Starting with version 6.1, the ContextHolderRequestHandlerAdvice has been introduced.
This advice takes some value from the request message as and stores it in the context holder.
The value is clear from the context when an execution is finished on the target MessageHandler.
The best way to think about this advice is similar to the programming flow where we store some value into a ThreadLocal, get access to it from the target call and then clean up the ThreadLocal after execution.
The ContextHolderRequestHandlerAdvice requires these constructor arguments: a Function<Message<?>, Object> as a value provider, Consumer<Object> as a context set callback and Runnable as a context clean up hook.
Following is a sample how a ContextHolderRequestHandlerAdvice can be used in combination with a o.s.i.file.remote.session.DelegatingSessionFactory:
@Bean
DelegatingSessionFactory<?> dsf(SessionFactory<?> one, SessionFactory<?> two) {
return new DelegatingSessionFactory<>(Map.of("one", one, "two", two), null);
}
@Bean
ContextHolderRequestHandlerAdvice contextHolderRequestHandlerAdvice(DelegatingSessionFactory<String> dsf) {
return new ContextHolderRequestHandlerAdvice(message -> message.getHeaders().get("FACTORY_KEY"),
dsf::setThreadKey, dsf::clearThreadKey);
}
@ServiceActivator(inputChannel = "in", adviceChain = "contextHolderRequestHandlerAdvice")
FtpOutboundGateway ftpOutboundGateway(DelegatingSessionFactory<?> sessionFactory) {
return new FtpOutboundGateway(sessionFactory, "ls", "payload");
}And it is just enough to send a message to the in channel with a FACTORY_KEY header set to either one or two.
The ContextHolderRequestHandlerAdvice sets the value from that header into a DelegatingSessionFactory via its setThreadKey.
Then when FtpOutboundGateway executes an ls command a proper delegating SessionFactory is chosen from the DelegatingSessionFactory according to the value in its ThreadLocal.
When the result is produced from the FtpOutboundGateway, a ThreadLocal value in the DelegatingSessionFactory is cleared according to the clearThreadKey() call from the ContextHolderRequestHandlerAdvice.
See Delegating Session Factory for more information.