Spring boot外部配置（配置中心化）详解_Java教程

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;

									}