一、原理
Feign 是一个 Java 到 HTTP 的客户端绑定器，灵感来自于 Retrofit 和 JAXRS-2.0 以及 WebSocket。Feign 的第一个目标是降低将 Denominator 无变化的绑定到 HTTP APIs 的复杂性，而不考虑 ReSTfulness。
Feign 使用 Jersey 和 CXF 等工具为 ReST 或 SOAP 服务编写 java 客户端。此外，Feign 允许您在 Apache HC 等http 库之上编写自己的代码。Feign 以最小的开销将代码连接到 http APIs，并通过可定制的解码器和错误处理（可以写入任何基于文本的 http APIs）将代码连接到 http APIs。
Feign 通过将注解处理为模板化请求来工作。参数在输出之前直接应用于这些模板。尽管 Feign 仅限于支持基于文本的 APIs，但它极大地简化了系统方面，例如重放请求。此外，Feign 使得对转换进行单元测试变得简单。
Feign 10.x 及以上版本是在 Java 8上构建的，应该在 Java 9、10 和 11上工作。对于需要 JDK 6兼容性的用户，请使用 Feign 9.x
二、处理过程图
三、Http Client 依赖
feign 在默认情况下使用 JDK 原生的 URLConnection 发送HTTP请求。(没有连接池，保持长连接) 。
可以通过修改 client 依赖换用底层的 client，不同的 http client 对请求的支持可能有差异。具体使用示例如下:
feign:
httpclient:
enable: false
okhttp:
enable: true
AND
<!-- Support PATCH Method-->
<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpclient</artifactId>
</dependency>
<!-- Do not support PATCH Method -->
<dependency>
<groupId>io.github.openfeign</groupId>
<artifactId>feign-okhttp</artifactId>
</dependency>
四、Http Client 配置
okhttp 配置源码
@Configuration(proxyBeanMethods = false)
@ConditionalOnMissingBean(okhttp3.OkHttpClient.class)
public class OkHttpFeignConfiguration {
private okhttp3.OkHttpClient okHttpClient;
@Bean
@ConditionalOnMissingBean(ConnectionPool.class)
public ConnectionPool httpClientConnectionPool(
FeignHttpClientProperties httpClientProperties,
OkHttpClientConnectionPoolFactory connectionPoolFactory) {
Integer maxTotalConnections = httpClientProperties.getMaxConnections();
Long timeToLive = httpClientProperties.getTimeToLive();
TimeUnit ttlUnit = httpClientProperties.getTimeToLiveUnit();
return connectionPoolFactory.create(maxTotalConnections, timeToLive, ttlUnit);
}
@Bean
public okhttp3.OkHttpClient client(OkHttpClientFactory httpClientFactory,
ConnectionPool connectionPool,
FeignHttpClientProperties httpClientProperties) {
Boolean followRedirects = httpClientProperties.isFollowRedirects();
Integer connectTimeout = httpClientProperties.getConnectionTimeout();
this.okHttpClient = httpClientFactory
.createBuilder(httpClientProperties.isDisableSslValidation())
.connectTimeout(connectTimeout, TimeUnit.MILLISECONDS)
.followRedirects(followRedirects).connectionPool(connectionPool).build();
return this.okHttpClient;
}
@PreDestroy
public void destroy() {
if (this.okHttpClient != null) {
this.okHttpClient.dispatcher().executorService().shutdown();
this.okHttpClient.connectionPool().evictAll();
}
}
}
HttpClient 配置源码
@Configuration(proxyBeanMethods = false)
@ConditionalOnMissingBean(CloseableHttpClient.class)
public class HttpClientFeignConfiguration {
private final Timer connectionManagerTimer = new Timer(
"FeignApacheHttpClientConfiguration.connectionManagerTimer", true);
private CloseableHttpClient httpClient;
@Autowired(required = false)
private RegistryBuilder registryBuilder;
@Bean
@ConditionalOnMissingBean(HttpClientConnectionManager.class)
public HttpClientConnectionManager connectionManager(
ApacheHttpClientConnectionManagerFactory connectionManagerFactory,
FeignHttpClientProperties httpClientProperties) {
final HttpClientConnectionManager connectionManager = connectionManagerFactory
.newConnectionManager(httpClientProperties.isDisableSslValidation(),
httpClientProperties.getMaxConnections(),
httpClientProperties.getMaxConnectionsPerRoute(),
httpClientProperties.getTimeToLive(),
httpClientProperties.getTimeToLiveUnit(), this.registryBuilder);
this.connectionManagerTimer.schedule(new TimerTask() {
@Override
public void run() {
connectionManager.closeExpiredConnections();
}
}, 30000, httpClientProperties.getConnectionTimerRepeat());
return connectionManager;
}
@Bean
@ConditionalOnProperty(value = "feign.compression.response.enabled",
havingValue = "true")
public CloseableHttpClient customHttpClient(
HttpClientConnectionManager httpClientConnectionManager,
FeignHttpClientProperties httpClientProperties) {
HttpClientBuilder builder = HttpClientBuilder.create().disableCookieManagement()
.useSystemProperties();
this.httpClient = createClient(builder, httpClientConnectionManager,
httpClientProperties);
return this.httpClient;
}
@Bean
@ConditionalOnProperty(value = "feign.compression.response.enabled",
havingValue = "false", matchIfMissing = true)
public CloseableHttpClient httpClient(ApacheHttpClientFactory httpClientFactory,
HttpClientConnectionManager httpClientConnectionManager,
FeignHttpClientProperties httpClientProperties) {
this.httpClient = createClient(httpClientFactory.createBuilder(),
httpClientConnectionManager, httpClientProperties);
return this.httpClient;
}
private CloseableHttpClient createClient(HttpClientBuilder builder,
HttpClientConnectionManager httpClientConnectionManager,
FeignHttpClientProperties httpClientProperties) {
RequestConfig defaultRequestConfig = RequestConfig.custom()
.setConnectTimeout(httpClientProperties.getConnectionTimeout())
.setRedirectsEnabled(httpClientProperties.isFollowRedirects()).build();
CloseableHttpClient httpClient = builder
.setDefaultRequestConfig(defaultRequestConfig)
.setConnectionManager(httpClientConnectionManager).build();
return httpClient;
}
@PreDestroy
public void destroy() throws Exception {
this.connectionManagerTimer.cancel();
if (this.httpClient != null) {
this.httpClient.close();
}
}
}
HttpClient 配置属性
@ConfigurationProperties(prefix = "feign.httpclient")
public class FeignHttpClientProperties {
/**
* Default value for disabling SSL validation.
*/
public static final boolean DEFAULT_DISABLE_SSL_VALIDATION = false;
/**
* Default value for max number od connections.
*/
public static final int DEFAULT_MAX_CONNECTIONS = 200;
/**
* Default value for max number od connections per route.
*/
public static final int DEFAULT_MAX_CONNECTIONS_PER_ROUTE = 50;
/**
* Default value for time to live.
*/
public static final long DEFAULT_TIME_TO_LIVE = 900L;
/**
* Default time to live unit.
*/
public static final TimeUnit DEFAULT_TIME_TO_LIVE_UNIT = TimeUnit.SECONDS;
/**
* Default value for following redirects.
*/
public static final boolean DEFAULT_FOLLOW_REDIRECTS = true;
/**
* Default value for connection timeout.
*/
public static final int DEFAULT_CONNECTION_TIMEOUT = 2000;
/**
* Default value for connection timer repeat.
*/
public static final int DEFAULT_CONNECTION_TIMER_REPEAT = 3000;
private boolean disableSslValidation = DEFAULT_DISABLE_SSL_VALIDATION;
private int maxConnections = DEFAULT_MAX_CONNECTIONS;
private int maxConnectionsPerRoute = DEFAULT_MAX_CONNECTIONS_PER_ROUTE;
private long timeToLive = DEFAULT_TIME_TO_LIVE;
private TimeUnit timeToLiveUnit = DEFAULT_TIME_TO_LIVE_UNIT;
private boolean followRedirects = DEFAULT_FOLLOW_REDIRECTS;
private int connectionTimeout = DEFAULT_CONNECTION_TIMEOUT;
private int connectionTimerRepeat = DEFAULT_CONNECTION_TIMER_REPEAT;
//省略 setter 和 getter 方法
}
五、部分注解
FeignClient 注解源码
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface FeignClient {
// 忽略了过时的属性
/**
* The name of the service with optional protocol prefix. Synonym for {@link #name()
* name}. A name must be specified for all clients, whether or not a url is provided.
* Can be specified as property key, eg: ${propertyKey}.
* @return the name of the service with optional protocol prefix
*/
@AliasFor("name")
String value() default "";
/**
* This will be used as the bean name instead of name if present, but will not be used
* as a service id.
* @return bean name instead of name if present
*/
String contextId() default "";
/**
* @return The service id with optional protocol prefix. Synonym for {@link #value()
* value}.
*/
@AliasFor("value")
String name() default "";
/**
* @return the <code>@Qualifier</code> value for the feign client.
*/
String qualifier() default "";
/**
* @return an absolute URL or resolvable hostname (the protocol is optional).
*/
String url() default "";
/**
* @return whether 404s should be decoded instead of throwing FeignExceptions
*/
boolean decode404() default false;
/**
* A custom configuration class for the feign client. Can contain override
* <code>@Bean</code> definition for the pieces that make up the client, for instance
* {@link feign.codec.Decoder}, {@link feign.codec.Encoder}, {@link feign.Contract}.
*
* @see FeignClientsConfiguration for the defaults
* @return list of configurations for feign client
*/
Class<?>[] configuration() default {};
/**
* Fallback class for the specified Feign client interface. The fallback class must
* implement the interface annotated by this annotation and be a valid spring bean.
* @return fallback class for the specified Feign client interface
*/
Class<?> fallback() default void.class;
/**
* Define a fallback factory for the specified Feign client interface. The fallback
* factory must produce instances of fallback classes that implement the interface
* annotated by {@link FeignClient}. The fallback factory must be a valid spring bean.
*
* @see feign.hystrix.FallbackFactory for details.
* @return fallback factory for the specified Feign client interface
*/
Class<?> fallbackFactory() default void.class;
/**
* @return path prefix to be used by all method-level mappings. Can be used with or
* without <code>@RibbonClient</code>.
*/
String path() default "";
/**
* @return whether to mark the feign proxy as a primary bean. Defaults to true.
*/
boolean primary() default true;
}
六、Feign Client 配置
FeignClient 配置源码
/**
* Feign client configuration.
*/
public static class FeignClientConfiguration {
private Logger.Level loggerLevel;
private Integer connectTimeout;
private Integer readTimeout;
private Class<Retryer> retryer;
private Class<ErrorDecoder> errorDecoder;
private List<Class<RequestInterceptor>> requestInterceptors;
private Boolean decode404;
private Class<Decoder> decoder;
private Class<Encoder> encoder;
private Class<Contract> contract;
private ExceptionPropagationPolicy exceptionPropagationPolicy;
//省略setter 和 getter
}
七、Spring boot 服务下使用示例
pom.xml 中引入依赖，部分特性需要额外的依赖扩展(诸如表单提交等) <dependencies> <!-- spring-cloud-starter-openfeign 支持负载均衡、重试、断路器等 --> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-openfeign</artifactId> <version>2.2.2.RELEASE</version> </dependency> <!-- Required to use PATCH. feign-okhttp not support PATCH Method --> <dependency> <groupId>io.github.openfeign</groupId> <artifactId>feign-httpclient</artifactId> <version>11.0</version> </dependency> </dependencies> 开启支持-使用 EnableFeignClients 注解 @SpringBootApplication @EnableFeignClients public class TyaleApplication { public static void main(String[] args) { SpringApplication.run(TyaleApplication.class, args); } } 接口注解-标记请求地址、请求header、请求方式、参数(是否必填)等 //如果是微服务内部调用则 value 可以直接指定对方服务在服务发现中的服务名，不需要 url @FeignClient(value = "tyale", url = "${base.uri}") public interface TyaleFeignClient { @PostMapping(value = "/token", consumes ="application/x-www-form-urlencoded") Map<String, Object> obtainToken(Map<String, ?> queryParam); @GetMapping(value = Constants.STATION_URI) StationPage stations(@RequestHeader("Accept-Language") String acceptLanguage, @RequestParam(name = "country") String country, @RequestParam(name = "order") String order, @RequestParam(name = "page", required = false) Integer page, @RequestParam(name = "pageSize") Integer pageSize); @PostMapping(value = Constants.PAYMENT_URI) PaymentDTO payment(@RequestHeader("Accept-Language") String acceptLanguage, @RequestBody PaymentRQ paymentRq); } FormEncoder 支持 @Configuration public class FeignFormConfiguration { @Autowired private ObjectFactory<HttpMessageConverters> messageConverters; @Bean @Primary public Encoder feignFormEncoder() { return new FormEncoder(new SpringEncoder(this.messageConverters)); } } 拦截器-自动添加header 或者 token 等 @Configuration public class FeignInterceptor implements RequestInterceptor { @Override public void apply(RequestTemplate requestTemplate) { requestTemplate.header(Constants.TOKEN_STR, "Bearer xxx"); } } ErrorCode-可以自定义错误响应码的处理 @Configuration public class TyaleErrorDecoder implements ErrorDecoder { @Override public Exception decode(String methodKey, Response response) { TyaleErrorException errorException = null; try { if (response.body() != null) { Charset utf8 = StandardCharsets.UTF_8; var body = Util.toString(response.body().asReader(utf8)); errorException = GsonUtils.fromJson(body, TyaleErrorException.class); } else { errorException = new TyaleErrorException(); } } catch (IOException ignored) { } return errorException; } } TyaleErrorException 类示例-处理返回失败响应码时的数据，不同的服务端可能需要不同的处理 @EqualsAndHashCode(callSuper = true) @Data @AllArgsConstructor @NoArgsConstructor public class TyaleErrorException extends Exception { /** * example: "./api/{service-name}/{problem-id}" */ private String type; /** * example: {title} */ private String title; /** * example: https://api/docs/index.html#error-handling */ private String documentation; /** * example: {code} */ private String status; } FeignClient 使用示例 @RestController @RequestMapping(value = "/rest/tyale") public class TyaleController { @Autowired private TyaleFeignClient feignClient; @GetMapping(value="/stations") public BaseResponseDTO<StationPage> stations() { try { String acceptLanguage = "en"; String country = "DE"; String order = "NAME"; Integer page = 0; Integer pageSize = 20; StationPage stationPage = feignClient.stations(acceptLanguage, country, order, page, pageSize); return ResponseBuilder.buildSuccessRS(stationPage); } catch (TyaleErrorException tyaleError) { System.out.println(tyaleError); //todo 处理异常返回时的响应 } return ResponseBuilder.buildSuccessRS(); } }
