spring-cloud-square源码速读（retrofit + okhttp篇）

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发布于 2021-12-07 09:02:55

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发布于 2021-12-07 09:02:55

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spring-cloud-square系列文章

本篇概览

本文是《spring-cloud-square学习》系列的终篇，上一篇咱们了解了spring-cloud-square-okhttp库的源码和原理，今天提升一点难度，看看spring-cloud-square的另一种类型的源码：spring-cloud-square-retrofit，也就是下图红框中的那种：

源码分析目标

接下来开始分析spring-cloud-square-retrofit工程的源码，如下图红框所示：

本篇目标非常明确，只搞清楚一件事：在使用spring-cloud-square的时候，以前文的consumer-retrofit-okhttp子工程为例，为什么咱们只写了HelloService接口，但却能通过Autowired注解使用HelloService的实现类？

提前小结

如果您想了解spring-cloud-square的retrofit部分的原理，却又苦于没有时间深入研究，可以看看下面这份提前小结的内容：
整个机制的运转，可以分为相对独立的四个部分：业务应用编码使用spring-cloud-square相关的注解、bean的factory注册到spring环境、bean的factory类在spring环境实例化、通过factory的实例在spring生产HelloService接口的实现类
根据上面的分析，最重要的应该是bean的factory类：RetrofitClientFactoryBean，它实现了FactoryBean接口，其getObject方法就是根据HelloService接口生成实现类和关键，最终会调用下图红框中的Retrofit.create方法创建实例：

Retrofit类并非spring-cloud的项目，而是来自Retrofit库，其create方法中使用了JDK的Proxy.newProxyInstance方法，该方法可以根据HelloService接口生成一个实现了该接口的实例：

在使用spring-cloud-square的retrofit + okhttp方案时，HelloService接口中使用的还是远程服务的服务名，而不是地址和端口，这是因为使用了spring-cloud-square-okhttp库，所以服务名转为地址+端口的逻辑与前文《spring-cloud-square源码速读(spring-cloud-square-okhttp篇)》保持一致
以上就是整个源码分析的结论了，我将涉及到的关联代码流程整理成简图，如下所示：

回顾应用如何使用spring-cloud-square-retrofit

在分析源码之前，先回顾一下《spring-cloud-square开发实战》中的代码，咱们当时是如何使用spring-cloud-square-retrofit的(对应demo中的consumer-retrofit-okhttp子工程)
新建配置类OkHttpClientConfig，使用了EnableRetrofitClients注解，向spring环境注册OkHttpClient.Builder实例：

@Configuration
@EnableRetrofitClients
class OkHttpClientConfig{
    @Bean
    @LoadBalanced
    public OkHttpClient.Builder okHttpClientBuilder() {
        return new OkHttpClient.Builder();
    }
}

定义HelloService接口，用注解RetrofitClient修饰，注解的值是远程调用的服务名，里面声明hello方法，用注解GET修饰，注解的值是远程调用的接口的path：

@RetrofitClient("provider")
public interface HelloService {
    @GET("/hello-obj")
    Call<HelloResponse> hello(@Query("name") String name);
}

在业务要做远程调用的时候，用Autowired注解修饰HelloService接口，即可调用HelloService.hello方法，至于接口对应的实例来自哪里，开发者不必关注：

@RestController
public class RemoteHello {
    @Autowired(required = false)
    HelloService helloService;

    @GetMapping("/remote-obj")
    public HelloResponse hello(@RequestParam("name") String name) throws IOException {
        return helloService.hello(name).execute().body();
    }
}

以上就是咱们开发业务代码时使用spring-cloud-square的关键操作，接下来就从源码角度来分析这些操作到底发挥了什么作用

源码分析(类定义注册阶段)

回忆一下咱们写的OkHttpClientConfig.java，里面使用了注解EnableRetrofitClients，这就是本次阅读代码的入口：

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import({ RetrofitConfiguration.class, RetrofitClientsRegistrar.class })
public @interface EnableRetrofitClients {
	String[] value() default {};
	String[] basePackages() default {};
	Class<?>[] basePackageClasses() default {};
	Class<?>[] defaultConfiguration() default {};
	Class<?>[] clients() default {};
}

从上述代码可见RetrofitConfiguration和RetrofitClientsRegistrar都会比实例化，RetrofitConfiguration过于简单就不看了，重点关注RetrofitClientsRegistrar，先来看它的类图，搞清楚继承和实现
如下图所示，RetrofitClientsRegistrar集成自AbstractRetrofitClientsRegistrar，而AbstractRetrofitClientsRegistrar又集成自ImportBeanDefinitionRegistrar

所以，RetrofitClientsRegistrar被实例化的时候，就相当于ImportBeanDefinitionRegistrar接口的实现类被实例化了，这个ImportBeanDefinitionRegistrar接口，相信熟悉spring的同学对其不会陌生，它是用来动态注册bean的，那么接下来的重点就是ImportBeanDefinitionRegistrar的registerBeanDefinitions方法的具体内容，看看它到底注册了什么bean
registerBeanDefinitions方法的代码在AbstractRetrofitClientsRegistrar.java中（请在上面的类图中找到AbstractRetrofitClientsRegistrar的位置），如下所示，由于EnableRetrofitClients修饰的是咱们创建的OkHttpClientConfig.java，所以下面的入参AnnotationMetadata是OkHttpClientConfig类的注解信息：

	@Override
	public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
		registerDefaultConfiguration(metadata, registry);
		registerRetrofitClients(metadata, registry);
	}

上述代码的第一个方法registerDefaultConfiguration是注册配置信息的，非重点，跳过
上述代码的第二个方法registerRetrofitClients，这是本篇的关键，请重点关注下面代码中的中文注释：

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

		Set<String> basePackages;

		Map<String, Object> attrs = metadata.getAnnotationAttributes(getAnnotationClass().getName());
		// 过滤条件：有RetrofitClient注解修饰的类，对应咱们代码中的HelloService.java
		AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(RetrofitClient.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)));
		}

		for (String basePackage : basePackages) {
			Set<BeanDefinition> candidateComponents = scanner.findCandidateComponents(basePackage);
			for (BeanDefinition candidateComponent : candidateComponents) {
				// 找到的结果就是HelloService接口
				if (candidateComponent instanceof AnnotatedBeanDefinition) {
					// verify annotated class is an interface
					AnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition) candidateComponent;
					AnnotationMetadata annotationMetadata = beanDefinition.getMetadata();
					Assert.isTrue(annotationMetadata.isInterface(),
							"@RetrofitClient can only be specified on an interface");

					// 取得修饰HelloService类的RetrofitClient注解的所有属性
					Map<String, Object> attributes = annotationMetadata
							.getAnnotationAttributes(RetrofitClient.class.getCanonicalName());
					// 根据这些属性，得到远程访问的服务名是provider
					String name = getClientName(attributes);
					// 在spring注册一个配置类，名为provider.RetrofitClientSpecification，
					// 由于修饰HelloService的RetrofitClient注解并没有什么属性，所以这个配置类没有什么内容
					registerClientConfiguration(registry, name, attributes.get("configuration"));
					
					// 这个方法要重点关注，
					// 入参annotationMetadata是HelloService的元信息，
					// attributes是修饰HelloService类的RetrofitClient注解的所有属性
					registerRetrofitClient(registry, annotationMetadata, attributes);
				}
			}
		}
	}

将上述代码中最后调用的registerRetrofitClient方法展开如下，这段代码做了件很重要的事情：注册BeanDefinition到spring，注册的name等于com.bolingcavalry.consumer.service.HelloService，对应的BeanDefinition的beanClass等于RetrofitClientFactoryBean：

private void registerRetrofitClient(BeanDefinitionRegistry registry, AnnotationMetadata annotationMetadata,
			Map<String, Object> attributes) {
		// 由于注解修饰的是HelloService类，所以这里className等于com.bolingcavalry.consumer.service.HelloService
		String className = annotationMetadata.getClassName();
		// 注意getFactoryBeanClass()方法，来自RetrofitClientsRegistrar类，返回值是RetrofitClientFactoryBean.class，
		// 因此，RetrofitClientFactoryBean就被带入了definition中，
		// 注意，这个definition变量的类型是BeanDefinitionBuilder,
		// 其内部有个成员变量beanDefinition，此时该成员变量的beanClass字段已经被设置为RetrofitClientFactoryBean.class
		BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(getFactoryBeanClass());
		validate(attributes);
		// HelloService的RetrofitClient注解没有设置url属性，因此这里是空字符串
		definition.addPropertyValue("url", getUrl(attributes));
		// RetrofitClient注解的value属性配置为远程服务名，这里是provider
		String name = getName(attributes);
		definition.addPropertyValue("name", name);
		// 类型就是HelloService
		definition.addPropertyValue("type", className);
		// by_type，意味着autowire注解修饰HelloService的时候，可以用HelloService获取对应的实现类
		definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);

		String alias = name + "RetrofitClient";
		
		// 通过BeanDefinitionBuilder得到了beanDefinition，
		// 这个beanDefinition的beanClass字段在前面已经被设置为RetrofitClientFactoryBean.class
		AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();
		
		beanDefinition.setPrimary(true);

		String qualifier = getQualifier(attributes);
		if (StringUtils.hasText(qualifier)) {
			alias = qualifier;
		}
		
		// 将注册BeanDefinition所需的两个参数beanName和beanDefinition放入BeanDefinitionHolder对象中
		BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className, new String[] { alias });
		// 完成BeanDefinition在spring环境的注册，name等于com.bolingcavalry.consumer.service.HelloService，对应的BeanDefinition的beanClass等于RetrofitClientFactoryBean(注意，这很重要)
		BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
	}

此刻，HelloService的类定义已经在spring完成了注册，接下来要看HelloService接口的实现类来自何处；

BeanDefinition中的RetrofitClientFactoryBean被实例化

在spring初始化过程中，上述红框中的代码会触发spring环境对HelloService接口实现类的实例化，完整的触发过程和详细堆栈就不细说了，这都是spring的标准处理流程，接下来会挑这里面的重点去看
首先就是大名鼎鼎的SpringApplication.refresh方法，这里面是bean的实例化逻辑，会执行一个重要方法，就是DefaultListableBeanFactory.doGetBeanNamesForType，这里面会遍历所有已注册的BeanDefinition，逐个处理，如下图：

DefaultListableBeanFactory.doGetBeanNamesForType继续执行，会到下一个重点：根据BeanDefinition创建bean，堆栈如下，这是用条件断点得到的：

doGetBean:256, AbstractBeanFactory (org.springframework.beans.factory.support) [2]
getTypeForFactoryBean:1709, AbstractBeanFactory (org.springframework.beans.factory.support)
getTypeForFactoryBean:899, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
isTypeMatch:637, AbstractBeanFactory (org.springframework.beans.factory.support)
doGetBeanNamesForType:583, DefaultListableBeanFactory (org.springframework.beans.factory.support)
getBeanNamesForType:542, DefaultListableBeanFactory (org.springframework.beans.factory.support)
beanNamesForTypeIncludingAncestors:265, BeanFactoryUtils (org.springframework.beans.factory)
findAutowireCandidates:1546, DefaultListableBeanFactory (org.springframework.beans.factory.support)
doResolveDependency:1343, DefaultListableBeanFactory (org.springframework.beans.factory.support)
resolveDependency:1300, DefaultListableBeanFactory (org.springframework.beans.factory.support)
resolveAutowiredArgument:887, ConstructorResolver (org.springframework.beans.factory.support)
createArgumentArray:791, ConstructorResolver (org.springframework.beans.factory.support)
instantiateUsingFactoryMethod:541, ConstructorResolver (org.springframework.beans.factory.support)
instantiateUsingFactoryMethod:1334, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
createBeanInstance:1177, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
doCreateBean:564, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
createBean:524, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
lambda$doGetBean$0:335, AbstractBeanFactory (org.springframework.beans.factory.support)
getObject:-1, 1485624601 (org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$488)
getSingleton:234, DefaultSingletonBeanRegistry (org.springframework.beans.factory.support)
doGetBean:333, AbstractBeanFactory (org.springframework.beans.factory.support) [1]
getBean:213, AbstractBeanFactory (org.springframework.beans.factory.support)
registerBeanPostProcessors:258, PostProcessorRegistrationDelegate (org.springframework.context.support)
registerBeanPostProcessors:762, AbstractApplicationContext (org.springframework.context.support)
refresh:567, AbstractApplicationContext (org.springframework.context.support)
refresh:769, SpringApplication (org.springframework.boot)
refresh:761, SpringApplication (org.springframework.boot)
refreshContext:426, SpringApplication (org.springframework.boot)
run:326, SpringApplication (org.springframework.boot)
loadContext:123, SpringBootContextLoader (org.springframework.boot.test.context)
loadContextInternal:99, DefaultCacheAwareContextLoaderDelegate (org.springframework.test.context.cache)
loadContext:124, DefaultCacheAwareContextLoaderDelegate (org.springframework.test.context.cache)
getApplicationContext:124, DefaultTestContext (org.springframework.test.context.support)
setUpRequestContextIfNecessary:190, ServletTestExecutionListener (org.springframework.test.context.web)
prepareTestInstance:132, ServletTestExecutionListener (org.springframework.test.context.web)
prepareTestInstance:244, TestContextManager (org.springframework.test.context)
postProcessTestInstance:138, SpringExtension (org.springframework.test.context.junit.jupiter)
lambda$invokeTestInstancePostProcessors$6:350, ClassBasedTestDescriptor (org.junit.jupiter.engine.descriptor)
execute:-1, 2001115307 (org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor$$Lambda$344)
executeAndMaskThrowable:355, ClassBasedTestDescriptor (org.junit.jupiter.engine.descriptor)
lambda$invokeTestInstancePostProcessors$7:350, ClassBasedTestDescriptor (org.junit.jupiter.engine.descriptor)
accept:-1, 1650113431 (org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor$$Lambda$343)
accept:-1, 796667727 (java.util.stream.StreamSpliterators$WrappingSpliterator$$Lambda$107)
accept:193, ReferencePipeline$3$1 (java.util.stream)
accept:175, ReferencePipeline$2$1 (java.util.stream)
forEachRemaining:1384, ArrayList$ArrayListSpliterator (java.util)
copyInto:482, AbstractPipeline (java.util.stream)
wrapAndCopyInto:472, AbstractPipeline (java.util.stream)
forEachRemaining:312, StreamSpliterators$WrappingSpliterator (java.util.stream)
forEachRemaining:743, Streams$ConcatSpliterator (java.util.stream)
forEachRemaining:742, Streams$ConcatSpliterator (java.util.stream)
forEach:580, ReferencePipeline$Head (java.util.stream)
invokeTestInstancePostProcessors:349, ClassBasedTestDescriptor (org.junit.jupiter.engine.descriptor)
lambda$instantiateAndPostProcessTestInstance$4:270, ClassBasedTestDescriptor (org.junit.jupiter.engine.descriptor)
execute:-1, 1547883191 (org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor$$Lambda$342)
execute:73, ThrowableCollector (org.junit.platform.engine.support.hierarchical)
instantiateAndPostProcessTestInstance:269, ClassBasedTestDescriptor (org.junit.jupiter.engine.descriptor)
lambda$testInstancesProvider$2:259, ClassBasedTestDescriptor (org.junit.jupiter.engine.descriptor)
get:-1, 795748540 (org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor$$Lambda$335)
orElseGet:267, Optional (java.util)
lambda$testInstancesProvider$3:258, ClassBasedTestDescriptor (org.junit.jupiter.engine.descriptor)
getTestInstances:-1, 361398902 (org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor$$Lambda$234)
getTestInstances:31, TestInstancesProvider (org.junit.jupiter.engine.execution)
lambda$prepare$0:101, TestMethodTestDescriptor (org.junit.jupiter.engine.descriptor)
execute:-1, 451312813 (org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor$$Lambda$334)
execute:73, ThrowableCollector (org.junit.platform.engine.support.hierarchical)
prepare:100, TestMethodTestDescriptor (org.junit.jupiter.engine.descriptor)
prepare:65, TestMethodTestDescriptor (org.junit.jupiter.engine.descriptor)
lambda$prepare$1:111, NodeTestTask (org.junit.platform.engine.support.hierarchical)
execute:-1, 1008315045 (org.junit.platform.engine.support.hierarchical.NodeTestTask$$Lambda$182)
execute:73, ThrowableCollector (org.junit.platform.engine.support.hierarchical)
prepare:111, NodeTestTask (org.junit.platform.engine.support.hierarchical)
execute:79, NodeTestTask (org.junit.platform.engine.support.hierarchical)
accept:-1, 1976870338 (org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService$$Lambda$201)
forEach:1259, ArrayList (java.util)
invokeAll:38, SameThreadHierarchicalTestExecutorService (org.junit.platform.engine.support.hierarchical)
lambda$executeRecursively$5:143, NodeTestTask (org.junit.platform.engine.support.hierarchical)
execute:-1, 1647809929 (org.junit.platform.engine.support.hierarchical.NodeTestTask$$Lambda$197)
execute:73, ThrowableCollector (org.junit.platform.engine.support.hierarchical)
lambda$executeRecursively$7:129, NodeTestTask (org.junit.platform.engine.support.hierarchical)
invoke:-1, 928294079 (org.junit.platform.engine.support.hierarchical.NodeTestTask$$Lambda$196)
around:137, Node (org.junit.platform.engine.support.hierarchical)
lambda$executeRecursively$8:127, NodeTestTask (org.junit.platform.engine.support.hierarchical)
execute:-1, 728885526 (org.junit.platform.engine.support.hierarchical.NodeTestTask$$Lambda$195)
execute:73, ThrowableCollector (org.junit.platform.engine.support.hierarchical)
executeRecursively:126, NodeTestTask (org.junit.platform.engine.support.hierarchical)
execute:84, NodeTestTask (org.junit.platform.engine.support.hierarchical)
accept:-1, 1976870338 (org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService$$Lambda$201)
forEach:1259, ArrayList (java.util)
invokeAll:38, SameThreadHierarchicalTestExecutorService (org.junit.platform.engine.support.hierarchical)
lambda$executeRecursively$5:143, NodeTestTask (org.junit.platform.engine.support.hierarchical)
execute:-1, 1647809929 (org.junit.platform.engine.support.hierarchical.NodeTestTask$$Lambda$197)
execute:73, ThrowableCollector (org.junit.platform.engine.support.hierarchical)
lambda$executeRecursively$7:129, NodeTestTask (org.junit.platform.engine.support.hierarchical)
invoke:-1, 928294079 (org.junit.platform.engine.support.hierarchical.NodeTestTask$$Lambda$196)
around:137, Node (org.junit.platform.engine.support.hierarchical)
lambda$executeRecursively$8:127, NodeTestTask (org.junit.platform.engine.support.hierarchical)
execute:-1, 728885526 (org.junit.platform.engine.support.hierarchical.NodeTestTask$$Lambda$195)
execute:73, ThrowableCollector (org.junit.platform.engine.support.hierarchical)
executeRecursively:126, NodeTestTask (org.junit.platform.engine.support.hierarchical)
execute:84, NodeTestTask (org.junit.platform.engine.support.hierarchical)
submit:32, SameThreadHierarchicalTestExecutorService (org.junit.platform.engine.support.hierarchical)
execute:57, HierarchicalTestExecutor (org.junit.platform.engine.support.hierarchical)
execute:51, HierarchicalTestEngine (org.junit.platform.engine.support.hierarchical)
execute:108, EngineExecutionOrchestrator (org.junit.platform.launcher.core)
execute:88, EngineExecutionOrchestrator (org.junit.platform.launcher.core)
lambda$execute$0:54, EngineExecutionOrchestrator (org.junit.platform.launcher.core)
accept:-1, 607932305 (org.junit.platform.launcher.core.EngineExecutionOrchestrator$$Lambda$150)
withInterceptedStreams:67, EngineExecutionOrchestrator (org.junit.platform.launcher.core)
execute:52, EngineExecutionOrchestrator (org.junit.platform.launcher.core)
execute:96, DefaultLauncher (org.junit.platform.launcher.core)
execute:75, DefaultLauncher (org.junit.platform.launcher.core)
startRunnerWithArgs:71, JUnit5IdeaTestRunner (com.intellij.junit5)
startRunnerWithArgs:33, IdeaTestRunner$Repeater (com.intellij.rt.junit)
prepareStreamsAndStart:221, JUnitStarter (com.intellij.rt.junit)
main:54, JUnitStarter (com.intellij.rt.junit)

根据上述堆栈，要细看AbstractBeanFactory的doGetBean方法，请关注中文注释：

protected <T> T doGetBean(
			String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
			throws BeansException {
		// 入参name等于"com.bolingcavalry.consumer.service.HelloService"
		String beanName = transformedBeanName(name);
		Object beanInstance;

		// Eagerly check singleton cache for manually registered singletons.
		Object sharedInstance = getSingleton(beanName);
		// sharedInstance等于null，因此下面的if判断不成立
		if (sharedInstance != null && args == null) {
			if (logger.isTraceEnabled()) {
				if (isSingletonCurrentlyInCreation(beanName)) {
					logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
							"' that is not fully initialized yet - a consequence of a circular reference");
				}
				else {
					logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
				}
			}
			beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, null);
		}

		else {
			// Fail if we're already creating this bean instance:
			// We're assumably within a circular reference.
			if (isPrototypeCurrentlyInCreation(beanName)) {
				throw new BeanCurrentlyInCreationException(beanName);
			}

			// Check if bean definition exists in this factory.
			BeanFactory parentBeanFactory = getParentBeanFactory();
			// parentBeanFactory等于null，因此下面的if判断不成立
			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
				// Not found -> check parent.
				String nameToLookup = originalBeanName(name);
				if (parentBeanFactory instanceof AbstractBeanFactory) {
					return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
							nameToLookup, requiredType, args, typeCheckOnly);
				}
				else if (args != null) {
					// Delegation to parent with explicit args.
					return (T) parentBeanFactory.getBean(nameToLookup, args);
				}
				else if (requiredType != null) {
					// No args -> delegate to standard getBean method.
					return parentBeanFactory.getBean(nameToLookup, requiredType);
				}
				else {
					return (T) parentBeanFactory.getBean(nameToLookup);
				}
			}
			
			// typeCheckOnly等于true，因此下面的if判断不成立
			if (!typeCheckOnly) {
				markBeanAsCreated(beanName);
			}

			StartupStep beanCreation = this.applicationStartup.start("spring.beans.instantiate")
					.tag("beanName", name);
			try {
				if (requiredType != null) {
					beanCreation.tag("beanType", requiredType::toString);
				}
				// 前面咱们分析过，BeanDefinition已经注册到spring环境了，
				// 此处调用getMergedLocalBeanDefinition即可取得这个BeanDefinition
				RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
				checkMergedBeanDefinition(mbd, beanName, args);

				// Guarantee initialization of beans that the current bean depends on.
				String[] dependsOn = mbd.getDependsOn();
				// HelloService的BeanDefinition没有依赖，
				// 因此dependsOn等于null，下面的if不成立
				if (dependsOn != null) {
					for (String dep : dependsOn) {
						if (isDependent(beanName, dep)) {
							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
									"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
						}
						registerDependentBean(dep, beanName);
						try {
							getBean(dep);
						}
						catch (NoSuchBeanDefinitionException ex) {
							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
									"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
						}
					}
				}

				// Create bean instance.
				// HelloService的bean是单例，因此下面的if判断成立
				if (mbd.isSingleton()) {
					// 这里是创建bean的关键！！！
					// getSingleton传入一个lambda表达式，方法内会调用该表达式，
					sharedInstance = getSingleton(beanName, () -> {
						try {
							// 根据BeanDefinition创建bean，
							// 实际上执行的是AbstractAutowireCapableBeanFactory.createBean方法
							return createBean(beanName, mbd, args);
						}
						catch (BeansException ex) {
							// Explicitly remove instance from singleton cache: It might have been put there
							// eagerly by the creation process, to allow for circular reference resolution.
							// Also remove any beans that received a temporary reference to the bean.
							destroySingleton(beanName);
							throw ex;
						}
					});
					beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
				}

				else if (mbd.isPrototype()) {
					// It's a prototype -> create a new instance.
					Object prototypeInstance = null;
					try {
						beforePrototypeCreation(beanName);
						prototypeInstance = createBean(beanName, mbd, args);
					}
					finally {
						afterPrototypeCreation(beanName);
					}
					beanInstance = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
				}

				else {
					String scopeName = mbd.getScope();
					if (!StringUtils.hasLength(scopeName)) {
						throw new IllegalStateException("No scope name defined for bean ´" + beanName + "'");
					}
					Scope scope = this.scopes.get(scopeName);
					if (scope == null) {
						throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
					}
					try {
						Object scopedInstance = scope.get(beanName, () -> {
							beforePrototypeCreation(beanName);
							try {
								return createBean(beanName, mbd, args);
							}
							finally {
								afterPrototypeCreation(beanName);
							}
						});
						
						beanInstance = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
					}
					catch (IllegalStateException ex) {
						throw new ScopeNotActiveException(beanName, scopeName, ex);
					}
				}
			}
			catch (BeansException ex) {
				beanCreation.tag("exception", ex.getClass().toString());
				beanCreation.tag("message", String.valueOf(ex.getMessage()));
				cleanupAfterBeanCreationFailure(beanName);
				throw ex;
			}
			finally {
				beanCreation.end();
			}
		}

		return adaptBeanInstance(name, beanInstance, requiredType);
	}

至此，RetrofitClientFactoryBean已经完成了实例化，接下来要去看HelloService接口背后的bean是怎么创建的

HelloService对应的bean是如何创建的

回顾一下，咱们的应用代码中用到HelloService的场景，如下图红框所示，使用Autowired注解修饰HelloService：

首先，上图中的RemoteHello是一定会创建bean的，在创建的过程中，DefaultListableBeanFactory.doResolveDependency方法负责处理RemoteHello依赖的bean，如下图所示，在此处触发了HelloService的bean的实例化

辗转反侧，再次走到了AbstractBeanFactory.doGetBean方法，这次会执行下图第二个红框中的getObjectForBeanInstance方法：

然后到了最关键的位置：AbstractBeanFactory.getObjectForBeanInstance方法，这里面将RetrofitClientFactoryBean当做factory用了，用来生产HelloService：

将上图红框2中的getObjectFromFactoryBean方法继续展开，进入FactoryBeanRegistrySupport.doGetObjectFromFactoryBean方法，这里完成了从spring框架到应用自定义之间的过渡：将bean的创建交给应用自己注册的Factory来处理：

在RetrofitClientFactoryBean.getObject中，执行loadBalance(builder, context, serviceIdUrl)：

loadBalance的实现在RetrofitClientFactoryBean中：

	protected Object loadBalance(Retrofit.Builder builder, RetrofitContext context, String serviceIdUrl) {
		// 应用代码的OkHttpClientConfig.java中，okHttpClientBuilder方法生成了OkHttpClient.Builder实例，此处的instances中就是这个实例
		Map<String, OkHttpClient.Builder> instances = context.getInstances(this.name, OkHttpClient.Builder.class);
		
		for (Map.Entry<String, OkHttpClient.Builder> entry : instances.entrySet()) {
			String beanName = entry.getKey();
			OkHttpClient.Builder clientBuilder = entry.getValue();
			// 应用代码的OkHttpClientConfig.java中，okHttpClientBuilder方法上已经用了LoadBalanced注解，
			//所以下面这个if判断为true
			if (applicationContext.findAnnotationOnBean(beanName, LoadBalanced.class) != null) {
				// 创建了OkHttpClient实例，传给了这个Retrofit.Builder
				builder.client(clientBuilder.build());
				// 使用这个Retrofit.Builder去创建retrofit，相当于把上面创建的OkHttpClient实例带给了retrofit
				// 所以，这个retrofit实例的底层就是OkHttpClient
				Retrofit retrofit = buildAndSave(context, builder);
				// type的类型是HelloService，
				// retrofit.create就是要创建一个实例,该实例实现了HelloService接口
				return retrofit.create(this.type);
			}
		}

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

从上面的分析可见，咱们只写HelloService接口不写HelloService实现的关键就是retrofit.create方法，传入了一个接口定义，就能返回该接口的实现类的实例，
说实话retrofit.create的源码并不属于spring-cloud-square，而是Retrofit自己的，在本文中看这段源码属于超纲，但我还是忍不住要看一下：

  public <T> T create(final Class<T> service) {
  	// 一些检查，例如service是不是接口
    validateServiceInterface(service);
    return (T)
    	// 这个实例是通过JDK的Proxy.newProxyInstance创建的
        Proxy.newProxyInstance(
            service.getClassLoader(),
            new Class<?>[] {service},
            new InvocationHandler() {
              private final Platform platform = Platform.get();
              private final Object[] emptyArgs = new Object[0];
				
			  // 业务应用执行HelloService的hello方法时，实际上执行的是下面的方法	
              @Override
              public @Nullable Object invoke(Object proxy, Method method, @Nullable Object[] args)
                  throws Throwable {
                // If the method is a method from Object then defer to normal invocation.
                if (method.getDeclaringClass() == Object.class) {
                  return method.invoke(this, args);
                }
                args = args != null ? args : emptyArgs;
                return platform.isDefaultMethod(method)
                    ? platform.invokeDefaultMethod(method, service, proxy, args)
                    : loadServiceMethod(method).invoke(args);
              }
            });
  }

至此终于真像大白，最终还是用Proxy.newProxyInstance生成了HelloService的代理类实例，作为HelloService.hello调用背后的真正实现
最后似乎还有一点疑问，就是HelloService的RetrofitClient注解的属性是服务名provider，那么真正网络请求的时候，是如何转成真实的地址和端口的呢？
再回头看看咱应用consumer-retrofit-okhttp的pom.xml文件，如下图红框所示，和前文一样，这里也使用了spring-cloud-square-okhttp，而且咱们写的OkHttpClientConfig.java和前文也是一样的，所以，根据服务名获取地址和端口的操作依旧可以用前文的分析来解释：

至于HelloService.hello方法，如何对应到web请求，请容我说一声：这是retrofit和okhttp之间的事情，在这里算是超纲了，篇幅所限，实在展不开了…

尾记：关于另一种spring-cloud-square类型：retrofit + webflux

之前的文章已经分析过，spring-cloud-square一共有三种类型，如下图所示，两个绿框中的源码都分析过了，还剩下的只有红色的retrofit + webflux组合：

欣宸还要再写一篇retrofit + webflux源码分析的文章？不不不，读源码太累，写出的文章，聪明的您读起来也累，所以就此打住吧
如果勤奋努力的您想独立阅读分析retrofit + webflux源码，这里给您一个建议，还记得本篇前面的那个类图吗，如下图，使用retrofit + webflux的时候，会用到spring-cloud-square-retrofit-webclient.jar，这个jar里面也有OkHttpClientConfig注解，它的import会实例化下图红框中的类，这个类就是您阅读源码的入口：