Spring Cloud 声明式的 Rest 客户端 Feign

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

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

eureka.client.registerWithEureka=false
eureka.client.serviceUrl.defaultZone=http://localhost:8089/eureka/

不使用Eureka的服务发现功能时，则可以通过<serviceId>.ribbon.listOfServers指定服务对应的服务器地址。这是属于Ribbon的功能，更多相关信息可以参考前面介绍过的Ribbon相关内容。

@FeignClient("hello")
public interface HelloService {
    @GetMapping("abc")
    String helloWorld();
  
}

@RestController
@RequestMapping("hello")
public class HelloController {
    @Autowired
    private HelloService helloService;
  
    @GetMapping
    public String helloWorld() {
        return this.helloService.helloWorld();
    }
}

@GetMapping("path_variable/{pathVariable}")
String pathVariable(@PathVariable("pathVariable") String pathVariable);
@PostMapping("request_body")
String requestBody(@RequestBody Map<String, Object> body);

@FeignClient(name="hello", url = "http://localhost:8901")
public interface HelloService {
    @GetMapping("abc")
    String helloWorld();
  
}

url属性对应的访问协议是可以忽略的，所以上面的配置也可以写成@FeignClient(name="hello", url = "localhost:8901")。

@Configuration
public class DefaultConfiguration {
    @Bean
    public Decoder decoder() {
        return new DefaultDecoder();
    }
  
    public static class DefaultDecoder implements Decoder {
        @Override
        public Object decode(Response response, Type type) throws IOException, DecodeException, FeignException {
            return "from default decode : " + Util.toString(response.body().asReader());
        }
    
    }
  
}

@FeignClient(name="${feign.client.hello}", configuration=HelloFeignConfiguration.class)
public interface HelloService {
    @GetMapping("hello")
    String helloWorld();
  
}

@Slf4j
public class HelloFeignConfiguration {
    @Bean
    public Decoder decoder() {
        return new HelloDecoder();
    }
  
    public static class HelloDecoder implements Decoder {
        @Override
        public Object decode(Response response, Type type) throws IOException, DecodeException, FeignException {
            log.info("receive message, type is {}", type);
            return "from hello decoder : " + Util.toString(response.body().asReader());
        }
    
    }
  
}

在上面的HelloFeignConfiguration类中，我们没有标注@Configuration，特定Feign Client使用的配置信息可以不加配置类上加@Configuration，也不建议加@Configuration。因为加了@Configuration，而其又在默认的bean扫描路径下，则其中的bean定义都会生效，则其将变为所有的Feign Client都共享的配置。 当同时存在默认的Feign Client配置和特定的Feign Client的配置时，特定的Feign Client的配置将拥有更高的优先级，即特定的Feign Client的配置将覆盖默认的Feign Client的配置。但是如果在特定的Feign Client中没有定义的配置，则仍将以默认的Feign Client中配置的为准。

<dependency>
    <groupId>io.github.openfeign</groupId>
    <artifactId>feign-httpclient</artifactId>
</dependency>

底层使用ApacheHttpClient时，如果bean容器中存在org.apache.http.impl.client.CloseableHttpClient类型的bean，则将使用该bean，否则将创建一个默认的CloseableHttpClient。

feign.client.config.hello.decoder=com.elim.spring.cloud.client.HelloFeignConfiguration.HelloDecoder
feign.client.config.hello.loggerLevel=FULL
feign.client.config.hello.connectTimeout=1000
feign.client.config.hello.readTimeout=1000

loggerLevel是用来指定Feign Client进行请求时需要打印的日志信息类型，可选值有下面这几种，默认是NONE。对应的日志信息只有日志打印级别为DEBUG时才会生效。

    /**
    * No logging.
    */
   NONE,
   /**
    * Log only the request method and URL and the response status code and execution time.
    */
   BASIC,
   /**
    * Log the basic information along with request and response headers.
    */
   HEADERS,
   /**
    * Log the headers, body, and metadata for both requests and responses.
    */
   FULL

feign.client.config.default.decoder=com.elim.spring.cloud.client.HelloFeignConfiguration.HelloDecoder
feign.client.config.default.loggerLevel=FULL
feign.client.config.default.connectTimeout=1000
feign.client.config.default.readTimeout=1000

feign.httpclient.maxConnections=200
feign.httpclient.maxConnectionsPerRoute=200
feign.httpclient.timeToLive=600

feign.httpclient.xxx只会对默认创建的CloseableHttpClient生效，如果自定义的CloseableHttpClient也希望响应通用的feign.httpclient.xxx参数，可以在创建自定义的CloseableHttpClient时注入FeignHttpClientProperties，从而读取对应的配置信息。

@Component
public class MyHttpMessageConverter extends AbstractHttpMessageConverter<MyObj> {
    private final StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
  
    public MyHttpMessageConverter() {
        super(MediaType.APPLICATION_JSON, MediaType.TEXT_PLAIN);
    }
  
    @Override
    protected boolean supports(Class<?> clazz) {
        return clazz.isAssignableFrom(MyObj.class);
    }
    @Override
    protected MyObj readInternal(Class<? extends MyObj> clazz, HttpInputMessage inputMessage)
            throws IOException, HttpMessageNotReadableException {
        String text = this.stringHttpMessageConverter.read(String.class, inputMessage);
        return new MyObj(text);
    }
    @Override
    protected void writeInternal(MyObj t, HttpOutputMessage outputMessage)
            throws IOException, HttpMessageNotWritableException {
        this.stringHttpMessageConverter.write(t.getText(), MediaType.TEXT_PLAIN, outputMessage);
    }
  
    @Data
    public static class MyObj {
        private final String text;
    }
  
}

@PostMapping("hello/converter")
MyObj customHttpMessageConverter(@RequestBody MyObj obj);

Spring Web的HttpMessageConverter只对使用SpringEncoder或SpringDecoder生效，如果你使用了自定义的Encoder或Decoder它们就没用了。

@Component
public class MyRequestInterceptor implements RequestInterceptor {
    @Override
    public void apply(RequestTemplate template) {
        template.header("request-id", UUID.randomUUID().toString());
    }
}

@Configuration
public class DefaultConfiguration {
    @Bean
    public BasicAuthRequestInterceptor basicAuthRequestInterceptor() {
        return new BasicAuthRequestInterceptor("username", "password");
    }
  
}

@Slf4j
public class LoggerDecoder extends ResponseEntityDecoder {
    public LoggerDecoder(ObjectFactory<HttpMessageConverters> messageConverters) {
        super(new SpringDecoder(messageConverters));
    }
    @Override
    public Object decode(Response response, Type type) throws IOException, FeignException {
        Object result = super.decode(response, type);
        log.info("请求[{}]的响应内容是：{}", response.request().url(), result);
        return result;
    }
}

@Slf4j
public class MyErrorDecoder extends ErrorDecoder.Default {
    @Override
    public Exception decode(String methodKey, Response response) {
        Exception exception = super.decode(methodKey, response);
        log.error("请求{}调用方法{}异常，状态码：{}", response.request().url(), methodKey, response.status());
        return exception;
    }
}

feign.client.config.default.errorDecoder=com.elim.spring.cloud.client.config.MyErrorDecoder

hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds=3000

如果想指定特定FeignClient的HystrixCommand配置，可以参考feign.hystrix.SetterFactory.Default.create(..)的源码其生成HystrixCommand的commandKey的方式。

@FeignClient(name="${feign.client.hello}", fallback=HelloServiceFallback.class)
public interface HelloService {
    @GetMapping("hello")
    String helloWorld();
  
    @GetMapping("hello/timeout/{timeout}")
    String timeout(@PathVariable("timeout") int timeout);
  
}

@Component
public class HelloServiceFallback implements HelloService {
    @Override
    public String helloWorld() {
        return "fallback for helloWorld";
    }
    @Override
    public String timeout(int timeout) {
        return "fallback for timeout";
    }
}

@Component
public class HelloServiceFallbackFactory implements FallbackFactory<HelloService> {
    @Override
    public HelloService create(Throwable cause) {
        return new HelloService() {
            @Override
            public String helloWorld() {
                return "fallback for helloWorld，reason is：" + cause.getMessage();
            }
            @Override
            public String timeout(int timeout) {
                return "fallback for timeout, reason is :" + cause.getMessage();
            }
        };
    }
}

@FeignClient(name="${feign.client.hello}", fallbackFactory=HelloServiceFallbackFactory.class)
public interface HelloService {
    //...
}

当同时指定了fallback和fallbackFactory时，fallback拥有更高的优先级。 当使用了fallback时，由于fallback指定的Class实现了@FeignClient标注的接口，而且也定义为了Spring bean，那么Spring bean容器中同时会拥有多个@FeignClient标注的接口类型的bean。那通过@Autowired进行注入时就会报错，考虑到这种情况，Spring Cloud Feign默认把@FeignClient标注的接口生成的代理类bean标注为@Primary，即通过@Autowired注入的默认是@FeignClient对应的代理类，如果不希望该代理类bean是Primary，可以通过@FeignClient(primary=false)定义。

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

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

请求内容的压缩由org.springframework.cloud.openfeign.encoding.FeignContentGzipEncodingAutoConfiguration进行自动配置。

• http://cloud.spring.io/spring-cloud-static/Finchley.SR1/multi/multi_spring-cloud-feign.html