最近在搭建Spring Cloud新項目，遇到了這個問題，記錄一下，以饗讀者。
關於怎麼配置多數據源，這裏不再贅述，簡單來說，就是配置多個bean，每個bean對應一個數據源。
有不懂的讀者，可以參考我之前的一篇博客，或者在網上搜素，都可以。
這篇博客比較老了，用的是xml配置文件。但是萬變不離其宗，本質上是一樣的，就是注入多個bean到Spring的IOC容器中。
在Spring Cloud環境下，我們配置了2個數據源以後，啓動項目會報錯。
報錯日誌如下：
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration': Injection of autowired dependencies failed;
nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private javax.sql.DataSource org.springframework.boot.autoconfigure.orm.jpa.JpaBaseConfiguration.dataSource;
nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [cn/sephora/platform/oms/backend/config/DataSourceConfig.class]: Initialization of bean failed;
nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSourceInitializer': Invocation of init method failed;
nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [javax.sql.DataSource] is defined: expected single matching bean but found 2: monitorDataSource,dataSource
更詳細的堆棧日誌如下：
2020-05-25 13:14:09,669 [main] ERROR org.springframework.boot.SpringApplication - [ - - ] - Application startup failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private javax.sql.DataSource org.springframework.boot.autoconfigure.orm.jpa.JpaBaseConfiguration.dataSource; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [cn/sephora/platform/oms/backend/config/DataSourceConfig.class]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSourceInitializer': Invocation of init method failed; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [javax.sql.DataSource] is defined: expected single matching bean but found 2: monitorDataSource,dataSource
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:334)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1214)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:543)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:368)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1123)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1018)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:510)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1054)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:829)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:538)
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:118)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:760)
at org.springframework.boot.SpringApplication.createAndRefreshContext(SpringApplication.java:360)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:306)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1185)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1174)
at cn.sephora.platform.oms.backend.Application.main(Application.java:26)
爲什麼呢？很簡單，你配置了2個數據源，都是javax.sql.DataSource的實現。
DataSourceAutoConfiguration這個類也向IOC容器注入了一個DataSource，這個DataSource是Spring集成的原生的DataSource。
那麼問題來了，當DataSourceAutoConfiguration向Spring的IOC容器中注入DataSource實例時，發現這個DataSource有2個實現，
Spring的IOC容器不知道該使用哪個？於是就拋出了上面的異常。
解決方案如下：在Spring啓動時，不要加載這個DataSourceAutoConfiguration就行了。
如下：在SpringBootApplication註解上，排除掉DataSourceAutoConfiguration.class
@SpringBootApplication(exclude={
DataSourceAutoConfiguration.class
})
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
這裏告訴我們一個要點：Spirng Cloud環境下，如果需要配置多數據源的話，一定不要注入DataSourceAutoConfiguration.class
更多關於搭建Spring Cloud項目的分享，稍後會奉上。