Honor zero maxRows in JDBC result processing

[noojung]

Overview

JDBC defines a maxRows value of zero as unlimited, but the client-side row limiting introduced in #34709 treats it as a limit of zero. As a result, queries using JdbcTemplate and JdbcClient can discard all rows returned by the driver when maxRows is set to 0. This appears to be a regression from the behavior in 6.2.x.

Problem

JdbcTemplate correctly passes zero to the driver through Statement#setMaxRows(0). However, the client-side row limiting added in #34709 only bypasses the limit when maxRows is -1.

For zero, the condition rowNum < maxRows is false before the first row is processed, so the affected result-processing paths stop before handling any of the rows returned by the driver.

These checks exist in RowMapperResultSetExtractor and in the RowCallbackHandler and stream adapters within JdbcTemplate.

JdbcClient operations that delegate to these paths are also affected when using withMaxRows(0).

Fix

Apply client-side limits only for positive maxRows values in RowMapperResultSetExtractor and in the RowCallbackHandler and stream adapters within JdbcTemplate.

Preserve the driver-side handling of -1 (not passed on) and 0 (passed on as no limit), and clarify the meaning of zero in the Javadoc.

Tests

Add regression tests for maxRows=0 across RowMapper, RowCallbackHandler, and stream-based result processing. The tests verify that all expected rows are returned. An H2 integration test also verifies that withMaxRows(0) on JdbcClient returns all matching rows.

Related Issues

• Discard further rows once maxRows has been reached #34709
• Specify fetchSize/maxRows/queryTimeout per statement in JdbcClient #35155
• JdbcTemplate does not apply values of zero for setMaxRows, setFetchSize and setQueryTimeout [SPR-12338] #16943

Reference

• JDBC Statement.setMaxRows(int)