springboot Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder 'name22' in

springboot Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder ‘name22’ in value “${name22}” 错误解决：

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2018-08-23 18:12:53.816 ERROR 12108 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userController': Injection of autowired dependencies failed; nested exception is java.lang.IllegalArgumentException: Could not resolve placeholder 'name22' in value "${name22}"
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:379) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1350) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:580) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$144/1493158871.getObject(Unknown Source) ~[na:na]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:760) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:869) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:759) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:395) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1255) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1243) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
	at springcloud.service.ServiceApplication6012.main(ServiceApplication6012.java:14) [classes/:na]
Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder 'name22' in value "${name22}"
	at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:172) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.util.PropertyPlaceholderHelper.replacePlaceholders(PropertyPlaceholderHelper.java:124) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.core.env.AbstractPropertyResolver.doResolvePlaceholders(AbstractPropertyResolver.java:237) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.core.env.AbstractPropertyResolver.resolveRequiredPlaceholders(AbstractPropertyResolver.java:211) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.PropertySourcesPlaceholderConfigurer.lambda$processProperties$0(PropertySourcesPlaceholderConfigurer.java:175) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
	at org.springframework.context.support.PropertySourcesPlaceholderConfigurer$$Lambda$170/1495161082.resolveStringValue(Unknown Source) ~[na:na]
    at org.springframework.beans.factory.support.AbstractBeanFactory.resolveEmbeddedValue(AbstractBeanFactory.java:839) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1086) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1065) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:584) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:91) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:373) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    ... 18 common frames omitted

Disconnected from the target VM, address: '127.0.0.1:52885', transport: 'socket'

springboot启动时会检索 @Value 对应配置文件中的key，当该key不存在时就会报：Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder异常，解决方案有两种：

1，设置 @Value 的默认值

@Value("${name22:default_name}")
private String name22;

上面代码中，当配置文件中 name22 key 不存在时，就会使用“default_name”作为默认值，key 与默认值用“:”符号分割。

2，在 Application 类中设置PropertySourcesPlaceholderConfigurer类的默认属性

// 设置@Value注解取值不到忽略（不报错）
@Bean
public static PropertySourcesPlaceholderConfigurer placeholderConfigurer() {
    PropertySourcesPlaceholderConfigurer c = new PropertySourcesPlaceholderConfigurer();
    c.setIgnoreUnresolvablePlaceholders(true);
    return c;
}