May 20, 2018 12:41:09 PM org.apache.catalina.startup.Catalina start
INFO: Server startup in 11579 ms
May 20, 2018 12:41:23 PM org.apache.catalina.core.ApplicationContext log
INFO: Marking servlet [LoginController] as unavailable
May 20, 2018 12:41:23 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Allocate exception for servlet [LoginController]
java.lang.ClassNotFoundException: controllers.LoginController
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1292)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1121)
    at org.apache.catalina.core.DefaultInstanceManager.loadClass(DefaultInstanceManager.java:540)
    at org.apache.catalina.core.DefaultInstanceManager.loadClassMaybePrivileged(DefaultInstanceManager.java:521)
    at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:150)
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1032)
    at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:761)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:133)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:494)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:651)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:412)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:754)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1385)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

<form method="post" action="LoginController">
                     <div class="form-group row">
                        <label for="email" class="col-sm-2 col-form-label">Email</label>
                        <div class="col-sm-10">
                          <input type="text" placeholder="Email">
                        </div>
                      </div>
                      <div class="form-group row">
                        <label for="password" class="col-sm-2 col-form-label">Password</label>
                        <div class="col-sm-10">
                          <input type="password" id="inputloginPassword" placeholder="Password">
                        </div>
                      </div>
                    <button type="submit" class="btn btn-primary btn-block btn-large">Let me in.</button>
                </form><br>

public class LoginController extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
 * @see HttpServlet#HttpServlet()
 */
public LoginController() {
    super();
    // TODO Auto-generated constructor stub
}

/**
 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
 */


/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    //response.getWriter().append("Served at: ").append(request.getContextPath());

    doPost(request,response);

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub

    String userName = request.getParameter("email");
    String password = request.getParameter("password");

    LoginBean loginBean = new LoginBean(); //creating object for LoginBean class, which is a normal java class, contains just setters and getters. Bean classes are efficiently used in java to access user information wherever required in the application.

    loginBean.setEmail(userName); //setting the username and password through the loginBean object then only you can get it in future.
     loginBean.setPassword(password);

    LoginQuery loginQuery = new LoginQuery(); //creating object for LoginDao. This class contains main logic of the application.

    String userValidate = loginQuery.LoginQuery(loginBean); //Calling authenticateUser function

    if(userValidate.equals("SUCCESS")) //If function returns success string then user will be rooted to Home page
     {
     request.setAttribute("userName", userName); //with setAttribute() you can define a "key" and value pair so that you can get it in future using getAttribute("key")
     request.getRequestDispatcher("/CustomerHome.jsp").forward(request, response);//RequestDispatcher is used to send the control to the invoked page.
     }
     else
     {
     request.setAttribute("errMessage", userValidate); //If authenticateUser() function returnsother than SUCCESS string it will be sent to Login page again. Here the error message returned from function has been stored in a errMessage key.
     request.getRequestDispatcher("/index.jsp").forward(request, response);//forwarding the request
     }
}

}