。