3.0.3-SNAPSHOT

This project provides OpenFeign integrations for Spring Boot apps through autoconfiguration and binding to the Spring Environment and other Spring programming model idioms.

1. Declarative REST Client: Feign

Feign is a declarative web service client. It makes writing web service clients easier. To use Feign create an interface and annotate it. It has pluggable annotation support including Feign annotations and JAX-RS annotations. Feign also supports pluggable encoders and decoders. Spring Cloud adds support for Spring MVC annotations and for using the same HttpMessageConverters used by default in Spring Web. Spring Cloud integrates Eureka, Spring Cloud CircuitBreaker, as well as Spring Cloud LoadBalancer to provide a load-balanced http client when using Feign.

1.1. How to Include Feign

To include Feign in your project use the starter with group org.springframework.cloud and artifact id spring-cloud-starter-openfeign. See the Spring Cloud Project page for details on setting up your build system with the current Spring Cloud Release Train.

Example spring boot app

@SpringBootApplication
@EnableFeignClients
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}
StoreClient.java
@FeignClient("stores")
public interface StoreClient {
    @RequestMapping(method = RequestMethod.GET, value = "/stores")
    List<Store> getStores();

    @RequestMapping(method = RequestMethod.GET, value = "/stores")
    Page<Store> getStores(Pageable pageable);

    @RequestMapping(method = RequestMethod.POST, value = "/stores/{storeId}", consumes = "application/json")
    Store update(@PathVariable("storeId") Long storeId, Store store);
}

In the @FeignClient annotation the String value ("stores" above) is an arbitrary client name, which is used to create a Spring Cloud LoadBalancer client. You can also specify a URL using the url attribute (absolute value or just a hostname). The name of the bean in the application context is the fully qualified name of the interface. To specify your own alias value you can use the qualifiers value of the @FeignClient annotation.

The load-balancer client above will want to discover the physical addresses for the "stores" service. If your application is a Eureka client then it will resolve the service in the Eureka service registry. If you don’t want to use Eureka, you can configure a list of servers in your external configuration using SimpleDiscoveryClient.

Spring Cloud OpenFeign supports all the features available for the blocking mode of Spring Cloud LoadBalancer. You can read more about them in the project documentation.

1.2. Overriding Feign Defaults

A central concept in Spring Cloud’s Feign support is that of the named client. Each feign client is part of an ensemble of components that work together to contact a remote server on demand, and the ensemble has a name that you give it as an application developer using the @FeignClient annotation. Spring Cloud creates a new ensemble as an ApplicationContext on demand for each named client using FeignClientsConfiguration. This contains (amongst other things) an feign.Decoder, a feign.Encoder, and a feign.Contract. It is possible to override the name of that ensemble by using the contextId attribute of the @FeignClient annotation.

Spring Cloud lets you take full control of the feign client by declaring additional configuration (on top of the FeignClientsConfiguration) using @FeignClient. Example:

@FeignClient(name = "stores", configuration = FooConfiguration.class)
public interface StoreClient {
    //..
}

In this case the client is composed from the components already in FeignClientsConfiguration together with any in FooConfiguration (where the latter will override the former).

FooConfiguration does not need to be annotated with @Configuration. However, if it is, then take care to exclude it from any @ComponentScan that would otherwise include this configuration as it will become the default source for feign.Decoder, feign.Encoder, feign.Contract, etc., when specified. This can be avoided by putting it in a separate, non-overlapping package from any @ComponentScan or @SpringBootApplication, or it can be explicitly excluded in @ComponentScan.
Using contextId attribute of the @FeignClient annotation in addition to changing the name of the ApplicationContext ensemble, it will override the alias of the client name and it will be used as part of the name of the configuration bean created for that client.
Previously, using the url attribute, did not require the name attribute. Using name is now required.

Placeholders are supported in the name and url attributes.

@FeignClient(name = "${feign.name}", url = "${feign.url}")
public interface StoreClient {
    //..
}

Spring Cloud OpenFeign provides the following beans by default for feign (BeanType beanName: ClassName):

  • Decoder feignDecoder: ResponseEntityDecoder (which wraps a SpringDecoder)

  • Encoder feignEncoder: SpringEncoder

  • Logger feignLogger: Slf4jLogger

  • MicrometerCapability micrometerCapability: If feign-micrometer is on the classpath and MeterRegistry is available

  • Contract feignContract: SpringMvcContract

  • Feign.Builder feignBuilder: FeignCircuitBreaker.Builder

  • Client feignClient: If Spring Cloud LoadBalancer is on the classpath, FeignBlockingLoadBalancerClient is used. If none of them is on the classpath, the default feign client is used.

spring-cloud-starter-openfeign supports spring-cloud-starter-loadbalancer. However, as is an optional dependency, you need to make sure it been added to your project if you want to use it.

The OkHttpClient and ApacheHttpClient and ApacheHC5 feign clients can be used by setting feign.okhttp.enabled or feign.httpclient.enabled or feign.httpclient.hc5.enabled to true, respectively, and having them on the classpath. You can customize the HTTP client used by providing a bean of either org.apache.http.impl.client.CloseableHttpClient when using Apache or okhttp3.OkHttpClient when using OK HTTP or org.apache.hc.client5.http.impl.classic.CloseableHttpClient when using Apache HC5.

Spring Cloud OpenFeign does not provide the following beans by default for feign, but still looks up beans of these types from the application context to create the feign client:

  • Logger.Level

  • Retryer

  • ErrorDecoder

  • Request.Options

  • Collection<RequestInterceptor>

  • SetterFactory

  • QueryMapEncoder

  • Capability (MicrometerCapability is provided by default)

A bean of Retryer.NEVER_RETRY with the type Retryer is created by default, which will disable retrying. Notice this retrying behavior is different from the Feign default one, where it will automatically retry IOExceptions, treating them as transient network related exceptions, and any RetryableException thrown from an ErrorDecoder.

Creating a bean of one of those type and placing it in a @FeignClient configuration (such as FooConfiguration above) allows you to override each one of the beans described. Example:

@Configuration
public class FooConfiguration {
    @Bean
    public Contract feignContract() {
        return new feign.Contract.Default();
    }

    @Bean
    public BasicAuthRequestInterceptor basicAuthRequestInterceptor() {
        return new BasicAuthRequestInterceptor("user", "password");
    }
}

This replaces the SpringMvcContract with feign.Contract.Default and adds a RequestInterceptor to the collection of RequestInterceptor.

@FeignClient also can be configured using configuration properties.

application.yml

feign:
    client:
        config:
            feignName:
                connectTimeout: 5000
                readTimeout: 5000
                loggerLevel: full
                errorDecoder: com.example.SimpleErrorDecoder
                retryer: com.example.SimpleRetryer
                defaultQueryParameters:
                    query: queryValue
                defaultRequestHeaders:
                    header: headerValue
                requestInterceptors:
                    - com.example.FooRequestInterceptor
                    - com.example.BarRequestInterceptor
                decode404: false
                encoder: com.example.SimpleEncoder
                decoder: com.example.SimpleDecoder
                contract: com.example.SimpleContract
                capabilities:
                    - com.example.FooCapability
                    - com.example.BarCapability
                metrics.enabled: false

Default configurations can be specified in the @EnableFeignClients attribute defaultConfiguration in a similar manner as described above. The difference is that this configuration will apply to all feign clients.

If you prefer using configuration properties to configured all @FeignClient, you can create configuration properties with default feign name.

You can use feign.client.config.feignName.defaultQueryParameters and feign.client.config.feignName.defaultRequestHeaders to specify query parameters and headers that will be sent with every request of the client named feignName.

application.yml

feign:
    client:
        config:
            default:
                connectTimeout: 5000
                readTimeout: 5000
                loggerLevel: basic

If we create both @Configuration bean and configuration properties, configuration properties will win. It will override @Configuration values. But if you want to change the priority to @Configuration, you can change feign.client.default-to-properties to false.

If we want to create multiple feign clients with the same name or url so that they would point to the same server but each with a different custom configuration then we have to use contextId attribute of the @FeignClient in order to avoid name collision of these configuration beans.

@FeignClient(contextId = "fooClient", name = "stores", configuration = FooConfiguration.class)
public interface FooClient {
    //..
}
@FeignClient(contextId = "barClient", name = "stores", configuration = BarConfiguration.class)
public interface BarClient {
    //..
}

It is also possible to configure FeignClient not to inherit beans from the parent context. You can do this by overriding the inheritParentConfiguration() in a FeignClientConfigurer bean to return false:

@Configuration
public class CustomConfiguration{

@Bean
public FeignClientConfigurer feignClientConfigurer() {
            return new FeignClientConfigurer() {

                @Override
                public boolean inheritParentConfiguration() {
                    return false;
                }
            };

        }
}
By default, Feign clients do not encode slash / characters. You can change this behaviour, by setting the value of feign.client.decodeSlash to false.

1.2.1. SpringEncoder configuration

In the SpringEncoder that we provide, we set null charset for binary content types and UTF-8 for all the other ones.

You can modify this behaviour to derive the charset from the Content-Type header charset instead by setting the value of feign.encoder.charset-from-content-type to true.

1.3. Timeout Handling

We can configure timeouts on both the default and the named client. OpenFeign works with two timeout parameters:

  • connectTimeout prevents blocking the caller due to the long server processing time.

  • readTimeout is applied from the time of connection establishment and is triggered when returning the response takes too long.

In case the server is not running or available a packet results in connection refused. The communication ends either with an error message or in a fallback. This can happen before the connectTimeout if it is set very low. The time taken to perform a lookup and to receive such a packet causes a significant part of this delay. It is subject to change based on the remote host that involves a DNS lookup.

1.4. Creating Feign Clients Manually

In some cases it might be necessary to customize your Feign Clients in a way that is not possible using the methods above. In this case you can create Clients using the Feign Builder API. Below is an example which creates two Feign Clients with the same interface but configures each one with a separate request interceptor.

@Import(FeignClientsConfiguration.class)
class FooController {

    private FooClient fooClient;

    private FooClient adminClient;

    @Autowired
    public FooController(Client client, Encoder encoder, Decoder decoder, Contract contract, MicrometerCapability micrometerCapability) {
        this.fooClient = Feign.builder().client(client)
                .encoder(encoder)
                .decoder(decoder)
                .contract(contract)
                .addCapability(micrometerCapability)
                .requestInterceptor(new BasicAuthRequestInterceptor("user", "user"))
                .target(FooClient.class, "https://PROD-SVC");

        this.adminClient = Feign.builder().client(client)
                .encoder(encoder)
                .decoder(decoder)
                .contract(contract)
                .addCapability(micrometerCapability)
                .requestInterceptor(new BasicAuthRequestInterceptor("admin", "admin"))
                .target(FooClient.class, "https://PROD-SVC");
    }
}
In the above example FeignClientsConfiguration.class is the default configuration provided by Spring Cloud OpenFeign.
PROD-SVC is the name of the service the Clients will be making requests to.
The Feign Contract object defines what annotations and values are valid on interfaces. The autowired Contract bean provides supports for SpringMVC annotations, instead of the default Feign native annotations.

You can also use the Builder`to configure FeignClient not to inherit beans from the parent context. You can do this by overriding calling `inheritParentContext(false) on the Builder.

1.5. Feign Spring Cloud CircuitBreaker Support

If Spring Cloud CircuitBreaker is on the classpath and feign.circuitbreaker.enabled=true, Feign will wrap all methods with a circuit breaker.

To disable Spring Cloud CircuitBreaker support on a per-client basis create a vanilla Feign.Builder with the "prototype" scope, e.g.:

@Configuration
public class FooConfiguration {
    @Bean
    @Scope("prototype")
    public Feign.Builder feignBuilder() {
        return Feign.builder();
    }
}

The circuit breaker name follows this pattern <feignClientName>#<calledMethod>. When calling a @FeignClient with name foo and the called interface method is bar then the circuit breaker name will be foo_bar.

1.6. Feign Spring Cloud CircuitBreaker Fallbacks

Spring Cloud CircuitBreaker supports the notion of a fallback: a default code path that is executed when they circuit is open or there is an error. To enable fallbacks for a given @FeignClient set the fallback attribute to the class name that implements the fallback. You also need to declare your implementation as a Spring bean.

@FeignClient(name = "test", url = "http://localhost:${server.port}/", fallback = Fallback.class)
    protected interface TestClient {

        @RequestMapping(method = RequestMethod.GET, value = "/hello")
        Hello getHello();

        @RequestMapping(method = RequestMethod.GET, value = "/hellonotfound")
        String getException();

    }

    @Component
    static class Fallback implements TestClient {

        @Override
        public Hello getHello() {
            throw new NoFallbackAvailableException("Boom!", new RuntimeException());
        }

        @Override
        public String getException() {
            return "Fixed response";
        }

    }

If one needs access to the cause that made the fallback trigger, one can use the fallbackFactory attribute inside @FeignClient.

@FeignClient(name = "testClientWithFactory", url = "http://localhost:${server.port}/",
            fallbackFactory = TestFallbackFactory.class)
    protected interface TestClientWithFactory {

        @RequestMapping(method = RequestMethod.GET, value = "/hello")
        Hello getHello();

        @RequestMapping(method = RequestMethod.GET, value = "/hellonotfound")
        String getException();

    }

    @Component
    static class TestFallbackFactory implements FallbackFactory<FallbackWithFactory> {

        @Override
        public FallbackWithFactory create(Throwable cause) {
            return new FallbackWithFactory();
        }

    }

    static class FallbackWithFactory implements TestClientWithFactory {

        @Override
        public Hello getHello() {
            throw new NoFallbackAvailableException("Boom!", new RuntimeException());
        }

        @Override
        public String getException() {
            return "Fixed response";
        }

    }

1.7. Feign and @Primary

When using Feign with Spring Cloud CircuitBreaker fallbacks, there are multiple beans in the ApplicationContext of the same type. This will cause @Autowired to not work because there isn’t exactly one bean, or one marked as primary. To work around this, Spring Cloud OpenFeign marks all Feign instances as @Primary, so Spring Framework will know which bean to inject. In some cases, this may not be desirable. To turn off this behavior set the primary attribute of @FeignClient to false.

@FeignClient(name = "hello", primary = false)
public interface HelloClient {
    // methods here
}

1.8. Feign Inheritance Support

Feign supports boilerplate apis via single-inheritance interfaces. This allows grouping common operations into convenient base interfaces.

UserService.java
public interface UserService {

    @RequestMapping(method = RequestMethod.GET, value ="/users/{id}")
    User getUser(@PathVariable("id") long id);
}
UserResource.java
@RestController
public class UserResource implements UserService {

}
UserClient.java
package project.user;

@FeignClient("users")
public interface UserClient extends UserService {

}
It is generally not advisable to share an interface between a server and a client. It introduces tight coupling, and also actually doesn’t work with Spring MVC in its current form (method parameter mapping is not inherited).

1.9. Feign request/response compression

You may consider enabling the request or response GZIP compression for your Feign requests. You can do this by enabling one of the properties:

feign.compression.request.enabled=true
feign.compression.response.enabled=true

Feign request compression gives you settings similar to what you may set for your web server:

feign.compression.request.enabled=true
feign.compression.request.mime-types=text/xml,application/xml,application/json
feign.compression.request.min-request-size=2048

These properties allow you to be selective about the compressed media types and minimum request threshold length.

For http clients except OkHttpClient, default gzip decoder can be enabled to decode gzip response in UTF-8 encoding:

feign.compression.response.enabled=true
feign.compression.response.useGzipDecoder=true

1.10. Feign logging

A logger is created for each Feign client created. By default the name of the logger is the full class name of the interface used to create the Feign client. Feign logging only responds to the DEBUG level.

application.yml
logging.level.project.user.UserClient: DEBUG

The Logger.Level object that you may configure per client, tells Feign how much to log. Choices are:

  • NONE, No logging (DEFAULT).

  • BASIC, Log only the request method and URL and the response status code and execution time.

  • HEADERS, Log the basic information along with request and response headers.

  • FULL, Log the headers, body, and metadata for both requests and responses.

For example, the following would set the Logger.Level to FULL:

@Configuration
public class FooConfiguration {
    @Bean
    Logger.Level feignLoggerLevel() {
        return Logger.Level.FULL;
    }
}

1.11. Feign Capability support

The Feign capabilities expose core Feign components so that these components can be modified. For example, the capabilities can take the Client, decorate it, and give the decorated instance back to Feign. The support for metrics libraries is a good real-life example for this. See Feign metrics.

Creating one or more Capability beans and placing them in a @FeignClient configuration lets you register them and modify the behavior of the involved client.

@Configuration
public class FooConfiguration {
    @Bean
    Capability customCapability() {
        return new CustomCapability();
    }
}

1.12. Feign metrics

If all of the following conditions are true, a MicrometerCapability bean is created and registered so that your Feign client publishes metrics to Micrometer:

  • feign-micrometer is on the classpath

  • A MeterRegistry bean is available

  • feign metrics properties are set to true (by default)

    • feign.metrics.enabled=true (for all clients)

    • feign.client.config.feignName.metrics.enabled=true (for a single client)

If your application already uses Micrometer, enabling metrics is as simple as putting feign-micrometer onto your classpath.

You can also disable the feature by either:

  • excluding feign-micrometer from your classpath

  • setting one of the feign metrics properties to false

    • feign.metrics.enabled=false

    • feign.client.config.feignName.metrics.enabled=false

feign.metrics.enabled=false disables metrics support for all Feign clients regardless of the value of the client-level flags: feign.client.config.feignName.metrics.enabled. If you want to enable or disable merics per client, don’t set feign.metrics.enabled and use feign.client.config.feignName.metrics.enabled.

You can also customize the MicrometerCapability by registering your own bean:

@Configuration
public class FooConfiguration {
    @Bean
    public MicrometerCapability micrometerCapability(MeterRegistry meterRegistry) {
        return new MicrometerCapability(meterRegistry);
    }
}

1.13. Feign @QueryMap support

The OpenFeign @QueryMap annotation provides support for POJOs to be used as GET parameter maps. Unfortunately, the default OpenFeign QueryMap annotation is incompatible with Spring because it lacks a value property.

Spring Cloud OpenFeign provides an equivalent @SpringQueryMap annotation, which is used to annotate a POJO or Map parameter as a query parameter map.

For example, the Params class defines parameters param1 and param2:

// Params.java
public class Params {
    private String param1;
    private String param2;

    // [Getters and setters omitted for brevity]
}

The following feign client uses the Params class by using the @SpringQueryMap annotation:

@FeignClient("demo")
public interface DemoTemplate {

    @GetMapping(path = "/demo")
    String demoEndpoint(@SpringQueryMap Params params);
}

If you need more control over the generated query parameter map, you can implement a custom QueryMapEncoder bean.

1.14. HATEOAS support

Spring provides some APIs to create REST representations that follow the HATEOAS principle, Spring Hateoas and Spring Data REST.

If your project use the org.springframework.boot:spring-boot-starter-hateoas starter or the org.springframework.boot:spring-boot-starter-data-rest starter, Feign HATEOAS support is enabled by default.

When HATEOAS support is enabled, Feign clients are allowed to serialize and deserialize HATEOAS representation models: EntityModel, CollectionModel and PagedModel.

@FeignClient("demo")
public interface DemoTemplate {

    @GetMapping(path = "/stores")
    CollectionModel<Store> getStores();
}

1.15. Spring @MatrixVariable Support

Spring Cloud OpenFeign provides support for the Spring @MatrixVariable annotation.

If a map is passed as the method argument, the @MatrixVariable path segment is created by joining key-value pairs from the map with a =.

If a different object is passed, either the name provided in the @MatrixVariable annotation (if defined) or the annotated variable name is joined with the provided method argument using =.

IMPORTANT

Even though, on the server side, Spring does not require the users to name the path segment placeholder same as the matrix variable name, since it would be too ambiguous on the client side, Spring Cloud OpenFeign requires that you add a path segment placeholder with a name matching either the name provided in the @MatrixVariable annotation (if defined) or the annotated variable name.

For example:

@GetMapping("/objects/links/{matrixVars}")
Map<String, List<String>> getObjects(@MatrixVariable Map<String, List<String>> matrixVars);

Note that both variable name and the path segment placeholder are called matrixVars.

@FeignClient("demo")
public interface DemoTemplate {

    @GetMapping(path = "/stores")
    CollectionModel<Store> getStores();
}

1.16. Feign CollectionFormat support

We support feign.CollectionFormat by providing the @CollectionFormat annotation.You can annotate a Feign client method with it by passing the desired feign.CollectionFormat as annotation value.

In the following example, the CSV format is used instead of the default EXPLODED to process the method.

@FeignClient(name = "demo")
    protected interface PageableFeignClient {

        @CollectionFormat(feign.CollectionFormat.CSV)
        @GetMapping(path = "/page")
        ResponseEntity performRequest(Pageable page);

    }
Set the CSV format while sending Pageable as a query parameter in order for it to be encoded correctly.

1.17. Reactive Support

As the OpenFeign project does not currently support reactive clients, such as Spring WebClient, neither does Spring Cloud OpenFeign.We will add support for it here as soon as it becomes available in the core project.

Until that is done, we recommend using feign-reactive for Spring WebClient support.

1.17.1. Early Initialization Errors

Depending on how you are using your Feign clients you may see initialization errors when starting your application. To work around this problem you can use an ObjectProvider when autowiring your client.

@Autowired
ObjectProvider<TestFeginClient> testFeginClient;

1.18. Spring Data Support

You may consider enabling Jackson Modules for the support org.springframework.data.domain.Page and org.springframework.data.domain.Sort decoding.

feign.autoconfiguration.jackson.enabled=true

1.19. Spring @RefreshScope Support

If Feign client refresh is enabled, each feign client is created with feign.Request.Options as a refresh-scoped bean. This means properties such as connectTimeout and readTimeout can be refreshed against any Feign client instance through POST /actuator/refresh.

By default, refresh behavior in Feign clients is disabled. Use the following property to enable refresh behavior:

feign.client.refresh-enabled=true
DO NOT annotate the @FeignClient interface with the @RefreshScope annotation.

2. Configuration properties

To see the list of all Spring Cloud OpenFeign related configuration properties please check the Appendix page.