spring.application.name=eureka
spring.cloud.config.uri=http://localhost:8888
spring.cloud.config.name=dev
spring.cloud.config.username=dev
spring.cloud.config.password=dev

 @Override
 public void initialize(ConfigurableApplicationContext applicationContext) {
  CompositePropertySource composite = new CompositePropertySource(
    BOOTSTRAP_PROPERTY_SOURCE_NAME);
  // 对在boostrap上下文类型为PropertySourceLocator的bean集合进行排序
  AnnotationAwareOrderComparator.sort(this.propertySourceLocators);
  boolean empty = true;
  ConfigurableEnvironment environment = applicationContext.getEnvironment();
  for (PropertySourceLocator locator : this.propertySourceLocators) {
   PropertySource<?> source = null;
   // 读取外部配置源
   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);
   }
   // 插入至Environment环境对象中
   insertPropertySources(propertySources, composite);
   reinitializeLoggingSystem(environment, logConfig, logFile);
   setLogLevels(applicationContext, environment);
   handleIncludedProfiles(environment);
  }
 }

 private void insertPropertySources(MutablePropertySources propertySources,
   CompositePropertySource composite) {
  // 外部源配置集合
  MutablePropertySources incoming = new MutablePropertySources();
  incoming.addFirst(composite);
  PropertySourceBootstrapProperties remoteProperties = new PropertySourceBootstrapProperties();
  // 从外部源配置源集合中读取PropertySourceBootstrapProperties的相关属性
  // 例如spring.cloud.config.overrideSystemProperties等属性
  Binder.get(environment(incoming)).bind("spring.cloud.config",
    Bindable.ofInstance(remoteProperties));
  // spring.cloud.config.allow-override=false或者spring.cloud.config.override-none=false且spring.cloud.config.override-system-properties=true
  if (!remoteProperties.isAllowOverride() || (!remoteProperties.isOverrideNone()
    && remoteProperties.isOverrideSystemProperties())) {
   propertySources.addFirst(composite);
   return;
  }
  // spring.cloud.config.override-none=true则处于最低读取位
  if (remoteProperties.isOverrideNone()) {
   propertySources.addLast(composite);
   return;
  }
  // 根据spring.cloud.config.override-system-properties属性判断是放在systemProperties前还是后
  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);
  }
 }

package com.example.configdemo.propertysource;

import org.springframework.cloud.bootstrap.config.PropertySourceLocator;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.core.env.Environment;
import org.springframework.core.env.MapPropertySource;
import org.springframework.core.env.PropertySource;

import java.util.HashMap;
import java.util.Map;

/**
 * @author nanco
 * @create 19/9/22
 * @description 自定义的PropertySourceLocator的顺序应该要比远程仓库读取方式要优先
 * @see org.springframework.cloud.config.client.ConfigServicePropertySourceLocator
 */
@Order(value = Ordered.HIGHEST_PRECEDENCE + 1)
public class CustomPropertySourceLocator implements PropertySourceLocator {

 private static final String OVERRIDE_ADD_MAPPING = "spring.resources.add-mappings";

 @Override
 public PropertySource<?> locate(Environment environment) {

  Map customMap = new HashMap<>(2);
  // 远程仓库此配置为false，本地进行复写
  customMap.put(OVERRIDE_ADD_MAPPING, "true");

  return new MapPropertySource("custom", customMap);
 }
}

package com.example.configdemo.propertysource;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * @author nanco
 * @create 19/9/22
 */
@Configuration
public class CustomBootstrapConfiguration {

 @Bean("customPropertySourceLocator")
 public CustomPropertySourceLocator propertySourceLocator() {
  return new CustomPropertySourceLocator();
 }
}

# Bootstrap components
org.springframework.cloud.bootstrap.BootstrapConfiguration=\
com.example.configdemo.propertysource.CustomBootstrapConfiguration