sc 使用了配置中心后，如何设置远程和本地配置的优先级

在 spring 中，如何获取一个 key 的值？

applicationContext.getEnvironment().getProperty("swagger.show")

那么 key 的优先级呢？spring 会加载所有的配置文件，获取 key 的 value 时，会从前往后遍历这些配置文件，找到了即返回。所以，靠前的优先级高

sc 中加载远程配置文件的逻辑：

// org.springframework.cloud.bootstrap.config.PropertySourceBootstrapConfiguration#initialize
@Override
public void initialize(ConfigurableApplicationContext applicationContext) {
    CompositePropertySource composite = new CompositePropertySource(
            BOOTSTRAP_PROPERTY_SOURCE_NAME);
    // NacosPropertySourceLocator 实现了这个接口，order 为 0
    AnnotationAwareOrderComparator.sort(this.propertySourceLocators);
    boolean empty = true;
    ConfigurableEnvironment environment = applicationContext.getEnvironment();
    for (PropertySourceLocator locator : this.propertySourceLocators) {
        PropertySource<?> source = null;
        // nacos 拉取配置
        source = locator.locate(environment);
        if (source == null) {
            continue;
        }
        logger.info("Located property source: " + source);
        composite.addPropertySource(source);
        empty = false;
    }
    if (!empty) {
        MutablePropertySources propertySources = environment.getPropertySources();
        String logConfig = environment.resolvePlaceholders("${logging.config:}");
        LogFile logFile = LogFile.get(environment);
        if (propertySources.contains(BOOTSTRAP_PROPERTY_SOURCE_NAME)) {
            propertySources.remove(BOOTSTRAP_PROPERTY_SOURCE_NAME);
        }
        // 把远程配置加入到 environment 中
        insertPropertySources(propertySources, composite);
        reinitializeLoggingSystem(environment, logConfig, logFile);
        setLogLevels(applicationContext, environment);
        handleIncludedProfiles(environment);
    }
}

确定配置优先级的逻辑：

// org.springframework.cloud.bootstrap.config.PropertySourceBootstrapConfiguration#insertPropertySources
private void insertPropertySources(MutablePropertySources propertySources,
        CompositePropertySource composite) {
    MutablePropertySources incoming = new MutablePropertySources();
    incoming.addFirst(composite);
    PropertySourceBootstrapProperties remoteProperties = new PropertySourceBootstrapProperties();
    Binder.get(environment(incoming)).bind("spring.cloud.config", Bindable.ofInstance(remoteProperties));
    if (!remoteProperties.isAllowOverride() || (!remoteProperties.isOverrideNone()
            && remoteProperties.isOverrideSystemProperties())) {
        // 远程配置优先级高
        propertySources.addFirst(composite);
        return;
    }
    if (remoteProperties.isOverrideNone()) {
        // 远程配置优先级低
        propertySources.addLast(composite);
        return;
    }
    if (propertySources
            .contains(StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME)) {
        if (!remoteProperties.isOverrideSystemProperties()) {
            propertySources.addAfter(
                    StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,
                    composite);
        }
        else {
            propertySources.addBefore(
                    StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,
                    composite);
        }
    }
    else {
        propertySources.addLast(composite);
    }
}

如果需要使用本地配置覆盖远程配置，设置 spring.cloud.config.overrideNone = true