春季：具有RowCallbackHandler的JdbcTemplate.query（）是否同时调用processRow（）？

Question

The Spring docs specify the RowCallbackHandler argument as an "object that will extract results, one row at a time". I see that processRow() is called once per row, but can these calls be concurrent?

I am having my RowCallbackHandler maintain state, including building a Collection of processed objects and occasionally submitting that Collection for further processing. I need to know if this Collection might be modified concurrently, or if I can trust that only one processRow() is happening at a time.

Answer 1

It is really up to you. If you've seen the source code, RowCallbackHandler you provide is wrapped in RowCallbackHandlerResultSetExtractor adapter class and then wrapped again in QueryStatementCallback (sic!).

Never mind, the point is: if you pass the same RowCallbackHandler instance to two concurrent query() executions, Spring will use the same object through all this layers. But if you create new instance of RowCallbackHandler per every query() execution, you are safe.

Answer 2

If I understand your question, it's 1 row at a time. The example code is from their result set extractor which calls this interface.

while (rs.next()) {
   this.rch.processRow(rs);
}