V2AS问路
OpenFeign远程调用原理
阅读原文时间：2023年07月09日阅读：1

　　之前对OpenFeign 了解到只用在接口上面打个注解，然后就可以通过内部调用去调用远程地址。研究完Feign生成对象以及代理对象的作用过程之后发现这个过程用到了Spring的好多东西，在之后的过程中可以借鉴这种思想。

　　查看Springboot项目一般从Enable入口，然后查看倒入的类。然后分析其IoC过程： 包括注册BeanDefinition、生成单例对象。

接口如下：

package cn.qz.cloud.service;

import cn.qz.cloud.utils.JSONResultUtil;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.*;

import java.util.List;
import java.util.Map;

@FeignClient(value = "CLOUD-PAYMENT-SERVICE")
public interface PaymentFeignService {

@GetMapping(value = "/pay/listAll")  
JSONResultUtil<List<Map<String, Object>>> listAll();

@GetMapping("/pay/getServerPort")  
JSONResultUtil<String> getServerPort();

/\*\*  
 \* 注意  
 \* 1. PathVariable 的value 属性必须有。 会在org.springframework.cloud.openfeign.annotation.PathVariableParameterProcessor#processArgument(org.springframework.cloud.openfeign.AnnotatedParameterProcessor.AnnotatedParameterContext, java.lang.annotation.Annotation, java.lang.reflect.Method) 进行验证  
 \*  
 \* @param map  
 \* @param queryParam  
 \* @param id  
 \* @return  
 \*/  
@PostMapping("/pay/testParam/{id}")

// JSONResultUtil> testParam(Map map, String queryParam, String id);
JSONResultUtil> testParam(@RequestBody Map map, @RequestParam("queryParam") String queryParam, @PathVariable("id") String id);

/\*\*  
 \* 当只有一个参数时可不写@RequestBody  
 \*  
 \* @param map  
 \* @return  
 \*/  
@PostMapping("/pay/testParam2")  
JSONResultUtil<Map<String, Object>> testParam2(Map<String, Object> map);

}

源码如下：

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;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@Documented
@Import({FeignClientsRegistrar.class})
public @interface EnableFeignClients {
String[] value() default {};

String\[\] basePackages() default {};

Class<?>\[\] basePackageClasses() default {};

Class<?>\[\] defaultConfiguration() default {};

Class<?>\[\] clients() default {};

}

可以看到是Import导入了FeignClientsRegistrar

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.Iterator;
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;

class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware {
private ResourceLoader resourceLoader;
private Environment environment;

FeignClientsRegistrar() {  
}

static void validateFallback(Class clazz) {  
    Assert.isTrue(!clazz.isInterface(), "Fallback class must implement the interface annotated by @FeignClient");  
}

static void validateFallbackFactory(Class clazz) {  
    Assert.isTrue(!clazz.isInterface(), "Fallback factory must produce instances of fallback classes that implement the interface annotated by @FeignClient");  
}

static String getName(String name) {  
    if (!StringUtils.hasText(name)) {  
        return "";  
    } else {  
        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 var3) {  
            ;  
        }

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

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 var2) {  
            throw new IllegalArgumentException(url + " is malformed", var2);  
        }  
    }

    return url;  
}

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;  
}

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

public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {  
    this.registerDefaultConfiguration(metadata, registry);  
    this.registerFeignClients(metadata, registry);  
}

private void registerDefaultConfiguration(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {  
    Map<String, Object> defaultAttrs = metadata.getAnnotationAttributes(EnableFeignClients.class.getName(), true);  
    if (defaultAttrs != null && defaultAttrs.containsKey("defaultConfiguration")) {  
        String name;  
        if (metadata.hasEnclosingClass()) {  
            name = "default." + metadata.getEnclosingClassName();  
        } else {  
            name = "default." + metadata.getClassName();  
        }

        this.registerClientConfiguration(registry, name, defaultAttrs.get("defaultConfiguration"));  
    }

}

public void registerFeignClients(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {  
    ClassPathScanningCandidateComponentProvider scanner = this.getScanner();  
    scanner.setResourceLoader(this.resourceLoader);  
    Map<String, Object> attrs = metadata.getAnnotationAttributes(EnableFeignClients.class.getName());  
    AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(FeignClient.class);  
    Class<?>\[\] clients = attrs == null ? null : (Class\[\])((Class\[\])attrs.get("clients"));  
    Object basePackages;  
    if (clients != null && clients.length != 0) {  
        final Set<String> clientClasses = new HashSet();  
        basePackages = new HashSet();  
        Class\[\] var9 = clients;  
        int var10 = clients.length;

        for(int var11 = 0; var11 < var10; ++var11) {  
            Class<?> clazz = var9\[var11\];  
            ((Set)basePackages).add(ClassUtils.getPackageName(clazz));  
            clientClasses.add(clazz.getCanonicalName());  
        }

        AbstractClassTestingTypeFilter filter = new AbstractClassTestingTypeFilter() {  
            protected boolean match(ClassMetadata metadata) {  
                String cleaned = metadata.getClassName().replaceAll("\\\\$", ".");  
                return clientClasses.contains(cleaned);  
            }  
        };  
        scanner.addIncludeFilter(new FeignClientsRegistrar.AllTypeFilter(Arrays.asList(filter, annotationTypeFilter)));  
    } else {  
        scanner.addIncludeFilter(annotationTypeFilter);  
        basePackages = this.getBasePackages(metadata);  
    }

    Iterator var17 = ((Set)basePackages).iterator();

    while(var17.hasNext()) {  
        String basePackage = (String)var17.next();  
        Set<BeanDefinition> candidateComponents = scanner.findCandidateComponents(basePackage);  
        Iterator var21 = candidateComponents.iterator();

        while(var21.hasNext()) {  
            BeanDefinition candidateComponent = (BeanDefinition)var21.next();  
            if (candidateComponent instanceof AnnotatedBeanDefinition) {  
                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 = this.getClientName(attributes);  
                this.registerClientConfiguration(registry, name, attributes.get("configuration"));  
                this.registerFeignClient(registry, annotationMetadata, attributes);  
            }  
        }  
    }

}

private void registerFeignClient(BeanDefinitionRegistry registry, AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {  
    String className = annotationMetadata.getClassName();  
    BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(FeignClientFactoryBean.class);  
    this.validate(attributes);  
    definition.addPropertyValue("url", this.getUrl(attributes));  
    definition.addPropertyValue("path", this.getPath(attributes));  
    String name = this.getName(attributes);  
    definition.addPropertyValue("name", name);  
    String contextId = this.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(2);  
    String alias = contextId + "FeignClient";  
    AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();  
    boolean primary = ((Boolean)attributes.get("primary")).booleanValue();  
    beanDefinition.setPrimary(primary);  
    String qualifier = this.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);  
    validateFallback(annotation.getClass("fallback"));  
    validateFallbackFactory(annotation.getClass("fallbackFactory"));  
}

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 = this.resolve(name);  
    return getName(name);  
}

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

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

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

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

protected ClassPathScanningCandidateComponentProvider getScanner() {  
    return new ClassPathScanningCandidateComponentProvider(false, this.environment) {  
        protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {  
            boolean isCandidate = false;  
            if (beanDefinition.getMetadata().isIndependent() && !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();  
    String\[\] var4 = (String\[\])((String\[\])attributes.get("value"));  
    int var5 = var4.length;

    int var6;  
    String pkg;  
    for(var6 = 0; var6 < var5; ++var6) {  
        pkg = var4\[var6\];  
        if (StringUtils.hasText(pkg)) {  
            basePackages.add(pkg);  
        }  
    }

    var4 = (String\[\])((String\[\])attributes.get("basePackages"));  
    var5 = var4.length;

    for(var6 = 0; var6 < var5; ++var6) {  
        pkg = var4\[var6\];  
        if (StringUtils.hasText(pkg)) {  
            basePackages.add(pkg);  
        }  
    }

    Class\[\] var8 = (Class\[\])((Class\[\])attributes.get("basePackageClasses"));  
    var5 = var8.length;

    for(var6 = 0; var6 < var5; ++var6) {  
        Class<?> clazz = var8\[var6\];  
        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;  
    } else {  
        String qualifier = (String)client.get("qualifier");  
        return StringUtils.hasText(qualifier) ? qualifier : null;  
    }  
}

private String getClientName(Map<String, Object> client) {  
    if (client == null) {  
        return null;  
    } else {  
        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;  
        } else {  
            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());  
}

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

private static class AllTypeFilter implements TypeFilter {  
    private final List<TypeFilter> delegates;

    AllTypeFilter(List<TypeFilter> delegates) {  
        Assert.notNull(delegates, "This argument is required, it must not be null");  
        this.delegates = delegates;  
    }

    public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {  
        Iterator var3 = this.delegates.iterator();

        TypeFilter filter;  
        do {  
            if (!var3.hasNext()) {  
                return true;  
            }

            filter = (TypeFilter)var3.next();  
        } while(filter.match(metadataReader, metadataReaderFactory));

        return false;  
    }  
}

}

　　在之前了解到IoC过程中会扫描到Import导入的类，然后判断是ImportBeanDefinitionRegistrar 的话会进行反射创建对象，然后调用Aware 相关方法，然后调用 registerBeanDefinitions 方法动态的注册Bean。

　　所以核心入口就是registerBeanDefinitions  方法。

1. registerDefaultConfiguration(metadata, registry); 方法详解

　　注册了一个org.springframework.cloud.openfeign.FeignClientSpecification 类

2. registerFeignClients(metadata, registry); 方法详解==注册Bean的核心也是在这里

　　这个就是扫描指定包下面所有带FeignClient 注解的类，然后扫描到之后解析属性，最后注册到IoC容器中。IoC容器中维护的是FeignClientFactoryBean 一个工厂Bean， 也就是真正服务于业务的bean会在其getObject()方法生成。所以核心就是查看这个FactoryBean 的生成过程。

1. 调用方法org.springframework.cloud.openfeign.FeignClientsRegistrar#getScanner 获取一个scanner， 用于扫描classpath 路径下指定的类。(这也是Spring 的套路)

2. scanner.setResourceLoader(this.resourceLoader);    给scanner 设置一个resourceLoader。 真正干活的是这个resourceLoader 去加载

3. 下面代码给scanner 家里一个扫描包含的注解类型，就是我们的FeignClient 注解。

AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(FeignClient.class);

scanner.addIncludeFilter(new AllTypeFilter(Arrays.asList(filter, annotationTypeFilter)));

4. 然后获取到EnableFeignClients 注解上的属性，如下：

没有指定扫描的包名，然后会取EnableFeignClients  所在类的包作为包路径进行扫描

5. 接下来就是遍历包名称集合，然后扫描得到BeanDefinition 对象。 然后获取到注解上面的属性，然后创建一个FeignClientFactoryBean 对象，并且将注解上的相关属性赋给Beandefinition内部的propertyValues 属性中。

(1) Set candidateComponents = scanner.findCandidateComponents(basePackage); 代码利用新建的扫描器扫描指定包中包含@FeignClient 注解的对象，

最终扫描会调用到org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider#scanCandidateComponents(这个也是SpringIoC过程自动扫描的重要方法)

扫描出的beanDefinition 对象包含一些重要的信息，包括：

(2) 接下来获取扫描到的注解上的属性。

(3) 然后调用org.springframework.cloud.openfeign.FeignClientsRegistrar#registerFeignClient进行注册到IoC容器中

第一步创建一个FeignClientFactoryBean构造器BeanDefinitionBuilder(从这里看出来我们后面拿到的service 对象实际是这个工厂生产出来的对象)

第二步解析注解上面的属性，对name、url、path、fallback等属性进行特殊处理后设置到BeanDefinition 的一个propertyValues 属性中记录起来(最后容器在创建对象完成属性注入时会根据BeanDefinition的propertyValues中的属性进行注入，这个是SpringIoC创建对象过程中的一个操作)。

第三步设置其primary 属性为true，然后生成一个alias 别名

第四步就是调用BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry); 注册到IoC容器中。

　　在上面了解到@FeignClient 只能用于接口中。

　　注入到容器的是一个FactoryBean， 则真正生成Bean 是FactoryBean的getObject 方法，而且是FactoryBean的创建是在IoC容器过程中创建的。SpringIoC创建完对象会先反射创建对象，然后属性注入，属性注入过程中会根据BeanDefinition对象的propertyValues 给反射的对象进行属性注入。

　　FactoryBean.getObject方法生成对象会在第一次使用bean时创建, 而不是在容器启动过程中就创建(也就是如果只声明不使用FactoryBean生成的对象不会进行创建)。

　　我们需要的target对象是一个接口，所以是需要用到JDK的动态代理来生成代理对象然后服务于业务。

org.springframework.cloud.openfeign.FeignClientFactoryBean源码如下：

package org.springframework.cloud.openfeign;

import feign.Client;
import feign.Contract;
import feign.Logger;
import feign.QueryMapEncoder;
import feign.RequestInterceptor;
import feign.Retryer;
import feign.Feign.Builder;
import feign.Logger.Level;
import feign.Request.Options;
import feign.Target.HardCodedTarget;
import feign.codec.Decoder;
import feign.codec.Encoder;
import feign.codec.ErrorDecoder;
import java.util.Iterator;
import java.util.Map;
import java.util.Objects;
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.FeignClientProperties.FeignClientConfiguration;
import org.springframework.cloud.openfeign.loadbalancer.FeignBlockingLoadBalancerClient;
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;

class FeignClientFactoryBean implements FactoryBean, InitializingBean, ApplicationContextAware {
private Class type;
private String name;
private String url;
private String contextId;
private String path;
private boolean decode404;
private ApplicationContext applicationContext;
private Class fallback;
private Class fallbackFactory;

FeignClientFactoryBean() {  
    this.fallback = Void.TYPE;  
    this.fallbackFactory = Void.TYPE;  
}

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

protected Builder feign(FeignContext context) {  
    FeignLoggerFactory loggerFactory = (FeignLoggerFactory)this.get(context, FeignLoggerFactory.class);  
    Logger logger = loggerFactory.create(this.type);  
    Builder builder = ((Builder)this.get(context, Builder.class)).logger(logger).encoder((Encoder)this.get(context, Encoder.class)).decoder((Decoder)this.get(context, Decoder.class)).contract((Contract)this.get(context, Contract.class));  
    this.configureFeign(context, builder);  
    return builder;  
}

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

}

protected void configureUsingConfiguration(FeignContext context, Builder builder) {  
    Level level = (Level)this.getOptional(context, Level.class);  
    if (level != null) {  
        builder.logLevel(level);  
    }

    Retryer retryer = (Retryer)this.getOptional(context, Retryer.class);  
    if (retryer != null) {  
        builder.retryer(retryer);  
    }

    ErrorDecoder errorDecoder = (ErrorDecoder)this.getOptional(context, ErrorDecoder.class);  
    if (errorDecoder != null) {  
        builder.errorDecoder(errorDecoder);  
    }

    Options options = (Options)this.getOptional(context, Options.class);  
    if (options != null) {  
        builder.options(options);  
    }

    Map<String, RequestInterceptor> requestInterceptors = context.getInstances(this.contextId, RequestInterceptor.class);  
    if (requestInterceptors != null) {  
        builder.requestInterceptors(requestInterceptors.values());  
    }

    QueryMapEncoder queryMapEncoder = (QueryMapEncoder)this.getOptional(context, QueryMapEncoder.class);  
    if (queryMapEncoder != null) {  
        builder.queryMapEncoder(queryMapEncoder);  
    }

    if (this.decode404) {  
        builder.decode404();  
    }

}

protected void configureUsingProperties(FeignClientConfiguration config, Builder builder) {  
    if (config != null) {  
        if (config.getLoggerLevel() != null) {  
            builder.logLevel(config.getLoggerLevel());  
        }

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

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

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

        if (config.getRequestInterceptors() != null && !config.getRequestInterceptors().isEmpty()) {  
            Iterator var7 = config.getRequestInterceptors().iterator();

            while(var7.hasNext()) {  
                Class<RequestInterceptor> bean = (Class)var7.next();  
                RequestInterceptor interceptor = (RequestInterceptor)this.getOrInstantiate(bean);  
                builder.requestInterceptor(interceptor);  
            }  
        }

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

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

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

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

    }  
}

private <T> T getOrInstantiate(Class<T> tClass) {  
    try {  
        return this.applicationContext.getBean(tClass);  
    } catch (NoSuchBeanDefinitionException var3) {  
        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);  
    } else {  
        return instance;  
    }  
}

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

protected <T> T loadBalance(Builder builder, FeignContext context, HardCodedTarget<T> target) {  
    Client client = (Client)this.getOptional(context, Client.class);  
    if (client != null) {  
        builder.client(client);  
        Targeter targeter = (Targeter)this.get(context, Targeter.class);  
        return targeter.target(this, builder, context, target);  
    } else {  
        throw new IllegalStateException("No Feign Client for loadBalancing defined. Did you forget to include spring-cloud-starter-netflix-ribbon?");  
    }  
}

public Object getObject() throws Exception {  
    return this.getTarget();  
}

<T> T getTarget() {  
    FeignContext context = (FeignContext)this.applicationContext.getBean(FeignContext.class);  
    Builder builder = this.feign(context);  
    if (!StringUtils.hasText(this.url)) {  
        if (!this.name.startsWith("http")) {  
            this.url = "http://" + this.name;  
        } else {  
            this.url = this.name;  
        }

        this.url = this.url + this.cleanPath();  
        return this.loadBalance(builder, context, new HardCodedTarget(this.type, this.name, this.url));  
    } else {  
        if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {  
            this.url = "http://" + this.url;  
        }

        String url = this.url + this.cleanPath();  
        Client client = (Client)this.getOptional(context, Client.class);  
        if (client != null) {  
            if (client instanceof LoadBalancerFeignClient) {  
                client = ((LoadBalancerFeignClient)client).getDelegate();  
            }

            if (client instanceof FeignBlockingLoadBalancerClient) {  
                client = ((FeignBlockingLoadBalancerClient)client).getDelegate();  
            }

            builder.client(client);  
        }

        Targeter targeter = (Targeter)this.get(context, Targeter.class);  
        return 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;  
}

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

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;  
}

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;  
}

public boolean equals(Object o) {  
    if (this == o) {  
        return true;  
    } else if (o != null && this.getClass() == o.getClass()) {  
        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);  
    } else {  
        return false;  
    }  
}

public int hashCode() {  
    return Objects.hash(new Object\[\]{this.applicationContext, this.decode404, this.fallback, this.fallbackFactory, this.name, this.path, this.type, this.url});  
}

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

}

首先：

1. org.springframework.cloud.openfeign.FeignClientFactoryBean#getObjectType 返回的类型是业务代码向容器索要Bean判断是否匹配的依据，其返回的是内部的type属性。 这个属性是在上面BeanDefinition内部维持的， 值夜就是我们声明@FeignClient 注解的类名称。

2. FeignClientFactoryBean 内部的属性是在IoC容器启动过程中创建完对象，然后属性注入阶段从BeanDefinition的propertyValues  中拿的。

接下来研究其getObject创建target对象过程中的主要操作。

org.springframework.cloud.openfeign.FeignClientFactoryBean实现了三个接口：FactoryBean, InitializingBean, ApplicationContextAware

FactoryBean 接口是生成对象； InitializingBean 是在属性注入之后检查contextId 和 name 属性；ApplicationContextAware 是获取ApplicationContext 对象工厂。注入FeignContext 的时机是在org.springframework.cloud.sleuth.instrument.web.client.feign.FeignContextBeanPostProcessor

getObject 调用getTarget 过程如下：

1. org.springframework.cloud.openfeign.FeignClientFactoryBean#feign 这里主要构造一个builder，主要包括如下操作：

构造了一个日志打印器（基于原来的接口创建的logger）、配置RequestInterceptor、Logger.Level、Retryer、QueryMapEncoder等属性

这里有两种配置方式吧，一种是基于Spring的Bean 注入的方式；一种是配置方式org.springframework.cloud.openfeign.FeignClientProperties.FeignClientConfiguration(其中这种方式可以基于全局配置，也可以对某个服务单独设置)

全局就是注入Bean的方式修改所有默认的，如果想单独修改某个服务相关的可以在yml 进行配置：

feign:
client:
config:
CLOUD-PAYMENT-SERVICE:
loggerLevel: BASIC

3. 然后在没有url 的情况下是按照服务名进行处理，拼接url 属性为http://服务名称。 如果有URL会按照URL的方式进行处理，并且如果URL没有加http:// 会在这里加上，也就是URL 可以只写域名加端口

4. 获取一个feign.Target.HardCodedTarget 对象，这个对象里面实际就是一个记录的功能，记录了

type： 也就是借口的类型

name: 服务名称

url: 地址信息

5. 调用org.springframework.cloud.openfeign.FeignClientFactoryBean#loadBalance 方法

第一步获取一个feign.Client 对象

第二步获取一个org.springframework.cloud.openfeign.Targeter 对象

第三步调用方法 org.springframework.cloud.openfeign.Targeter#target 创建一个代理对象，这个方法逻辑如下

(1)调用方法org.springframework.cloud.openfeign.HystrixTargeter#target：

(2) 上面方法调用feign.Feign.Builder#target(feign.Target)

    public <T> T target(Target<T> target) {  
        return this.build().newInstance(target);  
    }

    public Feign build() {  
        Factory synchronousMethodHandlerFactory = new Factory(this.client, this.retryer, this.requestInterceptors, this.logger, this.logLevel, this.decode404, this.closeAfterDecode, this.propagationPolicy);  
        ParseHandlersByName handlersByName = new ParseHandlersByName(this.contract, this.options, this.encoder, this.decoder, this.queryMapEncoder, this.errorDecoder, synchronousMethodHandlerFactory);  
        return new ReflectiveFeign(handlersByName, this.invocationHandlerFactory, this.queryMapEncoder);  
    }

　　这里是创建一个工厂，然后调用下面方法

(3)feign.ReflectiveFeign#newInstance

public <T> T newInstance(Target<T> target) {  
    Map<String, MethodHandler> nameToHandler = this.targetToHandlersByName.apply(target);  
    Map<Method, MethodHandler> methodToHandler = new LinkedHashMap();  
    List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList();  
    Method\[\] var5 = target.type().getMethods();  
    int var6 = var5.length;

    for(int var7 = 0; var7 < var6; ++var7) {  
        Method method = var5\[var7\];  
        if (method.getDeclaringClass() != Object.class) {  
            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)));  
            }  
        }  
    }

    InvocationHandler handler = this.factory.create(target, methigeodToHandler);  
    T proxy = Proxy.newProxyInstance(target.type().getClassLoader(), new Class\[\]{target.type()}, handler);  
    Iterator var12 = defaultMethodHandlers.iterator();

    while(var12.hasNext()) {  
        DefaultMethodHandler defaultMethodHandler = (DefaultMethodHandler)var12.next();  
        defaultMethodHandler.bindTo(proxy);  
    }

    return proxy;  
}

这里的重点就是获取到一个methodToHandler对象，这个就是维护一个方法与队应处理器的map，内容如下：

然后调用feign.InvocationHandlerFactory.Default#create 创建InvocationHandler, 这个是JDK代理需要的参数。feign.ReflectiveFeign.FeignInvocationHandler 如下：

static class FeignInvocationHandler implements InvocationHandler {

private final Target target;  
private final Map<Method, MethodHandler> dispatch;

FeignInvocationHandler(Target target, Map<Method, MethodHandler> dispatch) {  
  this.target = checkNotNull(target, "target");  
  this.dispatch = checkNotNull(dispatch, "dispatch for %s", target);  
}

@Override  
public Object invoke(Object proxy, Method method, Object\[\] args) throws Throwable {  
  if ("equals".equals(method.getName())) {  
    try {  
      Object otherHandler =  
          args.length > 0 && args\[0\] != null ? Proxy.getInvocationHandler(args\[0\]) : null;  
      return equals(otherHandler);  
    } catch (IllegalArgumentException e) {  
      return false;  
    }  
  } else if ("hashCode".equals(method.getName())) {  
    return hashCode();  
  } else if ("toString".equals(method.getName())) {  
    return toString();  
  }

  return dispatch.get(method).invoke(args);  
}

@Override  
public boolean equals(Object obj) {  
  if (obj instanceof FeignInvocationHandler) {  
    FeignInvocationHandler other = (FeignInvocationHandler) obj;  
    return target.equals(other.target);  
  }  
  return false;  
}

@Override  
public int hashCode() {  
  return target.hashCode();  
}

@Override  
public String toString() {  
  return target.toString();  
}

} 

接下来就是用Proxy.newProxyInstance 创建代理对象并且返回，这就是JDK的动态代理了。

补充：feign.ReflectiveFeign#newInstance 方法第一行是实例化过程中重要的一步，验证方法的参数以及对参数对应注解的解析以及封装也是在这一步

第一行代码如下：

Map nameToHandler = targetToHandlersByName.apply(target);

1. feign.ReflectiveFeign.ParseHandlersByName#apply  获取方法与其对应的MethodHandler 用于后期动态代理中调用。

public Map<String, MethodHandler> apply(Target key) {  
  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, queryMapEncoder);  
    } else if (md.bodyIndex() != null) {  
      buildTemplate = new BuildEncodedTemplateFromArgs(md, encoder, queryMapEncoder);  
    } else {  
      buildTemplate = new BuildTemplateByResolvingArgs(md, queryMapEncoder);  
    }  
    result.put(md.configKey(),  
        factory.create(key, md, buildTemplate, options, decoder, errorDecoder));  
  }  
  return result;  
}

2. feign.Contract.BaseContract#parseAndValidatateMetadata(java.lang.Class)  这里进行检查方法参数、解析与封装成List 对象

@Override  
public List<MethodMetadata> parseAndValidatateMetadata(Class<?> targetType) {  
  checkState(targetType.getTypeParameters().length == 0, "Parameterized types unsupported: %s",  
      targetType.getSimpleName());  
  checkState(targetType.getInterfaces().length <= 1, "Only single inheritance supported: %s",  
      targetType.getSimpleName());  
  if (targetType.getInterfaces().length == 1) {  
    checkState(targetType.getInterfaces()\[0\].getInterfaces().length == 0,  
        "Only single-level inheritance supported: %s",  
        targetType.getSimpleName());  
  }  
  Map<String, MethodMetadata> result = new LinkedHashMap<String, MethodMetadata>();  
  for (Method method : targetType.getMethods()) {  
    if (method.getDeclaringClass() == Object.class ||  
        (method.getModifiers() & Modifier.STATIC) != 0 ||  
        Util.isDefault(method)) {  
      continue;  
    }  
    MethodMetadata metadata = parseAndValidateMetadata(targetType, method);  
    checkState(!result.containsKey(metadata.configKey()), "Overrides unsupported: %s",  
        metadata.configKey());  
    result.put(metadata.configKey(), metadata);  
  }  
  return new ArrayList<>(result.values());  
}

(1) 首先进行了类合法性校验：

泛型类是不被支持的

代理的类的接口数量为0个或者1个

如果有继承的接口再判断父接口的父接口是不是为空， 也就是只能实现单继承

(2) 然后获取到所有的方法进行遍历解析获得一个MethodMetadata 对象，主要的操作是：org.springframework.cloud.openfeign.support.SpringMvcContract#parseAndValidateMetadata

public MethodMetadata parseAndValidateMetadata(Class<?> targetType, Method method) {  
    this.processedMethods.put(Feign.configKey(targetType, method), method);  
    MethodMetadata md = super.parseAndValidateMetadata(targetType, method);

    RequestMapping classAnnotation = findMergedAnnotation(targetType,  
            RequestMapping.class);  
    if (classAnnotation != null) {  
        // produces - use from class annotation only if method has not specified this  
        if (!md.template().headers().containsKey(ACCEPT)) {  
            parseProduces(md, method, classAnnotation);  
        }

        // consumes -- use from class annotation only if method has not specified this  
        if (!md.template().headers().containsKey(CONTENT\_TYPE)) {  
            parseConsumes(md, method, classAnnotation);  
        }

        // headers -- class annotation is inherited to methods, always write these if  
        // present  
        parseHeaders(md, method, classAnnotation);  
    }  
    return md;  
}

这里会调用父类方法：feign.Contract.BaseContract#parseAndValidateMetadata

protected MethodMetadata parseAndValidateMetadata(Class<?> targetType, Method method) {  
  MethodMetadata data = new MethodMetadata();  
  data.returnType(Types.resolve(targetType, targetType, method.getGenericReturnType()));  
  data.configKey(Feign.configKey(targetType, method));

  if (targetType.getInterfaces().length == 1) {  
    processAnnotationOnClass(data, targetType.getInterfaces()\[0\]);  
  }  
  processAnnotationOnClass(data, targetType);

  for (Annotation methodAnnotation : method.getAnnotations()) {  
    processAnnotationOnMethod(data, methodAnnotation, method);  
  }  
  checkState(data.template().method() != null,  
      "Method %s not annotated with HTTP method type (ex. GET, POST)",  
      method.getName());  
  Class<?>\[\] parameterTypes = method.getParameterTypes();  
  Type\[\] genericParameterTypes = method.getGenericParameterTypes();

  Annotation\[\]\[\] parameterAnnotations = method.getParameterAnnotations();  
  int count = parameterAnnotations.length;  
  for (int i = 0; i < count; i++) {  
    boolean isHttpAnnotation = false;  
    if (parameterAnnotations\[i\] != null) {  
      isHttpAnnotation = processAnnotationsOnParameter(data, parameterAnnotations\[i\], i);  
    }  
    if (parameterTypes\[i\] == URI.class) {  
      data.urlIndex(i);  
    } else if (!isHttpAnnotation && parameterTypes\[i\] != Request.Options.class) {  
      checkState(data.formParams().isEmpty(),  
          "Body parameters cannot be used with form parameters.");  
      checkState(data.bodyIndex() == null, "Method has too many Body parameters: %s", method);  
      data.bodyIndex(i);  
      data.bodyType(Types.resolve(targetType, targetType, genericParameterTypes\[i\]));  
    }  
  }

  if (data.headerMapIndex() != null) {  
    checkMapString("HeaderMap", parameterTypes\[data.headerMapIndex()\],  
        genericParameterTypes\[data.headerMapIndex()\]);  
  }

  if (data.queryMapIndex() != null) {  
    if (Map.class.isAssignableFrom(parameterTypes\[data.queryMapIndex()\])) {  
      checkMapKeys("QueryMap", genericParameterTypes\[data.queryMapIndex()\]);  
    }  
  }

  return data;  
}

1》初始化一个 MethodMetadata 之后， Annotation[][] parameterAnnotations = method.getParameterAnnotations(); 获取一个方法参数对应的注解数组，二维数组是每一行代表对应的参数位置

比如下面方法：

/\*\*  
 \* 注意  
 \* 1. PathVariable 的value 属性必须有。 会在org.springframework.cloud.openfeign.annotation.PathVariableParameterProcessor#processArgument(org.springframework.cloud.openfeign.AnnotatedParameterProcessor.AnnotatedParameterContext, java.lang.annotation.Annotation, java.lang.reflect.Method) 进行验证  
 \*  
 \* @param map  
 \* @param queryParam  
 \* @param id  
 \* @return  
 \*/  
@PostMapping("/pay/testParam/{id}")

// JSONResultUtil> testParam(@RequestBody Map map, @RequestParam("queryParam") String queryParam, @PathVariable("id") String id);
// 下面这种写可以， 参数上不写任何注解默认会作为body 处理，但是body 只能出现一个， 多个会在启动过程中检查报错
JSONResultUtil> testParam(Map map, @RequestParam("queryParam") String queryParam, @PathVariable("id") String id);

获取到的数组为：

2》然后循环处理方法的参数

　　org.springframework.cloud.openfeign.support.SpringMvcContract#processAnnotationsOnParameter

protected boolean processAnnotationsOnParameter(MethodMetadata data,  
        Annotation\[\] annotations, int paramIndex) {  
    boolean isHttpAnnotation = false;

    AnnotatedParameterProcessor.AnnotatedParameterContext context = new SimpleAnnotatedParameterContext(  
            data, paramIndex);  
    Method method = this.processedMethods.get(data.configKey());  
    for (Annotation parameterAnnotation : annotations) {  
        AnnotatedParameterProcessor processor = this.annotatedArgumentProcessors  
                .get(parameterAnnotation.annotationType());  
        if (processor != null) {  
            Annotation processParameterAnnotation;  
            // synthesize, handling @AliasFor, while falling back to parameter name on  
            // missing String #value():  
            processParameterAnnotation = synthesizeWithMethodParameterNameAsFallbackValue(  
                    parameterAnnotation, method, paramIndex);  
            isHttpAnnotation |= processor.processArgument(context,  
                    processParameterAnnotation, method);  
        }  
    }

    if (isHttpAnnotation && data.indexToExpander().get(paramIndex) == null) {  
        TypeDescriptor typeDescriptor = createTypeDescriptor(method, paramIndex);  
        if (this.conversionService.canConvert(typeDescriptor,  
                STRING\_TYPE\_DESCRIPTOR)) {  
            Param.Expander expander = this.convertingExpanderFactory  
                    .getExpander(typeDescriptor);  
            if (expander != null) {  
                data.indexToExpander().put(paramIndex, expander);  
            }  
        }  
    }  
    return isHttpAnnotation;  
}

　　根据参数对应的注解数组信息 annotations 进行解析，根据注解类型从annotatedArgumentProcessors获取到对应的参数解析器，然后调用processor.processArgument(context, processParameterAnnotation, method);  进行处理。

比如默认的注解类型与参数解析器关系如下：

　　这里会进行参数的注解验证。 默认什么注解也不写会作为RequestBody 解析，也就是获取到对应参数的顺序标记为bodyIndex，用于后面方法调用时解析body。(这里注意最多有一个RequestBody, 如果多个会在checkState(data.bodyIndex() == null, "Method has too many Body parameters: %s", method); 验证时报错)

　　经过上面处理获取到的MethodMetadata如下：

3. 然后根据方法创建MethodHandler 对象存入Map 中返回去供使用

public MethodHandler create(Target<?> target,  
                            MethodMetadata md,  
                            RequestTemplate.Factory buildTemplateFromArgs,  
                            Options options,  
                            Decoder decoder,  
                            ErrorDecoder errorDecoder) {  
  return new SynchronousMethodHandler(target, client, retryer, requestInterceptors, logger,  
      logLevel, md, buildTemplateFromArgs, options, decoder,  
      errorDecoder, decode404, closeAfterDecode, propagationPolicy);  
}

　　到此，Feign 代理注册以及对象创建完成。所以调用过程中的就是feign.ReflectiveFeign.FeignInvocationHandler#invoke方法。

基于JDK的动态代理其入口是在InvocationHandler的invoke方法，上面是：feign.ReflectiveFeign.FeignInvocationHandler#invoke

@Override  
public Object invoke(Object proxy, Method method, Object\[\] args) throws Throwable {  
  if ("equals".equals(method.getName())) {  
    try {  
      Object otherHandler =  
          args.length > 0 && args\[0\] != null ? Proxy.getInvocationHandler(args\[0\]) : null;  
      return equals(otherHandler);  
    } catch (IllegalArgumentException e) {  
      return false;  
    }  
  } else if ("hashCode".equals(method.getName())) {  
    return hashCode();  
  } else if ("toString".equals(method.getName())) {  
    return toString();  
  }

  return dispatch.get(method).invoke(args);  
}

　　可以看到toString、equals、hashcode方法特殊处理，指挥就是根据Method 对象获取到对应的MethodHandler 进行调用。

1. 调用到feign.SynchronousMethodHandler#invoke

@Override
public Object invoke(Object[] argv) throws Throwable {
RequestTemplate template = buildTemplateFromArgs.create(argv);
Options options = findOptions(argv);
Retryer retryer = this.retryer.clone();
while (true) {
try {
return executeAndDecode(template, options);
} catch (RetryableException e) {
try {
retryer.continueOrPropagate(e);
} catch (RetryableException th) {
Throwable cause = th.getCause();
if (propagationPolicy == UNWRAP && cause != null) {
throw cause;
} else {
throw th;
}
}
if (logLevel != Logger.Level.NONE) {
logger.logRetry(metadata.configKey(), logLevel);
}
continue;
}
}
}

(1) RequestTemplate.from(metadata.template());    根据上面创建对象过程中解析出来的RequestTemplate克隆一个RequestTemplate

(2) 将参数解析出来，存放到： varBuilder

(3) resolve(argv, mutable, varBuilder); 根据解析出的参数替换url 中的变量以及queries 中需要的变量以及设置一些请求头

(4) feign.SynchronousMethodHandler#executeAndDecode 开始处理

Object executeAndDecode(RequestTemplate template, Options options) throws Throwable {
Request request = targetRequest(template);

if (logLevel != Logger.Level.NONE) {  
  logger.logRequest(metadata.configKey(), logLevel, request);  
}

Response response;  
long start = System.nanoTime();  
try {  
  response = client.execute(request, options);  
} catch (IOException e) {  
  if (logLevel != Logger.Level.NONE) {  
    logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime(start));  
  }  
  throw errorExecuting(request, e);  
}  
long elapsedTime = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start);

boolean shouldClose = true;  
try {  
  if (logLevel != Logger.Level.NONE) {  
    response =  
        logger.logAndRebufferResponse(metadata.configKey(), logLevel, response, elapsedTime);  
  }  
  if (Response.class == metadata.returnType()) {  
    if (response.body() == null) {  
      return response;  
    }  
    if (response.body().length() == null ||  
        response.body().length() > MAX\_RESPONSE\_BUFFER\_SIZE) {  
      shouldClose = false;  
      return response;  
    }  
    // Ensure the response body is disconnected  
    byte\[\] bodyData = Util.toByteArray(response.body().asInputStream());  
    return response.toBuilder().body(bodyData).build();  
  }  
  if (response.status() >= 200 && response.status() < 300) {  
    if (void.class == metadata.returnType()) {  
      return null;  
    } else {  
      Object result = decode(response);  
      shouldClose = closeAfterDecode;  
      return result;  
    }  
  } else if (decode404 && response.status() == 404 && void.class != metadata.returnType()) {  
    Object result = decode(response);  
    shouldClose = closeAfterDecode;  
    return result;  
  } else {  
    throw errorDecoder.decode(metadata.configKey(), response);  
  }  
} catch (IOException e) {  
  if (logLevel != Logger.Level.NONE) {  
    logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime);  
  }  
  throw errorReading(request, response, e);  
} finally {  
  if (shouldClose) {  
    ensureClosed(response.body());  
  }  
}

}

第一步： 这里首先调用这个方法对FeignInteceptor 拦截器做处理 feign.SynchronousMethodHandler#targetRequest， 并且将信息封装到feign.Request 类中

Request targetRequest(RequestTemplate template) {
for (RequestInterceptor interceptor : requestInterceptors) {
interceptor.apply(template);
}
return target.apply(template);
}

第二步：打印request 对象

第三步：org.springframework.cloud.sleuth.instrument.web.client.feign.TraceLoadBalancerFeignClient#execute 调用

@Override  
public Response execute(Request request, Request.Options options) throws IOException {  
    if (log.isDebugEnabled()) {  
        log.debug("Before send");  
    }  
    Response response = null;  
    Span fallbackSpan = tracer().nextSpan().start();  
    try {  
        response = super.execute(request, options);  
        if (log.isDebugEnabled()) {  
            log.debug("After receive");  
        }  
        return response;  
    }  
    catch (Exception e) {  
        if (log.isDebugEnabled()) {  
            log.debug("Exception thrown", e);  
        }  
        if (e instanceof IOException || e.getCause() != null  
                && e.getCause() instanceof ClientException  
                && ((ClientException) e.getCause())  
                        .getErrorType() == ClientException.ErrorType.GENERAL) {  
            if (log.isDebugEnabled()) {  
                log.debug(  
                        "General exception was thrown, so most likely the traced client wasn't called. Falling back to a manual span");  
            }  
            fallbackSpan = tracingFeignClient().handleSend(  
                    new HashMap<>(request.headers()), request, fallbackSpan);  
            tracingFeignClient().handleReceive(fallbackSpan, response, e);  
        }  
        throw e;  
    }  
    finally {  
        fallbackSpan.abandon();  
    }  
}

转交给父类org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient#execute

public Response execute(Request request, Request.Options options) throws IOException {  
    try {  
        URI asUri = URI.create(request.url());  
        String clientName = asUri.getHost();  
        URI uriWithoutHost = cleanUrl(request.url(), clientName);  
        FeignLoadBalancer.RibbonRequest ribbonRequest = new FeignLoadBalancer.RibbonRequest(  
                this.delegate, request, uriWithoutHost);

        IClientConfig requestConfig = getClientConfig(options, clientName);  
        return lbClient(clientName)  
                .executeWithLoadBalancer(ribbonRequest, requestConfig).toResponse();  
    }  
    catch (ClientException e) {  
        IOException io = findIOException(e);  
        if (io != null) {  
            throw io;  
        }  
        throw new RuntimeException(e);  
    }  
}

　　之后调用com.netflix.client.AbstractLoadBalancerAwareClient#executeWithLoadBalancer(S, com.netflix.client.config.IClientConfig)  ， 也就是请求交给ribbon

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