There is an amazing mechanism is spring: Spring Application Events, I see it helps to build loosely coupled application, implement observer pattern, reactor pattern.
My question is, what is the trigger in Spring application architecture when Spring Application Events is absolutely inevitable? Actually any application classes relationship can be build using events only as well as using class associations and hierarchy only (i'm talking about monolith service now).
May be it's more architectural question, but what is the threshold when it's need to consider events between objects inside a spring application?
Could it be definitely seen the cases when Spring Application Events absolutely needed?
Spring Security pushes events on certain event occurrences. See list of events
In some cases, it's much better to push message instead invoke a method in a classical way. Eg if you need to invoke the same function I multiple places in the code, just to notify another object.
It allows us to build a system which utilizes event-driven architecture. Read more
Helps in solving a producer-consumer problem
Send emails by pushing event object to ApplicationEventPublisher See Spring Higher-Order Components and #EnableEmailSending
Related
I'm trying to implement suppliers using Spring Cloud Function and Kafka. I need that one supplier should publish after every 10 secs and other should publish after every 30 secs. I could see from documentation, I can change delay using spring.cloud.stream.poller.fixed-delay property. Reference
But I need to set different delay for each topic. Is there any way to do it?
From the spring-cloud-function perspective there isn't any kind of polling as it is not the responsibility of the framework.
From the spring-cloud-stream perspective that uses spring-cloud-function indeed there is a mechanism that you have described. However, keep in mind that spring-cloud-stream is primarily designed to support concept of microservices (not your general messaging framework) and in microservices we embrace do one thing but do it well without affecting others approach. So having more then one supplier kind of goes against this model.
If you are building a general purpose messaging app, then i'd suggest to use Spring Integration framework which provides all the necessary hooks to accomplish what you need, but will require a bit more configuration details.
I have a use case where I would like build a common interface or service which can update entities of application. Example case is shown as below:
Now every application has to handle update functionality of entities. Rather than implementing update functionality in n application module. I would like to build a common interface or server in spring boot.
Service will be like below:
My question is how to design service/interface which can used for above scenario. Any api or tool which can help me to achieve this. I dont want to write code for update in every application module.
Thanks in advance.
Last year I was thinking about the similar concept to yours, but in Apache Camel framework context. I haven't got enough time and motivation to do so, but your post encouraged me to give it a try - perhaps mostly because I've found your concept very similar to mine.
This is how I see it:
So basically I considered an environment with application that might uses N modules/plugins that enriches application's features, i.e. processing feature etc. Application uses module/plugin when it is available in the classpath - considering Java background. When the module is not available application works without its functionality like it was never there. Moreover I wanted to implement it purely using framework capabilities - in this case Spring - without ugly hacks/ifs in the source code.
Three solutions come to my mind:
- using request/response interceptors and modifying(#ControllerAdvice)
- using Spring AOP to intercept method invocations in *Service proxy classes
- using Apache Camel framework to create a routes for processing entities
Here's the brief overview of POC that I implemented:
I've chosen Spring AOP because I've never been using it before on my own.
simple EmployeeService that simulates saving employee - EmployeeEntity
3 processors that simulates Processing Modules that could be located outside the application. These three modules change properties of EmployeeEntity in some way.
one Aspect that intercepts "save" method in EmployeeService and handles invocation of available processors
In the next steps I'd like to externalize these Processors so these are some kind of pluggable jar files.
I'm wondering if this is something that you wanted to achieve?
link to Spring AOP introduction here: https://docs.spring.io/spring/docs/5.0.5.RELEASE/spring-framework-reference/core.html#aop
link to repository of mentioned POC: https://github.com/bkpawlowski/spring-aop
I have a Spring MVC app that needs to send email notification each time and event occur. Those events are detected in three different classes so I need my email service to watch for them. How can I control if an event have occurred? I was thinking in use an observer pattern but I'm not sure if this is a good idea and I don't know how to know what event I'm processing.
I guess whether using an observer is a good idea depends on your application architecture and your design preferences. If you do choose to go with the event approach, Spring provides infrastructure to support that.
In order to implement the event approach with Spring you will need a publish, a listener and an event definition. You will achieve that with classes that implement ApplicationEventPublisherAware, ApplicationListener and ApplicationEvent
You can find a detailed explanation at http://techighost.com/event-handling-with-spring-framework/
I am currently studying Spring.
While reading a Spring book, I met a part regarding Event.
By using context.publishEvent(..), I could trigger the event.
But I don't know what It's exactly for.
I can use other Method instead of using complicated publishEvent.
Please, tell me. thank you.
Spring Events are used to implement publish-subscribe model (or observer pattern) where two not-related parts of code must be somehow connected.
Think of the analogy of web applications where servlet container creates http sessions and your code is informed about this using javax.servlet.http.HttpSessionListener.
Spring uses this mechanism internally. It's much more visible in Spring Security where several parts of the code are informed about e.g., successfull authentication.
Is there a way to decouple ManagedBeans from each other in a way that it is possible to send and receive custom events - probably over the (cool) FacesContext?! I do not want to inject Beans as ManagedProperty, to reduce direct dependencies. Unfortunately #ListenerFor and all that new stuff does only work for components and renderers and seems completely the wrong approach.
Those of you who are familiar with Adobe Flex' event mechanism know what I mean and what I expect from a standardized web UI framework.
Please let me know an elegant way that is included in the JSF specification without the need to implement another framework around.
Is there a way to decouple ManagedBeans from each other in a way that it is possible to send and receive custom events - probably over the (cool) FacesContext?!
Not without adding the event to a component, and you would have to add it before the Event phase of the JSF lifecycle.
I do not want to inject Beans as ManagedProperty, to reduce direct dependencies
Just because you are not injecting needed dependencies into your bean, doesn't mean that those dependencies wouldn't exist anyway if you are trying to go with an event driven model. At least by injecting the dependencies you explicitly declare what the managed bean depends on. This seems like a much more maintainable solution than what you are proposing.
Those of you who are familiar with Adobe Flex' event mechanism know what I mean and what I expect from a standardized web UI framework.
You expect a desktop based event driven model in a web application framework? This is apples to oranges. Adobe Flex is a Rich Internet Application that behaves like a desktop application while communicating with outside web services. JSF is a web application framework standard for web based components powered by javascript and ajax, with reusable server components and a server lifecycle which includes an event phase for components.
Please let me know an elegant way that is included in the JSF specification without the need to implement another framework around.
Your language implies that you do not find JSF elegant and that you are actively trying to make it something that it is not. Please do not do this, you will create a nightmare for yourself and anybody who has to maintain your application.
JSF requires a different way of thinking about web application development than what you are used to. If you find it this unpalatable then I suggest abandoning it for a web application framework that fits your comfortability level. You mentioned Flex, there is also Silverlight with .NET.