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 */@Overrideprotected 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 */@Overrideprotected 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
@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;}总结
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