使用Java[duplicate]在循环中关闭结果集

Question

这个问题应该很简单，而且可能会让人恼火，但我仍然对使用Java关闭结果集感到怀疑。每个语句都应该这样做，或者结果集应该只在final中关闭？

       try {
        Class.forName(<driver class>);                
        con = DriverManager.getConnection(
            "IP", 
            "username",
            "password");
        for(String dealId : items) {
            String sql= "SQL Query";
            preparedStatement = con.prepareStatement(sql);
            rs = preparedStatement.executeQuery();
            while(rs.next()) {
                count += rs.getInt("total");                    
            }
            // Result should be closed here as the statement got executed?
        }
        System.out.println(count);
        if(items.size() == count) {
            dealsBelongToTheParty = true;
        }

    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        rs.close(); // Or this is right?
        preparedStatement.close();
        if(!con.isClosed())
            con.close();
    }

Answer 1

https://docs.oracle.com/javase/7/docs/api/java/sql/ResultSet.html

"当生成ResultSet对象的语句对象被关闭、重新执行或用于从多个结果序列中检索下一个结果时，ResultSet对象会自动关闭。"

因此，您不必担心关闭ResultSet。

Answer 2

我建议使用Java 7 try with resources（下面的代码假设查询中使用了循环vardealId）

Class.forName(<driver class>);                
try (Connection con = DriverManager.getConnection(
        "IP", "username", "password")) {
    for(String dealId : items) {
        String sql= "SQL Query with " + dealId;
        // resources are opened by order 
        try (PreparedStatement preparedStatement = con.prepareStatement(sql);
             ResultSet rs = preparedStatement.executeQuery()) {
            while(rs.next()) {
                count += rs.getInt("total");                    
            }
        } // resources are implicitly closed in reverse order of open
    }
} catch (Exception e) {
    e.printStackTrace();
}

System.out.println(count);
if(items.size() == count) {
    dealsBelongToTheParty = true;
}