TYPE_FORWARD_ONLY类型ResultSet能否调用absolute方法移动行指针？

Great question—this is a tricky edge case that boils down to how absolute(int row) behaves when row=0 and the specifics of your JDBC driver implementation. Let’s break this down clearly:

The API Docs vs. Real-World Behavior #

The Java 7 ResultSet docs state that absolute() throws SQLException if the result set type is TYPE_FORWARD_ONLY, but there’s an easy-to-miss exception here:

SQLException - if a database access error occurs; this method is called on a closed result set, or the result set type is TYPE_FORWARD_ONLY

This description is a bit generalized. The key nuance is that absolute(0) doesn’t violate the "forward-only" constraint for many drivers, making it a special case.

Why the Example Code Doesn’t Throw an Exception #

When you call rs.absolute(0), you’re moving the cursor to the position before the first row—this is actually the default initial state of any new ResultSet. For forward-only result sets, drivers like Derby (used in the example) allow this operation because:

• It doesn’t require "jumping" past the current cursor position; you’re just resetting to the starting point
• The JDBC specification implicitly permits this edge case, even if the API docs don’t explicitly call it out

When You Will Get an Exception #

If you call absolute() with any non-zero value (positive or negative) on a TYPE_FORWARD_ONLY ResultSet, you’ll get the SQLException as promised. For example:

• rs.absolute(1): Trying to jump directly to the first row (violates forward-only rules, since you haven’t traversed to it sequentially)
• rs.absolute(-1): Trying to jump to the last row (clearly breaks the forward-only constraint)

Final Takeaway #

You can safely use absolute(0) on a TYPE_FORWARD_ONLY ResultSet with most mainstream drivers (Derby, MySQL, PostgreSQL, etc.), but never rely on absolute(n) for any non-zero n—that will always throw an exception per the API contract.

内容的提问来源于stack exchange，提问作者dreinoso