问java.sql.SQLException:语句已经关闭

EN

public class CpiDaoBase {

protected Connection con = null;

public void test(){
cpiDAOBase.openDbConnection();
ps = new cpiDAOBase().con.prepareStatement(INSERT_CARRIER);
ps.executeQuery();
... blah blah blah
 }

 public void openDbConnection() throws CpiSystemException
    {
        try {
            if (con == null || con.isClosed()) {
                con = CpiDataSource.getNonTxConnection();
            }
        } catch (SQLException e) {
            log.error(e.getMessage(), e);
            new CpiSystemException("SQLException caused by con.isClosed(): " + e.getMessage());
        }
    }   
}

public class CpiDataSource {
    public static Connection getNonTxConnection() throws CpiSystemException {
    try {
        if (nonTxDs == null) 
        {
            if(log.isDebugEnabled()){
                log.debug("nonTxDs is null");
            }
            init();
        }
        return nonTxDs.getConnection();
    } catch (NamingException e) 
    {
        log.error("cpiPoolDataSource is not available !" + e);
        throw new CpiSystemException("cpiPoolDataSource is not available !");
    } catch (SQLException e) 
    {
        log.error("Failed to get connection from datasource !" + e);
        throw new CpiSystemException("Failed to get connection from datasource !");
    } catch (Exception e) 
    {
        log.error("Exception \n" + e);
        throw new CpiSystemException(e.getMessage());
    }
}
}