I want in an action of the state machine to write code that uses spring reactor. How can I return a result from the subscriber to the state machine?
Don't quite understand what you're asking but most likely every attempt to use reactive libs with state machine would be hacks and probably not provide good results.
Originally we wanted to have reactor integration with 2.0.x but we had to postpone this work to 2.1.x and initial 2.x is now going to be a simple boot2 upgrade.
Related
Spring boot 2.1.5
Project Reactor 3.2.9
I am setting up a bunch of rest reactive APIs using the above-mentioned frameworks and I am running into an annoying problem with MDC (mapped diagnostic context). My applications are in JAVA.
MDC relies on thread locals to store the current query's mapped context to put in the logs. That system, obviously, is not perfect and contradicts the reactive pattern since the different steps of your execution will be executed through different threads.
I have run into the same problem with the Play Reactive framework but found a workaround there by copying the mapped context transparently from one actor to another.
For spring and reactor, I could not find a satisfying solution yet.
Some random examples found on the internet:
First - It works but forces you to use a bunch of utility methods
Same thing
Second - It tries to copy the context during the onNext publisher event but seems to lose some features on the way of doing that. The signal context, for example, is lost.
I am in need of a proper solution to deal with this:
A library which would make the link between MDC and reactor?
A way to tweak reactor/spring to achieve it transparently?
Any advice?
"I could not find a satisfying solution yet."
Working with contexts is the only solution for the moment. Since as you said threadlocals goes against everything that has to do with reactive programming. Using thread local as a storage point during a request is a resource heavy way of solving things and in my opinion poor design. Unless logging frameworks themselves come up with a better solution to the problem we developers must pass the data through the context to accommodate for the logging frameworks blocking nature.
Reactive programming is a paradigm shift in the programming world. Other things like database drivers, that use threadlocal to rollback transactions are also in big trouble. the JDBC database driver spec is defined as blocking in nature, and atm. there has been attempts by spring and the R2DBC project to define a new JDBC driver spec that is inherently non/blocking. This means that all vendors must rewrite ther database driver implementations from scratch.
Reactive program is so new that lots of libraries need to rewrite entire codebases. The logging frameworks as we know it needs to be rewritten from the ground up which is a huge task. And the context in reactive is actually something that should not even be in reactive programming, it was implemented just to accommodate for MDC problems.
It's actually a lot of overhead needing to pass data from thread to thread.
So what can we do?
push on logging frameworks, and/or help logging frameworks to rewrite their codebase
Accept that there is no "tweak" that will magically fix this
use the context and the way suggested in the blogposts
Project reactor context
We are currently investigating spring state machine and we have a very similar need to the eventservice sample with a pool and context switching using a repository, the only problem is redis is linux only (for production) and we can not lean on that... is there a clean out-of-the-box way to integrate persistence using spring data or will i have to write my own implementation for StateMachinePersister.
https://github.com/spring-projects/spring-statemachine/tree/master/spring-statemachine-samples/eventservice/src/main/java/demo/eventservice
should i go about using AbstractStateMachinePersister or StateMachinePersist?
thanks!
There is no OOB spring data integration so you need to use low level API's to build your own persist impl. Having said that, spring data support has been in my mind but just haven't had time to push it forward. PR's highly appreciated ;)
StateMachinePersister is an interface to follow which AbstractStateMachinePersister implements.
I have too many emails. I should write scheduler in order to send messages to them. Messages are different. I use spring framework 4.x.
I can write simple class, which connects to SMTP server. But in this case I should write my thread library too in order to send emails parallel.
Do spring have already written library which give me more flexible way to do this tasks? I do not want to use threads. It will be nice if spring already have this functionality.
Do I need Spring integration for this?
Best regards,
Yes, you definitely can do that with Spring Integration, because there is an ExecutorChannel implementation with can be supplied with an TaskExecutor from the Spring Core:
<channel id="sendEmailChannel">
<dispatcher task-executor="threadPoolTaskExecutor"/>
</channel>
<int-mail:outbound-channel-adapter channel="sendEmailChannel" mail-sender="mailSender"/>
But anyway you should keep in mind that all Spring Integration components are based on the Java and that ExecutorService is used on the background.
From other side if you need only the mail sending stuff from the Spring Integration, it would be an overhead and can simply use Core Spring Framework legacy like JavaMailSender as a bean and #Async for the sendMail method to achieve your parallel requirement.
UPDATE
could you tell me whether I need JMS for this situation?
I don't see any JMS-related stuff here. You don't have (or at least don't show) any real integration points in your solution. The same I can say even about Spring Integration just for email sending. However with the Spring Boot your SI config will be enough short. From other side if you'll study Spring Integration better eventually you'll get more gain to rely on the Integration components for your systems, as internally, as well as externally with other systems through JMS, AMQP, Kafka etc.
To be honest: a lot of years ago my first acquaintance with Spring Integration was due the requirement to get files from the FTP and have ability to pick up new files automatically. I found the solution only in the Spring Integration 1.0.0.M1. After that short XML config for the <int-ftp:inbound-channel-adapter> I loved Spring Integration and since that time it became as a part of my life. :-)
So, it's up to you to go ahead with Spring Integration in your simple app, or just follow with more formal solution with JavaMailSender direct usage.
You should use java executors framework. For example you can write something like the code below:
ExecutorService executor = Executors.newWorkStealingPool();
executor.execute(() -> mailSender.send(mail));
I would like to set up an infrastructure for integration testing.
Currently we bootstrap tomcat using maven and then execute httpunit tests.
But the current solution has few drawbacks.
Any changes committed to the database need to be rollback manually in the end if the test
Running code coverage on integration test is not straight forward (we are using sonar).
My goals are:
Allow automatic rollback between tests (hopefully using String #transaction and #rollback)
Simple straight forward code coverage
Using #RunWith that will bootstrap the system from JUnit and not externally
Interacting with live servlets and javascript (I consider switching from httpuinit to selenium…)
Reasonable execution time (at least not longer than the existing execution time)
The goals above look reasonable to me and common to many Java/J2ee projects.
I was thinking to achieve those goals by using Arquillian and Arquillian Spring Framework Extension component.
See also https://github.com/arquillian/arquillian-showcase/
Does anyone have and experience with Arquillian and with Arquillian Spring Framework Extension?
Can you share issues best practices and lesson learned?
Can anyone suggest an alternative approach to the above?
I can't fully answer your question. only some tips
Regarding the automatic rollback. In my case. Using liquibase to init the test data on "hsqldb" or "h2" which could be set as in-memory pattern. Then no need to roll back.
For Arquillian. It's a good real testing approach. What i learned is that "Arauillian Spring Framework Extension" is just a extension. You have to bind to a specific container like "jboss, glasshfish,tomcat" to make the test run.
But i don't know how to apply for a spring-based javaSE program which do not need application server support.
My lesson learned is the jboss port conflict. since jboss-dist is set 8080 as default http port. But our company proxy is same as 8080. So i can't use maven to get the jboss-dist artifact.
Hope others can give more info.
Does anybody has an experience with Spring Integration project as embedded ESB?
I'm highly interesting in such use cases as:
Reading files from directory on schedule basis
Getting data from JDBC data source
Modularity and possibility to start/stop/redeploy module on the fly (e.g. one module can scan directory on schedule basis, another call query from jdbc data source etc.)
repeat/retry policy
UPDATE:
I found answers on all my questions except "Getting data from JDBC data source". Is it technically possible?
Remember, "ESB" is just a marketing term designed to sell more expensive software, it's not a magic bullet. You need to consider the specific jobs you need your software to do, and pick accordingly. If Spring Integration seems to fit the bill, I wouldn't be too concerned if it doesn't look much like an uber-expensive server installation.
The Spring Integration JDBC adapters are available in 2.0, and we just released GA last week. Here's the relevant section from the reference manual: http://static.springsource.org/spring-integration/docs/latest-ga/reference/htmlsingle/#jdbc
This link describes the FileSucker with Spring Integration. Read up on your Enterprise Integration patterns for more info I think.
I kinda think you need to do a bit more investigation your self, or do a couple of tries on some of your usecases. Then we can discuss whats good and bad
JDBC Adapters appear to be a work in progress.
Even if there is no specific adapter available, remember that Spring Integration is a thin wrapper around POJOs. You'll be able to access JDBC in any component e.g. your service activators.
See here for a solution based on a polling inbound channel adapter too.