Reusing Helidon SE services

This guide shows how reuse Helidon SE Service in your Helidon MP application.

What You Need

For this 10 minute tutorial, you will need the following:

Prerequisite product versions for Helidon 4.4.1
Java SE 21 (Open JDK 21)Helidon requires Java 21+ (25+ recommended).
Maven 3.8+Helidon requires Maven 3.8+.
Docker 18.09+If you want to build and run Docker containers.
Kubectl 1.16.5+If you want to deploy to Kubernetes, you need kubectl and a Kubernetes cluster (you can install one on your desktop).
Verify Prerequisites
java -version
mvn --version
docker --version
kubectl version
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Setting JAVA_HOME
# On Mac
export JAVA_HOME=`/usr/libexec/java_home -v 21`

# On Linux
# Use the appropriate path to your JDK
export JAVA_HOME=/usr/lib/jvm/jdk-21
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Helidon MP supports WebServer routing which brings possibility for reusing io.helidon.webserver.HttpService implementations in Helidon MP. Such feature can be quite useful for common solutions for filtering, auditing, logging or augmenting REST endpoints in hybrid Helidon SE/MP environment.

Let’s define simple Helidon SE Service for adding special header to every REST response:

public class CoolingService implements HttpService, Handler {

    public static final HeaderName COOL_HEADER_NAME = HeaderNames.create("Cool-Header");
    public static final String COOLING_VALUE = "This is way cooler response than ";

    @Override
    public void routing(HttpRules rules) {
        rules.any(this);
    }

    @Override
    public void handle(ServerRequest req, ServerResponse res) {
        res.headers().add(COOL_HEADER_NAME, COOLING_VALUE);
        res.next();
    }
}
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It’s easy to use it with Helidon SE:

WebServer.builder()
        .routing(it -> it
                .register("/cool", new CoolingService())) 
        .config(config)
        .mediaContext(it -> it
                .addMediaSupport(JsonpSupport.create()))
        .build()
        .start();
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  • register service with routing path

And not much harder to use it with Helidon MP:

@ApplicationScoped
public class MyBean {

    @Produces
    @ApplicationScoped
    @RoutingPath("/cool")
    public HttpService coolService() {
        return new CoolingService();
    }

}
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You can leverage annotations: