Thursday, 14 December 2017
Welcome to the second in a multi-part series of blog posts about creating Eclipse Vert.x applications with Infinispan. In the previous blog post we have seen how to create a REST API. The purpose of this tutorial is to showcase how to create a PUSH API implemented with Vert.x and using Infinispan as a server.
All the code of this tutorial is available in this GitHub repository. The backend is a Java project using Maven, so all the needed dependencies can be found in the pom.xml. The front is a super simple react application.
Creating a REST API is very straightforward. But today, even if we are heavily using REST, we don’t always want to use request/response or polling, but instead we want to push directly from the server to the client. In this example, we are going to create an API that pushes every new value inserted in the default cache of Infinispan. These values are cute names, as we did in the REST API example.
We are using two features here :
Infinispan client listeners
Vert.x bridge between the Event Bus and the browser
Infinispan Listeners provide a way to the client get notified when something happens in a cache.
Vert.x is a reactive framework, which means that uses RxJava too, and provides a fancy API on top of it.
First, we are going to create a new verticle called SendCuteNamesAPI. This verticle extends the CacheAccessVerticle we created in the previous blog post. CacheAccessVerticle initialises the connection with Infinispan using the Hot Rod protocol.
Now we need to create a SocketJSHandler. This handler has a method called bridge, where we configure some BridgeOptions. Obviously we don’t want the client to be able to read everything traveling on the event bus, and this won’t happen. We configure an address, 'cute-names', and we add the permission to read and write to this address.
This handler is passed to the event bus route, where the path is /eventbus/*.
Finally, we create a http server as we did in the REST API example. The difference is that instead of calling listen method, we call rxListen and subscribe.
Using Infinispan listeners is very easy.
First, we are going to create a class that has the @ClientListener annotation. The client listener has to be added to the cache client configuration. We add a protected method called addConfigToCache that will be called just after the initialisation of the defaultCache in the abstract CacheAccessVerticle. Verticles extending the abstract class can now add custom configuration to the client.
We want to be notified when a new entry is created. In this case, our listener has to contain a method with the @ClientCacheEntryCreated annotation on it. The signature of the method has to include a ClientCacheEntryCreatedEvent<String> parameter. This parameter will hold the 'key' of the entry that has been created.
Finally, we use the key to retrieve the name using the getAsync method and then publish the value in the Vert.x event bus to the address where the socket listener is permitted to read : cute-names.
Now we can run the main method and whenever we post a new name, we will see in the logs that the client listener is notified!
We are going to create a super simple react application that will just display hello. React community is huge, so there are lot’s of tutorials out there to create a hello world client application. This application has a single component that displays "Hello".
The react application runs calling npm install and npm start in http://localhost:9000/.
We have learned how to create PUSH APIs with Vert.x, powered by Infinispan. The repository has some unit tests. Feedback is more than welcome to improve the code and the provided examples. I hope you enjoyed this tutorial ! On the next tutorials we will talk about Infinispan as the cluster manager for Vert.x. Stay tuned !
Tags: reactive listeners vert.x push api react