java - 新的 jre7 try block 资源

Question

如果我做类似的事情

    try (
        Connection conn = Database.getConnection();
        PreparedStatement ps = conn.prepareStatement("SELECT * FROM table WHERE something = ? LIMIT 1");
    ) {
        ps.setString(1, "hello world");
        ResultSet results = ps.executeQuery();
        if(results.next()) {
            // blah
        }
    } catch(SQLException e) {
        e.printStackTrace();
    }

当 PreparedStatement 关闭时，ResultSet 是否仍会关闭，还是我还必须显式关闭 ResultSet？

Answer 1

根据 javax.sql.Statement.close()方法的 JavaDoc:

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

那么，回答您的问题 - 是的，ResultSet将在您的案例中自动关闭，因为相关 Statement在 try-with-resources 关闭 block 。

但是，请注意显式关闭ResultSet s 是一个推荐遵循的良好实践，因此您按照良好实践修改后的代码如下所示:

try (
    Connection conn = Database.getConnection();
    PreparedStatement ps = prepareStatement(conn, "SELECT * FROM table WHERE something = ? LIMIT 1", param);
    ResultSet results = ps.executeQuery();
) {        
    if(results.next()) {
        // blah
    }
} catch(SQLException e) {
    e.printStackTrace();
}

private static PreparedStatement prepareStatement(Connection connection, String sql, String param) throws SQLException {
    final PreparedStatement ps = conn.prepareStatement(sql);
    ps.setString(1, param);
    return ps;
}