Using the REST Client

This guide is about the REST Client compatible with RESTEasy Classic which used to be the default JAX-RS implementation until Quarkus 2.8.

It is now recommended to use RESTEasy Reactive, which supports equally well traditional blocking workloads and reactive workloads. For more information about RESTEasy Reactive, please see the REST Client Reactive guide and, for the server side, the introductory REST JSON guide or the more detailed RESTEasy Reactive guide.

This guide explains how to use the RESTEasy REST Client in order to interact with REST APIs with very little effort.

there is another guide if you need to write server JSON REST APIs.

Prerequisites

To complete this guide, you need:

  • Roughly 15 minutes

  • An IDE

  • JDK 11+ installed with JAVA_HOME configured appropriately

  • Apache Maven 3.8.1+

  • Optionally the Quarkus CLI if you want to use it

  • Optionally Mandrel or GraalVM installed and configured appropriately if you want to build a native executable (or Docker if you use a native container build)

Solution

We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example.

Clone the Git repository: git clone https://github.com/quarkusio/quarkus-quickstarts.git, or download an archive.

The solution is located in the rest-client-quickstart directory.

Creating the Maven project

First, we need a new project. Create a new project with the following command:

CLI
quarkus create app org.acme:rest-client-quickstart \
    --extension=resteasy,resteasy-jackson,rest-client,rest-client-jackson \
    --no-code
cd rest-client-quickstart

To create a Gradle project, add the --gradle or --gradle-kotlin-dsl option.

For more information about how to install the Quarkus CLI and use it, please refer to the Quarkus CLI guide.

Maven
mvn io.quarkus.platform:quarkus-maven-plugin:2.9.1.Final:create \
    -DprojectGroupId=org.acme \
    -DprojectArtifactId=rest-client-quickstart \
    -Dextensions="resteasy,resteasy-jackson,rest-client,rest-client-jackson" \
    -DnoCode
cd rest-client-quickstart

To create a Gradle project, add the -DbuildTool=gradle or -DbuildTool=gradle-kotlin-dsl option.

This command generates the Maven project with a REST endpoint and imports:

  • the resteasy and resteasy-jackson extensions for the REST server support;

  • the rest-client and rest-client-jackson extensions for the REST client support.

If you already have your Quarkus project configured, you can add the rest-client and the rest-client-jackson extensions to your project by running the following command in your project base directory:

CLI
quarkus extension add 'rest-client,rest-client-jackson'
Maven
./mvnw quarkus:add-extension -Dextensions="rest-client,rest-client-jackson"
Gradle
./gradlew addExtension --extensions="rest-client,rest-client-jackson"

This will add the following to your pom.xml:

pom.xml
<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-rest-client</artifactId>
</dependency>
<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-rest-client-jackson</artifactId>
</dependency>
build.gradle
implementation("io.quarkus:quarkus-rest-client")
implementation("io.quarkus:quarkus-rest-client-jackson")

Setting up the model

In this guide we will be demonstrating how to consume part of the REST API supplied by the stage.code.quarkus.io service. Our first order of business is to set up the model we will be using, in the form of an Extension POJO.

Create a src/main/java/org/acme/rest/client/Extension.java file and set the following content:

package org.acme.rest.client;

import java.util.List;

public class Extension {

    public String id;
    public String name;
    public String shortName;
    public List<String> keywords;

}

The model above is only a subset of the fields provided by the service, but it suffices for the purposes of this guide.

Create the interface

Using the RESTEasy REST Client is as simple as creating an interface using the proper JAX-RS and MicroProfile annotations. In our case the interface should be created at src/main/java/org/acme/rest/client/ExtensionsService.java and have the following content:

package org.acme.rest.client;

import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;
import org.jboss.resteasy.annotations.jaxrs.QueryParam;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import java.util.Set;

@Path("/extensions")
@RegisterRestClient
public interface ExtensionsService {

    @GET
    Set<Extension> getById(@QueryParam String id);
}

The getById method gives our code the ability to get an extension by id from the Code Quarkus API. The client will handle all the networking and marshalling leaving our code clean of such technical details.

The purpose of the annotations in the code above is the following:

  • @RegisterRestClient allows Quarkus to know that this interface is meant to be available for CDI injection as a REST Client

  • @Path, @GET and @PathParam are the standard JAX-RS annotations used to define how to access the service

When a JSON extension is installed such as quarkus-rest-client-jackson or quarkus-rest-client-jsonb, Quarkus will use the application/json media type by default for most return values, unless the media type is explicitly set via @Produces or @Consumes annotations (there are some exceptions for well known types, such as String and File, which default to text/plain and application/octet-stream respectively).

If you don’t want JSON by default you can set quarkus.resteasy-json.default-json=false and the default will change back to being auto-negotiated. If you set this you will need to add @Produces(MediaType.APPLICATION_JSON) and @Consumes(MediaType.APPLICATION_JSON) to your endpoints in order to use JSON.

If you don’t rely on the JSON default, it is heavily recommended to annotate your endpoints with the @Produces and @Consumes annotations to define precisely the expected content-types. It will allow to narrow down the number of JAX-RS providers (which can be seen as converters) included in the native executable.

Path Parameters

If the GET request requires path parameters you can leverage the @PathParam("parameter-name") annotation instead of (or in addition to) the @QueryParam. Path and query parameters can be combined, as required, as illustrated in a mock example below.

package org.acme.rest.client;

import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;
import org.jboss.resteasy.annotations.jaxrs.PathParam;
import org.jboss.resteasy.annotations.jaxrs.QueryParam;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import java.util.Set;

@Path("/extensions")
@RegisterRestClient
public interface ExtensionsService {

    @GET
    @Path("/stream/{stream}")
    Set<Extension> getByStream(@PathParam String stream, @QueryParam("id") String id);
}

Create the configuration

In order to determine the base URL to which REST calls will be made, the REST Client uses configuration from application.properties. The name of the property needs to follow a certain convention which is best displayed in the following code:

# Your configuration properties
quarkus.rest-client."org.acme.rest.client.ExtensionsService".url=https://stage.code.quarkus.io/api # (1)
quarkus.rest-client."org.acme.rest.client.ExtensionsService".scope=javax.inject.Singleton # (2)
1 Having this configuration means that all requests performed using ExtensionsService will use https://stage.code.quarkus.io as the base URL. Using the configuration above, calling the getById method of ExtensionsService with a value of io.quarkus:quarkus-rest-client would result in an HTTP GET request being made to https://stage.code.quarkus.io/api/extensions?id=io.quarkus:quarkus-rest-client.
2 Having this configuration means that the default scope of ExtensionsService will be @Singleton. Supported scope values are @Singleton, @Dependent, @ApplicationScoped and @RequestScoped. The default scope is @Dependent. The default scope can also be defined on the interface.

Note that org.acme.rest.client.ExtensionsService must match the fully qualified name of the ExtensionsService interface we created in the previous section.

The standard MicroProfile Rest Client properties notation can also be used to configure the client:

org.acme.rest.client.ExtensionsService/mp-rest/url=https://stage.code.quarkus.io/api
org.acme.rest.client.ExtensionsService/mp-rest/scope=javax.inject.Singleton

If a property is specified via both the Quarkus notation and the MicroProfile notation, the Quarkus notation takes a precedence.

To facilitate the configuration, you can use the @RegisterRestClient configKey property that allows to use another configuration root than the fully qualified name of your interface.

@RegisterRestClient(configKey="extensions-api")
public interface ExtensionsService {
    [...]
}
# Your configuration properties
quarkus.rest-client.extensions-api.url=https://stage.code.quarkus.io/api
quarkus.rest-client.extensions-api.scope=javax.inject.Singleton

Disabling Hostname Verification

To disable the SSL hostname verification for a specific REST client, add the following property to your configuration:

quarkus.rest-client.extensions-api.hostname-verifier=io.quarkus.restclient.NoopHostnameVerifier

Disabling SSL verifications

To disable all SSL verifications, add the following property to your configuration:

quarkus.tls.trust-all=true

This setting should not be used in production as it will disable any kind of SSL verification.

Create the JAX-RS resource

Create the src/main/java/org/acme/rest/client/ExtensionsResource.java file with the following content:

package org.acme.rest.client;

import org.eclipse.microprofile.rest.client.inject.RestClient;
import org.jboss.resteasy.annotations.jaxrs.PathParam;

import javax.inject.Inject;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import java.util.Set;

@Path("/extension")
public class ExtensionsResource {

    @Inject
    @RestClient
    ExtensionsService extensionsService;

    @GET
    @Path("/id/{id}")
    public Set<Extension> id(@PathParam String id) {
        return extensionsService.getById(id);
    }
}

Note that in addition to the standard CDI @Inject annotation, we also need to use the MicroProfile @RestClient annotation to inject ExtensionsService.

Update the test

We also need to update the functional test to reflect the changes made to the endpoint. Edit the src/test/java/org/acme/rest/client/ExtensionsResourceTest.java file and change the content of the testExtensionIdEndpoint method to:

package org.acme.rest.client;

import static io.restassured.RestAssured.given;
import static org.hamcrest.CoreMatchers.hasItem;
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.Matchers.greaterThan;

import org.acme.rest.client.resources.WireMockExtensionsResource;
import org.junit.jupiter.api.Test;

import io.quarkus.test.common.QuarkusTestResource;
import io.quarkus.test.junit.QuarkusTest;

@QuarkusTest
@QuarkusTestResource(WireMockExtensionsResource.class)
public class ExtensionsResourceTest {

    @Test
    public void testExtensionsIdEndpoint() {
        given()
            .when().get("/extension/id/io.quarkus:quarkus-rest-client")
            .then()
            .statusCode(200)
            .body("$.size()", is(1),
                "[0].id", is("io.quarkus:quarkus-rest-client"),
                "[0].name", is("REST Client"),
                "[0].keywords.size()", greaterThan(1),
                "[0].keywords", hasItem("rest-client"));
    }
}

The code above uses REST Assured's json-path capabilities.

Async Support

The rest client supports asynchronous rest calls. Async support comes in 2 flavors: you can return a CompletionStage or a Uni (requires the quarkus-rest-client-mutiny extension). Let’s see it in action by adding a getByIdAsync method in our ExtensionsService REST interface. The code should look like:

package org.acme.rest.client;

import java.util.Set;
import java.util.concurrent.CompletionStage;

import javax.ws.rs.GET;
import javax.ws.rs.Path;

import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;
import org.jboss.resteasy.annotations.jaxrs.QueryParam;

@Path("/extensions")
@RegisterRestClient
public interface ExtensionsService {

    @GET
    Set<Extension> getById(@QueryParam String id);

    @GET
    CompletionStage<Set<Extension>> getByIdAsync(@QueryParam String id);

}

Open the src/main/java/org/acme/rest/client/ExtensionsResource.java file and update it with the following content:

package org.acme.rest.client;

import java.util.Set;
import java.util.concurrent.CompletionStage;

import javax.inject.Inject;
import javax.ws.rs.GET;
import javax.ws.rs.Path;

import org.eclipse.microprofile.rest.client.inject.RestClient;
import org.jboss.resteasy.annotations.jaxrs.PathParam;

@Path("/extension")
public class ExtensionsResource {

    @Inject
    @RestClient
    ExtensionsService extensionsService;

    @GET
    @Path("/id/{id}")
    public Set<Extension> id(@PathParam String id) {
        return extensionsService.getById(id);
    }

    @GET
    @Path("/id-async/{id}")
    public CompletionStage<Set<Extension>> idAsync(@PathParam String id) {
        return extensionsService.getByIdAsync(id);
    }

}

To test asynchronous methods, add the test method below in ExtensionsResourceTest:

@Test
public void testExtensionIdAsyncEndpoint() {
    given()
        .when().get("/extension/id-async/io.quarkus:quarkus-rest-client")
        .then()
        .statusCode(200)
        .body("$.size()", is(1),
            "[0].id", is("io.quarkus:quarkus-rest-client"),
            "[0].name", is("REST Client"),
            "[0].keywords.size()", greaterThan(1),
            "[0].keywords", hasItem("rest-client"));
}

The Uni version is very similar:

package org.acme.rest.client;

import java.util.Set;
import java.util.concurrent.CompletionStage;

import javax.ws.rs.GET;
import javax.ws.rs.Path;

import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;
import org.jboss.resteasy.annotations.jaxrs.QueryParam;

import io.smallrye.mutiny.Uni;

@Path("/extensions")
@RegisterRestClient
public interface ExtensionsService {

    // ...

    @GET
    Uni<Set<Extension>> getByIdAsUni(@QueryParam String id);
}

The ExtensionsResource becomes:

package org.acme.rest.client;

import java.util.Set;
import java.util.concurrent.CompletionStage;

import javax.inject.Inject;
import javax.ws.rs.GET;
import javax.ws.rs.Path;

import org.eclipse.microprofile.rest.client.inject.RestClient;
import org.jboss.resteasy.annotations.jaxrs.PathParam;

import io.smallrye.mutiny.Uni;

@Path("/extension")
public class ExtensionsResource {

    @Inject
    @RestClient
    ExtensionsService extensionsService;


    // ...

    @GET
    @Path("/id-uni/{id}")
    public Uni<Set<Extension>> idMutiny(@PathParam String id) {
        return extensionsService.getByIdAsUni(id);
    }
}
Mutiny

The previous snippet uses Mutiny reactive types. If you are not familiar with Mutiny, check Mutiny - an intuitive reactive programming library.

When returning a Uni, every subscription invokes the remote service. It means you can re-send the request by re-subscribing on the Uni, or use a retry as follows:

@Inject @RestClient ExtensionsService extensionsService;

// ...

extensionsService.getByIdAsUni(id)
    .onFailure().retry().atMost(10);

If you use a CompletionStage, you would need to call the service’s method to retry. This difference comes from the laziness aspect of Mutiny and its subscription protocol. More details about this can be found in the Mutiny documentation.

Custom headers support

The MicroProfile REST client allows amending request headers by registering a ClientHeadersFactory with the @RegisterClientHeaders annotation.

Let’s see it in action by adding a @RegisterClientHeaders annotation pointing to a RequestUUIDHeaderFactory class in our ExtensionsService REST interface:

package org.acme.rest.client;

import java.util.Set;
import java.util.concurrent.CompletionStage;

import javax.ws.rs.GET;
import javax.ws.rs.Path;

import org.eclipse.microprofile.rest.client.annotation.RegisterClientHeaders;
import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;
import org.jboss.resteasy.annotations.jaxrs.QueryParam;

import io.smallrye.mutiny.Uni;

@Path("/extensions")
@RegisterRestClient
@RegisterClientHeaders(RequestUUIDHeaderFactory.class)
public interface ExtensionsService {

    @GET
    Set<Extension> getById(@QueryParam String id);

    @GET
    CompletionStage<Set<Extension>> getByIdAsync(@QueryParam String id);

    @GET
    Uni<Set<Extension>> getByIdAsUni(@QueryParam String id);
}

And the RequestUUIDHeaderFactory would look like:

package org.acme.rest.client;

import org.eclipse.microprofile.rest.client.ext.ClientHeadersFactory;

import javax.enterprise.context.ApplicationScoped;
import javax.ws.rs.core.MultivaluedHashMap;
import javax.ws.rs.core.MultivaluedMap;
import java.util.UUID;

@ApplicationScoped
public class RequestUUIDHeaderFactory implements ClientHeadersFactory {

    @Override
    public MultivaluedMap<String, String> update(MultivaluedMap<String, String> incomingHeaders, MultivaluedMap<String, String> clientOutgoingHeaders) {
        MultivaluedMap<String, String> result = new MultivaluedHashMap<>();
        result.add("X-request-uuid", UUID.randomUUID().toString());
        return result;
    }
}

As you see in the example above, you can make your ClientHeadersFactory implementation a CDI bean by annotating it with a scope-defining annotation, such as @Singleton, @ApplicationScoped, etc.

Default header factory

You can also use @RegisterClientHeaders annotation without any custom factory specified. In that case the DefaultClientHeadersFactoryImpl factory will be used and all headers listed in org.eclipse.microprofile.rest.client.propagateHeaders configuration property will be amended. Individual header names are comma-separated.

@Path("/extensions")
@RegisterRestClient
@RegisterClientHeaders
public interface ExtensionsService {

    @GET
    Set<Extension> getById(@QueryParam String id);

    @GET
    CompletionStage<Set<Extension>> getByIdAsync(@QueryParam String id);

    @GET
    Uni<Set<Extension>> getByIdAsUni(@QueryParam String id);
}
org.eclipse.microprofile.rest.client.propagateHeaders=Authorization,Proxy-Authorization

Package and run the application

Run the application with:

CLI
quarkus dev
Maven
./mvnw quarkus:dev
Gradle
./gradlew --console=plain quarkusDev

You should see a JSON object containing some basic information about the REST Client extension.

As usual, the application can be packaged using:

CLI
quarkus build
Maven
./mvnw clean package
Gradle
./gradlew build

And executed with java -jar target/quarkus-app/quarkus-run.jar.

You can also generate the native executable with:

CLI
quarkus build --native
Maven
./mvnw package -Dnative
Gradle
./gradlew build -Dquarkus.package.type=native

REST Client and RESTEasy interactions

In Quarkus, the REST Client extension and the RESTEasy extension share the same infrastructure. One important consequence of this consideration is that they share the same list of providers (in the JAX-RS meaning of the word).

For instance, if you declare a WriterInterceptor, it will by default intercept both the servers calls and the client calls, which might not be the desired behavior.

However, you can change this default behavior and constrain a provider to:

  • only consider client calls by adding the @ConstrainedTo(RuntimeType.CLIENT) annotation to your provider;

  • only consider server calls by adding the @ConstrainedTo(RuntimeType.SERVER) annotation to your provider.

Using a Mock HTTP Server for tests

Setting up a mock HTTP server, against which tests are run, is a common testing pattern. Examples of such servers are Wiremock and Hoverfly. In this section we’ll demonstrate how Wiremock can be leveraged for testing the ExtensionsService which was developed above.

First of all, Wiremock needs to be added as a test dependency. For a Maven project that would happen like so:

pom.xml
<dependency>
    <groupId>com.github.tomakehurst</groupId>
    <artifactId>wiremock-jre8</artifactId>
    <scope>test</scope>
    <version>${wiremock.version}</version> (1)
</dependency>
1 Use a proper Wiremock version. All available versions can be found here.
build.gradle
testImplementation("com.github.tomakehurst:wiremock-jre8:$wiremockVersion") (1)
1 Use a proper Wiremock version. All available versions can be found here.

In Quarkus tests when some service needs to be started before the Quarkus tests are ran, we utilize the @io.quarkus.test.common.QuarkusTestResource annotation to specify a io.quarkus.test.common.QuarkusTestResourceLifecycleManager which can start the service and supply configuration values that Quarkus will use.

For more details about @QuarkusTestResource refer to this part of the documentation.

Let’s create an implementation of QuarkusTestResourceLifecycleManager called WiremockExtensions like so:

package org.acme.rest.client;

import java.util.Collections;
import java.util.Map;

import com.github.tomakehurst.wiremock.WireMockServer;
import io.quarkus.test.common.QuarkusTestResourceLifecycleManager;

import static com.github.tomakehurst.wiremock.client.WireMock.*; (1)

public class WireMockExtensions implements QuarkusTestResourceLifecycleManager {  (2)

    private WireMockServer wireMockServer;

    @Override
    public Map<String, String> start() {
        wireMockServer = new WireMockServer();
        wireMockServer.start(); (3)

        wireMockServer.stubFor(get(urlEqualTo("/extensions?id=io.quarkus:quarkus-rest-client"))   (4)
                .willReturn(aResponse()
                        .withHeader("Content-Type", "application/json")
                        .withBody(
                            "[{" +
                            "\"id\": \"io.quarkus:quarkus-rest-client\"," +
                            "\"name\": \"REST Client\"" +
                            "}]"
                        )));

        wireMockServer.stubFor(get(urlMatching(".*")).atPriority(10).willReturn(aResponse().proxiedFrom("https://stage.code.quarkus.io/api")));   (5)

        return Collections.singletonMap("quarkus.rest-client.\"org.acme.rest.client.ExtensionsService\".url", wireMockServer.baseUrl()); (6)
    }

    @Override
    public void stop() {
        if (null != wireMockServer) {
            wireMockServer.stop();  (7)
        }
    }
}
1 Statically importing the methods in the Wiremock package makes it easier to read the test.
2 The start method is invoked by Quarkus before any test is run and returns a Map of configuration properties that apply during the test execution.
3 Launch Wiremock.
4 Configure Wiremock to stub the calls to /extensions?id=io.quarkus:quarkus-rest-client by returning a specific canned response.
5 All HTTP calls that have not been stubbed are handled by calling the real service. This is done for demonstration purposes, as it is not something that would usually happen in a real test.
6 As the start method returns configuration that applies for tests, we set the rest-client property that controls the base URL which is used by the implementation of ExtensionsService to the base URL where Wiremock is listening for incoming requests.
7 When all tests have finished, shutdown Wiremock.

The ExtensionsResourceTest test class needs to be annotated like so:

@QuarkusTest
@QuarkusTestResource(WireMockExtensions.class)
public class ExtensionsResourceTest {

}

@QuarkusTestResource applies to all tests, not just ExtensionsResourceTest.