SpringCloud - Feign与Ribbon请求负载均衡实践

<dependencies>
  <dependency><!-- 自己定义的api -->
    <groupId>com.web.springcloud</groupId>
    <artifactId>microservicecloud-api</artifactId>
    <version>${project.version}</version>
  </dependency>
  <!-- Cloud-Feign相关 -->
  <dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-feign</artifactId>
  </dependency>
  <!-- Cloud-Ribbon相关 -->
  <dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-eureka</artifactId>
  </dependency>
  <dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-ribbon</artifactId>
  </dependency>
  <dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-config</artifactId>
  </dependency>
    <!-- Spring Boot相关 -->
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>
  <!-- 修改后立即生效，热部署相关 -->
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>springloaded</artifactId>
  </dependency>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
  </dependency>
</dependencies>

<!-- Cloud-Feign相关 -->
<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-starter-feign</artifactId>
</dependency>

package com.web.springcloud.service;
import java.util.List;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import com.web.springcloud.entities.Dept;
//绑定服务实例与接口
@FeignClient(value = "MICROSERVICECLOUD-DEPT")//注意这里
public interface DeptClientService{
  @RequestMapping(value = "/dept/get/{id}", method = RequestMethod.GET)
  public Dept get(@PathVariable("id") long id);
  @RequestMapping(value = "/dept/list", method = RequestMethod.GET)
  public List<Dept> list();
  @RequestMapping(value = "/dept/add", method = RequestMethod.POST)
  public boolean add(Dept dept);
}

@RestController
public class DeptController_Consumer
{
  @Autowired
  private DeptClientService service;
  //引入公共Module(api)中的DeptClientService ，直接调用
  @RequestMapping(value = "/consumer/dept/get/{id}")
  public Dept get(@PathVariable("id") Long id)
  {
    return this.service.get(id);
  }
  @RequestMapping(value = "/consumer/dept/list")
  public List<Dept> list()
  {
    return this.service.list();
  }
  @RequestMapping(value = "/consumer/dept/add")
  public Object add(Dept dept)
  {
    return this.service.add(dept);
  }
}

@SpringBootApplication
@EnableEurekaClient 
@EnableFeignClients(basePackages={"com.web.springcloud"})//启用Feign
@ComponentScan("com.web.springcloud")
public class DeptConsumer80_Feign_App
{
  public static void main(String[] args)
  {
    SpringApplication.run(DeptConsumer80_Feign_App.class, args);
  }
}

/**
 * Annotation for interfaces declaring that a REST client with that interface should be
 * created (e.g. for autowiring into another component). If ribbon is available it will be
 * used to load balance the backend requests, and the load balancer can be configured
 * using a <code>@RibbonClient</code> with the same name (i.e. value) as the feign client.
 *
 * @author Spencer Gibb
 * @author Venil Noronha
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface FeignClient {
  /**
   * 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}.
   */
  @AliasFor("name")
  String value() default "";
  /**
   * The service id with optional protocol prefix. Synonym for {@link #value() value}.
   *// 已经过时，使用name替代
   * @deprecated use {@link #name() name} instead
   */
  @Deprecated
  String serviceId() default "";
  /**
   * The service id with optional protocol prefix. Synonym for {@link #value() value}.
   */
  @AliasFor("value")
  String name() default "";
  // 即，ServiceId===name===value
  /**
   * Sets the <code>@Qualifier</code> value for the feign client.
   */
  String qualifier() default "";
  /**
   * An absolute URL or resolvable hostname (the protocol is optional).
   */
  String url() default "";
  /**
   * Whether 404s should be decoded instead of throwing FeignExceptions
   */
  boolean decode404() default false;
  /**
   * A custom <code>@Configuration</code> 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
   */
  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.
   */
  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.
   */
  Class<?> fallbackFactory() default void.class;
  /**
   * Path prefix to be used by all method-level mappings. Can be used with or without
   * <code>@RibbonClient</code>.
   */
  String path() default "";
  /**
   * Whether to mark the feign proxy as a primary bean. Defaults to true.
   */
  boolean primary() default true;
}

@Configuration
public class FeignClientsConfiguration {
  // 请求/响应信息转换器
  @Autowired
  private ObjectFactory<HttpMessageConverters> messageConverters;
  @Autowired(required = false)
  private List<AnnotatedParameterProcessor> parameterProcessors = new ArrayList<>();
  @Autowired(required = false)
  private List<FeignFormatterRegistrar> feignFormatterRegistrars = new ArrayList<>();
  @Autowired(required = false)
  private Logger logger;
  @Bean
  @ConditionalOnMissingBean
  public Decoder feignDecoder() {
    return new ResponseEntityDecoder(new SpringDecoder(this.messageConverters));
  }
  @Bean
  @ConditionalOnMissingBean
  public Encoder feignEncoder() {
    return new SpringEncoder(this.messageConverters);
  }
  @Bean
  @ConditionalOnMissingBean
  public Contract feignContract(ConversionService feignConversionService) {
    return new SpringMvcContract(this.parameterProcessors, feignConversionService);
  }
  // 注册FormattingConversionService--数据类型转换
  @Bean
  public FormattingConversionService feignConversionService() {
    FormattingConversionService conversionService = new DefaultFormattingConversionService();
    for (FeignFormatterRegistrar feignFormatterRegistrar : feignFormatterRegistrars) {
      feignFormatterRegistrar.registerFormatters(conversionService);
    }
    return conversionService;
  }
  // 与Hystrix整合
  @Configuration
  @ConditionalOnClass({ HystrixCommand.class, HystrixFeign.class })
  protected static class HystrixFeignConfiguration {
    @Bean
    @Scope("prototype")
    @ConditionalOnMissingBean
    @ConditionalOnProperty(name = "feign.hystrix.enabled", matchIfMissing = false)
    public Feign.Builder feignHystrixBuilder() {
      return HystrixFeign.builder();
    }
  }
  @Bean
  @ConditionalOnMissingBean
  public Retryer feignRetryer() {
    return Retryer.NEVER_RETRY;
  }
  @Bean
  @Scope("prototype")
  @ConditionalOnMissingBean
  public Feign.Builder feignBuilder(Retryer retryer) {
    return Feign.builder().retryer(retryer);
  }
  //如果缺少FeignLoggerFactory就注册FeignLoggerFactory
  @Bean
  @ConditionalOnMissingBean(FeignLoggerFactory.class)
  public FeignLoggerFactory feignLoggerFactory() {
    return new DefaultFeignLoggerFactory(logger);
  }
}

/**
 * Scans for interfaces that declare they are feign clients (via {@link FeignClient
 * <code>@FeignClient</code>}). 
 * // 扫描那些声明为feign client 的接口
 * Configures component scanning directives for use with
 * {@link org.springframework.context.annotation.Configuration
 * <code>@Configuration</code>} classes.
 *
 * @author Spencer Gibb
 * @author Dave Syer
 * @since 1.0
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(FeignClientsRegistrar.class)
public @interface EnableFeignClients {
  /**
   * Alias for the {@link #basePackages()} attribute. Allows for more concise annotation
   * declarations e.g.: {@code @ComponentScan("org.my.pkg")} instead of
   * {@code @ComponentScan(basePackages="org.my.pkg")}.
   * @return the array of 'basePackages'.
   */
  String[] value() default {};
  /**
   * Base packages to scan for annotated components.
   * <p>
   * {@link #value()} is an alias for (and mutually exclusive with) this attribute.
   * <p>//  value与该属性是互斥，不能共同使用。
   * Use {@link #basePackageClasses()} for a type-safe alternative to String-based
   * package names.
   *
   * @return the array of 'basePackages'.
   */
  String[] basePackages() default {};
  /**
   * Type-safe alternative to {@link #basePackages()} for specifying the packages to
   * scan for annotated components. The package of each class specified will be scanned.
   * <p>// 指定扫描的基础类型，可以与basePackages共同使用
   * Consider creating a special no-op marker class or interface in each package that
   * serves no purpose other than being referenced by this attribute.
   *
   * @return the array of 'basePackageClasses'.
   */
  Class<?>[] basePackageClasses() default {};
  /**
   * A custom <code>@Configuration</code> for all feign clients. 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
   */
  Class<?>[] defaultConfiguration() default {};
  /**
   * List of classes annotated with @FeignClient. If not empty, disables classpath scanning.
   * @return
   */
  Class<?>[] clients() default {};
}