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83 lines
3.6 KiB
Plaintext
83 lines
3.6 KiB
Plaintext
= Dependency Injection
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:experimental:
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In the previous step you created a basic RESTful Java application with Quarkus. In this step we'll add a custom bean using dependency injection (DI). Quarkus DI solution is based on the http://docs.jboss.org/cdi/spec/2.0/cdi-spec.html[Contexts and Dependency Injection for Java 2.0 specification,window=_blank]. Because of the dynamic nature of some CDI APIs which conflict with native compilation, only a subset of the CDI features are implemented - see also the https://quarkus.io/guides/cdi-reference#supported_features[list,window=_blank] of supported features.
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== Add Custom Bean
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Let’s modify the application and add a companion bean. In CodeReady, right-click on the `org.acme.people.service` package in the project browser and select _New_ --> _Java Class_. Name the class `GreetingService`.
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image::newclass.png[newclass,600]
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image::classname.png[classname,400]
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Next, copy the below code into the class (remove the existing content before pasting in this code):
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[source,java,role="copypaste"]
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----
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package org.acme.people.service;
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import javax.enterprise.context.ApplicationScoped;
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@ApplicationScoped
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public class GreetingService {
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private String hostname = System.getenv().getOrDefault("HOSTNAME", "unknown");
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public String greeting(String name) {
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return "hello " + name + " from " + hostname;
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}
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}
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----
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This is an injectable bean that implements a `greeting()` method returning a string `hello <hostname>` (where `<hostname>` is the Linux hostname of the machine on which the code runs).
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Next, open the existing `GreetingResource.java` class file and add a new field and method above the existing `hello` method:
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[source,java,role="copypaste"]
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----
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@Inject
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GreetingService service;
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@GET
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@Produces(MediaType.TEXT_PLAIN)
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@Path("/greeting/{name}")
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public String greeting(@PathParam("name") String name) {
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return service.greeting(name);
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}
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----
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This will cause our new `GreetingResource` class to be instantiated and injected as the `service` field, and then the method `greeting` accesses this service to return the name.
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You will get red error squigglies when you paste this code due to missing import statements:
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image::importerror.png[error,800]
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Use the _Assistant_ > _Organize Imports_ menu option to fix this and import the right classes.
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image::assistant.png[assistant,800]
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You may need to choose from multiple matches, e.g. make sure you choose to import `javax.ws.rs.PathParam` when fixing the missing `PathParam` import. In general, look for `javax` or other well-known names to import. If you get it wrong you'll find out soon enough.
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image::importselect.png[select,800]
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[WARNING]
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====
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If you do not get red squigglies, or you can't make them disappear, try to close the file and re-open it, or reload your web browser. This is a known issue with Che on recent versions of Kubernetes.
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====
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== Inspect the results
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Check that it works as expected by loading the new endpoint using the same blue Preview URL and adding the `/hello/greeting/quarkus` to the end of the URL, just as you did before.
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Note we are exercising our new bean using the `/hello/greeting/quarkus` endpoint, and you should see `hello quarkus from <hostname>`.
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[NOTE]
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====
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In this case, the hostname is the hostname from the pod the app is running on within Kubernetes and will change later on.
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====
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== Congratulations!
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It's a familiar CDI-based environment for you Enterprise Java developers out there, with powerful mechanisms to reload your code _as you type_ (or very close to realtime). In the next step, we'll create some tests for our app, which should also be familiar to _all_ developers.
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