前言

在項(xiàng)目中為了靈活配置，我們常采用配置文件，常見(jiàn)的配置文件就比如xml和properties，springboot允許使用properties和yaml文件作為外部配置。現(xiàn)在編譯器對(duì)于yaml語(yǔ)言的支持還不夠好，目前還是使用properties文件作為外部配置。

在Spring cloud config出來(lái)之前, 自己實(shí)現(xiàn)了基于ZK的配置中心, 杜絕了本地properties配置文件, 原理很簡(jiǎn)單, 只是重載了PropertyPlaceholderConfigurer的mergeProperties() :

/**
 * 重載合并屬性實(shí)現(xiàn)
 * 先加載file properties， 然后并入ZK配置中心讀取的properties
 *
 * @return 合并后的屬性集合
 * @throws IOException 異常
 */
@Override
protected Properties mergeProperties() throws IOException {
 Properties result = new Properties();
 // 加載父類(lèi)的配置
 Properties mergeProperties = super.mergeProperties();
 result.putAll(mergeProperties);
 // 加載從zk中讀取到的配置
 Map<String, String> configs = loadZkConfigs();
 result.putAll(configs);
 return result;
}

這個(gè)實(shí)現(xiàn)在spring項(xiàng)目里用起來(lái)還是挺順手的, 但是近期部分spring-boot項(xiàng)目里發(fā)現(xiàn)這種placeholder的實(shí)現(xiàn)跟spring boot的@ConfigurationProperties(prefix = "xxx") 不能很好的配合工作,

也就是屬性沒(méi)有被resolve處理, 用@Value的方式確可以讀到, 但是@Value配置起來(lái)如果屬性多的話還是挺繁瑣的, 還是傾向用@ConfigurationProperties的prefix, 于是看了下spring boot的文檔發(fā)現(xiàn) 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).

不難發(fā)現(xiàn)其會(huì)檢查Java system propeties里的屬性, 也就是說(shuō), 只要把mergerProperties讀到的屬性寫(xiě)入Java system props里即可, 看了下源碼, 找到個(gè)切入點(diǎn)

/**
 * 重載處理屬性實(shí)現(xiàn)
 * 根據(jù)選項(xiàng), 決定是否將合并后的props寫(xiě)入系統(tǒng)屬性, Spring boot需要
 *
 * @param beanFactoryToProcess
 * @param props    合并后的屬性
 * @throws BeansException
 */
@Override
protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props) throws BeansException {
 // 原有邏輯
  super.processProperties(beanFactoryToProcess, props);
 // 寫(xiě)入到系統(tǒng)屬性
 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);
  }
 }
}

為避免影響過(guò)大, 設(shè)置了個(gè)開(kāi)關(guān), 是否寫(xiě)入系統(tǒng)屬性, 如果是spring boot的項(xiàng)目, 就開(kāi)啟, 這樣對(duì)線上非spring boot項(xiàng)目做到影響最小, 然后spring boot的@ConfigurationProperties完美讀到屬性;

具體代碼見(jiàn): 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;
}

總結(jié)

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