原创

Feign源码总结

入门

如何使用feign？

1.添加依赖

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>

2.编写feign接口

OrderFeignClient：

package com.lzhpo.order_service_02.feign;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

/**
 * <p> Author：lzhpo </p>
 * <p> Title：</p>
 * <p> Description：
 * 使用feign
 * </p>
 */
@FeignClient(name = "product-service")  //调用远程哪个服务
public interface OrderFeignClient {

    /**
     * 根据商品ID查询商品
     *
     * 注意：@RequestMapping("/api/v1/product/find")的值要和商品服务product-service的接口一致。
     *
     * 使用Ribbon的时候写的 restTemplate.getForObject() 这些方法，
     * 现在使用feign，feign里面自带了ribbon，而且简化了代码，直接写接口即可，标明哪个服务即可。
     *
     * @param productId
     * @return
     */
    @RequestMapping("/api/v1/product/find")
    String findByProductId(@RequestParam("productId") Integer productId);

    /**
     * 扣减库存
     *
     * 注意：@RequestMapping("/api/v1/product/updateSubtractProductNum")的值要和商品服务product-service的接口一致。
     *
     * @param productName
     * @return
     */
    @RequestMapping("/api/v1/product/updateSubtractProductNum")
    String updateSubtractProductNum(@RequestParam("productName") String productName);
}

注意事项：feign接口的请求地址要和商品服务product-service一致。

3.使用feign接口

直接注入编写的feign接口使用即可。

4.启动类

添加注解：@EnableFeignClients，表示使用feign。

RestTemplate这段代码表示使用RestTemplate。

源码分析

feign核心类介绍

feign.Feign.Builder 设置发送http请求的相关参数，比如http客户端，重试策略，编解码，超时时间等等
- feign.Contract.Default 解析接口方法的元数据，构建http请求模板
- feign.Client 发送http请求客户端，默认实现feign.Client.Default，使用的是java.net包实现的
- Retryer 重试，默认实现feign.Retryer.Default，超时延迟100ms开始重试，每隔1s重试一次，重试4次
- Options 超时时间，默认连接超时10s，读超时60s
- feign.codec.Encoder 编码器
- feign.codec.Decoder 解码器
- RequestInterceptor 请求拦截器，可以在发送http请求之前执行此拦截器
- feign.Contract 接口以及方法元数据解析器
  以上参数都可以自己扩展
HardCodedTarget 定于目标接口和url
ReflectiveFeign 生成动态代理类，基于jdk的动态代理实现
feign.InvocationHandlerFactory.Default 接口方法统一拦截器创建工厂
FeignInvocationHandler 接口统一方法拦截器
ParseHandlersByName 解析接口方法元数据
SynchronousMethodHandler.Factory 接口方法的拦截器创建工厂
SynchronousMethodHandler 接口方法的拦截器，真正拦截的核心，这里真正发起http请求，处理返回结果。

开启`@EnableFeignClients`注解到底给我们做了什么事情呢？

扫描EnableFeignClients注解上的配置信息，注册默认的配置类，这个配置类是对所有feignclient的都是生效的，即为全局的配置。
扫描带有@FeignClient注解的接口，并注册配置类（此时的配置类针对当前feignclient生效）和FeignClientFactoryBean，此bean实现了FactoryBean接口，我们知道spring有两种类型的bean对象，一种是普通的bean，另一种则是工厂bean（FactoryBean），它返回的其实是getObject方法返回的对象（更多关于FactoryBean的相关信息请查看spring官方文档）。getObject方法就是集成原生feign的核心方法，当spring注入feignclient接口时，getObject方法会被调用，得到接口的代理类。

注意事项：在FeignClient指定配置类时，切记不要被spring容器扫描到，不然会对全局生效。

Feign的三个自动加载配置类

自动加载配置类FeignAutoConfiguration，FeignClientsConfiguration，FeignRibbonClientAutoConfiguration，这三个类为feign提供了所有的配置类，默认情况下所加载的类情况：

feign.Feign.Builder 当引入了Hytrix并开启参数feign.hystrix.enabled=true后，则会加载feign.hystrix.HystrixFeign.Builder，此时feign就具备降级熔断的功能了。
feign.Client 此实现类的加载分两种情况：
- 使用url方式：feign.Client.Default，使用java原生的方式（java.net包）发起http请求，也可以自己扩展。
- 使用name方式：LoadBalancerFeignClient，集成了ribbon，实现服务发现与负载均衡，但是真正发起http请求还是java原生的方式
  此处是一扩展点，当我们引入ApacheHttpClient时，http客户端就会使用apache的httpClient；当我们引入OkHttpClient时，http客户端就会使用okhttp3.OkHttpClient。
feign.Retryer 默认Retryer.NEVER_RETRY，不进行重试，这里也可以自己实现Retryer接口实现自己的重试策略，但是feign在集成了ribbon的情况下，最好保持默认不进行重试，因为ribbon也会有重试策略，如果feign也开启重试，容易产生混乱；其实在低版本中spring-cloud-feing重试默认并不是NEVER_RETRY，可能spring-cloud-feing也意识到这样做的问题，所以在D版中改成NEVER_RETRY了。
feign.Request.Options 默认设置连接超时时间是10，读超时时间是60s。这里也可以更改，分两种情况：
- 使用url方式：必须通过这个参数来设置，才生效
```
@Configuration
public class MyConfig {
    @Bean
    public Request.Options options(){
        Request.Options o = new Options(1000, 1000);
        return o;
    }
}
```
  然后在注解上@FeignClient指定：
```
@FeignClient(name="",url="",configuration= {MyConfig.class})
```
  注意此类不能被spring容器扫描到，否则会对全局生效。你也可以通过注解@EnableFeignClients来全局指定：
```
@EnableFeignClients(defaultConfiguration=MyConfig.class)
```
- 使用name方式：此时已经集成了ribbon，可以使用以下配置来设置，如果你此时也配置了Options，以下配置会被覆盖
```
# 对所有的feignclient生效
ribbon.ReadTimeout=10000
ribbon.ConnectTimeout=2000

# 对指定的feignclien生效
[feignclientName].ribbon.ReadTimeout=10000
[feignclientName].ribbon.ConnectTimeout=2000
```
  如果开启Hytrix，hytrix也有超时时间设置，但是hytrix是封装在feign基础之上的，上文已有分析。
```
hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds=10000
```
  你也可以关闭hytrix的超时时间
```
hystrix.command.default.execution.timeout.enabled=false
```
feign.codec.Decoder 解码器，默认使用了HttpMessageConverters来实现
feign.codec.Encoder 编码器，默认使用了HttpMessageConverters来实现
feign.Contract 默认提供springmvc的注解解析，支持@RequestMapping，@RequestBody，@RequestParam，@PathVariable

最后三种也是spring-cloud-feign替换原生feign的默认实现，对springMVC的相关支持。

Feign Bean创建

Feign组件初始化是从@EnableFeignClients注解开始的：

EnableFeignClients源码：

/*
 * Copyright 2013-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.openfeign;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.context.annotation.Import;

/**
 * Scans for interfaces that declare they are feign clients (via
 * {@link org.springframework.cloud.openfeign.FeignClient} <code>@FeignClient</code>).
 * Configures component scanning directives for use with
 * {@link org.springframework.context.annotation.Configuration}
 * <code>@Configuration</code> classes.
 *
 * @author Spencer Gibb
 * @author Dave Syer
 * @since 1.0
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(FeignClientsRegistrar.class)  //导入了Feign组件的注册器，用于扫描Feign组件与初始化Feign组件的Bean定义信息
public @interface EnableFeignClients {

    /**
     * Alias for the {@link #basePackages()} attribute. Allows for more concise annotation
     * declarations e.g.: {@code @ComponentScan("org.my.pkg")} instead of
     * {@code @ComponentScan(basePackages="org.my.pkg")}.
     * @return the array of 'basePackages'.
     */
    String[] value() default {};

    /**
     * 扫描包。
     *
     * Base packages to scan for annotated components.
     * <p>
     * {@link #value()} is an alias for (and mutually exclusive with) this attribute.
     * <p>
     * Use {@link #basePackageClasses()} for a type-safe alternative to String-based
     * package names.
     * @return the array of 'basePackages'.
     */
    String[] basePackages() default {};

    /**
     * Type-safe alternative to {@link #basePackages()} for specifying the packages to
     * scan for annotated components. The package of each class specified will be scanned.
     * <p>
     * Consider creating a special no-op marker class or interface in each package that
     * serves no purpose other than being referenced by this attribute.
     * @return the array of 'basePackageClasses'.
     */
    Class<?>[] basePackageClasses() default {};

    /**
     * 定义@FeignClient组件的配置类，在配置类中可以自己定义Feign请求的Decoder解码器、Encoder编码器、Contract组件扫描构造器。
     *
     * A custom <code>@Configuration</code> for all feign clients. Can contain override
     * <code>@Bean</code> definition for the pieces that make up the client, for instance
     * {@link feign.codec.Decoder}, {@link feign.codec.Encoder}, {@link feign.Contract}.
     *
     * @see FeignClientsConfiguration for the defaults
     * @return list of default configurations
     */
    Class<?>[] defaultConfiguration() default {};

    /**
     * List of classes annotated with @FeignClient. If not empty, disables classpath
     * scanning.
     * @return list of FeignClient classes
     */
    Class<?>[] clients() default {};

}

核心有2个方法，basePackages与defaultConfiguration，前者用于定义扫描包路径，后者用于定义@FeignClient组件的配置类，在配置类中可以自己定义Feign请求的Decoder解码器、Encoder编码器、Contract组件扫描构造器。
在注解上有一个关键注解@Import(FeignClientsRegistrar.class)，导入了Feign组件的注册器，用于扫描Feign组件与初始化Feign组件的Bean定义信息。

FeignClientsRegistrar源码：

/*
 * Copyright 2013-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.openfeign;

import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.URL;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.springframework.beans.factory.annotation.AnnotatedBeanDefinition;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanDefinitionHolder;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionReaderUtils;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.context.EnvironmentAware;
import org.springframework.context.ResourceLoaderAware;
import org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.annotation.AnnotationAttributes;
import org.springframework.core.env.Environment;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.core.type.ClassMetadata;
import org.springframework.core.type.classreading.MetadataReader;
import org.springframework.core.type.classreading.MetadataReaderFactory;
import org.springframework.core.type.filter.AbstractClassTestingTypeFilter;
import org.springframework.core.type.filter.AnnotationTypeFilter;
import org.springframework.core.type.filter.TypeFilter;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

/**
 * Feign组件的注册器，用于扫描Feign组件与初始化Feign组件的Bean定义信息。
 *
 * @author Spencer Gibb
 * @author Jakub Narloch
 * @author Venil Noronha
 * @author Gang Li
 */
class FeignClientsRegistrar
        implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware {

    // patterned after Spring Integration IntegrationComponentScanRegistrar
    // and RibbonClientsConfigurationRegistgrar

    private ResourceLoader resourceLoader;

    private Environment environment;

    FeignClientsRegistrar() {
    }

    /**
     * Fallback类必须实现@FeignClient注释的接口
     *
     * @param clazz
     */
    static void validateFallback(final Class clazz) {
        Assert.isTrue(!clazz.isInterface(),
                "Fallback class must implement the interface annotated by @FeignClient");
    }

    /**
     * Fallback工厂必须生成回退类的实例，以实现@FeignClient注释的接口
     *
     * @param clazz
     */
    static void validateFallbackFactory(final Class clazz) {
        Assert.isTrue(!clazz.isInterface(), "Fallback factory must produce instances "
                + "of fallback classes that implement the interface annotated by @FeignClient");
    }

    /**
     * 获取feign组件的名称
     *
     * @param name
     * @return
     */
    static String getName(String name) {
        if (!StringUtils.hasText(name)) {
            return "";
        }

        String host = null;
        try {
            String url;
            if (!name.startsWith("http://") && !name.startsWith("https://")) {
                url = "http://" + name;
            }
            else {
                url = name;
            }
            host = new URI(url).getHost();

        }
        catch (URISyntaxException e) {
        }
        Assert.state(host != null, "Service id not legal hostname (" + name + ")");
        return name;
    }

    /**
     * 获取feign组件的地址
     *
     * @param url
     * @return
     */
    static String getUrl(String url) {
        if (StringUtils.hasText(url) && !(url.startsWith("#{") && url.contains("}"))) {
            if (!url.contains("://")) {
                url = "http://" + url;
            }
            try {
                new URL(url);
            }
            catch (MalformedURLException e) {
                throw new IllegalArgumentException(url + " is malformed", e);
            }
        }
        return url;
    }

    /**
     * 获取feign组件的路径
     *
     * @param path
     * @return
     */
    static String getPath(String path) {
        if (StringUtils.hasText(path)) {
            path = path.trim();
            if (!path.startsWith("/")) {
                path = "/" + path;
            }
            if (path.endsWith("/")) {
                path = path.substring(0, path.length() - 1);
            }
        }
        return path;
    }

    @Override
    public void setResourceLoader(ResourceLoader resourceLoader) {
        this.resourceLoader = resourceLoader;
    }

    /**
     * 定义配置类
     *
     * @param metadata
     * @param registry
     */
    @Override
    public void registerBeanDefinitions(AnnotationMetadata metadata,
            BeanDefinitionRegistry registry) {
        registerDefaultConfiguration(metadata, registry);
        registerFeignClients(metadata, registry);
    }

    /**
     * 自定义配置Bean
     *
     * @param metadata
     * @param registry
     */
    private void registerDefaultConfiguration(AnnotationMetadata metadata,
            BeanDefinitionRegistry registry) {
        Map<String, Object> defaultAttrs = metadata
                .getAnnotationAttributes(EnableFeignClients.class.getName(), true);
        //如果存在自定义配置则定义配置Bean
        if (defaultAttrs != null && defaultAttrs.containsKey("defaultConfiguration")) {
            String name;
            if (metadata.hasEnclosingClass()) {
                name = "default." + metadata.getEnclosingClassName();
            }
            else {
                name = "default." + metadata.getClassName();
            }
            registerClientConfiguration(registry, name,
                    defaultAttrs.get("defaultConfiguration"));
        }
    }

    public void registerFeignClients(AnnotationMetadata metadata,
            BeanDefinitionRegistry registry) {
        ClassPathScanningCandidateComponentProvider scanner = getScanner();
        scanner.setResourceLoader(this.resourceLoader);

        Set<String> basePackages;

        Map<String, Object> attrs = metadata
                .getAnnotationAttributes(EnableFeignClients.class.getName());
        //指定扫描类注解类型为@FeignClient的类
        AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(
                FeignClient.class);
        final Class<?>[] clients = attrs == null ? null
                : (Class<?>[]) attrs.get("clients");
        if (clients == null || clients.length == 0) {
            scanner.addIncludeFilter(annotationTypeFilter);
            basePackages = getBasePackages(metadata);
        }
        else {
            final Set<String> clientClasses = new HashSet<>();
            basePackages = new HashSet<>();
            for (Class<?> clazz : clients) {
                basePackages.add(ClassUtils.getPackageName(clazz));
                clientClasses.add(clazz.getCanonicalName());
            }
            AbstractClassTestingTypeFilter filter = new AbstractClassTestingTypeFilter() {
                @Override
                protected boolean match(ClassMetadata metadata) {
                    String cleaned = metadata.getClassName().replaceAll("\\$", ".");
                    return clientClasses.contains(cleaned);
                }
            };
            scanner.addIncludeFilter(
                    new AllTypeFilter(Arrays.asList(filter, annotationTypeFilter)));
        }
        //扫描定义的Feign组件包路径
        for (String basePackage : basePackages) {
            Set<BeanDefinition> candidateComponents = scanner
                    .findCandidateComponents(basePackage);
            for (BeanDefinition candidateComponent : candidateComponents) {
                if (candidateComponent instanceof AnnotatedBeanDefinition) {
                    // verify annotated class is an interface
                    AnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition) candidateComponent;
                    AnnotationMetadata annotationMetadata = beanDefinition.getMetadata();
                    Assert.isTrue(annotationMetadata.isInterface(),
                            "@FeignClient can only be specified on an interface");

                    Map<String, Object> attributes = annotationMetadata
                            .getAnnotationAttributes(
                                    FeignClient.class.getCanonicalName());

                    String name = getClientName(attributes);
                    registerClientConfiguration(registry, name,
                            attributes.get("configuration"));

                    registerFeignClient(registry, annotationMetadata, attributes);
                }
            }
        }
    }

    private void registerFeignClient(BeanDefinitionRegistry registry,
            AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {
        String className = annotationMetadata.getClassName();
        /**
         * 核心代码：
         * 定义Feign组件的创建工厂FeignClientFactoryBean。
         *         BeanDefinitionBuilder definition = BeanDefinitionBuilder
         *                 .genericBeanDefinition(FeignClientFactoryBean.class);
         *         validate(attributes);
         */
        BeanDefinitionBuilder definition = BeanDefinitionBuilder
                .genericBeanDefinition(FeignClientFactoryBean.class);
        validate(attributes);
        definition.addPropertyValue("url", getUrl(attributes));
        definition.addPropertyValue("path", getPath(attributes));
        String name = getName(attributes);
        definition.addPropertyValue("name", name);
        String contextId = getContextId(attributes);
        definition.addPropertyValue("contextId", contextId);
        definition.addPropertyValue("type", className);
        definition.addPropertyValue("decode404", attributes.get("decode404"));
        definition.addPropertyValue("fallback", attributes.get("fallback"));
        definition.addPropertyValue("fallbackFactory", attributes.get("fallbackFactory"));
        definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);

        String alias = contextId + "FeignClient";
        AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();

        boolean primary = (Boolean) attributes.get("primary"); // has a default, won't be
                                                                // null

        beanDefinition.setPrimary(primary);

        String qualifier = getQualifier(attributes);
        if (StringUtils.hasText(qualifier)) {
            alias = qualifier;
        }

        BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className,
                new String[] { alias });
        BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
    }

    private void validate(Map<String, Object> attributes) {
        AnnotationAttributes annotation = AnnotationAttributes.fromMap(attributes);
        // This blows up if an aliased property is overspecified
        // FIXME annotation.getAliasedString("name", FeignClient.class, null);
        validateFallback(annotation.getClass("fallback"));
        validateFallbackFactory(annotation.getClass("fallbackFactory"));
    }

    /* for testing */ String getName(Map<String, Object> attributes) {
        String name = (String) attributes.get("serviceId");
        if (!StringUtils.hasText(name)) {
            name = (String) attributes.get("name");
        }
        if (!StringUtils.hasText(name)) {
            name = (String) attributes.get("value");
        }
        name = resolve(name);
        return getName(name);
    }

    private String getContextId(Map<String, Object> attributes) {
        String contextId = (String) attributes.get("contextId");
        if (!StringUtils.hasText(contextId)) {
            return getName(attributes);
        }

        contextId = resolve(contextId);
        return getName(contextId);
    }

    private String resolve(String value) {
        if (StringUtils.hasText(value)) {
            return this.environment.resolvePlaceholders(value);
        }
        return value;
    }

    private String getUrl(Map<String, Object> attributes) {
        String url = resolve((String) attributes.get("url"));
        return getUrl(url);
    }

    private String getPath(Map<String, Object> attributes) {
        String path = resolve((String) attributes.get("path"));
        return getPath(path);
    }

    protected ClassPathScanningCandidateComponentProvider getScanner() {
        return new ClassPathScanningCandidateComponentProvider(false, this.environment) {
            @Override
            protected boolean isCandidateComponent(
                    AnnotatedBeanDefinition beanDefinition) {
                boolean isCandidate = false;
                if (beanDefinition.getMetadata().isIndependent()) {
                    if (!beanDefinition.getMetadata().isAnnotation()) {
                        isCandidate = true;
                    }
                }
                return isCandidate;
            }
        };
    }

    protected Set<String> getBasePackages(AnnotationMetadata importingClassMetadata) {
        Map<String, Object> attributes = importingClassMetadata
                .getAnnotationAttributes(EnableFeignClients.class.getCanonicalName());

        Set<String> basePackages = new HashSet<>();
        for (String pkg : (String[]) attributes.get("value")) {
            if (StringUtils.hasText(pkg)) {
                basePackages.add(pkg);
            }
        }
        for (String pkg : (String[]) attributes.get("basePackages")) {
            if (StringUtils.hasText(pkg)) {
                basePackages.add(pkg);
            }
        }
        for (Class<?> clazz : (Class[]) attributes.get("basePackageClasses")) {
            basePackages.add(ClassUtils.getPackageName(clazz));
        }

        if (basePackages.isEmpty()) {
            basePackages.add(
                    ClassUtils.getPackageName(importingClassMetadata.getClassName()));
        }
        return basePackages;
    }

    private String getQualifier(Map<String, Object> client) {
        if (client == null) {
            return null;
        }
        String qualifier = (String) client.get("qualifier");
        if (StringUtils.hasText(qualifier)) {
            return qualifier;
        }
        return null;
    }

    private String getClientName(Map<String, Object> client) {
        if (client == null) {
            return null;
        }
        String value = (String) client.get("contextId");
        if (!StringUtils.hasText(value)) {
            value = (String) client.get("value");
        }
        if (!StringUtils.hasText(value)) {
            value = (String) client.get("name");
        }
        if (!StringUtils.hasText(value)) {
            value = (String) client.get("serviceId");
        }
        if (StringUtils.hasText(value)) {
            return value;
        }

        throw new IllegalStateException("Either 'name' or 'value' must be provided in @"
                + FeignClient.class.getSimpleName());
    }

    private void registerClientConfiguration(BeanDefinitionRegistry registry, Object name,
            Object configuration) {
        BeanDefinitionBuilder builder = BeanDefinitionBuilder
                .genericBeanDefinition(FeignClientSpecification.class);
        builder.addConstructorArgValue(name);
        builder.addConstructorArgValue(configuration);
        registry.registerBeanDefinition(
                name + "." + FeignClientSpecification.class.getSimpleName(),
                builder.getBeanDefinition());
    }

    @Override
    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }

    /**
     * Helper class to create a {@link TypeFilter} that matches if all the delegates
     * match.
     *
     * @author Oliver Gierke
     */
    private static class AllTypeFilter implements TypeFilter {

        private final List<TypeFilter> delegates;

        /**
         * Creates a new {@link AllTypeFilter} to match if all the given delegates match.
         * @param delegates must not be {@literal null}.
         */
        AllTypeFilter(List<TypeFilter> delegates) {
            Assert.notNull(delegates, "This argument is required, it must not be null");
            this.delegates = delegates;
        }

        @Override
        public boolean match(MetadataReader metadataReader,
                MetadataReaderFactory metadataReaderFactory) throws IOException {

            for (TypeFilter filter : this.delegates) {
                if (!filter.match(metadataReader, metadataReaderFactory)) {
                    return false;
                }
            }

            return true;
        }

    }

}

FeignClientsRegistrar的核心：

接下来可以查看Feign代理Bean实例是如何创建的的，参见FeignClientFactoryBean源码：

/*
 * Copyright 2013-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.openfeign;

import java.util.Map;
import java.util.Objects;

import feign.Client;
import feign.Contract;
import feign.Feign;
import feign.Logger;
import feign.QueryMapEncoder;
import feign.Request;
import feign.RequestInterceptor;
import feign.Retryer;
import feign.Target.HardCodedTarget;
import feign.codec.Decoder;
import feign.codec.Encoder;
import feign.codec.ErrorDecoder;

import org.springframework.beans.BeanUtils;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

/**
 * Feign代理Bean实例是如何创建的
 *
 * @author Spencer Gibb
 * @author Venil Noronha
 * @author Eko Kurniawan Khannedy
 * @author Gregor Zurowski
 */
class FeignClientFactoryBean
        implements FactoryBean<Object>, InitializingBean, ApplicationContextAware {

    /***********************************
     * WARNING! Nothing in this class should be @Autowired. It causes NPEs because of some
     * lifecycle race condition.
     ***********************************/

    private Class<?> type;

    private String name;

    private String url;

    private String contextId;

    private String path;

    private boolean decode404;

    private ApplicationContext applicationContext;

    private Class<?> fallback = void.class;

    private Class<?> fallbackFactory = void.class;

    @Override
    public void afterPropertiesSet() throws Exception {
        Assert.hasText(this.contextId, "Context id must be set");
        Assert.hasText(this.name, "Name must be set");
    }

    protected Feign.Builder feign(FeignContext context) {
        FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class);
        Logger logger = loggerFactory.create(this.type);

        // @formatter:off
        //FeignContext继承自BeanFactoty，所以可以用于获取Bean
        //1、builder使用的Encoder、Decoder、Contract都来自FeignClientsConfiguration自动配置类中定义
        Feign.Builder builder = get(context, Feign.Builder.class)
                // required values
                .logger(logger)
                .encoder(get(context, Encoder.class))
                .decoder(get(context, Decoder.class))
                .contract(get(context, Contract.class));
        // @formatter:on

        configureFeign(context, builder);

        return builder;
    }

    protected void configureFeign(FeignContext context, Feign.Builder builder) {
        FeignClientProperties properties = this.applicationContext
                .getBean(FeignClientProperties.class);
        if (properties != null) {
            if (properties.isDefaultToProperties()) {
                configureUsingConfiguration(context, builder);
                configureUsingProperties(
                        properties.getConfig().get(properties.getDefaultConfig()),
                        builder);
                configureUsingProperties(properties.getConfig().get(this.contextId),
                        builder);
            }
            else {
                configureUsingProperties(
                        properties.getConfig().get(properties.getDefaultConfig()),
                        builder);
                configureUsingProperties(properties.getConfig().get(this.contextId),
                        builder);
                configureUsingConfiguration(context, builder);
            }
        }
        else {
            configureUsingConfiguration(context, builder);
        }
    }

    protected void configureUsingConfiguration(FeignContext context,
            Feign.Builder builder) {
        Logger.Level level = getOptional(context, Logger.Level.class);
        if (level != null) {
            builder.logLevel(level);
        }
        Retryer retryer = getOptional(context, Retryer.class);
        if (retryer != null) {
            builder.retryer(retryer);
        }
        ErrorDecoder errorDecoder = getOptional(context, ErrorDecoder.class);
        if (errorDecoder != null) {
            builder.errorDecoder(errorDecoder);
        }
        Request.Options options = getOptional(context, Request.Options.class);
        if (options != null) {
            builder.options(options);
        }
        //2、装入Feign请求的拦截器
        Map<String, RequestInterceptor> requestInterceptors = context
                .getInstances(this.contextId, RequestInterceptor.class);
        if (requestInterceptors != null) {
            builder.requestInterceptors(requestInterceptors.values());
        }
        QueryMapEncoder queryMapEncoder = getOptional(context, QueryMapEncoder.class);
        if (queryMapEncoder != null) {
            builder.queryMapEncoder(queryMapEncoder);
        }
        if (this.decode404) {
            builder.decode404();
        }
    }

    protected void configureUsingProperties(
            FeignClientProperties.FeignClientConfiguration config,
            Feign.Builder builder) {
        if (config == null) {
            return;
        }

        if (config.getLoggerLevel() != null) {
            builder.logLevel(config.getLoggerLevel());
        }

        if (config.getConnectTimeout() != null && config.getReadTimeout() != null) {
            builder.options(new Request.Options(config.getConnectTimeout(),
                    config.getReadTimeout()));
        }

        if (config.getRetryer() != null) {
            Retryer retryer = getOrInstantiate(config.getRetryer());
            builder.retryer(retryer);
        }

        if (config.getErrorDecoder() != null) {
            ErrorDecoder errorDecoder = getOrInstantiate(config.getErrorDecoder());
            builder.errorDecoder(errorDecoder);
        }

        if (config.getRequestInterceptors() != null
                && !config.getRequestInterceptors().isEmpty()) {
            // this will add request interceptor to builder, not replace existing
            for (Class<RequestInterceptor> bean : config.getRequestInterceptors()) {
                RequestInterceptor interceptor = getOrInstantiate(bean);
                builder.requestInterceptor(interceptor);
            }
        }

        if (config.getDecode404() != null) {
            if (config.getDecode404()) {
                builder.decode404();
            }
        }

        if (Objects.nonNull(config.getEncoder())) {
            builder.encoder(getOrInstantiate(config.getEncoder()));
        }

        if (Objects.nonNull(config.getDecoder())) {
            builder.decoder(getOrInstantiate(config.getDecoder()));
        }

        if (Objects.nonNull(config.getContract())) {
            builder.contract(getOrInstantiate(config.getContract()));
        }
    }

    private <T> T getOrInstantiate(Class<T> tClass) {
        try {
            return this.applicationContext.getBean(tClass);
        }
        catch (NoSuchBeanDefinitionException e) {
            return BeanUtils.instantiateClass(tClass);
        }
    }

    protected <T> T get(FeignContext context, Class<T> type) {
        T instance = context.getInstance(this.contextId, type);
        if (instance == null) {
            throw new IllegalStateException(
                    "No bean found of type " + type + " for " + this.contextId);
        }
        return instance;
    }

    protected <T> T getOptional(FeignContext context, Class<T> type) {
        return context.getInstance(this.contextId, type);
    }

    protected <T> T loadBalance(Feign.Builder builder, FeignContext context,
            HardCodedTarget<T> target) {
        Client client = getOptional(context, Client.class);
        if (client != null) {
            builder.client(client);
            Targeter targeter = get(context, Targeter.class);
            return targeter.target(this, builder, context, target);
        }

        throw new IllegalStateException(
                "No Feign Client for loadBalancing defined. Did you forget to include spring-cloud-starter-netflix-ribbon?");
    }

    /**
     * getObject是核心方法，方法中定义好了如何去初始化一个FeignClient组件，在代理Bean中织入了哪些方法
     *
     * @return
     * @throws Exception
     */
    @Override
    public Object getObject() throws Exception {
        return getTarget();
    }

    /**
     * @param <T> the target type of the Feign client
     * @return a {@link Feign} client created with the specified data and the context
     * information
     */
    <T> T getTarget() {
        //从Spring Context中获取到Feign的Builder
        FeignContext context = this.applicationContext.getBean(FeignContext.class);
        Feign.Builder builder = feign(context);

        //@FeignClient注解没有配置URL属性
        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));
        }
        //处理@FeignClient URL属性(主机名)存在的情况
        if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {
            this.url = "http://" + this.url;
        }
        String url = this.url + cleanPath();
        //获取到调用客户端：Spring封装了基于Ribbon的客户端（LoadBalancerFeignClient）
        //1、Feign自己封装的Request（基于java.net原生），2、OkHttpClient（新一代/HTTP2），3、ApacheHttpClient（常规）
        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();
            }
            //设置调用客户端
            builder.client(client);
        }
        //DefaultTargeter或者HystrixTargeter，其中HystrixTargeter带熔断和降级功能
        //主要用户在Builder中配置调用失败回调方法
        Targeter targeter = get(context, Targeter.class);
        //Bean创建实际目标封装，最终生成InvocationHandler
        return (T) targeter.target(this, builder, context,
                new HardCodedTarget<>(this.type, this.name, url));
    }

    private String cleanPath() {
        String path = this.path.trim();
        if (StringUtils.hasLength(path)) {
            if (!path.startsWith("/")) {
                path = "/" + path;
            }
            if (path.endsWith("/")) {
                path = path.substring(0, path.length() - 1);
            }
        }
        return path;
    }

    @Override
    public Class<?> getObjectType() {
        return this.type;
    }

    @Override
    public boolean isSingleton() {
        return true;
    }

    public Class<?> getType() {
        return this.type;
    }

    public void setType(Class<?> type) {
        this.type = type;
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getContextId() {
        return this.contextId;
    }

    public void setContextId(String contextId) {
        this.contextId = contextId;
    }

    public String getUrl() {
        return this.url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public String getPath() {
        return this.path;
    }

    public void setPath(String path) {
        this.path = path;
    }

    public boolean isDecode404() {
        return this.decode404;
    }

    public void setDecode404(boolean decode404) {
        this.decode404 = decode404;
    }

    public ApplicationContext getApplicationContext() {
        return this.applicationContext;
    }

    @Override
    public void setApplicationContext(ApplicationContext context) throws BeansException {
        this.applicationContext = context;
    }

    public Class<?> getFallback() {
        return this.fallback;
    }

    public void setFallback(Class<?> fallback) {
        this.fallback = fallback;
    }

    public Class<?> getFallbackFactory() {
        return this.fallbackFactory;
    }

    public void setFallbackFactory(Class<?> fallbackFactory) {
        this.fallbackFactory = fallbackFactory;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
        FeignClientFactoryBean that = (FeignClientFactoryBean) o;
        return Objects.equals(this.applicationContext, that.applicationContext)
                && this.decode404 == that.decode404
                && Objects.equals(this.fallback, that.fallback)
                && Objects.equals(this.fallbackFactory, that.fallbackFactory)
                && Objects.equals(this.name, that.name)
                && Objects.equals(this.path, that.path)
                && Objects.equals(this.type, that.type)
                && Objects.equals(this.url, that.url);
    }

    @Override
    public int hashCode() {
        return Objects.hash(this.applicationContext, this.decode404, this.fallback,
                this.fallbackFactory, this.name, this.path, this.type, this.url);
    }

    @Override
    public String toString() {
        return new StringBuilder("FeignClientFactoryBean{").append("type=")
                .append(this.type).append(", ").append("name='").append(this.name)
                .append("', ").append("url='").append(this.url).append("', ")
                .append("path='").append(this.path).append("', ").append("decode404=")
                .append(this.decode404).append(", ").append("applicationContext=")
                .append(this.applicationContext).append(", ").append("fallback=")
                .append(this.fallback).append(", ").append("fallbackFactory=")
                .append(this.fallbackFactory).append("}").toString();
    }

}

最核心的是getObject方法，方法中定义好了如何去初始化一个FeignClient组件，在代理Bean中织入了哪些方法。

上述工厂Bean创建代理对象时，使用到Feign的其他组件，如：Encoder、Decoder、Contract等。

当调用target方法时，实际会触发FeignBuiler组件的newInstance源码如下：

public <T> T newInstance(Target<T> target) {
//核心方法，解析定义的@FeignClient组件中的方法和请求路径
   Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
   Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();
   List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();

   for (Method method : target.type().getMethods()) {
     if (method.getDeclaringClass() == Object.class) {
       continue;
     } else if(Util.isDefault(method)) {
       DefaultMethodHandler handler = new DefaultMethodHandler(method);
       defaultMethodHandlers.add(handler);
       methodToHandler.put(method, handler);
     } else {
       methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method)));
     }
   }
//调用工厂Bean，创建执行Handler
   InvocationHandler handler = factory.create(target, methodToHandler);
   T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(), new Class<?>[]{target.type()}, handler);

   for(DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {
     defaultMethodHandler.bindTo(proxy);
   }
   return proxy;
 }
 //请求方法和路径解析器
 static final class ParseHandlersByName {

   private final Contract contract;
   private final Options options;
   private final Encoder encoder;
   private final Decoder decoder;
   private final ErrorDecoder errorDecoder;
   private final SynchronousMethodHandler.Factory factory;

   ParseHandlersByName(Contract contract, Options options, Encoder encoder, Decoder decoder,
                       ErrorDecoder errorDecoder, SynchronousMethodHandler.Factory factory) {
     this.contract = contract;
     this.options = options;
     this.factory = factory;
     this.errorDecoder = errorDecoder;
     this.encoder = checkNotNull(encoder, "encoder");
     this.decoder = checkNotNull(decoder, "decoder");
   }

   public Map<String, MethodHandler> apply(Target key) {
 //核心方法：解析@FeignClient组件，Feign自带的则解析自己的注解格式，Spring提供了解析MVC注解的SpringMvcContract
     List<MethodMetadata> metadata = contract.parseAndValidatateMetadata(key.type());
     Map<String, MethodHandler> result = new LinkedHashMap<String, MethodHandler>();
     for (MethodMetadata md : metadata) {
       BuildTemplateByResolvingArgs buildTemplate;
       if (!md.formParams().isEmpty() && md.template().bodyTemplate() == null) {
         buildTemplate = new BuildFormEncodedTemplateFromArgs(md, encoder);
       } else if (md.bodyIndex() != null) {
         buildTemplate = new BuildEncodedTemplateFromArgs(md, encoder);
       } else {
         buildTemplate = new BuildTemplateByResolvingArgs(md);
       }
       result.put(md.configKey(),
                  factory.create(key, md, buildTemplate, options, decoder, errorDecoder));
     }
     return result;
   }
 }

看一下Targeter的实现类DefaultTargeter类：

/*
 * Copyright 2013-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.openfeign;

import feign.Feign;
import feign.Target;

/**
 * @author Spencer Gibb
 */
class DefaultTargeter implements Targeter {

    @Override
    public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign,
            FeignContext context, Target.HardCodedTarget<T> target) {
        //简单暴力，直接调用Feign Builer字段的设置目标对象方法
        return feign.target(target);
    }

}

再看一下带熔断功能的HystrixTargeter：

/*
 * Copyright 2013-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.openfeign;

import feign.Feign;
import feign.Target;
import feign.hystrix.FallbackFactory;
import feign.hystrix.HystrixFeign;
import feign.hystrix.SetterFactory;

/**
 * 带熔断功能的HystrixTargeter
 *
 * @author Spencer Gibb
 * @author Erik Kringen
 */
@SuppressWarnings("unchecked")
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);
    }

}

Feign组件配置

Feign组件的配置主要有3个自动化配置类：

FeignAutoConfiguration：配置Feign上下文（FeignContext）、配置Targeter、配置Client(仅仅组件)。

/*
 * Copyright 2013-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.openfeign;

import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.TimeUnit;

import javax.annotation.PreDestroy;

import feign.Client;
import feign.Feign;
import feign.httpclient.ApacheHttpClient;
import feign.okhttp.OkHttpClient;
import okhttp3.ConnectionPool;
import org.apache.http.client.HttpClient;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.config.RegistryBuilder;
import org.apache.http.conn.HttpClientConnectionManager;
import org.apache.http.impl.client.CloseableHttpClient;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.cloud.client.actuator.HasFeatures;
import org.springframework.cloud.commons.httpclient.ApacheHttpClientConnectionManagerFactory;
import org.springframework.cloud.commons.httpclient.ApacheHttpClientFactory;
import org.springframework.cloud.commons.httpclient.OkHttpClientConnectionPoolFactory;
import org.springframework.cloud.commons.httpclient.OkHttpClientFactory;
import org.springframework.cloud.openfeign.support.FeignHttpClientProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * @author Spencer Gibb
 * @author Julien Roy
 */
@Configuration
@ConditionalOnClass(Feign.class)
@EnableConfigurationProperties({ FeignClientProperties.class,
        FeignHttpClientProperties.class })
public class FeignAutoConfiguration {

    @Autowired(required = false)
    private List<FeignClientSpecification> configurations = new ArrayList<>();

    @Bean
    public HasFeatures feignFeature() {
        return HasFeatures.namedFeature("Feign", Feign.class);
    }

    /**
     * 配置Feign上下文
     *
     * @return
     */
    @Bean
    public FeignContext feignContext() {
        FeignContext context = new FeignContext();
        context.setConfigurations(this.configurations);
        return context;
    }

    @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();
        }

    }

    // the following configuration is for alternate feign clients if
    // ribbon is not on the class path.
    // see corresponding configurations in FeignRibbonClientAutoConfiguration
    // for load balanced ribbon clients.
    @Configuration
    @ConditionalOnClass(ApacheHttpClient.class)
    @ConditionalOnMissingClass("com.netflix.loadbalancer.ILoadBalancer")
    @ConditionalOnMissingBean(CloseableHttpClient.class)
    @ConditionalOnProperty(value = "feign.httpclient.enabled", matchIfMissing = true)
    protected static class HttpClientFeignConfiguration {

        private final Timer connectionManagerTimer = new Timer(
                "FeignApacheHttpClientConfiguration.connectionManagerTimer", true);

        @Autowired(required = false)
        private RegistryBuilder registryBuilder;

        private CloseableHttpClient httpClient;

        @Bean
        @ConditionalOnMissingBean(HttpClientConnectionManager.class)
        public HttpClientConnectionManager connectionManager(
                ApacheHttpClientConnectionManagerFactory connectionManagerFactory,
                FeignHttpClientProperties httpClientProperties) {
            final HttpClientConnectionManager connectionManager = connectionManagerFactory
                    .newConnectionManager(httpClientProperties.isDisableSslValidation(),
                            httpClientProperties.getMaxConnections(),
                            httpClientProperties.getMaxConnectionsPerRoute(),
                            httpClientProperties.getTimeToLive(),
                            httpClientProperties.getTimeToLiveUnit(),
                            this.registryBuilder);
            this.connectionManagerTimer.schedule(new TimerTask() {
                @Override
                public void run() {
                    connectionManager.closeExpiredConnections();
                }
            }, 30000, httpClientProperties.getConnectionTimerRepeat());
            return connectionManager;
        }

        @Bean
        public CloseableHttpClient httpClient(ApacheHttpClientFactory httpClientFactory,
                HttpClientConnectionManager httpClientConnectionManager,
                FeignHttpClientProperties httpClientProperties) {
            RequestConfig defaultRequestConfig = RequestConfig.custom()
                    .setConnectTimeout(httpClientProperties.getConnectionTimeout())
                    .setRedirectsEnabled(httpClientProperties.isFollowRedirects())
                    .build();
            this.httpClient = httpClientFactory.createBuilder()
                    .setConnectionManager(httpClientConnectionManager)
                    .setDefaultRequestConfig(defaultRequestConfig).build();
            return this.httpClient;
        }

        @Bean
        @ConditionalOnMissingBean(Client.class)
        public Client feignClient(HttpClient httpClient) {
            return new ApacheHttpClient(httpClient);
        }

        @PreDestroy
        public void destroy() throws Exception {
            this.connectionManagerTimer.cancel();
            if (this.httpClient != null) {
                this.httpClient.close();
            }
        }

    }

    @Configuration
    @ConditionalOnClass(OkHttpClient.class)
    @ConditionalOnMissingClass("com.netflix.loadbalancer.ILoadBalancer")
    @ConditionalOnMissingBean(okhttp3.OkHttpClient.class)
    @ConditionalOnProperty("feign.okhttp.enabled")
    protected static class OkHttpFeignConfiguration {

        private okhttp3.OkHttpClient okHttpClient;

        @Bean
        @ConditionalOnMissingBean(ConnectionPool.class)
        public ConnectionPool httpClientConnectionPool(
                FeignHttpClientProperties httpClientProperties,
                OkHttpClientConnectionPoolFactory connectionPoolFactory) {
            Integer maxTotalConnections = httpClientProperties.getMaxConnections();
            Long timeToLive = httpClientProperties.getTimeToLive();
            TimeUnit ttlUnit = httpClientProperties.getTimeToLiveUnit();
            return connectionPoolFactory.create(maxTotalConnections, timeToLive, ttlUnit);
        }

        @Bean
        public okhttp3.OkHttpClient client(OkHttpClientFactory httpClientFactory,
                ConnectionPool connectionPool,
                FeignHttpClientProperties httpClientProperties) {
            Boolean followRedirects = httpClientProperties.isFollowRedirects();
            Integer connectTimeout = httpClientProperties.getConnectionTimeout();
            Boolean disableSslValidation = httpClientProperties.isDisableSslValidation();
            this.okHttpClient = httpClientFactory.createBuilder(disableSslValidation)
                    .connectTimeout(connectTimeout, TimeUnit.MILLISECONDS)
                    .followRedirects(followRedirects).connectionPool(connectionPool)
                    .build();
            return this.okHttpClient;
        }

        @PreDestroy
        public void destroy() {
            if (this.okHttpClient != null) {
                this.okHttpClient.dispatcher().executorService().shutdown();
                this.okHttpClient.connectionPool().evictAll();
            }
        }

        @Bean
        @ConditionalOnMissingBean(Client.class)
        public Client feignClient(okhttp3.OkHttpClient client) {
            return new OkHttpClient(client);
        }

    }

}

FeignClientsConfiguration：Decoder、Encoder、Retryer、Contract（SpringMvcContract）、FeignBuilder。

/*
 * Copyright 2013-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.openfeign;

import java.util.ArrayList;
import java.util.List;

import com.fasterxml.jackson.databind.Module;
import com.netflix.hystrix.HystrixCommand;
import feign.Contract;
import feign.Feign;
import feign.Logger;
import feign.Retryer;
import feign.codec.Decoder;
import feign.codec.Encoder;
import feign.hystrix.HystrixFeign;
import feign.optionals.OptionalDecoder;

import org.springframework.beans.factory.ObjectFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.autoconfigure.data.web.SpringDataWebProperties;
import org.springframework.boot.autoconfigure.http.HttpMessageConverters;
import org.springframework.cloud.openfeign.support.PageJacksonModule;
import org.springframework.cloud.openfeign.support.PageableSpringEncoder;
import org.springframework.cloud.openfeign.support.ResponseEntityDecoder;
import org.springframework.cloud.openfeign.support.SpringDecoder;
import org.springframework.cloud.openfeign.support.SpringEncoder;
import org.springframework.cloud.openfeign.support.SpringMvcContract;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;
import org.springframework.core.convert.ConversionService;
import org.springframework.format.support.DefaultFormattingConversionService;
import org.springframework.format.support.FormattingConversionService;

/**
 * @author Dave Syer
 * @author Venil Noronha
 */
@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;

    @Autowired(required = false)
    private SpringDataWebProperties springDataWebProperties;

    @Bean
    @ConditionalOnMissingBean
    public Decoder feignDecoder() {
        return new OptionalDecoder(
                new ResponseEntityDecoder(new SpringDecoder(this.messageConverters)));
    }

    @Bean
    @ConditionalOnMissingBean
    @ConditionalOnMissingClass("org.springframework.data.domain.Pageable")
    public Encoder feignEncoder() {
        return new SpringEncoder(this.messageConverters);
    }

    @Bean
    @ConditionalOnClass(name = "org.springframework.data.domain.Pageable")
    @ConditionalOnMissingBean
    public Encoder feignEncoderPageable() {
        PageableSpringEncoder encoder = new PageableSpringEncoder(
                new SpringEncoder(this.messageConverters));
        if (springDataWebProperties != null) {
            encoder.setPageParameter(
                    springDataWebProperties.getPageable().getPageParameter());
            encoder.setSizeParameter(
                    springDataWebProperties.getPageable().getSizeParameter());
            encoder.setSortParameter(
                    springDataWebProperties.getSort().getSortParameter());
        }
        return encoder;
    }

    @Bean
    @ConditionalOnMissingBean
    public Contract feignContract(ConversionService feignConversionService) {
        return new SpringMvcContract(this.parameterProcessors, feignConversionService);
    }

    @Bean
    public FormattingConversionService feignConversionService() {
        FormattingConversionService conversionService = new DefaultFormattingConversionService();
        for (FeignFormatterRegistrar feignFormatterRegistrar : this.feignFormatterRegistrars) {
            feignFormatterRegistrar.registerFormatters(conversionService);
        }
        return conversionService;
    }

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

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

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

    @Bean
    @ConditionalOnClass(name = "org.springframework.data.domain.Page")
    public Module pageJacksonModule() {
        return new PageJacksonModule();
    }

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

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

    }

}

FeignRibbonClientAutoConfiguration：Request Options（超时配置）、配置Client(带负载均衡)。

/*
 * Copyright 2013-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.openfeign.ribbon;

import com.netflix.loadbalancer.ILoadBalancer;
import feign.Feign;
import feign.Request;

import org.springframework.boot.autoconfigure.AutoConfigureBefore;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.cloud.client.loadbalancer.LoadBalancedRetryFactory;
import org.springframework.cloud.netflix.ribbon.SpringClientFactory;
import org.springframework.cloud.openfeign.FeignAutoConfiguration;
import org.springframework.cloud.openfeign.support.FeignHttpClientProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.context.annotation.Primary;

/**
 * Autoconfiguration to be activated if Feign is in use and needs to be use Ribbon as a
 * load balancer.
 *
 * @author Dave Syer
 */
@ConditionalOnClass({ ILoadBalancer.class, Feign.class })
@Configuration
@AutoConfigureBefore(FeignAutoConfiguration.class)
@EnableConfigurationProperties({ FeignHttpClientProperties.class })
// Order is important here, last should be the default, first should be optional
// see
// https://github.com/spring-cloud/spring-cloud-netflix/issues/2086#issuecomment-316281653
@Import({ HttpClientFeignLoadBalancedConfiguration.class,
        OkHttpFeignLoadBalancedConfiguration.class,
        DefaultFeignLoadBalancedConfiguration.class })
public class FeignRibbonClientAutoConfiguration {

    @Bean
    @Primary
    @ConditionalOnMissingBean
    @ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
    public CachingSpringLoadBalancerFactory cachingLBClientFactory(
            SpringClientFactory factory) {
        return new CachingSpringLoadBalancerFactory(factory);
    }

    @Bean
    @Primary
    @ConditionalOnMissingBean
    @ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate")
    public CachingSpringLoadBalancerFactory retryabeCachingLBClientFactory(
            SpringClientFactory factory, LoadBalancedRetryFactory retryFactory) {
        return new CachingSpringLoadBalancerFactory(factory, retryFactory);
    }

    /**
     * 配置超时设置，默认连接超时10秒，读取超时60秒
     * 
     * @return
     */
    @Bean
    @ConditionalOnMissingBean
    public Request.Options feignRequestOptions() {
        return LoadBalancerFeignClient.DEFAULT_OPTIONS;
    }

}

Feign初始化结构为动态代理过程

上文已经完成了feign初始化结构为动态代理的整个过程，简单的捋一遍：

初始化Feign.Builder传入参数，构造ReflectiveFeign
ReflectiveFeign通过内部类ParseHandlersByName的Contract属性，解析接口生成MethodMetadata
ParseHandlersByName根据MethodMetadata生成RequestTemplate工厂
ParseHandlersByName创建SynchronousMethodHandler，传入MethodMetadata、RequestTemplate工厂和Feign.Builder相关参数
ReflectiveFeign创建FeignInvocationHandler，传入参数SynchronousMethodHandler，绑定DefaultMethodHandler
ReflectiveFeign根据FeignInvocationHandler创建Proxy

关键的几个类是：

ReflectiveFeign 初始化入口
FeignInvocationHandler 实现动态代理的InvocHandler
SynchronousMethodHandler 方法处理器，方法调用处理器
MethodMetadata 方法元数据

Feign的执行过程

分为三层方便理解：

三层分别为：

代理层动态代理调用层
转换层方法转http请求，解码http响应
网络层 http请求发送

Feign接口调用过程总结

1、接口的动态代理Proxy调用接口方法会执行的FeignInvocationHandler
2、FeignInvocationHandler通过方法签名在属性Map<Method, MethodHandler> dispatch中找到SynchronousMethodHandler，调用invoke方法
3、SynchronousMethodHandler的invoke方法根据传入的方法参数，通过自身属性工厂对象RequestTemplate.Factory创建RequestTemplate，工厂里面会用根据需要进行Encode
4、SynchronousMethodHandler遍历自身属性RequestInterceptor列表，对RequestTemplate进行改造
4、SynchronousMethodHandler调用自身Target属性的apply方法，将RequestTemplate转换为Request对象
5、SynchronousMethodHandler调用自身Client的execute方法，传入Request对象
6、Client将Request转换为http请求，发送后将http响应转换为Response对象
7、SynchronousMethodHandler调用Decoder的方法对Response对象解码后返回
8、返回的对象最后返回到Proxy

配置与优化

超时时间配置

Spring Feign组件的超时配置主要存在3块：

一块是FeignClientsConfiguration的LoadBalancerFeignClient.DEFAULT_OPTIONS，连接超时10S，读取超时60S;
一块是RibbonClientConfiguration的ribbonClientConfig(),连接超时2S，读取超时5S；
一块是Hystrix组件的执行超时配置，hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds;

在Feign中上述配置优先级与顺序为：

当Request.Options等于LoadBalancerFeignClient.DEFAULT_OPTIONS时，以RibbonClientConfiguration中配置的超时时间为准；
当Request.Options不等于LoadBalancerFeignClient.DEFAULT_OPTIONS，以自定义的超时时间配置为准；
Hystrix组件的执行超时配置用于控制调用请求执行超时，和具体HTTP请求无关，需要和上述2个配置配合使用，需大于上述2条超时时间配置；

RibbonClientConfiguration中的FeignOptionsClientConfig支持动态配置，具体可以查看DefaultClientConfigImpl源码。

请求重试

Feign的重试是通过配置Retryer来实现，在FeignClientsConfiguration自动配置类中，配置了一个默认的Retryer.NEVER_RETRY，表示用不重试。不重试和重试超过限制次数都是抛出异常来停止重试。可以通过自定义Retryer来覆盖默认的配置，但需要注意Hystrix的执行超时，2个中较短的时间为请求最终执行的时间。

编码/消息头处理

对具体调用请求可以通过3种方式来进行编解码处理：

定义RequestInterceptor，在请求前处理编码与附加消息头;
自定义Encoder，在编码阶段处理请求头;
在@FeignClient组件接口@RequestMapping的headers属性中附带消息头信息；

连接池

Feign默认使用的请求客户端并没有建立连接池，可以考虑使用ApacheHttpClient与OkHttpClient进行Client的替换，并池话发起HTTP请求。

其他事项

在定义Feign组件时，@RequestMapping注解只加在方法上，不要放在类上，Spring MVC自带的Dispacher请求映射会扫描所有带@RequestMapping类，容易导致一些不必要的问题；
Feign组件目前只支持@RequestMapping注解定义请求路径和配置，赞不支持Spring MVC新出的@GetMapping、@PostMapping等注解，具体扫描和处理参考SpringMvcContract源码。

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正文到此结束

所属分类：Java开发

本文标签： Feign SpringCloud Spring Boot
版权声明： 本站原创文章，于2018年06月17日由刘昭坡发布，转载请注明出处

Feign源码总结

入门

如何使用feign？

1.添加依赖

2.编写feign接口

3.使用feign接口

4.启动类

源码分析

feign核心类介绍

开启`@EnableFeignClients`注解到底给我们做了什么事情呢？

Feign的三个自动加载配置类

Feign Bean创建

Feign组件配置

Feign初始化结构为动态代理过程

Feign的执行过程

Feign接口调用过程总结

配置与优化

超时时间配置

请求重试

编码/消息头处理

连接池

其他事项

会打篮球的程序猿

热门推荐

相关文章

说给你听

微信公众号

本文目录

标签云

近期评论

Feign源码总结

入门

如何使用feign？

1.添加依赖

2.编写feign接口

3.使用feign接口

4.启动类

源码分析

feign核心类介绍

开启@EnableFeignClients注解到底给我们做了什么事情呢？

Feign的三个自动加载配置类

Feign Bean创建

Feign组件配置

Feign初始化结构为动态代理过程

Feign的执行过程

Feign接口调用过程总结

配置与优化

超时时间配置

请求重试

编码/消息头处理

连接池

其他事项

会打篮球的程序猿

热门推荐

相关文章

说给你听

微信公众号

本文目录

标签云

近期评论

开启`@EnableFeignClients`注解到底给我们做了什么事情呢？