• 了解需求
  • 先主线, 找到入口

  • 技术设计的整理(云笔记)

    Dubbo服务的注册流程

    服务发布步骤

  • 注解 

    1. @DubboService(
    2.      loadbalance = "random",
    3.      cluster = "failover",
    4.      retries = 2)

  • 注解扫描 

    1. @DubboComponentScan

    引发思考

  • 扫描注解（解析注解）

  • url驱动， url的组装
  • 注册到zookeeper（？）

  • 启动服务（根据url中配置的协议、端口去发布对应的服务） （？）

    dubbo源码

    dubbo服务发布有两种形式

  • xml 形式 dubbo:service

  • @DubboService/ @Service

    Dubbo注解的解析流程

    DubboComponetScan

    无非就是，把哪个bean注册到了Spring IOC容器

    ServiceAnnotationBeanPostProcessor

  1. @Override
  2. public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
  4.     Set<String> packagesToScan = getPackagesToScan(importingClassMetadata);
  6.     registerServiceAnnotationBeanPostProcessor(packagesToScan, registry);
  8.     // @since 2.7.6 Register the common beans
  9.     registerCommonBeans(registry);
  10. }

ServiceAnnotationBeanPostProcessor

  1. public ServiceAnnotationBeanPostProcessor(Set<String> packagesToScan) {
  2.     super(packagesToScan);
  3. }

BeanDefinitionRegistryPostProcessor

bean装载完成之后，会触发下面这个方法.

  1. public ServiceAnnotationBeanPostProcessor(Set<String> packagesToScan) {
  2.     super(packagesToScan);
  3. }
  1.     @Override
  2.     public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
  4.         // @since 2.7.5
  5.         registerInfrastructureBean(registry, DubboBootstrapApplicationListener.BEAN_NAME, DubboBootstrapApplicationListener.class);
  7.         Set<String> resolvedPackagesToScan = resolvePackagesToScan(packagesToScan);
  9.         if (!CollectionUtils.isEmpty(resolvedPackagesToScan)) {
  10.             registerServiceBeans(resolvedPackagesToScan, registry);
  11.         } else {
  12.             if (logger.isWarnEnabled()) {
  13.                 logger.warn("packagesToScan is empty , ServiceBean registry will be ignored!");
  14.             }
  15.         }
  17.     }

注册一个DubboBootstrapApplicationListener

这个bean会在spring 容器的上下文装载完成之后，触发监听

  1. public class DubboBootstrapApplicationListener extends OneTimeExecutionApplicationContextEventListener
  2.         implements Ordered {
  4.     /**
  5.      * The bean name of {@link DubboBootstrapApplicationListener}
  6.      *
  7.      * @since 2.7.6
  8.      */
  9.     public static final String BEAN_NAME = "dubboBootstrapApplicationListener";
  11.     private final DubboBootstrap dubboBootstrap;
  13.     public DubboBootstrapApplicationListener() {
  14.         this.dubboBootstrap = DubboBootstrap.getInstance();
  15.     }
  17.     @Override
  18.     public void onApplicationContextEvent(ApplicationContextEvent event) {
  19.         if (event instanceof ContextRefreshedEvent) {
  20.             onContextRefreshedEvent((ContextRefreshedEvent) event);
  21.         } else if (event instanceof ContextClosedEvent) {
  22.             onContextClosedEvent((ContextClosedEvent) event);
  23.         }
  24.     }

registerServiceBeans

  1. private void registerServiceBeans(Set<String> packagesToScan, BeanDefinitionRegistry registry) {
  3.     DubboClassPathBeanDefinitionScanner scanner =
  4.         new DubboClassPathBeanDefinitionScanner(registry, environment, resourceLoader);
  6.     BeanNameGenerator beanNameGenerator = resolveBeanNameGenerator(registry);
  8.     scanner.setBeanNameGenerator(beanNameGenerator);
  10.     // refactor @since 2.7.7
  11.     serviceAnnotationTypes.forEach(annotationType -> {
  12.         scanner.addIncludeFilter(new AnnotationTypeFilter(annotationType));
  13.     });
  15.     for (String packageToScan : packagesToScan) {
  17.         // Registers @Service Bean first
  18.         scanner.scan(packageToScan);
  20.         // Finds all BeanDefinitionHolders of @Service whether @ComponentScan scans or not.
  21.         Set<BeanDefinitionHolder> beanDefinitionHolders =
  22.             findServiceBeanDefinitionHolders(scanner, packageToScan, registry, beanNameGenerator);
  24.         if (!CollectionUtils.isEmpty(beanDefinitionHolders)) {
  26.             for (BeanDefinitionHolder beanDefinitionHolder : beanDefinitionHolders) {
  27.                 registerServiceBean(beanDefinitionHolder, registry, scanner);
  28.             }
  30.             if (logger.isInfoEnabled()) {
  31.                 logger.info(beanDefinitionHolders.size() + " annotated Dubbo's @Service Components { " +
  32.                             beanDefinitionHolders +
  33.                             " } were scanned under package[" + packageToScan + "]");
  34.             }
  36.         } else {
  38.             if (logger.isWarnEnabled()) {
  39.                 logger.warn("No Spring Bean annotating Dubbo's @Service was found under package["
  40.                             + packageToScan + "]");
  41.             }
  43.         }
  45.     }
  47. }

registerServiceBean

和服务有关的信息，实际上都在我们刚刚定义的@DubboService
[DemoService]

  • 服务以什么协议发布
  • 服务的负载均衡策略
  • 服务的容错策略
  • 服务发布端口

org.apache.dubbo.config.spring.ServiceBean

  1. private void registerServiceBean(BeanDefinitionHolder beanDefinitionHolder, BeanDefinitionRegistry registry,
  2.                                      DubboClassPathBeanDefinitionScanner scanner) {
  4.     Class<?> beanClass = resolveClass(beanDefinitionHolder);
  6.     Annotation service = findServiceAnnotation(beanClass);
  8.     /**
  9.          * The {@link AnnotationAttributes} of @Service annotation
  10.          */
  11.     AnnotationAttributes serviceAnnotationAttributes = getAnnotationAttributes(service, false, false);
  13.     Class<?> interfaceClass = resolveServiceInterfaceClass(serviceAnnotationAttributes, beanClass);
  15.     String annotatedServiceBeanName = beanDefinitionHolder.getBeanName();
  17.     AbstractBeanDefinition serviceBeanDefinition =
  18.         buildServiceBeanDefinition(service, serviceAnnotationAttributes, interfaceClass, annotatedServiceBeanName);
  20.     // ServiceBean Bean name
  21.     String beanName = generateServiceBeanName(serviceAnnotationAttributes, interfaceClass);
  23.     if (scanner.checkCandidate(beanName, serviceBeanDefinition)) { // check duplicated candidate bean
  24.         registry.registerBeanDefinition(beanName, serviceBeanDefinition);
  26.         if (logger.isInfoEnabled()) {
  27.             logger.info("The BeanDefinition[" + serviceBeanDefinition +
  28.                         "] of ServiceBean has been registered with name : " + beanName);
  29.         }
  31.     } else {
  33.         if (logger.isWarnEnabled()) {
  34.             logger.warn("The Duplicated BeanDefinition[" + serviceBeanDefinition +
  35.                         "] of ServiceBean[ bean name : " + beanName +
  36.                         "] was be found , Did @DubboComponentScan scan to same package in many times?");
  37.         }
  39.     }
  41. }

registry.registerBeanDefinition(beanName, serviceBeanDefinition);

最终通过上述代码，讲一个 dubbo中提供的ServiceBean注入到Spring IOC容器

ServiceBean的初始化阶段

  1. public ServiceBean() {
  2.     super();
  3.     this.service = null;
  4. }

当ServiceBean初始化完成之后，会调用下面的方法.

  1. @Override
  2. public void afterPropertiesSet() throws Exception {
  3.     if (StringUtils.isEmpty(getPath())) {
  4.         if (StringUtils.isNotEmpty(beanName)
  5.             && StringUtils.isNotEmpty(getInterface())
  6.             && beanName.startsWith(getInterface())) {
  7.             setPath(beanName);
  8.         }
  9.     }
  10. }

DubboBootstrapApplicationListener

启动dubbo服务

  1. private void onContextRefreshedEvent(ContextRefreshedEvent event) {
  2.     dubboBootstrap.start();
  3. }
  • 元数据/远程配置信息的初始化
  • 拼接url（）
  • 如果是dubbo协议，则启动netty server

  • 服务注册

    start()

    1. public DubboBootstrap start() {
    2.   if (started.compareAndSet(false, true)) {
    3.       ready.set(false);
    4.       initialize();
    5.       if (logger.isInfoEnabled()) {
    6.           logger.info(NAME + " is starting...");
    7.       }
    8.       // 1. export Dubbo Services
    9.       exportServices();
    11.       // Not only provider register
    12.       if (!isOnlyRegisterProvider() || hasExportedServices()) {
    13.           // 2. export MetadataService
    14.           exportMetadataService();
    15.           //3. Register the local ServiceInstance if required
    16.           registerServiceInstance();
    17.       }
    19.       referServices();
    20.       if (asyncExportingFutures.size() > 0) {
    21.           new Thread(() -> {
    22.               try {
    23.                   this.awaitFinish();
    24.               } catch (Exception e) {
    25.                   logger.warn(NAME + " exportAsync occurred an exception.");
    26.               }
    27.               ready.set(true);
    28.               if (logger.isInfoEnabled()) {
    29.                   logger.info(NAME + " is ready.");
    30.               }
    31.           }).start();
    32.       } else {
    33.           ready.set(true);
    34.           if (logger.isInfoEnabled()) {
    35.               logger.info(NAME + " is ready.");
    36.           }
    37.       }
    38.       if (logger.isInfoEnabled()) {
    39.           logger.info(NAME + " has started.");
    40.       }
    41.   }
    42.   return this;
    43. }

    exportServices

    发布dubbo服务

  1. private void exportServices() {
  2.     configManager.getServices().forEach(sc -> {
  3.         // TODO, compatible with ServiceConfig.export()
  4.         ServiceConfig serviceConfig = (ServiceConfig) sc;
  5.         serviceConfig.setBootstrap(this);
  7.         if (exportAsync) {
  8.             ExecutorService executor = executorRepository.getServiceExporterExecutor();
  9.             Future<?> future = executor.submit(() -> {
  10.                 sc.export();
  11.                 exportedServices.add(sc);
  12.             });
  13.             asyncExportingFutures.add(future);
  14.         } else {
  15.             sc.export();
  16.             exportedServices.add(sc);
  17.         }
  18.     });
  19. }

遍历所有dubbo服务，进行服务发布.

  1. <dubbo:service beanName="ServiceBean:com.msbedu.springboot.dubbo.springbootdubbosampleprovider.services.IDemoService" />
  2. <dubbo:service beanName="ServiceBean:com.msbedu.springboot.dubbo.ISayHelloService" />
  3. dubbo://ip:port?com.msbedu.springboot.dubbo.springbootdubbosampleprovider.services.IDemoService&xxx&xxx
  4. dubbo://ip:port?com.msbedu.springboot.dubbo.ISayHelloService&xxx&xxx

一个接口需要发布几次？
一个dubbo服务需要发布几次，取决于协议的配置数，如果一个dubbo服务配置了3个协议，rest、webservice、dubbo。
dubbo://
rest://
webservice://

export

  1. public synchronized void export() {
  2.     if (!shouldExport()) {
  3.         return;
  4.     }
  6.     if (bootstrap == null) {
  7.         bootstrap = DubboBootstrap.getInstance();
  8.         bootstrap.init();
  9.     }
  11.     checkAndUpdateSubConfigs();
  13.     //init serviceMetadata
  14.     serviceMetadata.setVersion(version);
  15.     serviceMetadata.setGroup(group);
  16.     serviceMetadata.setDefaultGroup(group);
  17.     serviceMetadata.setServiceType(getInterfaceClass());
  18.     serviceMetadata.setServiceInterfaceName(getInterface());
  19.     serviceMetadata.setTarget(getRef());
  21.     if (shouldDelay()) {
  22.         DELAY_EXPORT_EXECUTOR.schedule(this::doExport, getDelay(), TimeUnit.MILLISECONDS);
  23.     } else {
  24.         doExport();
  25.     }
  27.     exported();
  28. }

doExportUrls

主要流程，根据开发者配置的协议列表，遍历协议列表逐项进行发布。

  1. private void doExportUrls() {
  2.     ServiceRepository repository = ApplicationModel.getServiceRepository();
  3.     ServiceDescriptor serviceDescriptor = repository.registerService(getInterfaceClass());
  4.     repository.registerProvider(
  5.         getUniqueServiceName(),
  6.         ref,
  7.         serviceDescriptor,
  8.         this,
  9.         serviceMetadata
  10.     );
  12.     List<URL> registryURLs = ConfigValidationUtils.loadRegistries(this, true);
  14.     for (ProtocolConfig protocolConfig : protocols) {
  15.         String pathKey = URL.buildKey(getContextPath(protocolConfig)
  16.                                       .map(p -> p + "/" + path)
  17.                                       .orElse(path), group, version);
  18.         // In case user specified path, register service one more time to map it to path.
  19.         repository.registerService(pathKey, interfaceClass);
  20.         // TODO, uncomment this line once service key is unified
  21.         serviceMetadata.setServiceKey(pathKey);
  22.         doExportUrlsFor1Protocol(protocolConfig, registryURLs);
  23.     }
  24. }

doExportUrlsFor1Protocol

  • 生成url

  • 根据url中配置的协议类型，调用指定协议进行服务的发布

    • 启动服务

    • 注册服务

      1. private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) {
      2. String name = protocolConfig.getName();
      3. if (StringUtils.isEmpty(name)) {
      4.    name = DUBBO;
      5. }
      6. //用来存储所有的配置信息
      7. * dubbo:service
      8.    dubbo:method
      9.        dubbo:argument
      10. Map<String, String> map = new HashMap<String, String>();
      11. map.put(SIDE_KEY, PROVIDER_SIDE);
      13. ServiceConfig.appendRuntimeParameters(map);
      14. AbstractConfig.appendParameters(map, getMetrics());
      15. AbstractConfig.appendParameters(map, getApplication());
      16. AbstractConfig.appendParameters(map, getModule());
      17. // remove 'default.' prefix for configs from ProviderConfig
      18. // appendParameters(map, provider, Constants.DEFAULT_KEY);
      19. AbstractConfig.appendParameters(map, provider);
      20. AbstractConfig.appendParameters(map, protocolConfig);
      21. AbstractConfig.appendParameters(map, this);
      22. MetadataReportConfig metadataReportConfig = getMetadataReportConfig();
      23. if (metadataReportConfig != null && metadataReportConfig.isValid()) {
      24.    map.putIfAbsent(METADATA_KEY, REMOTE_METADATA_STORAGE_TYPE);
      25. }
      26. if (CollectionUtils.isNotEmpty(getMethods())) {
      27.    for (MethodConfig method : getMethods()) {
      28.        AbstractConfig.appendParameters(map, method, method.getName());
      29.        String retryKey = method.getName() + ".retry";
      30.        if (map.containsKey(retryKey)) {
      31.            String retryValue = map.remove(retryKey);
      32.            if ("false".equals(retryValue)) {
      33.                map.put(method.getName() + ".retries", "0");
      34.            }
      35.        }
      36.        List<ArgumentConfig> arguments = method.getArguments();
      37.        if (CollectionUtils.isNotEmpty(arguments)) {
      38.            for (ArgumentConfig argument : arguments) {
      39.                // convert argument type
      40.                if (argument.getType() != null && argument.getType().length() > 0) {
      41.                    Method[] methods = interfaceClass.getMethods();
      42.                    // visit all methods
      43.                    if (methods.length > 0) {
      44.                        for (int i = 0; i < methods.length; i++) {
      45.                            String methodName = methods[i].getName();
      46.                            // target the method, and get its signature
      47.                            if (methodName.equals(method.getName())) {
      48.                                Class<?>[] argtypes = methods[i].getParameterTypes();
      49.                                // one callback in the method
      50.                                if (argument.getIndex() != -1) {
      51.                                    if (argtypes[argument.getIndex()].getName().equals(argument.getType())) {
      52.                                        AbstractConfig.appendParameters(map, argument, method.getName() + "." + argument.getIndex());
      53.                                    } else {
      54.                                        throw new IllegalArgumentException("Argument config error : the index attribute and type attribute not match :index :" + argument.getIndex() + ", type:" + argument.getType());
      55.                                    }
      56.                                } else {
      57.                                    // multiple callbacks in the method
      58.                                    for (int j = 0; j < argtypes.length; j++) {
      59.                                        Class<?> argclazz = argtypes[j];
      60.                                        if (argclazz.getName().equals(argument.getType())) {
      61.                                            AbstractConfig.appendParameters(map, argument, method.getName() + "." + j);
      62.                                            if (argument.getIndex() != -1 && argument.getIndex() != j) {
      63.                                                throw new IllegalArgumentException("Argument config error : the index attribute and type attribute not match :index :" + argument.getIndex() + ", type:" + argument.getType());
      64.                                            }
      65.                                        }
      66.                                    }
      67.                                }
      68.                            }
      69.                        }
      70.                    }
      71.                } else if (argument.getIndex() != -1) {
      72.                    AbstractConfig.appendParameters(map, argument, method.getName() + "." + argument.getIndex());
      73.                } else {
      74.                    throw new IllegalArgumentException("Argument config must set index or type attribute.eg: <dubbo:argument index='0' .../> or <dubbo:argument type=xxx .../>");
      75.                }
      77.            }
      78.        }
      79.    } // end of methods for
      80. }
      82. if (ProtocolUtils.isGeneric(generic)) {
      83.    map.put(GENERIC_KEY, generic);
      84.    map.put(METHODS_KEY, ANY_VALUE);
      85. } else {
      86.    String revision = Version.getVersion(interfaceClass, version);
      87.    if (revision != null && revision.length() > 0) {
      88.        map.put(REVISION_KEY, revision);
      89.    }
      91.    String[] methods = Wrapper.getWrapper(interfaceClass).getMethodNames();
      92.    if (methods.length == 0) {
      93.        logger.warn("No method found in service interface " + interfaceClass.getName());
      94.        map.put(METHODS_KEY, ANY_VALUE);
      95.    } else {
      96.        map.put(METHODS_KEY, StringUtils.join(new HashSet<String>(Arrays.asList(methods)), ","));
      97.    }
      98. }
      100. /**
      101.     * Here the token value configured by the provider is used to assign the value to ServiceConfig#token
      102.     */
      103. if(ConfigUtils.isEmpty(token) && provider != null) {
      104.    token = provider.getToken();
      105. }
      107. if (!ConfigUtils.isEmpty(token)) {
      108.    if (ConfigUtils.isDefault(token)) {
      109.        map.put(TOKEN_KEY, UUID.randomUUID().toString());
      110.    } else {
      111.        map.put(TOKEN_KEY, token);
      112.    }
      113. }
      114. //init serviceMetadata attachments
      115. serviceMetadata.getAttachments().putAll(map);
      117. // export service
      118. String host = findConfigedHosts(protocolConfig, registryURLs, map);
      119. Integer port = findConfigedPorts(protocolConfig, name, map);
      120. URL url = new URL(name, host, port, getContextPath(protocolConfig).map(p -> p + "/" + path).orElse(path), map);
      122. // You can customize Configurator to append extra parameters
      123. if (ExtensionLoader.getExtensionLoader(ConfiguratorFactory.class)
      124.    .hasExtension(url.getProtocol())) {
      125.    url = ExtensionLoader.getExtensionLoader(ConfiguratorFactory.class)
      126.        .getExtension(url.getProtocol()).getConfigurator(url).configure(url);
      127. }
      129. String scope = url.getParameter(SCOPE_KEY);
      130. // don't export when none is configured
      131. if (!SCOPE_NONE.equalsIgnoreCase(scope)) {
      133.    // export to local if the config is not remote (export to remote only when config is remote)
      134.    if (!SCOPE_REMOTE.equalsIgnoreCase(scope)) {
      135.        exportLocal(url);
      136.    }
      137.    // export to remote if the config is not local (export to local only when config is local)
      138.    if (!SCOPE_LOCAL.equalsIgnoreCase(scope)) {
      139.        if (CollectionUtils.isNotEmpty(registryURLs)) {
      140.            for (URL registryURL : registryURLs) {
      141.                //if protocol is only injvm ,not register
      142.                if (LOCAL_PROTOCOL.equalsIgnoreCase(url.getProtocol())) {
      143.                    continue;
      144.                }
      145.                url = url.addParameterIfAbsent(DYNAMIC_KEY, registryURL.getParameter(DYNAMIC_KEY));
      146.                URL monitorUrl = ConfigValidationUtils.loadMonitor(this, registryURL);
      147.                if (monitorUrl != null) {
      148.                    url = url.addParameterAndEncoded(MONITOR_KEY, monitorUrl.toFullString());
      149.                }
      150.                if (logger.isInfoEnabled()) {
      151.                    if (url.getParameter(REGISTER_KEY, true)) {
      152.                        logger.info("Register dubbo service " + interfaceClass.getName() + " url " + url + " to registry " + registryURL);
      153.                    } else {
      154.                        logger.info("Export dubbo service " + interfaceClass.getName() + " to url " + url);
      155.                    }
      156.                }
      158.                // For providers, this is used to enable custom proxy to generate invoker
      159.                String proxy = url.getParameter(PROXY_KEY);
      160.                if (StringUtils.isNotEmpty(proxy)) {
      161.                    registryURL = registryURL.addParameter(PROXY_KEY, proxy);
      162.                }
      164.                Invoker<?> invoker = PROXY_FACTORY.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(EXPORT_KEY, url.toFullString()));
      165.                DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this);
      167.                Exporter<?> exporter = PROTOCOL.export(wrapperInvoker);
      168.                exporters.add(exporter);
      169.            }
      170.        } else {
      171.            if (logger.isInfoEnabled()) {
      172.                logger.info("Export dubbo service " + interfaceClass.getName() + " to url " + url);
      173.            }
      174.            Invoker<?> invoker = PROXY_FACTORY.getInvoker(ref, (Class) interfaceClass, url);
      175.            DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this);
      177.            Exporter<?> exporter = PROTOCOL.export(wrapperInvoker);
      178.            exporters.add(exporter);
      179.        }
      180.        /**
      181.             * @since 2.7.0
      182.             * ServiceData Store
      183.             */
      184.        WritableMetadataService metadataService = WritableMetadataService.getExtension(url.getParameter(METADATA_KEY, DEFAULT_METADATA_STORAGE_TYPE));
      185.        if (metadataService != null) {
      186.            metadataService.publishServiceDefinition(url);
      187.        }
      188.    }
      189. }
      190. this.urls.add(url);
      191. }
  1. dubbo://192.168.1.104:20880/com.msbedu.springboot.dubbo.springbootdubbosampleprovider.services.IDemoService?anyhost=true&application=spring-boot-dubbo-sample-provider&bind.ip=192.168.1.104&bind.port=20880&default=true&deprecated=false&dubbo=2.0.2&dynamic=true&generic=false&interface=com.msbedu.springboot.dubbo.springbootdubbosampleprovider.services.IDemoService&methods=getTxt&pid=225512&qos.accept.foreign.ip=false&qos.enable=true&qos.port=8888&release=2.7.7&side=provider&timestamp=1597498654297 
  2. & loadbalance=msbloadbalance
  4. consumer://ip:port....&

dubbo中的扩展点

  1. ExtensionLoader.getExtensionLoader(ConfiguratorFactory.class).hasExtension(url.getProtocol())
  • Java中的spi
  • SpringFactoriesLoader

  • Dubbo SPI

    Dubbo中的扩展点

    指定名称的扩展点

    1. ExtensionLoader.getExtensionLoader(Protocol.class).getExtension("name");

  • 找到Protocol的全路径名称， 在/META-INF/dubbo/intenal

  • 在指定文件中找到“name”对应的实现类.

    自定义扩展点

  • 在resource/META-INF/dubbo/ org.apache.dubbo.rpc.cluster.LoadBalance

  • 实现扩展点 

    1. public class msbDefineLoadBalance extends AbstractLoadBalance{
    2.  @Override
    3.  protected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation invocation) {
    5.      return null;
    6.  }
    7. }

  • 测试 

    1. //解析URL
    2. String loadbalance="random";
    3. //URL loadbalance="msbloadbalance"
    4. //loadlance=msbloadbalance
    5. LoadBalance loadBalance=ExtensionLoader.getExtensionLoader(LoadBalance.class).getExtension(loadbalance);
    6. System.out.println(loadBalance);

    扩展点的特征

    在类级别标准@SPI(RandomLoadBalance.NAME).
    其中，括号内的数据，表示当前扩展点的默认扩展点。

    指定名称的扩展点的原理

  • 思考实现步骤的拆解

    自适应扩展点

    1. ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();

    激活扩展点

    1. ExtensionLoader.getExtensionLoader(Protocol.class).getActiveExtension