Spring boot外部配置（配置中心化）详解

前言

在项目中为了灵活配置，我们常采用配置文件，常见的配置文件就比如xml和properties，springboot允许使用properties和yaml文件作为外部配置。现在编译器对于yaml语言的支持还不够好，目前还是使用properties文件作为外部配置。

在Spring cloud config出来之前, 自己实现了基于ZK的配置中心, 杜绝了本地properties配置文件, 原理很简单, 只是重载了PropertyPlaceholderConfigurer的mergeProperties() :

/**
 * 重载合并属性实现
 * 先加载file properties， 然后并入ZK配置中心读取的properties
 *
 * @return 合并后的属性集合
 * @throws IOException 异常
 */
@Override
protected Properties mergeProperties() throws IOException {
 Properties result = new Properties();
 // 加载父类的配置
 Properties mergeProperties = super.mergeProperties();
 result.putAll(mergeProperties);
 // 加载从zk中读取到的配置
 Map<String, String> configs = loadZkConfigs();
 result.putAll(configs);
 return result;
}

这个实现在spring项目里用起来还是挺顺手的, 但是近期部分spring-boot项目里发现这种placeholder的实现跟spring boot的@ConfigurationProperties(prefix = "xxx") 不能很好的配合工作,

也就是属性没有被resolve处理, 用@Value的方式确可以读到, 但是@Value配置起来如果属性多的话还是挺繁琐的, 还是倾向用@ConfigurationProperties的prefix, 于是看了下spring boot的文档发现 PropertySource

order:

* Devtools global settings properties on your home directory (~/.spring-boot-devtools.properties when devtools is active).

* @TestPropertySource annotations on your tests.

* @SpringBootTest#properties annotation attribute on your tests.

* Command line arguments.

* Properties from SPRING_APPLICATION_JSON (inline JSON embedded in an environment variable or system property)

* ServletConfig init parameters.

* ServletContext init parameters.

* JNDI attributes from java:comp/env.

* Java System properties (System.getProperties()).

* OS environment variables.

* A RandomValuePropertySource that only has properties in random.*.

* Profile-specific application properties outside of your packaged jar (application-{profile}.properties and YAML variants)

* Profile-specific application properties packaged inside your jar (application-{profile}.properties and YAML variants)

* Application properties outside of your packaged jar (application.properties and YAML variants).

* Application properties packaged inside your jar (application.properties and YAML variants).

* @PropertySource annotations on your @Configuration classes.

* Default properties (specified using SpringApplication.setDefaultProperties).

不难发现其会检查Java system propeties里的属性, 也就是说, 只要把mergerProperties读到的属性写入Java system props里即可, 看了下源码, 找到个切入点

/**
 * 重载处理属性实现
 * 根据选项, 决定是否将合并后的props写入系统属性, Spring boot需要
 *
 * @param beanFactoryToProcess
 * @param props    合并后的属性
 * @throws BeansException
 */
@Override
protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props) throws BeansException {
 // 原有逻辑
  super.processProperties(beanFactoryToProcess, props);
 // 写入到系统属性
 if (writePropsToSystem) {
  // write all properties to system for spring boot
  Enumeration<?> propertyNames = props.propertyNames();
  while (propertyNames.hasMoreElements()) {
    String propertyName = (String) propertyNames.nextElement();
    String propertyValue = props.getProperty(propertyName);
    System.setProperty(propertyName, propertyValue);
  }
 }
}

为避免影响过大, 设置了个开关, 是否写入系统属性, 如果是spring boot的项目, 就开启, 这样对线上非spring boot项目做到影响最小, 然后spring boot的@ConfigurationProperties完美读到属性;

具体代码见: org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor

@Override
public Object postProcessBeforeInitialization(Object bean, String beanName)
  throws BeansException {
 ConfigurationProperties annotation = AnnotationUtils
   .findAnnotation(bean.getClass(), ConfigurationProperties.class);
 if (annotation != null) {
  postProcessBeforeInitialization(bean, beanName, annotation);
 }
 annotation = this.beans.findFactoryAnnotation(beanName,
 ConfigurationProperties.class);
 if (annotation != null) {
  postProcessBeforeInitialization(bean, beanName, annotation);
 }
 return bean;
}

总结

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