You can use a RecursiveLeafOnlyDirectoryScanner but note the comment in its JavaDoc - it's not suitable for very large directory trees.
Code:
<int-file:inbound-channel-adapter id="filesIn"
scanner="recursiveScanner"
directory="file:${java.io.tmpdir}/spring-integration-samples/input"
filename-pattern="*.txt">
<int:poller fixed-delay="600000" />
</file:inbound-channel-adapter>
<bean id="recursiveScanner" class="org.springframework.integration.file.RecursiveLeafOnlyDirectoryScanner" />
Gary P. Russell
Spring Integration Team
SpringSource, a division of VMware