目录
使用nacos作为配置中心，其实就是将nacos当做一个服务端，将各个微服务看成是客户端，我们将各个微服务的配置文件统一存放在nacos上，然后各个微服务从nacos上拉取配置即可。
配置中心的使用：
在这个过程中，启动主程序时报错：
异常：java.lang.IllegalArgumentException: Could not resolve placeholder 'spring.datasource.druid.username' in value "${spring.datasource.druid.username}"
2023-05-17 19:33:57.875 ERROR 12820 --- [ main] o.s.boot.SpringApplication : Application run failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSourceConfig': Injection of autowired dependencies failed; nested exception is java.lang.IllegalArgumentException: Could not resolve placeholder 'spring.datasource.druid.username' in value "${spring.datasource.druid.username}"
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:405) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1431) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:619) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:955) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918) ~[spring-context-5.3.22.jar:5.3.22]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.22.jar:5.3.22]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145) ~[spring-boot-2.6.11.jar:2.6.11]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:745) ~[spring-boot-2.6.11.jar:2.6.11]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:420) ~[spring-boot-2.6.11.jar:2.6.11]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:307) ~[spring-boot-2.6.11.jar:2.6.11]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1317) ~[spring-boot-2.6.11.jar:2.6.11]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) ~[spring-boot-2.6.11.jar:2.6.11]
at com.buba.UserApp.main(UserApp.java:17) ~[classes/:na]
Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder 'spring.datasource.druid.username' in value "${spring.datasource.druid.username}"
at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:180) ~[spring-core-5.3.22.jar:5.3.22]
at org.springframework.util.PropertyPlaceholderHelper.replacePlaceholders(PropertyPlaceholderHelper.java:126) ~[spring-core-5.3.22.jar:5.3.22]
at org.springframework.core.env.AbstractPropertyResolver.doResolvePlaceholders(AbstractPropertyResolver.java:239) ~[spring-core-5.3.22.jar:5.3.22]
at org.springframework.core.env.AbstractPropertyResolver.resolveRequiredPlaceholders(AbstractPropertyResolver.java:210) ~[spring-core-5.3.22.jar:5.3.22]
at org.springframework.context.support.PropertySourcesPlaceholderConfigurer.lambda$processProperties$0(PropertySourcesPlaceholderConfigurer.java:191) ~[spring-context-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.support.AbstractBeanFactory.resolveEmbeddedValue(AbstractBeanFactory.java:936) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1332) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1311) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:656) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:639) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:119) ~[spring-beans-5.3.22.jar:5.3.22]
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:399) ~[spring-beans-5.3.22.jar:5.3.22]
... 17 common frames omitted2023-05-17 19:33:57.875 ERROR 12820 --- [ main] o.s.boot.SpringApplication : Application run failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSourceConfig': Injection of autowired dependencies failed; nested exception is java.lang.IllegalArgumentException: Could not resolve placeholder 'spring.datasource.druid.username' in value "${spring.datasource.druid.username}"
at
这个错误是springboot在启动时,无法解析application.properties配置文件中的${XXXXXXXXX}所导致的。
报错之前yml配置文件:
spring:
application:
name: user-server
cloud:
nacos:
discovery:
username: nacos
password: nacos
server-addr: 192.168.177.129:8848
config:
server-addr: 192.168.177.129:8848
file-extension: yaml如何解决呢？
spring:
application:
name: user-server
cloud:
nacos:
discovery:
username: nacos
password: nacos
server-addr: 192.168.177.129:8848
config:
username: nacos
password: nacos
server-addr: 192.168.177.129:8848
file-extension: yaml
在之前解决Nacos页面没有登录这个过程，所以设置了鉴权认证，所以配置中心也需要。
修正配置文件后,springboot应用就可以正常启动了。这也是在使用配置文件时错误之一。所以我们在编写properties配置时,需要注意:
1. 属性名要与官方文档对应,区分大小写
2. 使用${propertyName}引用其他属性时,属性名也要正确
3. 如果出现无法解析占位符的异常,首先应检查占位符中的属性名是否正确