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Feign makes writing java http clients easier
Quick Overview
Spring Cloud OpenFeign is a declarative HTTP client that makes writing web service clients easier. It's built on top of the popular Feign library and integrates seamlessly with the Spring Cloud ecosystem, providing features like service discovery, load balancing, and circuit breakers.
Pros
- Declarative HTTP Client: Spring Cloud OpenFeign abstracts away the boilerplate code required to make HTTP requests, allowing developers to focus on defining the service interfaces.
- Integration with Spring Cloud: OpenFeign integrates with other Spring Cloud components, such as Ribbon for load balancing and Hystrix for circuit breaking, making it easy to build resilient microservices.
- Extensibility: OpenFeign can be extended with custom encoders, decoders, and other functionality, allowing developers to tailor it to their specific needs.
- Testability: The declarative nature of OpenFeign makes it easy to write unit tests for service clients, improving overall code quality.
Cons
- Complexity: While the integration with Spring Cloud provides many benefits, it can also add complexity to the overall system, especially for smaller projects.
- Performance: The abstraction and dynamic proxy generation used by OpenFeign can introduce a small amount of overhead compared to manual HTTP client implementation.
- Learning Curve: Developers new to the Spring Cloud ecosystem may need to invest time in understanding the various components and how they work together.
- Vendor Lock-in: By using Spring Cloud OpenFeign, developers may become more tied to the Spring ecosystem, which could make it harder to migrate to other frameworks or libraries in the future.
Code Examples
Defining a Service Interface
@FeignClient(name = "example-service")
public interface ExampleService {
@GetMapping("/hello")
String sayHello();
@PostMapping("/users")
User createUser(@RequestBody User user);
}
This code defines a Feign client interface that represents an external service. The @FeignClient annotation specifies the name of the service, and the method annotations (@GetMapping, @PostMapping) define the HTTP methods and endpoints to be used.
Configuring Feign
@Configuration
public class FeignConfiguration {
@Bean
public Logger.Level feignLoggerLevel() {
return Logger.Level.FULL;
}
}
This configuration class sets the Feign logger level to FULL, which will log the full request and response details. This can be useful for debugging and troubleshooting.
Using the Feign Client
@Service
public class ExampleService {
private final ExampleService exampleService;
public ExampleService(ExampleService exampleService) {
this.exampleService = exampleService;
}
public String sayHello() {
return exampleService.sayHello();
}
public User createUser(User user) {
return exampleService.createUser(user);
}
}
This service class uses the ExampleService Feign client to interact with the external service. The client is injected into the service, and the service methods delegate to the corresponding Feign client methods.
Getting Started
To get started with Spring Cloud OpenFeign, you'll need to add the following dependency to your project's pom.xml file:
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>
Then, in your main application class, add the @EnableFeignClients annotation:
@SpringBootApplication
@EnableFeignClients
public class MyApplication {
public static void main(String[] args) {
SpringApplication.run(MyApplication.class, args);
}
}
Finally, define your Feign client interfaces as shown in the code examples above, and start using them in your application services.
Competitor Comparisons
Feign makes writing java http clients easier
Pros of OpenFeign/feign
- Lightweight and Flexible: OpenFeign/feign is a lightweight and flexible HTTP client that can be used independently of any specific framework or library.
- Customizable: OpenFeign/feign provides a high degree of customization, allowing developers to tailor the client to their specific needs.
- Minimal Dependencies: OpenFeign/feign has minimal dependencies, making it easier to integrate into existing projects.
Cons of OpenFeign/feign
- Limited Integration: OpenFeign/feign lacks the deep integration with the Spring ecosystem that spring-cloud/spring-cloud-openfeign provides.
- Lack of Spring-specific Features: spring-cloud/spring-cloud-openfeign offers additional features and utilities that are specific to the Spring framework, which may be beneficial for Spring-based projects.
Code Comparison
OpenFeign/feign:
interface GitHub {
@RequestLine("GET /repos/{owner}/{repo}/contributors")
List<Contributor> contributors(@Param("owner") String owner, @Param("repo") String repo);
@RequestLine("POST /repos/{owner}/{repo}/issues")
void createIssue(Issue issue, @Param("owner") String owner, @Param("repo") String repo);
}
spring-cloud/spring-cloud-openfeign:
@FeignClient(name = "github", url = "https://api.github.com")
public interface GitHubClient {
@GetMapping("/repos/{owner}/{repo}/contributors")
List<Contributor> getContributors(@PathVariable("owner") String owner, @PathVariable("repo") String repo);
@PostMapping("/repos/{owner}/{repo}/issues")
void createIssue(@RequestBody Issue issue, @PathVariable("owner") String owner, @PathVariable("repo") String repo);
}
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//// DO NOT EDIT THIS FILE. IT WAS GENERATED. Manual changes to this file will be lost when it is generated again. Edit the files in the src/main/asciidoc/ directory instead. ////
[[features]] == Features
- Declarative REST Client: Feign creates a dynamic implementation of an interface decorated with JAX-RS or Spring MVC annotations
[[building]] == Building
:jdkversion: 17
[[basic-compile-and-test]] == Basic Compile and Test
To build the source you will need to install JDK {jdkversion}.
Spring Cloud uses Maven for most build-related activities, and you should be able to get off the ground quite quickly by cloning the project you are interested in and typing
$ ./mvnw install
NOTE: You can also install Maven (>=3.3.3) yourself and run the mvn command
in place of ./mvnw in the examples below. If you do that you also
might need to add -P spring if your local Maven settings do not
contain repository declarations for spring pre-release artifacts.
NOTE: Be aware that you might need to increase the amount of memory
available to Maven by setting a MAVEN_OPTS environment variable with
a value like -Xmx512m -XX:MaxPermSize=128m. We try to cover this in
the .mvn configuration, so if you find you have to do it to make a
build succeed, please raise a ticket to get the settings added to
source control.
The projects that require middleware (i.e. Redis) for testing generally require that a local instance of Docker is installed and running.
[[documentation]] == Documentation
The spring-cloud-build module has a "docs" profile, and if you switch
that on it will try to build asciidoc sources using https://docs.antora.org/antora/latest/[Antora] from
modules/ROOT/.
As part of that process it will look for a
docs/src/main/asciidoc/README.adoc and process it by loading all the includes, but not
parsing or rendering it, just copying it to ${main.basedir}
(defaults to $\{basedir}, i.e. the root of the project). If there are
any changes in the README it will then show up after a Maven build as
a modified file in the correct place. Just commit it and push the change.
[[working-with-the-code]] == Working with the code If you don't have an IDE preference we would recommend that you use https://www.springsource.com/developer/sts[Spring Tools Suite] or https://eclipse.org[Eclipse] when working with the code. We use the https://eclipse.org/m2e/[m2eclipse] eclipse plugin for maven support. Other IDEs and tools should also work without issue as long as they use Maven 3.3.3 or better.
[[activate-the-spring-maven-profile]] === Activate the Spring Maven profile Spring Cloud projects require the 'spring' Maven profile to be activated to resolve the spring milestone and snapshot repositories. Use your preferred IDE to set this profile to be active, or you may experience build errors.
[[importing-into-eclipse-with-m2eclipse]] === Importing into eclipse with m2eclipse We recommend the https://eclipse.org/m2e/[m2eclipse] eclipse plugin when working with eclipse. If you don't already have m2eclipse installed it is available from the "eclipse marketplace".
NOTE: Older versions of m2e do not support Maven 3.3, so once the
projects are imported into Eclipse you will also need to tell
m2eclipse to use the right profile for the projects. If you
see many different errors related to the POMs in the projects, check
that you have an up to date installation. If you can't upgrade m2e,
add the "spring" profile to your settings.xml. Alternatively you can
copy the repository settings from the "spring" profile of the parent
pom into your settings.xml.
[[importing-into-eclipse-without-m2eclipse]] === Importing into eclipse without m2eclipse If you prefer not to use m2eclipse you can generate eclipse project metadata using the following command:
[indent=0]
$ ./mvnw eclipse:eclipse
The generated eclipse projects can be imported by selecting import existing projects
from the file menu.
[[contributing]] == Contributing
NOTE: Spring Cloud is released under the non-restrictive Apache 2.0 license. If you would like to contribute to this section of the documentation or if you find an error, please find the source code and issue trackers in the project at {github-project}[github].
[[license]] == License
The project license file is available https://raw.githubusercontent.com/spring-cloud/spring-cloud-openfeign/main/LICENSE.txt[here].
Top Related Projects
Feign makes writing java http clients easier
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