NullPointerException в java при попытке подключения к базе данных MySQL

Question

У меня возникли проблемы с подключением базы данных MySQL. Я пытаюсь установить соединение между сервером и клиентом. Я получаю NullPointerException на линии с Statement stat = this.conn.createStatement();

Я могу выполнить ping на сервере от моего клиента. Брандмауэр также отключен на сервере.

Как вы можете видеть на следующем изображении, я добавил драйвер MySQL jdbc в проект.

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException 
at testdatabaseconn.DatabaseConn.closeConnection(DatabaseConn.java:58) 
at testdatabaseconn.DatabaseConn.loadAccount(DatabaseConn.java:44) 
at testdatabaseconn.TestDatabaseConn$1.handle(TestDatabaseConn.java:37) 
at testdatabaseconn.TestDatabaseConn$1.handle(TestDatabaseConn.java:30) 
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86) 
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238) 
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191) 
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59) 
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58) 
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114) 
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56) 
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114) 
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56) 
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114) 
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74) 
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49) 
at javafx.event.Event.fireEvent(Event.java:198) 
at javafx.scene.Node.fireEvent(Node.java:8216) 
at javafx.scene.control.Button.fire(Button.java:185) 
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182) 
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96) 
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89) 
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218) 
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80) 
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238) 
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191) 
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59) 
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58) 
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114) 
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56) 
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114) 
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56) 
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114) 
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74) 
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54) 
at javafx.event.Event.fireEvent(Event.java:198) 
at javafx.scene.Scene$MouseHandler.process(Scene.java:3724) 
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3452) 
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1728) 
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2461) 
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:348) 
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:273) 
at java.security.AccessController.doPrivileged(Native Method) 
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:382) 
at com.sun.glass.ui.View.handleMouseEvent(View.java:553) 
at com.sun.glass.ui.View.notifyMouse(View.java:925) 

DatabaseConn.java

public class DatabaseConn { 

    private Connection conn; 

    public String loadAccount() throws SQLException, IOException, ClassNotFoundException { 
     String username = null; 

     try { 
      this.initConnection(); 

      Statement stat = this.conn.createStatement(); 
      String accountQuery = "SELECT username FROM account WHERE username = 'Ruubje'"; 

      ResultSet persoonResults = stat.executeQuery(accountQuery); 


      while (persoonResults.next()) { 
       username = persoonResults.getString("username"); 
      } 

     } catch (SQLException | IllegalArgumentException ex) { 
      throw new IOException(ex.getMessage()); 
     } finally { 
      this.closeConnection(); 
     } 

     return username; 
    } 

    private void initConnection() throws SQLException, ClassNotFoundException { 
     Class.forName("com.mysql.jdbc.Driver"); 

     conn = DriverManager.getConnection("jdbc:mysql://[IPADDRESS]:3306/lms", "root", "usbw"); 
    } 

    private void closeConnection() { 
     try { 
      conn.close(); 
      conn = null; 
     } catch (SQLException ex) { 
      System.err.println(ex.getMessage()); 
     } 
    } 
} 

Кто-нибудь есть какие-либо идеи?

Answer 1

Вы должны проверить соед не равно нулю:

private void closeConnection() { try { if(conn != null){ conn.close(); conn = null; } } catch (SQLException ex) { System.err.println(ex.getMessage()); } }