Java JDBC 结果集已关闭

Question

运行此代码时，我收到 ResultSet 关闭错误。调用的方法和数据如下:

日志输出:

[2014-05-05 22:34:09.169 Debug] select count(*) as total from companies
[2014-05-05 22:34:09.170 Debug] ResultSet closed

方法:

public static Boolean recordsExist(String string, Connection c) {
    try {
        String[] query = string.split("\\*");
        String sql = "select count(*) as total" + query[1];
        ResultSet resultset = queryDB(sql, c);
        resultset.next();
        int count = resultset.getInt(1);
        Log.debug(Integer.toString(count));
        resultset.close();
        if (count > 0) {
            Log.debug("recordsExist returning true");
            return true;
        } else {
            Log.debug("recordsExist returning false");
            return false;
        }

    } catch (Exception e) {
        Log.debug(e.getMessage());
        return false;
    }
}

public static ResultSet queryDB(String sql, Connection c) throws SQLException {
    Log.debug(sql);
    Statement s = c.createStatement();
    ResultSet resultset = s.executeQuery(sql);
    s.close();
    return resultset;
}

指定的 SQL 字符串:

select * from companies

Answer 1

来自Java API :

Note:When a Statement object is closed, its current ResultSet object, if one exists, is also closed.

在关闭Statement之前，您需要处理ResultSet中的数据。沿着这些思路的东西应该有效:

public static Boolean recordsExist(String string, Connection c) {
    try {
        String[] query = string.split("\\*");
        String sql = "select count(*) as total" + query[1];
        return queryDB(sql, c);


    } catch (Exception e) {
        Log.debug(e.getMessage());
        return false;
    }
}

public static boolean queryDB(String sql, Connection c) throws SQLException {
    Log.debug(sql);
    Statement s = c.createStatement();
    ResultSet resultset = s.executeQuery(sql);
    boolean result = processResult(resultset);
    s.close();
    return result;
}

public static boolean processResult(ResultSet resultset) {
    resultset.next();
    int count = resultset.getInt(1);
    Log.debug(Integer.toString(count));
    resultset.close(); 
    if (count > 0) {
        Log.debug("recordsExist returning true");
        return true;
    } else {
        Log.debug("recordsExist returning false");
        return false;
    }

}

我还会考虑添加更多错误处理，以确保不会泄漏资源。例如，如果处理结果时发生异常，那么您的语句将无法正确关闭。