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.
PUSH API
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
The Event Bus Bridge that connects to the browser, uses SockJS. SockJS is a JavaScript library that provides a WebSocket API, but it can be used with browsers that don't support web-sockets (see the website of the project for more detailed information). Vert.x supports this library and creates a bridge between your browser and your back-end easily through the Event Bus.
Creating an Event Bus bridge
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.
Getting notified and publishing
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!
Client code
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/.
Now we need to connect the client to the backend with SockJS. Vert.x provides a JavaScript library for that: vertx3-eventbus-client, built on top of SockJS. We create an EventBus object that will connect to http://localhost:8082/eventbus as we configured in the SendCuteNamesAPI. We register a handler on the 'cute-names' address. The body of the message will contain the new cute name published in the event bus. Every time the handler is called, we update the component's state, and it will be rendered.
