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public final class DBConnector implements Runnable {
  private final String query;
  
  DBConnector(String query) {
    this.query = query;
  }
	
  private static ThreadLocal<Connection> connectionHolder = new ThreadLocal<Connection>() {
    Connection connection = null;

    @Override public Connection initialValue() {		
      try {
        // Username and password are hard coded for brevity
        connection = DriverManager.getConnection
          ("jdbc:driver:name", "username", "password");  	    	      
      } catch (SQLException e) {
        // Forward to handler
      }
      return connection;
    }
		
    @Override public void set(Connection con) {
      if(connection == null) { // Shuts down connection when con = null passed 		       
        try {
          connection.close();
        } catch (SQLException e) {
          // Forward to handler 
        }	       		       
      } else {
        connection = con; 
      }
    }
  };

  public static Connection getConnection() {
    return connectionHolder.get();
  }

  public static void shutdownConnection() { // Allows client to close connection anytime
    connectionHolder.set(null);
  }

  public void run() {
    Connection dbConnection = getConnection();
    Statement stmt;
    try {
      stmt = dbConnection.createStatement();		
      ResultSet rs = stmt.executeQuery(query);
    } catch (SQLException e) {
      // Forward to handler	 
    }    
    // ...
  }

  public static void main(String[] args) throws InterruptedException {
    DBConnector connector = new DBConnector("suitable query");
    Thread thread = new Thread(connector);
    thread.start();
    Thread.sleep(5000);
    connector.shutdown();
  }
}