Spring Cloud与微服务构建（七）声明式调用Feign 7.3 FeignClient的配置

Feign Client默认的配置类为FeignClientsConfiguration，这个类在spring-cloud-netflix-core的jar包下。打开这个类，可以发现这个类注入了很多Feign相关的配置Bean，包括FeignRetryer、FeignLoggerFactor和FormattiongConversionService等。另外，Decoder、Encoder和Contract这3个类在没有Bean被注入的情况下，会自动注入默认配置的Bean，即ResponseEntityDecoder、SpringEncoder和SpringMvcContract。默认注入的配置如下。

• Decoder feignDecoder：ResponseEntityDecoder
• Encoder feignEncoder：SpringEncoder
• Logger feignLogger：Slf4jLogger
• Contract feignContract：SpringMvcContract
• Feign.Buider feignBuilder：HystrixFeign.Builder。

FeignClientsConfiguration的配置类部分代码如下，@ConditionalOnMissingBean注解表示如果没有注入该类的Bean就会默认注入一个Bean。

@Configuration
public class FeignClientsConfiguration {
    @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;

    public FeignClientsConfiguration() {
    }

    @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);
    }

    @Bean
    public FormattingConversionService feignConversionService() {
        FormattingConversionService conversionService = new DefaultFormattingConversionService();
        Iterator var2 = this.feignFormatterRegistrars.iterator();

        while(var2.hasNext()) {
            FeignFormatterRegistrar feignFormatterRegistrar = (FeignFormatterRegistrar)var2.next();
            feignFormatterRegistrar.registerFormatters(conversionService);
        }

        return conversionService;
    }

    @Bean
    @ConditionalOnMissingBean
    public Retryer feignRetryer() {
        return Retryer.NEVER_RETRY;
    }

    @Bean
    @Scope("prototype")
    @ConditionalOnMissingBean
    public Builder feignBuilder(Retryer retryer) {
        return Feign.builder().retryer(retryer);
    }

    @Bean
    @ConditionalOnMissingBean({FeignLoggerFactory.class})
    public FeignLoggerFactory feignLoggerFactory() {
        return new DefaultFeignLoggerFactory(this.logger);
    }

    @Configuration
    @ConditionalOnClass({HystrixCommand.class, HystrixFeign.class})
    protected static class HystrixFeignConfiguration {
        protected HystrixFeignConfiguration() {
        }

        @Bean
        @Scope("prototype")
        @ConditionalOnMissingBean
        @ConditionalOnProperty(
            name = {"feign.hystrix.enabled"},
            matchIfMissing = false
        )
        public Builder feignHystrixBuilder() {
            return HystrixFeign.builder();
        }
    }
}

重写FeignClientsCnfiguration类中的Bean，覆盖掉默认的配置Bean，从而达到自定义配置的目的。例如Feign默认的配置在请求失败后，重试次数为0，即不重试（Retryer,NEVER_RETRY）。现在希望在请求失败后能够重试，这时需要写一个配置FeignConfig类，在该类中注入Retryer的Bean，覆盖掉默认的Retryer的Bean，并将FeignConfig指定为FeignClient的配置类。FeignConfig类的代码如下

@Configuration
public class FeignClientsConfiguration {
    @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;

    public FeignClientsConfiguration() {
    }

    @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);
    }

    @Bean
    public FormattingConversionService feignConversionService() {
        FormattingConversionService conversionService = new DefaultFormattingConversionService();
        Iterator var2 = this.feignFormatterRegistrars.iterator();

        while(var2.hasNext()) {
            FeignFormatterRegistrar feignFormatterRegistrar = (FeignFormatterRegistrar)var2.next();
            feignFormatterRegistrar.registerFormatters(conversionService);
        }

        return conversionService;
    }

    @Bean
    @ConditionalOnMissingBean
    public Retryer feignRetryer() {
        return Retryer.NEVER_RETRY;
    }

    @Bean
    @Scope("prototype")
    @ConditionalOnMissingBean
    public Builder feignBuilder(Retryer retryer) {
        return Feign.builder().retryer(retryer);
    }

    @Bean
    @ConditionalOnMissingBean({FeignLoggerFactory.class})
    public FeignLoggerFactory feignLoggerFactory() {
        return new DefaultFeignLoggerFactory(this.logger);
    }

    @Configuration
    @ConditionalOnClass({HystrixCommand.class, HystrixFeign.class})
    protected static class HystrixFeignConfiguration {
        protected HystrixFeignConfiguration() {
        }

        @Bean
        @Scope("prototype")
        @ConditionalOnMissingBean
        @ConditionalOnProperty(
            name = {"feign.hystrix.enabled"},
            matchIfMissing = false
        )
        public Builder feignHystrixBuilder() {
            return HystrixFeign.builder();
        }
    }
}