SpringCloud集成了很多第三方框架，把它的全部源码拿出来解析几本书都讲不完，也不太现实，本文带领读者分析其中一小部分源码（其余源码读者有兴趣可以继续跟进），包括eureka-server、config、zuul的starter部分，分析其启动原理。 

如果我们开发出一套框架，要和SpringBoot集成，就需要放到它的starter里。因此我们分析启动原理，直接从每个框架的starter开始分析即可。

Eureka-Server源码解析

我们知道，要实现注册与发现，需要在启动类加上@EnableEurekaServer注解，我们进入其源码：

@EnableDiscoveryClient//表示eurekaserver也是一个客户端服务@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Import(EurekaServerMarkerConfiguration.class)public @interface EnableEurekaServer {}

注意看@Import注解，这个注解导入了EurekaServerMarkerConfiguration类，继续跟进这个类：

/** * Responsible for adding in a marker bean to activate * {@link EurekaServerAutoConfiguration} * * @author Biju Kunjummen */@Configurationpublic class EurekaServerMarkerConfiguration {    @Bean    public Marker eurekaServerMarkerBean() {        return new Marker();    }    class Marker {    }}

通过上面的注释，我们继续查看EurekaServerAutoConfiguration类的源码：

@Configuration@Import(EurekaServerInitializerConfiguration.class)@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)@EnableConfigurationProperties({ EurekaDashboardProperties.class,        InstanceRegistryProperties.class })@PropertySource("classpath:/eureka/server.properties")public class EurekaServerAutoConfiguration extends WebMvcConfigurerAdapter {    /**     * List of packages containing Jersey resources required by the Eureka server     */    private static String[] EUREKA_PACKAGES = new String[] { "com.netflix.discovery",            "com.netflix.eureka" };    @Autowired    private ApplicationInfoManager applicationInfoManager;    @Autowired    private EurekaServerConfig eurekaServerConfig;    @Autowired    private EurekaClientConfig eurekaClientConfig;    @Autowired    private EurekaClient eurekaClient;    @Autowired    private InstanceRegistryProperties instanceRegistryProperties;    public static final CloudJacksonJson JACKSON_JSON = new CloudJacksonJson();    @Bean    public HasFeatures eurekaServerFeature() {        return HasFeatures.namedFeature("Eureka Server",                EurekaServerAutoConfiguration.class);    }    //如果eureka.client.registerWithEureka=true，则把自己注册进去    @Configuration    protected static class EurekaServerConfigBeanConfiguration {        @Bean        @ConditionalOnMissingBean        public EurekaServerConfig eurekaServerConfig(EurekaClientConfig clientConfig) {            EurekaServerConfigBean server = new EurekaServerConfigBean();            if (clientConfig.shouldRegisterWithEureka()) {                // Set a sensible default if we are supposed to replicate                server.setRegistrySyncRetries(5);            }            return server;        }    }    //实例化eureka-server的界面    @Bean    @ConditionalOnProperty(prefix = "eureka.dashboard", name = "enabled", matchIfMissing = true)    public EurekaController eurekaController() {        return new EurekaController(this.applicationInfoManager);    }    static {        CodecWrappers.registerWrapper(JACKSON_JSON);        EurekaJacksonCodec.setInstance(JACKSON_JSON.getCodec());    }    @Bean    public ServerCodecs serverCodecs() {        return new CloudServerCodecs(this.eurekaServerConfig);    }    private static CodecWrapper getFullJson(EurekaServerConfig serverConfig) {        CodecWrapper codec = CodecWrappers.getCodec(serverConfig.getJsonCodecName());        return codec == null ? CodecWrappers.getCodec(JACKSON_JSON.codecName()) : codec;    }    private static CodecWrapper getFullXml(EurekaServerConfig serverConfig) {        CodecWrapper codec = CodecWrappers.getCodec(serverConfig.getXmlCodecName());        return codec == null ? CodecWrappers.getCodec(CodecWrappers.XStreamXml.class)                : codec;    }    class CloudServerCodecs extends DefaultServerCodecs {        public CloudServerCodecs(EurekaServerConfig serverConfig) {            super(getFullJson(serverConfig),                    CodecWrappers.getCodec(CodecWrappers.JacksonJsonMini.class),                    getFullXml(serverConfig),                    CodecWrappers.getCodec(CodecWrappers.JacksonXmlMini.class));        }    }    @Bean    public PeerAwareInstanceRegistry peerAwareInstanceRegistry(            ServerCodecs serverCodecs) {        this.eurekaClient.getApplications(); // force initialization        return new InstanceRegistry(this.eurekaServerConfig, this.eurekaClientConfig,                serverCodecs, this.eurekaClient,                this.instanceRegistryProperties.getExpectedNumberOfRenewsPerMin(),                this.instanceRegistryProperties.getDefaultOpenForTrafficCount());    }    @Bean    @ConditionalOnMissingBean    public PeerEurekaNodes peerEurekaNodes(PeerAwareInstanceRegistry registry,            ServerCodecs serverCodecs) {        return new PeerEurekaNodes(registry, this.eurekaServerConfig,                this.eurekaClientConfig, serverCodecs, this.applicationInfoManager);    }    @Bean    public EurekaServerContext eurekaServerContext(ServerCodecs serverCodecs,            PeerAwareInstanceRegistry registry, PeerEurekaNodes peerEurekaNodes) {        return new DefaultEurekaServerContext(this.eurekaServerConfig, serverCodecs,                registry, peerEurekaNodes, this.applicationInfoManager);    }    @Bean    public EurekaServerBootstrap eurekaServerBootstrap(PeerAwareInstanceRegistry registry,            EurekaServerContext serverContext) {        return new EurekaServerBootstrap(this.applicationInfoManager,                this.eurekaClientConfig, this.eurekaServerConfig, registry,                serverContext);    }    /**     * Register the Jersey filter     */    @Bean    public FilterRegistrationBean jerseyFilterRegistration(            javax.ws.rs.core.Application eurekaJerseyApp) {        FilterRegistrationBean bean = new FilterRegistrationBean();        bean.setFilter(new ServletContainer(eurekaJerseyApp));        bean.setOrder(Ordered.LOWEST_PRECEDENCE);        bean.setUrlPatterns(                Collections.singletonList(EurekaConstants.DEFAULT_PREFIX + "/*"));        return bean;    }    /**     * Construct a Jersey {@link javax.ws.rs.core.Application} with all the resources     * required by the Eureka server.     */    @Bean    public javax.ws.rs.core.Application jerseyApplication(Environment environment,            ResourceLoader resourceLoader) {        ClassPathScanningCandidateComponentProvider provider = new ClassPathScanningCandidateComponentProvider(                false, environment);        // Filter to include only classes that have a particular annotation.        //        provider.addIncludeFilter(new AnnotationTypeFilter(Path.class));        provider.addIncludeFilter(new AnnotationTypeFilter(Provider.class));        // Find classes in Eureka packages (or subpackages)        //        Set
    
     > classes = new HashSet
     
      >();        for (String basePackage : EUREKA_PACKAGES) {            Set
      
        beans = provider.findCandidateComponents(basePackage);            for (BeanDefinition bd : beans) {                Class
        cls = ClassUtils.resolveClassName(bd.getBeanClassName(),                        resourceLoader.getClassLoader());                classes.add(cls);            }        }        // Construct the Jersey ResourceConfig        //        Map
       
         propsAndFeatures = new HashMap
        
         ();        propsAndFeatures.put(                // Skip static content used by the webapp                ServletContainer.PROPERTY_WEB_PAGE_CONTENT_REGEX,                EurekaConstants.DEFAULT_PREFIX + "/(fonts|images|css|js)/.*");        DefaultResourceConfig rc = new DefaultResourceConfig(classes);        rc.setPropertiesAndFeatures(propsAndFeatures);        return rc;    }    @Bean    public FilterRegistrationBean traceFilterRegistration(            @Qualifier("webRequestLoggingFilter") Filter filter) {        FilterRegistrationBean bean = new FilterRegistrationBean();        bean.setFilter(filter);        bean.setOrder(Ordered.LOWEST_PRECEDENCE - 10);        return bean;    }}
        
       
      
     
    

这个类上有一个注解：@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)，这后面指定的类就是刚才那个类，而@ConditionalOnBean这个注解的作用是：仅仅在当前上下文中存在某个对象时，才会实例化一个Bean。 

因此，启动时就会实例化EurekaServerAutoConfiguration这个类。 @EnableConfigurationProperties({ EurekaDashboardProperties.class, InstanceRegistryProperties.class }) 这个注解就是定义了一些eureka的配置项。

Config源码解析

通过上面的方法，我们找到了ConfigServerAutoConfiguration类：

@Configuration@ConditionalOnBean(ConfigServerConfiguration.Marker.class)@EnableConfigurationProperties(ConfigServerProperties.class)@Import({ EnvironmentRepositoryConfiguration.class, CompositeConfiguration.class, ResourceRepositoryConfiguration.class,        ConfigServerEncryptionConfiguration.class, ConfigServerMvcConfiguration.class, TransportConfiguration.class })public class ConfigServerAutoConfiguration {}

可以发现这个类是空的，只是多了几个注解， 

@EnableConfigurationProperties(ConfigServerProperties.class)表示开启config配置属性。 最核心的注解是：@Import，他将其他一些配置类导入进这个类，其中： EnvironmentRepositoryConfiguration：环境配置类，内置了以下几种环境配置： 1.Native

@Configuration    @Profile("native")    protected static class NativeRepositoryConfiguration {        @Autowired        private ConfigurableEnvironment environment;        @Bean        public NativeEnvironmentRepository nativeEnvironmentRepository() {            return new NativeEnvironmentRepository(this.environment);        }    }

2.git

@Configuration    @Profile("git")    protected static class GitRepositoryConfiguration extends DefaultRepositoryConfiguration {}

3.subversion

@Configuration    @Profile("subversion")    protected static class SvnRepositoryConfiguration {        @Autowired        private ConfigurableEnvironment environment;        @Autowired        private ConfigServerProperties server;        @Bean        public SvnKitEnvironmentRepository svnKitEnvironmentRepository() {            SvnKitEnvironmentRepository repository = new SvnKitEnvironmentRepository(this.environment);            if (this.server.getDefaultLabel()!=null) {                repository.setDefaultLabel(this.server.getDefaultLabel());            }            return repository;        }    }

4.vault

@Configuration    @Profile("subversion")    protected static class SvnRepositoryConfiguration {        @Autowired        private ConfigurableEnvironment environment;        @Autowired        private ConfigServerProperties server;        @Bean        public SvnKitEnvironmentRepository svnKitEnvironmentRepository() {            SvnKitEnvironmentRepository repository = new SvnKitEnvironmentRepository(this.environment);            if (this.server.getDefaultLabel()!=null) {                repository.setDefaultLabel(this.server.getDefaultLabel());            }            return repository;    }    }

//从代码可以看到Git是配置中心默认环境

@Bean        public MultipleJGitEnvironmentRepository defaultEnvironmentRepository() {            MultipleJGitEnvironmentRepository repository = new MultipleJGitEnvironmentRepository(this.environment);            repository.setTransportConfigCallback(this.transportConfigCallback);            if (this.server.getDefaultLabel()!=null) {                repository.setDefaultLabel(this.server.getDefaultLabel());            }            return repository;        }

我们进入MultipleJGitEnvironmentRepository类：

@ConfigurationProperties("spring.cloud.config.server.git")public class MultipleJGitEnvironmentRepository extends JGitEnvironmentRepository {}

这个类表示可以支持配置多个Git仓库，它继承自JGitEnvironmentRepository类：

public class JGitEnvironmentRepository extends AbstractScmEnvironmentRepository        implements EnvironmentRepository, SearchPathLocator, InitializingBean {/**     * Get the working directory ready.     */    public String refresh(String label) {        Git git = null;        try {            git = createGitClient();            if (shouldPull(git)) {                fetch(git, label);                // checkout after fetch so we can get any new branches, tags,                // ect.                checkout(git, label);                if (isBranch(git, label)) {                    // merge results from fetch                    merge(git, label);                    if (!isClean(git)) {                        logger.warn("The local repository is dirty. Resetting it to origin/" + label + ".");                        resetHard(git, label, "refs/remotes/origin/" + label);                    }                }            } else {                // nothing to update so just checkout                checkout(git, label);            }            // always return what is currently HEAD as the version            return git.getRepository().getRef("HEAD").getObjectId().getName();        } catch (RefNotFoundException e) {            throw new NoSuchLabelException("No such label: " + label, e);        } catch (NoRemoteRepositoryException e) {            throw new NoSuchRepositoryException("No such repository: " + getUri(), e);        } catch (GitAPIException e) {            throw new NoSuchRepositoryException("Cannot clone or checkout repository: " + getUri(), e);        } catch (Exception e) {            throw new IllegalStateException("Cannot load environment", e);        } finally {            try {                if (git != null) {                    git.close();                }            } catch (Exception e) {                this.logger.warn("Could not close git repository", e);            }        }    }}

refresh方法的作用就是configserver会从我们配置的git仓库拉取配置下来。

Zuul源码解析

同理，我们找到Zuul的配置类ZuulProxyAutoConfiguration：

@Configuration@Import({ RibbonCommandFactoryConfiguration.RestClientRibbonConfiguration.class,        RibbonCommandFactoryConfiguration.OkHttpRibbonConfiguration.class,        RibbonCommandFactoryConfiguration.HttpClientRibbonConfiguration.class })@ConditionalOnBean(ZuulProxyMarkerConfiguration.Marker.class)public class ZuulProxyAutoConfiguration extends ZuulServerAutoConfiguration {    @SuppressWarnings("rawtypes")    @Autowired(required = false)    private List
    
      requestCustomizers = Collections.emptyList();    @Autowired    private DiscoveryClient discovery;    @Autowired    private ServiceRouteMapper serviceRouteMapper;    @Override    public HasFeatures zuulFeature() {        return HasFeatures.namedFeature("Zuul (Discovery)", ZuulProxyAutoConfiguration.class);    }    @Bean    @ConditionalOnMissingBean(DiscoveryClientRouteLocator.class)    public DiscoveryClientRouteLocator discoveryRouteLocator() {        return new DiscoveryClientRouteLocator(this.server.getServletPrefix(), this.discovery, this.zuulProperties,                this.serviceRouteMapper);    }    //以下是过滤器，也就是之前zuul提到的实现的ZuulFilter接口    // pre filters    //路由之前    @Bean    public PreDecorationFilter preDecorationFilter(RouteLocator routeLocator, ProxyRequestHelper proxyRequestHelper) {        return new PreDecorationFilter(routeLocator, this.server.getServletPrefix(), this.zuulProperties,                proxyRequestHelper);    }    // route filters    // 路由时    @Bean    public RibbonRoutingFilter ribbonRoutingFilter(ProxyRequestHelper helper,            RibbonCommandFactory
      ribbonCommandFactory) {        RibbonRoutingFilter filter = new RibbonRoutingFilter(helper, ribbonCommandFactory, this.requestCustomizers);        return filter;    }    @Bean    @ConditionalOnMissingBean(SimpleHostRoutingFilter.class)    public SimpleHostRoutingFilter simpleHostRoutingFilter(ProxyRequestHelper helper, ZuulProperties zuulProperties) {        return new SimpleHostRoutingFilter(helper, zuulProperties);    }    @Bean    public ApplicationListener
     
       zuulDiscoveryRefreshRoutesListener() {        return new ZuulDiscoveryRefreshListener();    }    @Bean    @ConditionalOnMissingBean(ServiceRouteMapper.class)    public ServiceRouteMapper serviceRouteMapper() {        return new SimpleServiceRouteMapper();    }    @Configuration    @ConditionalOnMissingClass("org.springframework.boot.actuate.endpoint.Endpoint")    protected static class NoActuatorConfiguration {        @Bean        public ProxyRequestHelper proxyRequestHelper(ZuulProperties zuulProperties) {            ProxyRequestHelper helper = new ProxyRequestHelper();            helper.setIgnoredHeaders(zuulProperties.getIgnoredHeaders());            helper.setTraceRequestBody(zuulProperties.isTraceRequestBody());            return helper;        }    }    @Configuration    @ConditionalOnClass(Endpoint.class)    protected static class RoutesEndpointConfiguration {        @Autowired(required = false)        private TraceRepository traces;        @Bean        public RoutesEndpoint zuulEndpoint(RouteLocator routeLocator) {            return new RoutesEndpoint(routeLocator);        }        @Bean        public RoutesMvcEndpoint zuulMvcEndpoint(RouteLocator routeLocator, RoutesEndpoint endpoint) {            return new RoutesMvcEndpoint(endpoint, routeLocator);        }        @Bean        public ProxyRequestHelper proxyRequestHelper(ZuulProperties zuulProperties) {            TraceProxyRequestHelper helper = new TraceProxyRequestHelper();            if (this.traces != null) {                helper.setTraces(this.traces);            }            helper.setIgnoredHeaders(zuulProperties.getIgnoredHeaders());            helper.setTraceRequestBody(zuulProperties.isTraceRequestBody());            return helper;        }    }    private static class ZuulDiscoveryRefreshListener implements ApplicationListener
      
        {        private HeartbeatMonitor monitor = new HeartbeatMonitor();        @Autowired        private ZuulHandlerMapping zuulHandlerMapping;        @Override        public void onApplicationEvent(ApplicationEvent event) {            if (event instanceof InstanceRegisteredEvent) {                reset();            }            else if (event instanceof ParentHeartbeatEvent) {                ParentHeartbeatEvent e = (ParentHeartbeatEvent) event;                resetIfNeeded(e.getValue());            }            else if (event instanceof HeartbeatEvent) {                HeartbeatEvent e = (HeartbeatEvent) event;                resetIfNeeded(e.getValue());            }        }        private void resetIfNeeded(Object value) {            if (this.monitor.update(value)) {                reset();            }        }        private void reset() {            this.zuulHandlerMapping.setDirty(true);        }    }}
      
     
    

通过@Import注解可以找到几个类： 

RibbonCommandFactoryConfiguration.RestClientRibbonConfiguration、RibbonCommandFactoryConfiguration.OkHttpRibbonConfiguration、RibbonCommandFactoryConfiguration.HttpClientRibbonConfiguration 我们知道zuul提供网关能力，通过上面这几个类就能分析到，它内部其实也是通过接口请求，找到每个服务提供的接口地址。 进入RibbonCommandFactoryConfiguration类：

public class RibbonCommandFactoryConfiguration {    //以下提供了3个不同的请求模式    @Configuration    @ConditionalOnRibbonRestClient    protected static class RestClientRibbonConfiguration {        @Autowired(required = false)        private Set
    
      zuulFallbackProviders = Collections.emptySet();        @Bean        @ConditionalOnMissingBean        public RibbonCommandFactory
      ribbonCommandFactory(                SpringClientFactory clientFactory, ZuulProperties zuulProperties) {            return new RestClientRibbonCommandFactory(clientFactory, zuulProperties,                    zuulFallbackProviders);        }    }    @Configuration    @ConditionalOnRibbonOkHttpClient    @ConditionalOnClass(name = "okhttp3.OkHttpClient")    protected static class OkHttpRibbonConfiguration {        @Autowired(required = false)        private Set
     
       zuulFallbackProviders = Collections.emptySet();        @Bean        @ConditionalOnMissingBean        public RibbonCommandFactory
       ribbonCommandFactory(                SpringClientFactory clientFactory, ZuulProperties zuulProperties) {            return new OkHttpRibbonCommandFactory(clientFactory, zuulProperties,                    zuulFallbackProviders);        }    }    @Configuration    @ConditionalOnRibbonHttpClient    protected static class HttpClientRibbonConfiguration {        @Autowired(required = false)        private Set
      
        zuulFallbackProviders = Collections.emptySet();        @Bean        @ConditionalOnMissingBean        public RibbonCommandFactory
        ribbonCommandFactory(                SpringClientFactory clientFactory, ZuulProperties zuulProperties) {            return new HttpClientRibbonCommandFactory(clientFactory, zuulProperties, zuulFallbackProviders);        }    }    @Target({ ElementType.TYPE, ElementType.METHOD })    @Retention(RetentionPolicy.RUNTIME)    @Documented    @Conditional(OnRibbonHttpClientCondition.class)    @interface ConditionalOnRibbonHttpClient { }    private static class OnRibbonHttpClientCondition extends AnyNestedCondition {        public OnRibbonHttpClientCondition() {            super(ConfigurationPhase.PARSE_CONFIGURATION);        }        @Deprecated //remove in Edgware"        @ConditionalOnProperty(name = "zuul.ribbon.httpclient.enabled", matchIfMissing = true)        static class ZuulProperty {}        @ConditionalOnProperty(name = "ribbon.httpclient.enabled", matchIfMissing = true)        static class RibbonProperty {}    }    @Target({ ElementType.TYPE, ElementType.METHOD })    @Retention(RetentionPolicy.RUNTIME)    @Documented    @Conditional(OnRibbonOkHttpClientCondition.class)    @interface ConditionalOnRibbonOkHttpClient { }    private static class OnRibbonOkHttpClientCondition extends AnyNestedCondition {        public OnRibbonOkHttpClientCondition() {            super(ConfigurationPhase.PARSE_CONFIGURATION);        }        @Deprecated //remove in Edgware"        @ConditionalOnProperty("zuul.ribbon.okhttp.enabled")        static class ZuulProperty {}        @ConditionalOnProperty("ribbon.okhttp.enabled")        static class RibbonProperty {}    }    @Target({ ElementType.TYPE, ElementType.METHOD })    @Retention(RetentionPolicy.RUNTIME)    @Documented    @Conditional(OnRibbonRestClientCondition.class)    @interface ConditionalOnRibbonRestClient { }    private static class OnRibbonRestClientCondition extends AnyNestedCondition {        public OnRibbonRestClientCondition() {            super(ConfigurationPhase.PARSE_CONFIGURATION);        }        @Deprecated //remove in Edgware"        @ConditionalOnProperty("zuul.ribbon.restclient.enabled")        static class ZuulProperty {}        @ConditionalOnProperty("ribbon.restclient.enabled")        static class RibbonProperty {}    }}
      
     
    

总结

前面带领大家分析了一小段源码，SpringCloud很庞大，不可能一一分析，文本的主要目的就是教大家如何分析源码，从何处下手，以便大家可以按照这种思路继续跟踪下去。