Learn QUARKUS with Real Code Examples

import javax.ws.rs.*
import javax.ws.rs.core.MediaType
import javax.enterprise.context.ApplicationScoped

@ApplicationScoped
@Path("/counter")
public class CounterResource {
    private int count = 0

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public int getCount() {
        return count
    }

    @POST
    @Path("/increment")
    @Produces(MediaType.APPLICATION_JSON)
    public int increment() {
        return ++count
    }

    @POST
    @Path("/decrement")
    @Produces(MediaType.APPLICATION_JSON)
    public int decrement() {
        return --count
    }

    @POST
    @Path("/reset")
    @Produces(MediaType.APPLICATION_JSON)
    public int reset() {
        count = 0
        return count
    }
}

Demonstrates a simple Quarkus REST API with a counter using JAX-RS annotations and in-memory state.

import javax.ws.rs.*
import javax.ws.rs.core.MediaType
import javax.enterprise.context.ApplicationScoped

@ApplicationScoped
@Path("/hello")
public class HelloResource {
    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public String hello() {
        return "Hello, Quarkus!"
    }
}

A minimal Quarkus REST API returning Hello World.

import javax.ws.rs.*
import javax.ws.rs.core.MediaType
import javax.enterprise.context.ApplicationScoped

@ApplicationScoped
@Path("/greet")
public class GreetResource {
    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public String greet(@QueryParam("name") String name) {
        return "Hello, " + (name != null ? name : "Guest")
    }
}

Demonstrates query parameters in Quarkus REST API.

import javax.ws.rs.*
import javax.ws.rs.core.MediaType
import javax.enterprise.context.ApplicationScoped
import java.util.Map

@ApplicationScoped
@Path("/json")
public class JsonResource {
    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public Map<String, String> json() {
        return Map.of("message", "Hello, Quarkus JSON")
    }
}

Return JSON response from Quarkus REST API.

import javax.ws.rs.*
import javax.ws.rs.core.MediaType
import javax.enterprise.context.ApplicationScoped

@ApplicationScoped
@Path("/form")
public class FormResource {
    @POST
    @Produces(MediaType.TEXT_PLAIN)
    @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
    public String handleForm(@FormParam("name") String name) {
        return "Hello, " + name
    }
}

Handle POST requests with form parameters.

import javax.ws.rs.*
import javax.ws.rs.core.MediaType
import javax.enterprise.context.ApplicationScoped

@ApplicationScoped
@Path("/user")
public class UserResource {
    @GET
    @Path("/{id}")
    @Produces(MediaType.TEXT_PLAIN)
    public String getUser(@PathParam("id") String id) {
        return "User ID: " + id
    }
}

Use path parameters in Quarkus REST API.

import javax.ws.rs.*
import javax.ws.rs.core.MediaType
import javax.enterprise.context.ApplicationScoped

@ApplicationScoped
@Path("/error")
public class ErrorResource {
    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public String error() {
        throw new WebApplicationException("This is an error", 400)
    }
}

Demonstrates basic exception handling in Quarkus.

import javax.ws.rs.*
import javax.ws.rs.core.Response
import javax.enterprise.context.ApplicationScoped

@ApplicationScoped
@Path("/redirect")
public class RedirectResource {
    @GET
    public Response redirect() {
        return Response.seeOther(URI.create("/counter")).build()
    }
}

Redirect request to another endpoint.

import javax.ws.rs.*
import javax.ws.rs.core.MediaType
import javax.enterprise.context.ApplicationScoped

@ApplicationScoped
@Path("")
public class MultiResource {
    @GET
    @Path("/")
    @Produces(MediaType.TEXT_PLAIN)
    public String home() {
        return "Home"
    }

    @GET
    @Path("/about")
    @Produces(MediaType.TEXT_PLAIN)
    public String about() {
        return "About"
    }
}

Handle multiple routes in one Quarkus application.

import javax.ws.rs.*
import javax.ws.rs.core.MediaType
import javax.enterprise.context.ApplicationScoped
import javax.inject.Inject

@ApplicationScoped
@Path("/bean")
public class BeanResource {
    @Inject
    CounterService service

    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public String getCount() {
        return "Count: " + service.getCount()
    }
}

@ApplicationScoped
class CounterService {
    private int count = 0
    public int getCount() { return count }
    public int increment() { return ++count }
}

Use CDI to inject a bean into a Quarkus REST API.