SpringCloud-Config 配置中心原理

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

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

spring.profile.active=git

@Configuration
@ConditionalOnMissingBean(value = EnvironmentRepository.class, search = SearchStrategy.CURRENT)
class DefaultRepositoryConfiguration {
    @Autowired
    private ConfigurableEnvironment environment;

    @Autowired
    private ConfigServerProperties server;

    @Autowired(required = false)
    private TransportConfigCallback customTransportConfigCallback;

    @Bean
    public MultipleJGitEnvironmentRepository defaultEnvironmentRepository(
            MultipleJGitEnvironmentRepositoryFactory gitEnvironmentRepositoryFactory,
            MultipleJGitEnvironmentProperties environmentProperties) throws Exception {
        return gitEnvironmentRepositoryFactory.build(environmentProperties);
    }
}

public interface EnvironmentRepository {
    Environment findOne(String application, String profile, String label);
}

@Override
    public synchronized Environment findOne(String application, String profile, String label) {
    //新建了一个本地仓库作为代理仓库来使用
  NativeEnvironmentRepository delegate = new NativeEnvironmentRepository(getEnvironment(),
                new NativeEnvironmentProperties());
    //获取本地仓库中指定应用的位置
        Locations locations = getLocations(application, profile, label);
        delegate.setSearchLocations(locations.getLocations());
      //根据这个路径搜索应用服务的配置信息
        Environment result = delegate.findOne(application, profile, "");
        result.setVersion(locations.getVersion());
        result.setLabel(label);
        return this.cleaner.clean(result, getWorkingDirectory().toURI().toString(),
                getUri());
    }

@Override
    public synchronized Locations getLocations(String application, String profile,
            String label) {
        if (label == null) {
            label = this.defaultLabel;
        }
    // 获取最新的版本号
        String version = refresh(label);
    // 根据最新的版本号返回 Locations 定位到资源的搜索路径
        return new Locations(application, profile, label, version,
                getSearchLocations(getWorkingDirectory(), application, profile, label));
    }

public String refresh(String label) {
        Git git = null;
        try {
      // 创建一个git客户端
            git = createGitClient();
      // 是否需要执行 git pull
            if (shouldPull(git)) {
                FetchResult fetchStatus = fetch(git, label);
                if (deleteUntrackedBranches && fetchStatus != null) {
                    deleteUntrackedLocalBranches(fetchStatus.getTrackingRefUpdates(), git);
                }
                // 获取后checkout，这样我们就可以获得任何新的分支、tag等。
                checkout(git, label);
                tryMerge(git, label);
            }
            else {
                // 没有什么要更新，所以只是checkout和merge。
                // 合并是因为远程分支以前可能已经更新过
                checkout(git, label);
                tryMerge(git, label);
            }
            // 返回当前的版本
            return git.getRepository().findRef("HEAD").getObjectId().getName();
        }
        catch (Exception e) {
            // 异常处理
        }
        finally {
            // 关闭git
        }
    }

@Configuration
@EnableConfigurationProperties
public class ConfigServiceBootstrapConfiguration {

    @Autowired
    private ConfigurableEnvironment environment;
  // 客户端配置属性
    @Bean
    public ConfigClientProperties configClientProperties() {
        ConfigClientProperties client = new ConfigClientProperties(this.environment);
        return client;
    }
  // 从远程服务器上请求对应的配置信息
    @Bean
    @ConditionalOnMissingBean(ConfigServicePropertySourceLocator.class)
    @ConditionalOnProperty(value = "spring.cloud.config.enabled", matchIfMissing = true)
    public ConfigServicePropertySourceLocator configServicePropertySource(ConfigClientProperties properties) {
        ConfigServicePropertySourceLocator locator = new ConfigServicePropertySourceLocator(
                properties);
        return locator;
    }

  // 重试机制
    @ConditionalOnProperty(value = "spring.cloud.config.fail-fast")
    @ConditionalOnClass({ Retryable.class, Aspect.class, AopAutoConfiguration.class })
    @Configuration
    @EnableRetry(proxyTargetClass = true)
    @Import(AopAutoConfiguration.class)
    @EnableConfigurationProperties(RetryProperties.class)
    protected static class RetryConfiguration {

        @Bean
        @ConditionalOnMissingBean(name = "configServerRetryInterceptor")
        public RetryOperationsInterceptor configServerRetryInterceptor(
                RetryProperties properties) {
            return RetryInterceptorBuilder
                    .stateless()
                    .backOffOptions(properties.getInitialInterval(),
                            properties.getMultiplier(), properties.getMaxInterval())
                    .maxAttempts(properties.getMaxAttempts()).build();
        }
    }
}

    @Override
    @Retryable(interceptor = "configServerRetryInterceptor")
    public PropertySource<?> locate(Environment environment) {
        ConfigClientProperties properties = this.defaultProperties.override(environment);
        CompositePropertySource composite = new CompositePropertySource("configService");
    // 实例化一个 restTemplate，用来调用服务端的 API
        RestTemplate restTemplate = this.restTemplate == null
                ? getSecureRestTemplate(properties)
                : this.restTemplate;
    // ...
        try {
      // labels ，对对应于profile 如，dev,pre,test这些
            String[] labels = new String[] { "" };
            if (StringUtils.hasText(properties.getLabel())) {
                labels = StringUtils.commaDelimitedListToStringArray(properties.getLabel());
            }
            String state = ConfigClientStateHolder.getState();
            // 遍历所有的标签，循环调用获取远程配置信息
            for (String label : labels) {
        // h获取远端环境配置信息
                Environment result = getRemoteEnvironment(restTemplate, properties,
                        label.trim(), state);
                if (result != null) {
                    log(result);
          // result.getPropertySources() can be null if using xml
          //使用 xml，可能会为 null
                    if (result.getPropertySources() != null) { 
                        for (PropertySource source : result.getPropertySources()) {
                            @SuppressWarnings("unchecked")
                            Map<String, Object> map = (Map<String, Object>) source
                                    .getSource();
                            composite.addPropertySource(
                                    new MapPropertySource(source.getName(), map));
                        }
                    }
          // 设置客户端状态和版本号信息
                    if (StringUtils.hasText(result.getState())
                            || StringUtils.hasText(result.getVersion())) {
                        HashMap<String, Object> map = new HashMap<>();
                        putValue(map, "config.client.state", result.getState());
                        putValue(map, "config.client.version", result.getVersion());
                        composite.addFirstPropertySource(
                                new MapPropertySource("configClient", map));
                    }
                    return composite;
                }
            }
        }
        catch (Exception e) {
            // ...
        }
    // 如果设置了fial fast ，失败时抛出异常
        if (properties.isFailFast()) {
            // ...
        }
    // ...
        return null;
    }

@Retryable(interceptor = "configServerRetryInterceptor")
    public List<ServiceInstance> getConfigServerInstances(String serviceId) {
        logger.debug("Locating configserver (" + serviceId + ") via discovery");
        List<ServiceInstance> instances = this.client.getInstances(serviceId);
        if (instances.isEmpty()) {
            throw new IllegalStateException(
                    "No instances found of configserver (" + serviceId + ")");
        }
        logger.debug("Located configserver (" + serviceId
                + ") via discovery. No of instances found: " + instances.size());
        return instances;
    }

@Override
    public PropertySource<?> locate(Environment environment) {
        if (environment instanceof ConfigurableEnvironment) {
      //省略 ...
            // 获取外部配置源
            PropertySource propertySource = create(propertySourceContext);
      //省略 ...
        }
        // ..
    }

private void findProperties(String path, List<String> children) {
        try {
            // 省略 ... 
            for (String child : children) {
                String childPath = path + "/" + child;
                List<String> childPathChildren = getChildren(childPath);
        // 获取节点信息
                byte[] bytes = getPropertyBytes(childPath);
                if (bytes == null || bytes.length == 0) {
                    if (childPathChildren == null || childPathChildren.isEmpty()) {
                        registerKeyValue(childPath, "");
                    }
                } else {
                    registerKeyValue(childPath, new String(bytes, Charset.forName("UTF-8")));
                }
                // 检查子节点，即使我们已经找到当前znode的值
                findProperties(childPath, childPathChildren);
            }
        } catch (Exception exception) {
            // 省略 ... 
        }
    }

@Configuration
    @ConditionalOnClass(RefreshEndpoint.class)
    protected static class ZkRefreshConfiguration {
        @Bean
        @ConditionalOnProperty(name = "spring.cloud.zookeeper.config.watcher.enabled", matchIfMissing = true)
        public ConfigWatcher configWatcher(ZookeeperPropertySourceLocator locator,
                CuratorFramework curator) {
            return new ConfigWatcher(locator.getContexts(), curator);
        }
    }