重用 PreparedStatement 导致 SQLException

Question

尝试使用资源会出现以下异常：

java.sql.SQLException: Operation not allowed after ResultSet closed

我的代码：

public Set<Tablet> viewAllTablets(int offset, int noOfRecords) throws OutOfRangeException {
    Set<Tablet> tabletSet = new HashSet<>();
    Tablet tablet = null;

    try(Connection connection = dataSource.getConnection();
        PreparedStatement preparedStatement = connection.prepareStatement("SELECT SQL_CALC_FOUND_ROWS * FROM tablets limit " + offset + ", " + noOfRecords + ";");
        ResultSet resultSet = preparedStatement.executeQuery();
        ResultSet resultSet1 = preparedStatement.executeQuery("SELECT FOUND_ROWS()");){

        while (resultSet.next()){
            tablet = new Tablet();
            tablet.setTabletId(resultSet.getInt("idTablet"));
            tablet.setName(resultSet.getString("name"));
            tablet.setNeedRecepie(resultSet.getBoolean("need_recipe"));
            tablet.setPrice(resultSet.getDouble("price"));
            tablet.setTypeId(resultSet.getInt("type_id"));
            tablet.setDescription(resultSet.getString("description"));
            tablet.setTabletType(TypeFactory.getType(tablet.getTypeId()));
            tablet.setWeight(resultSet.getDouble("weight_of_pack"));
            tablet.setPillsCount(resultSet.getInt("pills_count"));
            tabletSet.add(tablet);
        }
        if(resultSet1.next())
            this.noOfRecords = resultSet1.getInt(1);
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return tabletSet;
}

Answer 1

在 PreparedStatement 上执行第二个查询会隐式关闭前一个查询中的 ResultSet。来自 Statement:

By default, only one ResultSet object per Statement object can be open at the same time.

使用两个不同的语句，大致如下（注意 resultSet1 是如何检索的）虽然我当然不知道您的 FOUND_ROWS 函数的要求是什么：

try (
    Connection connection = dataSource.getConnection();
    PreparedStatement preparedStatement = connection.prepareStatement("SELECT SQL_CALC_FOUND_ROWS * FROM tablets limit " + offset + ", " + noOfRecords + ";");
    ResultSet resultSet = preparedStatement.executeQuery();
    ResultSet resultSet1 = connection.createStatement().executeQuery("SELECT FOUND_ROWS()"); // ****
    ) {
    while (resultSet.next()) {
        tablet = new Tablet();
        tablet.setTabletId(resultSet.getInt("idTablet"));
        tablet.setName(resultSet.getString("name"));
        tablet.setNeedRecepie(resultSet.getBoolean("need_recipe"));
        tablet.setPrice(resultSet.getDouble("price"));
        tablet.setTypeId(resultSet.getInt("type_id"));
        tablet.setDescription(resultSet.getString("description"));
        tablet.setTabletType(TypeFactory.getType(tablet.getTypeId()));
        tablet.setWeight(resultSet.getDouble("weight_of_pack"));
        tablet.setPillsCount(resultSet.getInt("pills_count"));
        tabletSet.add(tablet);
    }
    if (resultSet1.next())
        this.noOfRecords = resultSet1.getInt(1);
} catch (SQLException e) {
    e.printStackTrace();
}

另外：不要在 PreparedStatement 上使用 Statement 的 executeQuery(String)。它真的不应该存在，它是 java.sql 包设计中的一个缺陷。事实上，Statement#executeQuery 的文档说：

Note:This method cannot be called on a PreparedStatement or CallableStatement.

重用 PreparedStatement 导致 SQLException

Reusing PreparedStatement causes SQLException

java

jdbc

try-with-resources