Что не так с SQL statmenr в методе isuservalid и if (valid ==true) statment

---

Когда я запускаю файл, он продолжает говорить null, когда их значения в базе данных. Кроме того, Кис говорит, что недопустимо в консоли, когда используется допустимый тег, он продолжает выводить недопустимый на консоль. Можете ли вы дайте мне знать, в чем проблема, пожалуйста.

Смотрите код ниже;

*/

// Creating web servlet for RFIDDao and creating public class which extends HttpServlet
@WebServlet("/RFIDDao")
public class RFIDDao extends HttpServlet {
	// Creating private static final serialVersionUID
	private static final long serialVersionUID = 1L;
	// Declaring GSON utility object
	// Connection = null and statement.
	Gson gson = new Gson();
	Connection conn = null;
	static Statement stmt;
	public static final String userid = "16038287"; // change this to be your student-id
	// Creating topic for the server
	public static final String TOPIC_SERVER = userid + "/server";
	public static final String BROKER_URL = "tcp://iot.eclipse.org:1883";
	//private MqttClient client;



	// Creating public void init method for ServletConfig which throws ServletException
	public void init(ServletConfig config) throws ServletException {
		// init method is run once at the start of the servlet loading
		// This will load the driver and establish a connection
		super.init(config);

		// Adding the mysql workbench username and assword, in order to connect to the database
		String user = "rashidd";
		String password = "rooSedef6";
		//  Usiing port 6306 instead of 3306 and connecting to the mudfoot server
		String url = "jdbc:mysql://mudfoot.doc.stu.mmu.ac.uk:6306/rashidd";



		// Loading the database driver
		try {
			Class.forName("com.mysql.jdbc.Driver").newInstance();
		} catch (Exception e) {
			System.out.println(e);
		} // close catch exception e

		// Creating try to get a connection with the user/pass
		try {
			conn = DriverManager.getConnection(url, user, password);
			// Print messages out onto the console
			System.out.println("Sensor to DB  server is up and running\n");
			System.out.println("Upload sensor data with http://localhost:8080/IOTServer/RFIDDao?sensorname=xxx&sensorvalue=nnn");
			System.out.println("View last sensor reading at  http://localhost:8080/IOTServer/RFIDDao?getdata=true\n\n");

			// System.out.println("DEBUG: Connection to database successful.");
			stmt = conn.createStatement();
			//System.out.println("debug: Statement created " + stmt);
		} catch (SQLException se) {
			se.printStackTrace();
			System.out.println(se);
			System.out.println("\nDid you alter the lines to set user/password in the sensor server code?");
		} // Close catch sql exception
	} // init()

	// Creating destroy method
	public void destroy() {
		try {
			conn.close();
		} catch (SQLException se) {
			System.out.println(se);
		} // Close catch sql exception se
	} // destroy()

	/***
	 * Creating rfiddao method,
	 * Super is a method which is used inside a sub-class method, to call a method in the super class. 
	 * Private method of the super-class would not be called. 
	 * Only public and protected methods can be called by the super keyword.
	 * It is also used by class constructors to invoke constructors of its parent class.
	 */
	public RFIDDao() {
		// Calling the super method
		super();

		/*try {
			client = new MqttClient(BROKER_URL, userid+"-server_publisher");
			// create mqtt session
			MqttConnectOptions options = new MqttConnectOptions();
			options.setCleanSession(false);
			options.setWill(client.getTopic(userid + "/LWT"), "I'm gone :(".getBytes(), 0, false);
			client.connect(options);
		} catch (MqttException e) {
			System.out.println("mqtt");
			e.printStackTrace();
			System.exit(1);
		}*/
	} // Close public RFIDDao method


	/**
	 * Creating do get method, to insert data into the database.
	 * Then retrieve the data, depending on sensorname
	 * Creating suser valid method which would then check if valid user is using valid tag to open the door.

	 *  getAllDoorLockStatus
	 *  Retrieve all RFID Data.
	 * @return
	 * @throws SQLException
	 */

	// doGet is a method which supports the servlet HTTP GET requests 
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setStatus(HttpServletResponse.SC_OK);
		// Declare a SensorData object to hold the incoming data
		SensorData oneSensor = new SensorData("unknown", "unknown");

		// Check to see whether the client is requesting data or sending it
		String getdata = request.getParameter("getdata");

		ServletRequest req = null;
//		SensorData sensordata = null;
		

		// if no getdata parameter, client is sending data
		if (getdata == null) {
			// getdata is null, therefore it is receiving data
			// Extracting the parameter data holding the sensordata
			String sensorJsonString = request.getParameter("sensordata");
			// Extracting the parameter data holding the sensorname
			String data = request.getParameter("sensorname");
			// Creating boolean for is user valid
			boolean valid = isUserValid(data);
			// If valid userhas been used return valid user/tag and door open
			if (valid == true) {
				System.out.println("valid user/tag");
				// Creating new sensor data object
				oneSensor = new SensorData(data, "Door open", "16038287");

				// send command to open the door
				PrintWriter writer = new PrintWriter(response.getOutputStream());
				writer.write("true"); // Writer = true
				writer.close();
			}
			// Otherwise, return invalid user/tag and door closed
			else {
				System.out.println("invalid user/tag");
				oneSensor = new SensorData(data, "Door closed", "16038287");
			} // Close else

			// Problem if sensordata parameter not sent, or is invalid json
			if (sensorJsonString != null) {
				// Converting the json string to an object of type SensorData
				// Also, calling the sensordata class
				oneSensor = gson.fromJson(sensorJsonString, SensorData.class);

				// Update sensor values and send back response
				PrintWriter out = response.getWriter();
				// Calling the updateSensorTable method
				try {
					updateSensorTable(oneSensor);
				} catch (Exception e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
				out.close(); // close out
			} // endif sensorJsonString not null
		} // end if getdata is null
		else { // Otherwise retrieve and return data in json format
			// retrive data sensor by sensorname parameter
			String sensorname = request.getParameter("sensorname");
			if (sensorname != null) {
				PrintWriter out = response.getWriter();
				out.println(retrieveSensorData(sensorname));
				out.close();
			}
		} // CLose else
	} // CLose protected void doget method

	// Creating do post method
	//doPost is used for HTTP POST requests 
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// Post is same as Get, so pass on parameters and do same
		doGet(request, response);
	} // CLose protected void dopost

	/**
	 *  Creating boolean to check if a valid user is trying to open the door, using specific sensor name (tagid)  = 1600ee15e9
	 *  Selecting everything from the door lock valid table where the id is '1600ee15e9'
	 *  This will then check in the second table if its valid user or not and then reutrn success message.
	 *  A tag data object is an instance of a class.
	 * @param sensorname
	 * @return
	 */
	public boolean isUserValid(String sensorname) {
		// Creating tag data object
		TagData oneSensor = new TagData("1600ee15e9", "VALID TAG", "Room101");
        
		try {
			// select everything from the door lock valid table where the sensorname is valid tag 9sensorname)
//			String sql = "SELECT sensorname FROM doorlockValid WHERE sensorname = '"+sensorname+"'";
			String sql = "SELECT * FROM doorlockValid WHERE sensorname=+sensorname";

			// execute sql query
			//stmt.executeUpdate(sql);
			stmt.executeQuery(sql);			
			System.out.println("DEBUG: statement correct" +stmt);
			System.out.println(sql); // print the query result
			System.out.println(">> Debug: All RFID data displayed");

			ResultSet resultset = null;


			// If sensor name is 1600ee15e9 then it's valid user and returns true
			if (resultset.getString("sensorname").equals(sensorname))
				return true;
		} catch (SQLException e) {
			System.out.println(e.getMessage());
		} catch (Exception e) {
			System.out.println(e.getMessage());
		} // CLose catch
		// Otherwise return false if invalid user is trying to open the door
		return false;
	} // CLose buplic booelan is user valid method


	// Creating static update sensor table to insert the status of the door lock to the database
	public static void updateSensorTable(SensorData oneSensor) throws Exception {
		try {
			// Creating the INSERT statement from the parameters
			// set time inserted to be the current time on database server
			String updateSQL = "insert into doorlock(userid, sensorname, sensorvalue, timeinserted) "
					+ "values('" + oneSensor.getUserid() + "','" + oneSensor.getSensorname() + "','"
					+ oneSensor.getSensorvalue() + "',"
					+ "now());";


			// Print out debug message to the console
			System.out.println("DEBUG: Update: " + updateSQL);
			// Execute query
			stmt.executeUpdate(updateSQL);
			//publish_to_Android(oneSensor);
			// Print debug message to the console
			System.out.println("DEBUG: Update successful ");
		} catch (SQLException se) {
			// Problem with update, return failure message
			System.out.println(se);
			System.out.println("\nDEBUG: Update error - see error trace above for help. ");
			return;
		} // CLose catch sql exception

		// all ok, return
		return;
	} // Close private void update sensor table method

	/**
	 *  Creating private string to  retrieveSensorData
	 * Declaring a string to hold the sql select, set its value to a select
	 * statement that will retrieve all values from the doorlock table
	 *  where the sensorname equals the parameter supplied "where sensorname='" + sensorname + "'".
	 *  Then adding the qualifier " order by timeinserted asc" to the sql
	 * statement to ensure that the data is returned in ascending order
	 *  (i.e. newest last).
	 * http://localhost:8080/IOTServer/RFIDDao?getdata&sensorname=4d004a5587
	 * http://localhost:8080/IOTServer/RFIDDao?getdata&sensorname=1600ee15e9
	 * @param sensorname
	 * @return
	 */
	private String retrieveSensorData(String sensorname) {
		//SELECT from mudfoot server where sensorname = the sensorname inserted
		//		String selectSQL = "select * from rashidd.doorlock where sensorname = \"" + sensorname + "\"";
		String selectSQL = "select * from rashidd.doorlock where sensorname='" + 
				sensorname + "' order by timeinserted asc";

		//String selectSQL = "select * from rashidd.doorlock";
		ResultSet rs = null; // creating variable for result set
		// Creating array list of sensor data
		ArrayList<SensorData> s = new ArrayList<>();


		// Declaring a Result set called rs
		// rs = ((java.sql.Statement) statement).executeQuery(selectSQL);//RESULT FROM
		// QUERY

		// Creating try to declare ArrayList of SensorData called allSensors to hold results,
		// and initialise it
		try {
			/**
			 *  iterate over the result set created by the select for each of
			 *  the columns in the table, putting them into oneSensor with
			 *  the corresponding set method for sensorname, sensorvalue, userid, timeinserted, using either
			 *  getString or getDouble and then execute query.
			 */

			rs = conn.createStatement().executeQuery(selectSQL);
			System.out.println("DEBUG: statement correct" +selectSQL);

			// Creating while resultset
			while (rs.next()) {
				// String sensorname, String sensorvalue, String userid, String sensordate
				SensorData oneSensor = new SensorData(rs.getString("sensorname"), rs.getString("sensorvalue"),
						rs.getString("userid"), rs.getString("timeinserted"));
				s.add(oneSensor); // add the data
			} // CLose while loop for rs.next
		} catch (SQLException ex) {
			System.out.println("Error in SQL " + ex.getMessage());
		} // Close catch sql exception e
		// Return the responce in json format
		return new Gson().toJson(s);
	} // Close private string retrieve sensor data

	// Creating public void publish to android to publish the sensor data to the application, in order to view the data on the appication
	//	public void publish_to_Android(SensorData a)throws Exception
	//	{
	//
	//		Gson g = new Gson();
	//		final MqttTopic motorTopic = client.getTopic(TOPIC_SERVER);
	//		motorTopic.publish(new MqttMessage(g.toJson(a).getBytes()));
	//
	//
	//	}
} // Close public class sensor server db

Что я уже пробовал:

Я пробовал отлаживать код еще ничего, а также проверял различные операторы в моем sql и тестировал их. Они работают в моем sql workbench, но не в eclipse.

---