前言
在項目中為了靈活配置，我們常採用配置文件，常見的配置文件就比如xml和properties，springboot允許使用properties和yaml文件作為外部配置。現在編譯器對於yaml語言的支持還不夠好，目前還是使用properties文件作為外部配置。
在Spring cloud config出來之前, 自己實現了基於ZK的配置中心, 杜絕了本地properties配置文件, 原理很簡單, 只是重載了PropertyPlaceholderConfigurer的mergeProperties() :
/** * 重載合併屬性實現* 先加載file properties， 然後併入ZK配置中心讀取的properties * * @return 合併後的屬性集合* @throws IOException 異常*/@Overrideprotected Properties mergeProperties() throws IOException { Properties result = new Properties(); // 加載父類的配置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;}這個實現在spring項目裡用起來還是挺順手的, 但是近期部分spring-boot項目裡發現這種placeholder的實現跟spring boot的@ConfigurationProperties(prefix = "xxx")不能很好的配合工作,
也就是屬性沒有被resolve處理, 用@Value的方式確可以讀到, 但是@Value配置起來如果屬性多的話還是挺繁瑣的, 還是傾向用@ConfigurationProperties的prefix, 於是看了下spring boot的文檔發現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).
不難發現其會檢查Java system propeties裡的屬性, 也就是說, 只要把mergerProperties讀到的屬性寫入Java system props裡即可, 看了下源碼, 找到個切入點
/** * 重載處理屬性實現* 根據選項, 決定是否將合併後的props寫入系統屬性, Spring boot需要* * @param beanFactoryToProcess * @param props 合併後的屬性* @throws BeansException */@Overrideprotected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props) throws BeansException { // 原有邏輯super.processProperties(beanFactoryToProcess, props); // 寫入到系統屬性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); } }}為避免影響過大, 設置了個開關, 是否寫入系統屬性, 如果是spring boot的項目, 就開啟, 這樣對線上非spring boot項目做到影響最小, 然後spring boot的@ConfigurationProperties完美讀到屬性;
具體代碼見: org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor
@Overridepublic 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
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