NamedParameterJdbcTemplate 返回可选<Integer>

Question

Is there any way to return Optional from NamedParameterJdbcTemplate?

My query some times can return empty. So I want beautiful way for check for emptyness. I dont want to do try catch for EmptyResultDataAccessException coz this little ugly.

Answer 1

From what I understand your issue appears to be that your ResultSet may sometimes be entirely empty, so it's not about the value being returned as null but rather not having any result in the first place, hence why you mention EmptyResultDataAccessException . In my answer I am going to assume you're interested only in the first result as otherwise it wouldn't really make sense.

There is no direct method available in NamedParameterJdbcTemplate but you can use lambdas to get you there. Specifically, you can get a list of all results and then use stream().findAny() to obtain an Optional .

More or less, it would go like this:

Optional<Integer> values = namedParameterJdbcTemplate.queryForList(...)
    .stream()
    .map(m -> (Integer)m.get("MY_COLUMN"))
    .findAny();

In doing the above, you may want to limit the number of results your query is going to return as you may otherwise putting excessive strain on your network and also on the server's memory. Depending on the database technology, there are SQL clauses like LIMIT and OFFSET (see https://www.postgresql.org/docs/8.1/queries-limit.html for Postgres orhttps://dev.mysql.com/doc/refman/5.5/en/limit-optimization.html for MySQL) to help you with the task.

It is however to be noted that if your query returns more than one row in the first place, you're effectively discarding some data and therefore it's probably safer to assume that you're doing it wrong in the first place (in other words: you must be sure your query will always return either zero or one result).

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Assuming instead you would always have exactly one row and one column but with the returned value being null, the easiest way to obtain an Optional would be to wrap the call in Optional.ofNullable . Example (pseudo-code, just to get the gist):

Optional<Integer> v = Optional<Integer>.ofNullable(namedParameterJdbcTemplate.queryForObject(...));