[cloud native] the ribbon is no longer used at the bottom of openfeign, which started in 2020.0.x

One 、 Preface

In front of Feign Series articles ：

1. SpringCloud And Feign A detailed case of implementing declarative client load balancing
2. SpringCloud And OpenFeign Realize the transfer of request header data between services （OpenFeign Interceptor RequestInterceptor Use ）
3. SpringCloud And OpenFeign Common configuration of （ Overtime 、 data compression 、 journal ）
4. SpringCloud And OpenFeign Core components （Encoder、Decoder、Contract）
5. SpringBoot Start in the startup process OpenFeign Entrance （ImportBeanDefinitionRegistrar Detailed explanation ）
6. Source analysis OpenFeign How to scan all FeignClient
7. Source analysis OpenFeign How to FeignClient Generate dynamic proxy class
8. Analysis of graphic source code OpenFeign Process request

We talked about the following ：

1. OpenFeign Overview 、 Why are they used Feign Instead of Ribbon?
2. Feign and OpenFeign The difference between ?
3. The details of the OpenFeign Implement declarative client load balancing cases
4. OpenFeign Middle interceptor RequestInterceptor Use
5. OpenFeign Some common configurations of （ Overtime 、 data compression 、 Log output ）
6. SpringCloud And OpenFeign Core components （Encoder、Decoder、Contract）
7. stay SpringBoot Start in the startup process OpenFeign Entrance
8. OpenFeign How to scan / Register all FeignClient
9. OpenFeign How to FeignClient Generate dynamic proxy class
10. OpenFeign Process request

This article is based on OpenFeign Higher version （SpringCloud 2020.0.x The version after the beginning of the version ） Discuss ：OpenFeign The difference between the new version and the old version （ Higher version OpenFeign The bottom layer does not use Ribbon Load balancing ）

PS： This article uses SpringCloud Higher version ：

<properties>
    <spring-boot.version>2.4.2</spring-boot.version>
    <spring-cloud.version>2020.0.1</spring-cloud.version>
    <spring-cloud-alibaba.version>2021.1</spring-cloud-alibaba.version>
</properties>

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-dependencies</artifactId>
            <version>${spring-boot.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
        <!-- Integrate spring cloud-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>${spring-cloud.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
        <!-- Integrate spring cloud alibaba-->
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-alibaba-dependencies</artifactId>
            <version>${spring-cloud-alibaba.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

PS： This article uses SpringCloud Low version ：

<properties>
    <spring-boot.version>2.3.7.RELEASE</spring-boot.version>
    <spring-cloud.version>Hoxton.SR9</spring-cloud.version>
    <spring-cloud-alibaba.version>2.2.6.RELEASE</spring-cloud-alibaba.version>
</properties>

Two 、 Differences between source code and main process versions

1、@FeignClientsRegistrar Open to FeignClient Scan

There is no difference in the main process here ;

stay SpringBoot Starting the process @FeignClientsRegistrar Annotations to open OpenFeign Entrance 、OpenFeign Scan all FeignClient The process of The high version is basically the same as the low version , See the article for the lower version ：FeignClientsRegistrar Annotations to open OpenFeign Entrance 、OpenFeign Scan all FeignClient.

The main process is as follows ：

1> Open the scanning FeignClient Entrance ：

1. Start the @EnableFeignClients The annotation will pass @Import Annotations in SpringBoot The startup process will ImportBeanDefinitionRegistrar Implementation class of interface FeignClientsRegistrar Injected into the startup class ConfigurationClass Properties of , Register the startup class BeanDefinition when , Will traverse and call its @Import All of the ImportBeanDefinitionRegistrar Interface registerBeanDefinitions() Method .

2> scanning FeignClient：

1. Get @EnableFeignClients Attributes related to the scanning package path configured in the annotation , Get the package path to scan ;
2. Get the scanner ClassPathScanningCandidateComponentProvider, Then add an annotation filter to it （AnnotationTypeFilter）, Only filter out the contents @FeignClient Annotated BeanDefinition;
3. Scanner findCandidateComponents(basePackage) Method scan out all annotations from the package path @FeignClient Annotate and conform to the interface of conditional assembly ; Then put it in BeanDefinitionRegistry Sign up for ;

2、 by FeignClient Generate dynamic proxy class

The difference is mainly reflected here ;

Register at FeignClient To Spring When the container , Built BeanDefinition Of beanClas yes FeignClientFactoryBean;FeignClientFactoryBean It's a factory , Save the @FeignClient All attribute values for annotation , stay Spring During container initialization , It will be based on the previously scanned FeignClient Information Architecture FeignClient Dynamic proxy class .

For the specific dynamic proxy class generation process, please refer to the blog ：OpenFeign How to FeignClient Generate dynamic proxy class ;

Bottom layer communication Client The difference between ？

In the use of Feign.Builder structure FeignClient When , Acquired Client yes FeignBlockingLoadBalancerClient（ The logic will be discussed later , stay OpenFeign The lower version is LoadBalancerFeignClient）; Used to generate FeignClient Of Targeter yes DefaultTargeter（ stay OpenFeign The lower version is HystrixTargeter, The higher version removed Hystrix, use Spring Cloud Circuit Breaker Make current limiting fuse ）;

It is embodied in FeignClientFactoryBean#loadBalance() Method , It is a load balancing FeignClient Dynamic proxy generation method ;

OpenFeign Low version ：

1> FeignBlockingLoadBalancerClient When to inject into Spring Containers ？

FeignBlockingLoadBalancerClient Injection into Spring The way of containers and OpenFeign Low version of the LoadBalancerFeignClient It's the same ;

Enter into FeignBlockingLoadBalancerClient Class , Look where it calls its only constructor ;

find FeignBlockingLoadBalancerClient It is found that its constructor is called in three places ,new An example is given ;

• DefaultFeignLoadBalancedConfiguration
• HttpClientFeignLoadBalancedConfiguration
• OkHttpFeignLoadBalancedConfiguration

Combined with the default configuration , Only DefaultFeignLoadBalancedConfiguration Medium Client Qualified assembly ;

By introducing Apache HttpClient Of maven Rely on the use of HttpClientFeignLoadBalancedConfiguration,

Or introduce OkHttpClient Of maven Depend on and be in application.yml The document specifies feign.okhttp.enabled The attribute is true Use OkHttpFeignLoadBalancedConfiguration.

2> DefaultTargeter Where to inject Spring Containers ？

DefaultTargeter Injection into Spring The way of containers and OpenFeign Low version of the HystrixTargeter It's the same ;

stay FeignAutoConfiguration Class Targeter Injection into Spring Container logic ;

3> The logic of subsequent generation of dynamic proxy classes is the same as that of the old version

Are reflected in ReflectiveFeign#newInstance() In the method ：

3、**Client Load balancing （ The core difference between ）

above-mentioned OpenFeign Obtained from the higher version Client yes FeignBlockingLoadBalancerClient, The lower version is LoadBalancerFeignClient,LoadBalancerFeignClient be based on Ribbon Load balancing ,FeignBlockingLoadBalancerClient It depends OpenFeign Realize load balancing by yourself ;

OpenFeign How to deal with a HTTP Request to see the blog ： Analysis of graphic source code OpenFeign Process request .

Next, take a look FeignBlockingLoadBalancerClient How to do load balancing ！！

1）FeignBlockingLoadBalancerClient Select a service instance