public class UserVerification {

  private static Connection connect = null;
  private static String host="localhost";
  private static String database="database";
  private static String username="root";
  private static String password="xxxx";


  public static Connection getConnection(){

   if(connect ==null){
            try{
             Class.forName("com.mysql.jdbc.Driver");
              String conn_string="jdbc:mysql://"+host+"/"+database;
              connect = DriverManager.getConnection(conn_string,username,password);
              return connect;
            }catch(Exception ex){
                ex.printStackTrace();
            }
        }else{
            return connect;
        }
        return connect;
    }

  public User checkUser(String user,String password){

      String sql="SELECT * FROM OFFICER  WHERE OUSERNAME='?' AND PASSWORDHASH=?";
      User u=null;
        try( Connection connect = getConnection();
             PreparedStatement pstmt = connect.prepareStatement(sql);
            ){
             pstmt.setString(1,user);
             pstmt.setString(2,HashGenerator.getMD5Hash(password));
             try (ResultSet rs = pstmt.executeQuery();){
               while(rs.next()){
                  String uname=rs.getString("USERNAME");
                  String pass=rs.getString("PASSWORDHASH");
                  u = new User(uname,pass);
                  break;
              }
             }
        }catch(SQLException ex){
            ex.printStackTrace();
        }
        return u;
  }
}

at UserVerification.checkUser(UserVerification.java:40)
at LoginServlet.doPost(LoginServlet.java:32)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:528)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1100)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:687)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1520)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1476)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)

try(something){
}

try{
    something
}
catch{
}

try{
    Connection connect = getConnection();
    PreparedStatement pstmt = connect.prepareStatement(sql);
    pstmt.setString(1,user);
    pstmt.setString(2,HashGenerator.getMD5Hash(password));
    try (ResultSet rs = pstmt.executeQuery();){
        while(rs.next()){
            String uname=rs.getString("USERNAME");
            String pass=rs.getString("PASSWORDHASH");
            u = new User(uname,pass);
            break;
        }
    }
}catch(SQLException ex){
    ex.printStackTrace();
}
return u;