spring cloud openfeign中Targeter的原理和作用是什么

发布时间：2021-06-30 15:27:45 作者：chen
来源：亿速云阅读：260

这篇文章主要介绍“spring cloud openfeign中Targeter的原理和作用是什么”，在日常操作中，相信很多人在spring cloud openfeign中Targeter的原理和作用是什么问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”spring cloud openfeign中Targeter的原理和作用是什么”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！

序

本文主要研究一下spring cloud openfeign的Targeter

Targeter

spring-cloud-openfeign-core-2.2.0.M1-sources.jar!/org/springframework/cloud/openfeign/Targeter.java

interface Targeter {

	<T> T target(FeignClientFactoryBean factory, Feign.Builder feign,
			FeignContext context, Target.HardCodedTarget<T> target);

}

Targeter定义了target方法，它接收FeignClientFactoryBean、Feign.Builder、FeignContext、Target.HardCodedTarget类型的参数

DefaultTargeter

spring-cloud-openfeign-core-2.2.0.M1-sources.jar!/org/springframework/cloud/openfeign/DefaultTargeter.java

class DefaultTargeter implements Targeter {

	@Override
	public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign,
			FeignContext context, Target.HardCodedTarget<T> target) {
		return feign.target(target);
	}

}

DefaultTargeter实现了Targeter接口，它的target方法直接使用的是Feign.Builder.target方法

Target

feign-core-10.2.3-sources.jar!/feign/Target.java

public interface Target<T> {

  /* The type of the interface this target applies to. ex. {@code Route53}. */
  Class<T> type();

  /* configuration key associated with this target. For example, {@code route53}. */
  String name();

  /* base HTTP URL of the target. For example, {@code https://api/v2}. */
  String url();

  public Request apply(RequestTemplate input);

  //......

}

Target接口定义了type、name、url、apply方法

HardCodedTarget

feign-core-10.2.3-sources.jar!/feign/Target.java

  public static class HardCodedTarget<T> implements Target<T> {

    private final Class<T> type;
    private final String name;
    private final String url;

    public HardCodedTarget(Class<T> type, String url) {
      this(type, url, url);
    }

    public HardCodedTarget(Class<T> type, String name, String url) {
      this.type = checkNotNull(type, "type");
      this.name = checkNotNull(emptyToNull(name), "name");
      this.url = checkNotNull(emptyToNull(url), "url");
    }

    @Override
    public Class<T> type() {
      return type;
    }

    @Override
    public String name() {
      return name;
    }

    @Override
    public String url() {
      return url;
    }

    /* no authentication or other special activity. just insert the url. */
    @Override
    public Request apply(RequestTemplate input) {
      if (input.url().indexOf("http") != 0) {
        input.target(url());
      }
      return input.request();
    }

    @Override
    public boolean equals(Object obj) {
      if (obj instanceof HardCodedTarget) {
        HardCodedTarget<?> other = (HardCodedTarget) obj;
        return type.equals(other.type)
            && name.equals(other.name)
            && url.equals(other.url);
      }
      return false;
    }

    @Override
    public int hashCode() {
      int result = 17;
      result = 31 * result + type.hashCode();
      result = 31 * result + name.hashCode();
      result = 31 * result + url.hashCode();
      return result;
    }

    @Override
    public String toString() {
      if (name.equals(url)) {
        return "HardCodedTarget(type=" + type.getSimpleName() + ", url=" + url + ")";
      }
      return "HardCodedTarget(type=" + type.getSimpleName() + ", name=" + name + ", url=" + url
          + ")";
    }
  }

HardCodedTarget实现了Target接口，其构造器接收type、name、url参数，其apply方法对于url是http开头的则设置RequestTemplate的target为url，然后构造request返回

HystrixTargeter

spring-cloud-openfeign-core-2.2.0.M1-sources.jar!/org/springframework/cloud/openfeign/HystrixTargeter.java

class HystrixTargeter implements Targeter {

	@Override
	public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign,
			FeignContext context, Target.HardCodedTarget<T> target) {
		if (!(feign instanceof feign.hystrix.HystrixFeign.Builder)) {
			return feign.target(target);
		}
		feign.hystrix.HystrixFeign.Builder builder = (feign.hystrix.HystrixFeign.Builder) feign;
		SetterFactory setterFactory = getOptional(factory.getName(), context,
				SetterFactory.class);
		if (setterFactory != null) {
			builder.setterFactory(setterFactory);
		}
		Class<?> fallback = factory.getFallback();
		if (fallback != void.class) {
			return targetWithFallback(factory.getName(), context, target, builder,
					fallback);
		}
		Class<?> fallbackFactory = factory.getFallbackFactory();
		if (fallbackFactory != void.class) {
			return targetWithFallbackFactory(factory.getName(), context, target, builder,
					fallbackFactory);
		}

		return feign.target(target);
	}

	private <T> T targetWithFallbackFactory(String feignClientName, FeignContext context,
			Target.HardCodedTarget<T> target, HystrixFeign.Builder builder,
			Class<?> fallbackFactoryClass) {
		FallbackFactory<? extends T> fallbackFactory = (FallbackFactory<? extends T>) getFromContext(
				"fallbackFactory", feignClientName, context, fallbackFactoryClass,
				FallbackFactory.class);
		return builder.target(target, fallbackFactory);
	}

	private <T> T targetWithFallback(String feignClientName, FeignContext context,
			Target.HardCodedTarget<T> target, HystrixFeign.Builder builder,
			Class<?> fallback) {
		T fallbackInstance = getFromContext("fallback", feignClientName, context,
				fallback, target.type());
		return builder.target(target, fallbackInstance);
	}

	private <T> T getFromContext(String fallbackMechanism, String feignClientName,
			FeignContext context, Class<?> beanType, Class<T> targetType) {
		Object fallbackInstance = context.getInstance(feignClientName, beanType);
		if (fallbackInstance == null) {
			throw new IllegalStateException(String.format(
					"No " + fallbackMechanism
							+ " instance of type %s found for feign client %s",
					beanType, feignClientName));
		}

		if (!targetType.isAssignableFrom(beanType)) {
			throw new IllegalStateException(String.format("Incompatible "
					+ fallbackMechanism
					+ " instance. Fallback/fallbackFactory of type %s is not assignable to %s for feign client %s",
					beanType, targetType, feignClientName));
		}
		return (T) fallbackInstance;
	}

	private <T> T getOptional(String feignClientName, FeignContext context,
			Class<T> beanType) {
		return context.getInstance(feignClientName, beanType);
	}

}

HystrixTargeter实现了Targeter接口，其target方法首先判断Feign.Builder类型是否是feign.hystrix.HystrixFeign.Builder，不是的话直接执行feign.target(target)返回
对于fallback不为void.class的使用targetWithFallback进行构造；对于fallbackFactory不为void.class的使用targetWithFallbackFactory进行构造；都不是的话则执行feign.target(target)返回
targetWithFallbackFactory方法使用HystrixFeign.Builder的target进行构造时使用的是fallbackFactory；而targetWithFallback方法使用的是fallbackInstance

FeignAutoConfiguration

spring-cloud-openfeign-core-2.2.0.M1-sources.jar!/org/springframework/cloud/openfeign/FeignAutoConfiguration.java

@Configuration
@ConditionalOnClass(Feign.class)
@EnableConfigurationProperties({ FeignClientProperties.class,
		FeignHttpClientProperties.class })
public class FeignAutoConfiguration {
	//......

	@Configuration
	@ConditionalOnClass(name = "feign.hystrix.HystrixFeign")
	protected static class HystrixFeignTargeterConfiguration {

		@Bean
		@ConditionalOnMissingBean
		public Targeter feignTargeter() {
			return new HystrixTargeter();
		}

	}

	@Configuration
	@ConditionalOnMissingClass("feign.hystrix.HystrixFeign")
	protected static class DefaultFeignTargeterConfiguration {

		@Bean
		@ConditionalOnMissingBean
		public Targeter feignTargeter() {
			return new DefaultTargeter();
		}

	}

	//......
}

FeignAutoConfiguration在有feign.hystrix.HystrixFeign时创建的是HystrixTargeter，否则创建的是DefaultTargeter

小结

Targeter定义了target方法，它接收FeignClientFactoryBean、Feign.Builder、FeignContext、Target.HardCodedTarget类型的参数
DefaultTargeter实现了Targeter接口，它的target方法直接使用的是Feign.Builder.target方法
HystrixTargeter实现了Targeter接口，其target方法首先判断Feign.Builder类型是否是feign.hystrix.HystrixFeign.Builder，不是的话直接执行feign.target(target)返回；否则对于fallback不为void.class的使用targetWithFallback进行构造；对于fallbackFactory不为void.class的使用targetWithFallbackFactory进行构造；都不是的话则执行feign.target(target)返回

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