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Using the REST Client

This guide explains how to use the REST Client Reactive in order to interact with REST APIs. REST Client Reactive is the REST Client implementation compatible with RESTEasy Reactive.

If your application uses a client and exposes REST endpoints, please use RESTEasy Reactive for the server part.

Prerequisites

To complete this guide, you need:

  • Roughly 15 minutes

  • An IDE

  • JDK 11+ installed with JAVA_HOME configured appropriately

  • Apache Maven 3.9.3

  • 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-reactive-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-reactive-quickstart \
    --extension='resteasy-reactive-jackson,rest-client-reactive-jackson' \
    --no-code
cd rest-client-reactive-quickstart

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

For more information about how to install and use the Quarkus CLI, see the Quarkus CLI guide.

Maven
mvn io.quarkus.platform:quarkus-maven-plugin:3.4.1:create \
    -DprojectGroupId=org.acme \
    -DprojectArtifactId=rest-client-reactive-quickstart \
    -Dextensions='resteasy-reactive-jackson,rest-client-reactive-jackson' \
    -DnoCode
cd rest-client-reactive-quickstart

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

For Windows users:

  • If using cmd, (don’t use backward slash \ and put everything on the same line)

  • If using Powershell, wrap -D parameters in double quotes e.g. "-DprojectArtifactId=rest-client-reactive-quickstart"

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

  • the resteasy-reactive-jackson extension for the REST server support. Use resteasy-reactive instead if you do not wish to use Jackson;

  • the rest-client-reactive-jackson extension for the REST client support. Use rest-client-reactive instead if you do not wish to use Jackson

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

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

This will add the following to your build file:

pom.xml
<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-rest-client-reactive-jackson</artifactId>
</dependency>
build.gradle
implementation("io.quarkus:quarkus-rest-client-reactive-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 a 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 REST Client Reactive is as simple as creating an interface using the proper Jakarta REST 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 jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.QueryParam;
import java.util.Set;

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

    @GET
    Set<Extension> getById(@QueryParam("id") 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 @QueryParam are the standard Jakarta REST annotations used to define how to access the service

When the quarkus-rest-client-reactive-jackson extension is installed, 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.

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 Jakarta REST providers (which can be seen as converters) included in the native executable.

The getById method above is a blocking call. It should not be invoked on the event loop. The Async Support section describes how to make non-blocking calls.

Query Parameters

The easiest way to specify a query parameter is to annotate a client method parameter with the @QueryParam or the @RestQuery. The @RestQuery is equivalent of the @QueryParam, but with optional name. Additionally, it can be also used to pass query parameters as a Map, which is convenient if parameters are not known in advance.

package org.acme.rest.client;

import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;
import org.jboss.resteasy.reactive.RestQuery;

import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.QueryParam;
import jakarta.ws.rs.core.MultivaluedMap;
import java.util.Map;
import java.util.Set;

@Path("/extensions")
@RegisterRestClient(configKey = "extensions-api")
public interface ExtensionsService {

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

    @GET
    Set<Extension> getByName(@RestQuery String name); (1)

    @GET
    Set<Extension> getByFilter(@RestQuery Map<String, String> filter); (2)

    @GET
    Set<Extension> getByFilters(@RestQuery MultivaluedMap<String, String> filters); (3)

}
1 Request query will include parameter with key name
2 Each Map entry represents exactly one query parameter
3 MultivaluedMap allows you to send array values

Using @ClientQueryParam

Another way to add query parameters to a request is to use @io.quarkus.rest.client.reactive.ClientQueryParam on either the REST client interface or a specific method of the interface. The annotation can specify the query parameter name while the value can either be a constant, a configuration property or it can be determined by invoking a method.

The following example shows the various possible usages:

@ClientQueryParam(name = "my-param", value = "${my.property-value}") (1)
public interface Client {
    @GET
    String getWithParam();

    @GET
    @ClientQueryParam(name = "some-other-param", value = "other") (2)
    String getWithOtherParam();

    @GET
    @ClientQueryParam(name = "param-from-method", value = "{with-param}") (3)
    String getFromMethod();

    default String withParam(String name) {
        if ("param-from-method".equals(name)) {
            return "test";
        }
        throw new IllegalArgumentException();
    }
}
1 By placing @ClientQueryParam on the interface, we ensure that my-param will be added to all requests of the client. Because we used the ${…​} syntax, the actual value of the parameter will be obtained using the my.property-value configuration property.
2 When getWithOtherParam is called, in addition to the my-param query parameter, some-other-param with the value of other will also be added.
3 when getFromMethod is called, in addition to the my-param query parameter, param-from-method with the value of test (because that’s what the withParam method returns when invoked with param-from-method) will also be added.

Note that if an interface method contains an argument annotated with @QueryParam, that argument will take priority over anything specified in any @ClientQueryParam annotation.

More information about this annotation can be found on the javadoc of @ClientQueryParam.

Form Parameters

Form parameters can be specified using @RestForm (or @FormParam) annotations:

package org.acme.rest.client;

import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;
import org.jboss.resteasy.reactive.RestForm;

import jakarta.ws.rs.PORT;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.Consumes;
import jakarta.ws.rs.FormParam;
import jakarta.ws.rs.core.MultivaluedMap;
import java.util.Map;
import java.util.Set;

@Path("/extensions")
@RegisterRestClient(configKey = "extensions-api")
public interface ExtensionsService {

    @POST
    @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
    Set<Extension> postId(@FormParam("id") Integer id);

    @POST
    @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
    Set<Extension> postName(@RestForm String name);

    @POST
    @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
    Set<Extension> postFilter(@RestForm Map<String, String> filter);

    @POST
    @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
    Set<Extension> postFilters(@RestForm MultivaluedMap<String, String> filters);

}

Using @ClientFormParam

Form parameters can also be specified using @ClientFormParam, similar to @ClientQueryParam:

@ClientFormParam(name = "my-param", value = "${my.property-value}")
public interface Client {
    @POST
    @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
    String postWithParam();

    @POST
    @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
    @ClientFormParam(name = "some-other-param", value = "other")
    String postWithOtherParam();

    @POST
    @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
    @ClientFormParam(name = "param-from-method", value = "{with-param}")
    String postFromMethod();

    default String withParam(String name) {
        if ("param-from-method".equals(name)) {
            return "test";
        }
        throw new IllegalArgumentException();
    }
}

More information about this annotation can be found on the javadoc of @ClientFormParam.

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 the example below.

package org.acme.rest.client;

import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;

import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.PathParam;
import jakarta.ws.rs.QueryParam;
import java.util.Set;

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

    @GET
    @Path("/stream/{stream}")
    Set<Extension> getByStream(@PathParam("stream") 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)
1 Having this configuration means that all requests performed using org.acme.rest.client.ExtensionsService will use https://stage.code.quarkus.io/api as the base URL. Using the configuration above, calling the getById method of ExtensionsService with a value of io.quarkus:quarkus-rest-client-reactive would result in an HTTP GET request being made to https://stage.code.quarkus.io/api/extensions?id=io.quarkus:quarkus-rest-client-reactive.

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

To facilitate the configuration, you can use the @RegisterRestClient configKey property that allows to use different 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=jakarta.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.verify-host=false

This setting should not be used in production as it will disable the SSL hostname verification.

HTTP/2 Support

HTTP/2 is disabled by default in REST Client. If you want to enable it, you can set:

// for all REST Clients:
quarkus.rest-client.http2=true
// or for a single REST Client:
quarkus.rest-client.extensions-api.http2=true

Alternatively, you can enable the Application-Layer Protocol Negotiation (alpn) TLS extension and the client will negotiate which HTTP version to use over the ones compatible by the server. By default, it will try to use HTTP/2 first and if it’s not enabled, it will use HTTP/1.1. If you want to enable it, you can set:

quarkus.rest-client.alpn=true
// or for a single REST Client:
quarkus.rest-client.extensions-api.alpn=true

Create the Jakarta REST 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 jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import java.util.Set;

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

    @RestClient (1)
    ExtensionsService extensionsService;


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

There are two interesting parts in this listing:

1 the client stub is injected with the @RestClient annotation instead of the usual CDI @Inject

Programmatic client creation with QuarkusRestClientBuilder

Instead of annotating the client with @RegisterRestClient, and injecting a client with @RestClient, you can also create REST Client programmatically. You do that with the QuarkusRestClientBuilder.

With this approach the client interface could look as follows:

package org.acme.rest.client;

import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.QueryParam;
import java.util.Set;

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

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

And the service as follows:

package org.acme.rest.client;

import io.quarkus.rest.client.reactive.QuarkusRestClientBuilder;

import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import java.net.URI;
import java.util.Set;

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

    private final ExtensionsService extensionsService;

    public ExtensionsResource() {
        extensionsService = QuarkusRestClientBuilder.newBuilder()
            .baseUri(URI.create("https://stage.code.quarkus.io/api"))
            .build(ExtensionsService.class);
    }

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

The QuarkusRestClientBuilder interface is a Quarkus-specific API to programmatically create clients with additional configuration options. Otherwise, you can also use the RestClientBuilder interface from the Microprofile API:

package org.acme.rest.client;

import org.eclipse.microprofile.rest.client.RestClientBuilder;

import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import java.net.URI;
import java.util.Set;

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

    private final ExtensionsService extensionsService;

    public ExtensionsResource() {
        extensionsService = RestClientBuilder.newBuilder()
            .baseUri(URI.create("https://stage.code.quarkus.io/api"))
            .build(ExtensionsService.class);
    }

    // ...
}

Use Custom HTTP Options

The REST Client Reactive internally uses the Vert.x HTTP Client to make the network connections. The REST Client Reactive extensions allows configuring some settings via properties, for example:

  • quarkus.rest-client.client-prefix.connect-timeout to configure the connect timeout in milliseconds.

  • quarkus.rest-client.client-prefix.max-redirects to limit the number of redirects.

However, there are many more options within the Vert.x HTTP Client to configure the connections. See all the options in the Vert.x HTTP Client Options API in this link.

To fully customize the Vert.x HTTP Client instance that the REST Client Reactive is internally using, you can provide your custom HTTP Client Options instance via CDI or when programmatically creating your client.

Let’s see an example about how to provide the HTTP Client Options via CDI:

package org.acme.rest.client;

import jakarta.enterprise.inject.Produces;
import jakarta.ws.rs.ext.ContextResolver;

import io.vertx.core.http.HttpClientOptions;
import io.quarkus.arc.Unremovable;

@Provider
public class CustomHttpClientOptions implements ContextResolver<HttpClientOptions> {

    @Override
    public HttpClientOptions getContext(Class<?> aClass) {
        HttpClientOptions options = new HttpClientOptions();
        // ...
        return options;
    }
}

Now, all the REST Clients will be using your custom HTTP Client Options.

Another approach is to provide the custom HTTP Client options when creating the client programmatically:

package org.acme.rest.client;

import io.quarkus.rest.client.reactive.QuarkusRestClientBuilder;

import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import java.net.URI;
import java.util.Set;

import io.vertx.core.http.HttpClientOptions;

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

    private final ExtensionsService extensionsService;

    public ExtensionsResource() {
        HttpClientOptions options = new HttpClientOptions();
        // ...

        extensionsService = QuarkusRestClientBuilder.newBuilder()
            .baseUri(URI.create("https://stage.code.quarkus.io/api"))
            .httpClientOptions(options) (1)
            .build(ExtensionsService.class);
    }

    // ...
}
1 the client will use the registered HTTP Client options over the HTTP Client options provided via CDI if any.

Redirection

A HTTP server can redirect a response to another location by sending a response with a status code that starts with "3" and a HTTP header "Location" holding the URL to be redirected to. When the REST Client receives a redirection response from a HTTP server, it won’t automatically perform another request to the new location. We can enable the automatic redirection in REST Client by adding the "follow-redirects" property:

  • quarkus.rest-client.follow-redirects to enable redirection for all REST clients.

  • quarkus.rest-client.<client-prefix>.follow-redirects to enable redirection for a specific REST client.

If this property is true, then REST Client will perform a new request that it receives a redirection response from the HTTP server.

Additionally, we can limit the number of redirections using the property "max-redirects".

One important note is that according to the RFC2616 specs, by default the redirection will only happen for GET or HEAD methods. However, in REST Client, you can provide your custom redirect handler to enable redirection on POST or PUT methods, or to follow a more complex logic, via either using the @ClientRedirectHandler annotation, CDI or programmatically when creating your client.

Let’s see an example about how to register your own custom redirect handler using the @ClientRedirectHandler annotation:

import jakarta.ws.rs.core.Response;

import io.quarkus.rest.client.reactive.ClientRedirectHandler;

@RegisterRestClient(configKey="extensions-api")
public interface ExtensionsService {
    @ClientRedirectHandler
    static URI alwaysRedirect(Response response) {
        if (Response.Status.Family.familyOf(response.getStatus()) == Response.Status.Family.REDIRECTION) {
            return response.getLocation();
        }

        return null;
    }
}

The "alwaysRedirect" redirect handler will only be used by the specified REST Client which in this example is the "ExtensionsService" client.

Alternatively, you can also provide a custom redirect handler for all your REST Clients via CDI:

import jakarta.ws.rs.core.Response;
import jakarta.ws.rs.ext.ContextResolver;
import jakarta.ws.rs.ext.Provider;

import org.jboss.resteasy.reactive.client.handlers.RedirectHandler;

@Provider
public class AlwaysRedirectHandler implements ContextResolver<RedirectHandler> {

    @Override
    public RedirectHandler getContext(Class<?> aClass) {
        return response -> {
            if (Response.Status.Family.familyOf(response.getStatus()) == Response.Status.Family.REDIRECTION) {
                return response.getLocation();
            }
            // no redirect
            return null;
        };
    }
}

Now, all the REST Clients will be using your custom redirect handler.

Another approach is to provide it programmatically when creating the client:

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

    private final ExtensionsService extensionsService;

    public ExtensionsResource() {
        extensionsService = QuarkusRestClientBuilder.newBuilder()
            .baseUri(URI.create("https://stage.code.quarkus.io/api"))
            .register(AlwaysRedirectHandler.class) (1)
            .build(ExtensionsService.class);
    }

    // ...
}
1 the client will use the registered redirect handler over the redirect handler provided via CDI if any.

Update the test

Next, we 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 test to:

package org.acme.rest.client;

import io.quarkus.test.junit.QuarkusTest;

import org.junit.jupiter.api.Test;

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

@QuarkusTest
public class ExtensionsResourceTest {

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

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

Async Support

To get the full power of the reactive nature of the client, you can use the non-blocking flavor of REST Client Reactive extension, which comes with support for CompletionStage and Uni. 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 org.eclipse.microprofile.rest.client.inject.RegisterRestClient;

import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.QueryParam;
import java.util.Set;
import java.util.concurrent.CompletionStage;

@Path("/extensions")
@RegisterRestClient(configKey = "extensions-api")
public interface ExtensionsService {

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

    @GET
    CompletionStage<Set<Extension>> getByIdAsync(@QueryParam("id") 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 org.eclipse.microprofile.rest.client.inject.RestClient;

import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import java.util.Set;
import java.util.concurrent.CompletionStage;

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

    @RestClient
    ExtensionsService extensionsService;


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

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

Please note that since the invocation is now non-blocking, the idAsync method will be invoked on the event loop, i.e. will not get offloaded to a worker pool thread and thus reducing hardware resource utilization. See Resteasy reactive execution model for more details.

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-reactive")
        .then()
        .statusCode(200)
        .body("$.size()", is(1),
            "[0].id", is("io.quarkus:quarkus-rest-client-reactive"),
            "[0].name", is("REST Client Reactive"),
            "[0].keywords.size()", greaterThan(1),
            "[0].keywords", hasItem("rest-client"));
}

The Uni version is very similar:

package org.acme.rest.client;

import io.smallrye.mutiny.Uni;
import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;

import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.QueryParam;
import java.util.Set;

@Path("/extensions")
@RegisterRestClient(configKey = "extensions-api")
public interface ExtensionsService {

    // ...

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

The ExtensionsResource becomes:

package org.acme.rest.client;

import io.smallrye.mutiny.Uni;
import org.eclipse.microprofile.rest.client.inject.RestClient;

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

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

    @RestClient
    ExtensionsService extensionsService;


    // ...

    @GET
    @Path("/id-uni/{id}")
    public Uni<Set<Extension>> idUni(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:

@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

There are a few ways in which you can specify custom headers for your REST calls:

  • by registering a ClientHeadersFactory or a ReactiveClientHeadersFactory with the @RegisterClientHeaders annotation

  • by programmatically registering a ClientHeadersFactory or a ReactiveClientHeadersFactory with the QuarkusRestClientBuilder.clientHeadersFactory(factory) method

  • by specifying the value of the header with @ClientHeaderParam

  • by specifying the value of the header by @HeaderParam

The code below demonstrates how to use each of these techniques:

package org.acme.rest.client;

import org.eclipse.microprofile.rest.client.annotation.ClientHeaderParam;
import org.eclipse.microprofile.rest.client.annotation.RegisterClientHeaders;
import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;

import jakarta.ws.rs.GET;
import jakarta.ws.rs.HeaderParam;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.QueryParam;
import java.util.Set;
import io.quarkus.rest.client.reactive.NotBody;

@Path("/extensions")
@RegisterRestClient
@RegisterClientHeaders(RequestUUIDHeaderFactory.class) (1)
@ClientHeaderParam(name = "my-header", value = "constant-header-value") (2)
@ClientHeaderParam(name = "computed-header", value = "{org.acme.rest.client.Util.computeHeader}") (3)
public interface ExtensionsService {

    @GET
    @ClientHeaderParam(name = "header-from-properties", value = "${header.value}") (4)
    @ClientHeaderParam(name = "header-from-method-param", value = "Bearer {token}") (5)
    Set<Extension> getById(@QueryParam("id") String id, @HeaderParam("jaxrs-style-header") String headerValue, @NotBody String token); (6)
}
1 There can be only one ClientHeadersFactory per class. With it, you can not only add custom headers, but you can also transform existing ones. See the RequestUUIDHeaderFactory class below for an example of the factory.
2 @ClientHeaderParam can be used on the client interface and on methods. It can specify a constant header value…​
3 …​ and a name of a method that should compute the value of the header. It can either be a static method or a default method in this interface. The method can take either no parameters, a single String parameter or a single io.quarkus.rest.client.reactive.ComputedParamContext parameter (which is very useful for code that needs to compute headers based on method parameters and naturally complements @io.quarkus.rest.client.reactive.NotBody).
4 …​ as well as a value from your application’s configuration
5 …​ or even any mixture of verbatim text, method parameters (referenced by name), a configuration value (as mentioned previously) and method invocations (as mentioned before)
6 …​ or as a normal Jakarta REST @HeaderParam annotated argument

When using Kotlin, if default methods are going to be leveraged, then the Kotlin compiler needs to be configured to use Java’s default interface capabilities. See this for more details.

A ClientHeadersFactory can look as follows:

package org.acme.rest.client;

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

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.ws.rs.core.MultivaluedHashMap;
import jakarta.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.

To specify a value for ${header.value}, simply put the following in your application.properties:

header.value=value of the header

Also, there is a reactive flavor of ClientHeadersFactory that allows doing blocking operations. For example:

package org.acme.rest.client;

import io.smallrye.mutiny.Uni;

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

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

@ApplicationScoped
public class GetTokenReactiveClientHeadersFactory extends ReactiveClientHeadersFactory {

    @Inject
    Service service;

    @Override
    public Uni<MultivaluedMap<String, String>> getHeaders(
            MultivaluedMap<String, String> incomingHeaders,
            MultivaluedMap<String, String> clientOutgoingHeaders) {
        return Uni.createFrom().item(() -> {
            MultivaluedHashMap<String, String> newHeaders = new MultivaluedHashMap<>();
            // perform blocking call
            newHeaders.add(HEADER_NAME, service.getToken());
            return newHeaders;
        });
    }
}

Default header factory

The @RegisterClientHeaders annotation can also be used without any custom factory specified. In that case the DefaultClientHeadersFactoryImpl factory will be used. If you make a REST client call from a REST resource, this factory will propagate all the headers listed in org.eclipse.microprofile.rest.client.propagateHeaders configuration property from the resource request to the client request. Individual header names are comma-separated.

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

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

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

Customizing the request

The REST Client Reactive supports further customization of the final request to be sent to the server via filters. The filters must implement either the interface ClientRequestFilter or ResteasyReactiveClientRequestFilter.

A simple example of customizing the request would be to add a custom header:

@Provider
public class TestClientRequestFilter implements ClientRequestFilter {

    @Override
    public void filter(ClientRequestContext requestContext) {
        requestContext.getHeaders().add("my_header", "value");
    }
}

Next, you can register your filter using the @RegisterProvider annotation:

@Path("/extensions")
@RegisterProvider(TestClientRequestFilter.class)
public interface ExtensionsService {

    // ...
}

Or programmatically using the .register() method:

QuarkusRestClientBuilder.newBuilder()
    .register(TestClientRequestFilter.class)
    .build(ExtensionsService.class)

Injecting the jakarta.ws.rs.ext.Providers instance in filters

The jakarta.ws.rs.ext.Providers is useful when we need to lookup the provider instances of the current client.

We can get the Providers instance in our filters from the request context as follows:

@Provider
public class TestClientRequestFilter implements ClientRequestFilter {

    @Override
    public void filter(ClientRequestContext requestContext) {
        Providers providers = ((ResteasyReactiveClientRequestContext) requestContext).getProviders();
        // ...
    }
}

Alternatively, you can implement the ResteasyReactiveClientRequestFilter interface instead of the ClientRequestFilter interface that will directly provide the ResteasyReactiveClientRequestContext context:

@Provider
public class TestClientRequestFilter implements ResteasyReactiveClientRequestFilter {

    @Override
    public void filter(ResteasyReactiveClientRequestFilter requestContext) {
        Providers providers = requestContext.getProviders();
        // ...
    }
}

Customizing the ObjectMapper in REST Client Reactive Jackson

The REST Client Reactive supports adding a custom ObjectMapper to be used only the Client using the annotation @ClientObjectMapper.

A simple example is to provide a custom ObjectMapper to the REST Client Reactive Jackson extension by doing:

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

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

    @ClientObjectMapper (1)
    static ObjectMapper objectMapper(ObjectMapper defaultObjectMapper) { (2)
        return defaultObjectMapper.copy() (3)
                .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
                .disable(DeserializationFeature.UNWRAP_ROOT_VALUE);
    }
}
1 The method must be annotated with @ClientObjectMapper.
2 It’s must be a static method. Also, the parameter defaultObjectMapper will be resolved via CDI. If not found, it will throw an exception at runtime.
3 In this example, we’re creating a copy of the default object mapper. You should NEVER modify the default object mapper, but create a copy instead.

Exception handling

The MicroProfile REST Client specification introduces the org.eclipse.microprofile.rest.client.ext.ResponseExceptionMapper whose purpose is to convert an HTTP response to an exception.

A simple example of implementing such a ResponseExceptionMapper for the ExtensionsService discussed above, could be:

public class MyResponseExceptionMapper implements ResponseExceptionMapper<RuntimeException> {

    @Override
    public RuntimeException toThrowable(Response response) {
        if (response.getStatus() == 500) {
            throw new RuntimeException("The remote service responded with HTTP 500");
        }
        return null;
    }
}

ResponseExceptionMapper also defines the getPriority method which is used in order to determine the priority with which ResponseExceptionMapper implementations will be called (implementations with a lower value for getPriority will be invoked first). If toThrowable returns an exception, then that exception will be thrown. If null is returned, the next implementation of ResponseExceptionMapper in the chain will be called (if there is any).

The class as written above, would not be automatically be used by any REST Client. To make it available to every REST Client of the application, the class needs to be annotated with @Provider (as long as quarkus.rest-client-reactive.provider-autodiscovery is not set to false). Alternatively, if the exception handling class should only apply to specific REST Client interfaces, you can either annotate the interfaces with @RegisterProvider(MyResponseExceptionMapper.class), or register it using configuration using the providers property of the proper quarkus.rest-client configuration group.

Using @ClientExceptionMapper

A simpler way to convert HTTP response codes of 400 or above is to use the @ClientExceptionMapper annotation.

For the ExtensionsService REST Client interface defined above, an example use of @ClientExceptionMapper would be:

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

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

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

    @ClientExceptionMapper
    static RuntimeException toException(Response response) {
        if (response.getStatus() == 500) {
            return new RuntimeException("The remote service responded with HTTP 500");
        }
        return null;
    }
}

Naturally this handling is per REST Client. @ClientExceptionMapper uses the default priority if the priority attribute is not set and the normal rules of invoking all handlers in turn apply.

Methods annotated with @ClientExceptionMapper can also take a java.lang.reflect.Method parameter which is useful if the exception mapping code needs to know the REST Client method that was invoked and caused the exception mapping code to engage.

Using @Blocking annotation in exception mappers

In cases that warrant using InputStream as the return type of REST Client method (such as when large amounts of data need to be read):

@Path("/echo")
@RegisterRestClient
public interface EchoClient {

    @GET
    InputStream get();
}

This will work as expected, but if you try to read this InputStream object in a custom exception mapper, you will receive a BlockingNotAllowedException exception. This is because ResponseExceptionMapper classes are run on the Event Loop thread executor by default - which does not allow to perform IO operations.

To make your exception mapper blocking, you can annotate the exception mapper with the @Blocking annotation:

@Provider
@Blocking (1)
public class MyResponseExceptionMapper implements ResponseExceptionMapper<RuntimeException> {

    @Override
    public RuntimeException toThrowable(Response response) {
        if (response.getStatus() == 500) {
            response.readEntity(String.class); (2)
            return new RuntimeException("The remote service responded with HTTP 500");
        }
        return null;
    }
}
1 With the @Blocking annotation, the MyResponseExceptionMapper exception mapper will be executed in the worker thread pool.
2 Reading the entity is now allowed because we’re executing the mapper on the worker thread pool.

Note that you can also use the @Blocking annotation when using @ClientExceptionMapper:

@Path("/echo")
@RegisterRestClient
public interface EchoClient {

    @GET
    InputStream get();

    @ClientExceptionMapper
    @Blocking
    static RuntimeException toException(Response response) {
        if (response.getStatus() == 500) {
            response.readEntity(String.class);
            return new RuntimeException("The remote service responded with HTTP 500");
        }
        return null;
    }
}

Multipart Form support

REST Client Reactive support multipart messages.

Sending Multipart messages

REST Client Reactive allows sending data as multipart forms. This way you can for example send files efficiently.

To send data as a multipart form, you can just use the regular @RestForm (or @FormParam) annotations:

    @POST
    @Path("/binary")
    String sendMultipart(@RestForm File file, @RestForm String otherField);

Parameters specified as File, Path, byte[] or Buffer are sent as files and default to the application/octet-stream MIME type. Other @RestForm parameter types default to the text/plain MIME type. You can override these defaults with the @PartType annotation.

Naturally, you can also group these parameters into a containing class:

    public static class Parameters {
        @RestForm
        File file;

        @RestForm
        String otherField;
    }

    @POST
    @Path("/binary")
    String sendMultipart(Parameters parameters);

Any @RestForm parameter of the type File, Path, byte[] or Buffer, as well as any annotated with @PartType automatically imply a @Consumes(MediaType.MULTIPART_FORM_DATA) on the method if there is no @Consumes present.

If there are @RestForm parameters that are not multipart-implying, then @Consumes(MediaType.APPLICATION_FORM_URLENCODED) is implied.

There are a few modes in which the form data can be encoded. By default, Rest Client Reactive uses RFC1738. You can override it by specifying the mode either on the client level, by setting io.quarkus.rest.client.multipart-post-encoder-mode RestBuilder property to the selected value of HttpPostRequestEncoder.EncoderMode or by specifying quarkus.rest-client.multipart-post-encoder-mode in your application.properties. Please note that the latter works only for clients created with the @RegisterRestClient annotation. All the available modes are described in the Netty documentation

You can also send JSON multiparts by specifying the @PartType annotation:

    public static class Person {
        public String firstName;
        public String lastName;
    }

    @POST
    @Path("/json")
    String sendMultipart(@RestForm @PartType(MediaType.APPLICATION_JSON) Person person);

Receiving Multipart Messages

REST Client Reactive also supports receiving multipart messages. As with sending, to parse a multipart response, you need to create a class that describes the response data, e.g.

public class FormDto {
    @RestForm (1)
    @PartType(MediaType.APPLICATION_OCTET_STREAM)
    public File file;

    @FormParam("otherField") (2)
    @PartType(MediaType.TEXT_PLAIN)
    public String textProperty;
}
1 uses the shorthand @RestForm annotation to make a field as a part of a multipart form
2 the standard @FormParam can also be used. It allows to override the name of the multipart part.

Then, create an interface method that corresponds to the call and make it return the FormDto:

    @GET
    @Produces(MediaType.MULTIPART_FORM_DATA)
    @Path("/get-file")
    FormDto data receiveMultipart();

At the moment, multipart response support is subject to the following limitations:

  • files sent in multipart responses can only be parsed to File, Path and FileDownload

  • each field of the response type has to be annotated with @PartType - fields without this annotation are ignored

REST Client Reactive needs to know the classes used as multipart return types upfront. If you have an interface method that produces multipart/form-data, the return type will be discovered automatically. However, if you intend to use the ClientBuilder API to parse a response as multipart, you need to annotate your DTO class with @MultipartForm.

The files you download are not automatically removed and can take up a lot of disk space. Consider removing the files when you are done working with them.

Multipart mixed / OData usage

It is not uncommon that an application has to interact with enterprise systems (like CRM systems) using a special protocol called OData. This protocol essentially uses a custom HTTP Content-Type which needs some glue code to work with the REST Client (creating the body is entirely up to the application - the REST Client can’t do much to help).

An example looks like the following:

@Path("/crm")
@RegisterRestClient
public interface CRMService {

    @POST
    @ClientHeaderParam(name = "Content-Type", value = "{calculateContentType}")  (1)
    String performBatch(@HeaderParam("Authorization") String accessToken, @NotBody String batchId, String body); (2)

    default String calculateContentType(ComputedParamContext context) {
        return "multipart/mixed;boundary=batch_" + context.methodParameters().get(1).value(); (3)
    }
}

The code uses the following pieces:

1 @ClientHeaderParam(name = "Content-Type", value = "{calculateContentType}") which ensures that the Content-Type header is created by calling the interface’s calculateContentType default method.
2 The aforementioned parameter needs to be annotated with @NotBody because it is only used to aid the construction of HTTP headers.
3 context.methodParameters().get(1).value() which allows the calculateContentType method to obtain the proper method parameter passed to the REST Client method.

As previously mentioned, the body parameter needs to be properly crafted by the application code to conform to the service’s requirements.

Receiving compressed messages

REST Client Reactive also supports receiving compressed messages using GZIP. You can enable the HTTP compression support by adding the property quarkus.http.enable-compression=true. When this feature is enabled and a server returns a response that includes the header Content-Encoding: gzip, REST Client Reactive will automatically decode the content and proceed with the message handling.

Proxy support

REST Client Reactive supports sending requests through a proxy. It honors the JVM settings for it but also allows to specify both:

  • global client proxy settings, with quarkus.rest-client.proxy-address, quarkus.rest-client.proxy-user, quarkus.rest-client.proxy-password, quarkus.rest-client.non-proxy-hosts

  • per-client proxy settings, with quarkus.rest-client.<my-client>.proxy-address, etc. These are applied only to clients injected with CDI, that is the ones created with @RegisterRestClient

If proxy-address is set on the client level, the client uses its specific proxy settings. No proxy settings are propagated from the global configuration or JVM properties.

If proxy-address is not set for the client but is set on the global level, the client uses the global settings. Otherwise, the client uses the JVM settings.

An example configuration for setting proxy:

# global proxy configuration is used for all clients
quarkus.rest-client.proxy-address=localhost:8182
quarkus.rest-client.proxy-user=<proxy user name>
quarkus.rest-client.proxy-password=<proxy password>
quarkus.rest-client.non-proxy-hosts=example.com

# per-client configuration overrides the global settings for a specific client
quarkus.rest-client.my-client.proxy-address=localhost:8183
quarkus.rest-client.my-client.proxy-user=<proxy user name>
quarkus.rest-client.my-client.proxy-password=<proxy password>
quarkus.rest-client.my-client.url=...
MicroProfile REST Client specification does not allow setting proxy credentials. In order to specify proxy user and proxy password programmatically, you need to cast your RestClientBuilder to RestClientBuilderImpl.

Package and run the application

Run the application with:

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

Open your browser to http://localhost:8080/extension/id/io.quarkus:quarkus-rest-client-reactive.

You should see a JSON object containing some basic information about this extension.

As usual, the application can be packaged using:

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

Logging traffic

REST Client Reactive can log the requests it sends and the responses it receives. To enable logging, add the quarkus.rest-client.logging.scope property to your application.properties and set it to:

  • request-response to log the request and response contents, or

  • all to also enable low level logging of the underlying libraries.

As HTTP messages can have large bodies, we limit the amount of body characters logged. The default limit is 100, you can change it by specifying quarkus.rest-client.logging.body-limit.

REST Client Reactive is logging the traffic with level DEBUG and does not alter logger properties. You may need to adjust your logger configuration to use this feature.

An example logging configuration:

quarkus.rest-client.logging.scope=request-response
quarkus.rest-client.logging.body-limit=50

quarkus.log.category."org.jboss.resteasy.reactive.client.logging".level=DEBUG
REST Client Reactive uses a default ClientLogger implementation. You can change it by providing a custom ClientLogger instance through CDI or when programmatically creating your client.

Mocking the client for tests

If you use a client injected with the @RestClient annotation, you can easily mock it for tests. You can do it with Mockito’s @InjectMock or with QuarkusMock.

This section shows how to replace your client with a mock. If you would like to get a more in-depth understanding of how mocking works in Quarkus, see the blog post on Mocking CDI beans.

Mocking does not work when using @QuarkusIntegrationTest.

Let’s assume you have the following client:

package io.quarkus.it.rest.client.main;

import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;

import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;


@Path("/")
@RegisterRestClient
public interface Client {
    @GET
    String get();
}

Mocking with InjectMock

The simplest approach to mock a client for tests is to use Mockito and @InjectMock.

First, add the following dependency to your application:

pom.xml
<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-junit5-mockito</artifactId>
    <scope>test</scope>
</dependency>
build.gradle
testImplementation("io.quarkus:quarkus-junit5-mockito")

Then, in your test you can simply use @InjectMock to create and inject a mock:

package io.quarkus.it.rest.client.main;

import static org.mockito.Mockito.when;

import org.eclipse.microprofile.rest.client.inject.RestClient;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

import io.quarkus.test.junit.QuarkusTest;
import io.quarkus.test.junit.mockito.InjectMock;

@QuarkusTest
public class InjectMockTest {

    @InjectMock
    @RestClient
    Client mock;

    @BeforeEach
    public void setUp() {
        when(mock.get()).thenReturn("MockAnswer");
    }

    @Test
    void doTest() {
        // ...
    }
}

Mocking with QuarkusMock

If Mockito doesn’t meet your needs, you can create a mock programmatically using QuarkusMock, e.g.:

package io.quarkus.it.rest.client.main;

import org.eclipse.microprofile.rest.client.inject.RestClient;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

import io.quarkus.test.junit.QuarkusMock;
import io.quarkus.test.junit.QuarkusTest;

@QuarkusTest
public class QuarkusMockTest {

    @BeforeEach
    public void setUp() {
        Client customMock = new Client() { (1)
            @Override
            public String get() {
                return "MockAnswer";
            }
        };
        QuarkusMock.installMockForType(customMock, Client.class, RestClient.LITERAL); (2)
    }
    @Test
    void doTest() {
        // ...
    }
}
1 here we use a manually created implementation of the client interface to replace the actual Client
2 note that RestClient.LITERAL has to be passed as the last argument of the installMockForType method

Using a Mock HTTP Server for tests

In some cases you may want to mock the remote endpoint - the HTTP server - instead of mocking the client itself. This may be especially useful for native tests, or for programmatically created clients.

You can easily mock an HTTP Server with Wiremock. The Wiremock section of the Quarkus - Using the REST Client describes how to set it up in detail.

Known limitations

While the REST Client Reactive extension aims to be a drop-in replacement for the REST Client extension, there are some differences and limitations:

  • the default scope of the client for the new extension is @ApplicationScoped while the quarkus-rest-client defaults to @Dependent To change this behavior, set the quarkus.rest-client-reactive.scope property to the fully qualified scope name.

  • it is not possible to set HostnameVerifier or SSLContext

  • a few things that don’t make sense for a non-blocking implementations, such as setting the ExecutorService, don’t work

Further reading

Quarkus is open. All dependencies of this project are available under the Apache Software License 2.0 or compatible license.

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