Fegin的源码分析

@EnableFeignClients

FeignClientsRegistrar

可以看到FeignClientsRegistrar 实现了三个接口

class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware

其中:实现 ImportBeanDefinitionRegistrar重写registerBeanDefinitions()方法重点关注

public interface ImportBeanDefinitionRegistrar {
    default void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry,
                                         BeanNameGenerator importBeanNameGenerator) {
        registerBeanDefinitions(importingClassMetadata, registry);
    }
    default void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    }
}

从FeignClientsRegistrar 类找到registerBeanDefinitions()方法

class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware{
    //......
    @Override
    public void registerBeanDefinitions(AnnotationMetadata metadata,
            BeanDefinitionRegistry registry) {
        registerDefaultConfiguration(metadata, registry);//注册配置
        registerFeignClients(metadata, registry);//注册FeignClients
    }
    //.....
}

到最后可以看到注册了bean定义.其中 BeanDefinitionBuilder 通过 FeignClientFactoryBean 来获取的

FeignClientFactoryBean

找到 FeignClientFactoryBean 的getObject()方法

class FeignClientFactoryBean implements FactoryBean<Object>, InitializingBean, ApplicationContextAware {
    @Override
    public Object getObject() throws Exception {
        return getTarget();
    }
    <T> T getTarget() {
        FeignContext context = this.applicationContext.getBean(FeignContext.class);
        Feign.Builder builder = feign(context);
        if (!StringUtils.hasText(this.url)) {
            if (!this.name.startsWith("http")) {
                this.url = "http://" + this.name;
            }
            else {
                this.url = this.name;
            }
            this.url += cleanPath();
            return (T) loadBalance(builder, context,
                                   new HardCodedTarget<>(this.type, this.name, this.url));
        }
        if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {
            this.url = "http://" + this.url;
        }
        String url = this.url + cleanPath();
        Client client = getOptional(context, Client.class);
        if (client != null) {
            if (client instanceof LoadBalancerFeignClient) {
                // not load balancing because we have a url,
                // but ribbon is on the classpath, so unwrap
                client = ((LoadBalancerFeignClient) client).getDelegate();
            }
            if (client instanceof FeignBlockingLoadBalancerClient) {
                // not load balancing because we have a url,
                // but Spring Cloud LoadBalancer is on the classpath, so unwrap
                client = ((FeignBlockingLoadBalancerClient) client).getDelegate();
            }
            builder.client(client);
        }
        Targeter targeter = get(context, Targeter.class);
        return (T) targeter.target(this, builder, context,
                                   new HardCodedTarget<>(this.type, this.name, url));
    }
}

targeter类

接着找到下面,可知使用了jdk代理生成代理类

总结:到这里就知道,Springboot先扫描将FeignClient的代理对象注到Spring容器.然后就是使用的时候调用代理对象进行调用

源码图解

手写Feign的调用逻辑

通过注解获取服务名,接口方法,参数等信息
通过服务名取注册中心的服务地址列表
通过http调用,即可完成

创建ClientDiscoveryFeignClient

这里没有新创建注解,简单使用feign注解模拟

package com.itmck.client;
import com.itmck.dto.User;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.*;
/**
 * 太阳当空照,花儿对我笑
 * <p>
 * Create by M ChangKe 2021/11/2 20:54
 * <p>
 * 注意事项:
 * 1:Feign 里面定义的接口，有多个@RequestParam，但只能有不超过一个@RequestBody
 * 2:@FeignClient指定configuration后FeignConfig不能添加@Configuration
 **/
@FeignClient(value = "springcloud-discovery")
public interface ClientDiscoveryFeignClient {
    @ResponseBody
    @GetMapping("/product/getProduct")
    String getProduct(@RequestParam("name") String name);
}

创建代理MyProxyFactory

package com.itmck.proxy;
import lombok.extern.slf4j.Slf4j;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.client.RestTemplate;
import javax.annotation.Resource;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.net.URI;
import java.util.List;
/**
 * 太阳当空照,花儿对我笑
 * <p>
 * Create by M ChangKe 2021/12/12 16:33
 *
 * [模拟feign的调用]
 * 逻辑就是使用jdk生成代理对象,通过http调用远程服务.
 *
 * 步骤:
 * 1)通过 DiscoveryClient discoveryClient 获取注册中心实例的信息,然后拿到url
 * 2)通过 RestTemplate restTemplate  模拟get请求调用步骤 1)拿到的url.
 *
 *
 **/
@Slf4j
@Component
public class MyProxyFactory {
    @Resource
    private RestTemplate restTemplate;
    @Resource
    private DiscoveryClient discoveryClient;
    public <T> Object getInstance(Class<T> clazz) {
        return Proxy.newProxyInstance(clazz.getClassLoader(), new Class[]{clazz}, (proxy, method, args1) -> restGetOps(method, args1));
    }
    public Object restGetOps(Method method, Object[] args) {
        String serviceName = null;
        String path = null;
        Class<?> declaringClass = method.getDeclaringClass();
        if (declaringClass.isAnnotationPresent(FeignClient.class)) {
            FeignClient feignClient = declaringClass.getAnnotation(FeignClient.class);
            serviceName = feignClient.value();
        }
        if (method.isAnnotationPresent(GetMapping.class)) {
            GetMapping getMapping = method.getAnnotation(GetMapping.class);
            String url = getMapping.value()[0];
            List<ServiceInstance> instances = discoveryClient.getInstances(serviceName);
            if (instances != null) {
                ServiceInstance serviceInstance = instances.get(0);
                if (serviceInstance != null) {
                    URI uri = serviceInstance.getUri();
                    path = uri.toString();
                }
            }
            url = path + url + "?name=" + args[0];
            log.info("url:{}", url);
            return restTemplate.getForObject(url, String.class);
        }
        return null;
    }
}

测试

启动类注入

package com.itmck;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.openfeign.EnableFeignClients;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;
/**
 * 太阳当空照,花儿对我笑
 * <p>
 * Create by M ChangKe 2021/12/12 11:32
 **/
@EnableFeignClients
@EnableDiscoveryClient
@SpringBootApplication
public class SpringCloudOpenfeignApplication {
    public static void main(String[] args) {
        SpringApplication.run(SpringCloudOpenfeignApplication.class, args);
    }
    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

调用

@RestController
public class MyFeignController {
    @Resource
    private MyProxyFactory myProxyFactory;
    @GetMapping("/hello")
    public String getStr() {
        ClientDiscoveryFeignClient clientDiscoveryFeignClient = (ClientDiscoveryFeignClient) myProxyFactory.getInstance(ClientDiscoveryFeignClient.class);
        String result = clientDiscoveryFeignClient.getProduct("mck");
        System.out.println(result);
        return result;
    }
}

结果:

Java 实战入门

如何手写feign客户端