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Spring Cloud之Feign

  1. 引入依赖
  2. 自定义Http Client
    1. Apache Http Client
    2. OkHttp
  3. FeignClient接口扫描
    1. Feign接口仅支持继承一个接口
  4. 自定义feign超时
  5. 问题记录
    1. 请求body为空对象时报错

引入依赖

build.gradle
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implementation 'org.springframework.cloud:spring-cloud-starter-openfeign'

自定义Http Client

Apache Http Client

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implementation 'io.github.openfeign:feign-httpclient'

OkHttp

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implementation 'io.github.openfeign:feign-okhttp'

FeignClient接口扫描

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@EnableFeignClients(basePackageClasses = {
        Application.class, // 本项目根路径
        OtherClient.class  // 其他包的Client
})
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

注意：使用@ComponentScan无效

Feign接口仅支持继承一个接口

Contract.parseAndValidateMetadata

自定义feign超时

全局默认

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feign.client.config.default.connect-timeout=10000
feign.client.config.default.read-timeout=60000

指定FeignClient的配置

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feign.client.config.myContextId.connect-timeout=10000
feign.client.config.myContextId.read-timeout=60000

Spring构造Feign Client流程

org.springframework.cloud.openfeign.FeignClientFactoryBean#configureFeign

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protected void configureFeign(FeignContext context, Feign.Builder builder) {
    FeignClientProperties properties = beanFactory != null ? beanFactory.getBean(FeignClientProperties.class)
            : applicationContext.getBean(FeignClientProperties.class);

    FeignClientConfigurer feignClientConfigurer = getOptional(context, FeignClientConfigurer.class);
    setInheritParentContext(feignClientConfigurer.inheritParentConfiguration());

    if (properties != null && inheritParentContext) {
        if (properties.isDefaultToProperties()) {
            configureUsingConfiguration(context, builder);
            configureUsingProperties(properties.getConfig().get(properties.getDefaultConfig()), builder);
            configureUsingProperties(properties.getConfig().get(contextId), builder);
        }
        else {
            configureUsingProperties(properties.getConfig().get(properties.getDefaultConfig()), builder);
            configureUsingProperties(properties.getConfig().get(contextId), builder);
            configureUsingConfiguration(context, builder);
        }
    }
    else {
        configureUsingConfiguration(context, builder);
    }
}

问题记录

请求body为空对象时报错

问题复现：

Feign接口定义如下

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@PostMapping("call")
Response call(@RequestBody Request request);

其中 Request 为空对象

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@Data
public class Request {

}

调用方执行时会出错

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feign.codec.EncodeException: Could not write request: no suitable HttpMessageConverter found for request type

解决方法

方案1：调用方增加配置（推荐）

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spring.jackson.serialization.fail-on-empty-beans=false

方案2：body不使用空对象

原理分析

Spring Feign使用HttpMessageConverters处理请求体，最终我们希望是MappingJackson2HttpMessageConverter来序列化我们的body对象，但前提需要通过它的canWrite方法，方法如下

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@Override
public boolean canWrite(Class<?> clazz, @Nullable MediaType mediaType) {
    if (!canWrite(mediaType)) {
        return false;
    }
    if (mediaType != null && mediaType.getCharset() != null) {
        Charset charset = mediaType.getCharset();
        if (!ENCODINGS.containsKey(charset.name())) {
            return false;
        }
    }
    AtomicReference<Throwable> causeRef = new AtomicReference<>();
    if (this.objectMapper.canSerialize(clazz, causeRef)) {
        return true;
    }
    logWarningIfNecessary(clazz, causeRef.get());
    return false;
}

注意其中的canSerialize方法，当ObjectMapper开启fail-on-empty-beans时（也是默认开启），canSerialize(Object.class)将返回false

所以我们需要关闭Spring管理的ObjectMapper的fail-on-empty-beans选项

  技术 / Java
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