java - 关闭连接后第二次调用PreparedStatement不起作用

Question

我正在尝试第二次执行 PreparedStatement，但如果我关闭 DriverManager.getConnection，则会失败

代码:

public void getRates(String id) throws Exception, DBException {

        Connection conn = null;
        ResultSet rs    = null;

        try {

            conn = getConnection();

            if (ratesQueryStmt == null){
                ratesQueryStmt = conn.prepareStatement(ratesQuery); 
            }
            ratesQueryStmt.setString(1, id);

            ratesQueryStmt.setQueryTimeout(m_nTimeout);

            rs = ratesQueryStmt.executeQuery();

            while (rs.next()){
                System.out.println("!!!\n\nDATE = " + rs.getString("RATE_DAY") + " PURCHASE_PRICE = " + rs.getString("PURCHASE_PRICE") + " SELLING_PRICE = " + rs.getString("SELLING_PRICE"));
            }

        }
        catch (SQLException e) {
            Utility.trace(m_session, "SQL exception - code: "+String.valueOf(e.getErrorCode())+" "+e.getMessage());
            throw e;
        }
        finally {
            DBAccess.closeEverything(rs, ratesQueryStmt, conn); //DO NOT WORK BECAUSE OF CLOSING CONNECTION (conn)
        }

所以第一次它工作得很好，但是当我尝试调用这个方法两次时它显示错误:(

        DBAccess.getInstance(mySession).getRates("USD"); //WORKS
        DBAccess.getInstance(mySession).getRates("EUR"); // NOT WORKING

错误堆栈

java.lang.NullPointerException
    at oracle.jdbc.dbaccess.DBDataSetImpl._createOrGetDBItem(DBDataSetImpl.java:825)
    at oracle.jdbc.dbaccess.DBDataSetImpl.setBytesBindItem(DBDataSetImpl.java:2520)
    at oracle.jdbc.driver.OraclePreparedStatement.setItem(OraclePreparedStatement.java:1248)
    at oracle.jdbc.driver.OraclePreparedStatement.setString(OraclePreparedStatement.java:1690)
    at asteros.DBAccess.getRates(DBAccess.java:141) //ratesQueryStmt.setString(1, id);

如果我不关闭连接，一切正常..

谢谢!

UPD: getConnection() 的来源

public Connection getConnection() throws Exception {
    Connection conn = null;
    try {

        Utility.trace(m_session, "DB string: "+m_strDBString+" user: "+m_strUser+" password: "+m_strPassword);
        System.out.println("DB string: "+m_strDBString+" user: "+m_strUser+" password: "+m_strPassword);

        Driver dr = new oracle.jdbc.driver.OracleDriver();
        DriverManager.registerDriver(dr);
        conn = DriverManager.getConnection(m_strDBString, m_strUser, m_strPassword);

    } catch (Exception e) {
        throw new Exception(e);
    }

    return conn;
}

Answer 1

PreparedStatement据我所知，实例与用于准备它们的连接相关联。关闭连接后，您将无法使用 PreparedStatement，即使您稍后打开另一个连接也是如此。