Spring @Value引发的一次“血案”

Spring @Value引发的一次“血案”

“血案”

在项目中使用Spring boot开发微服务，需要从application.properties读取一个配置项，示例如下：

    @Value("${test.boolean}")
    private boolean testBoolean;

结果一次升级过程中，误将配置项test.boolean的值写成空字符串""，直接导致服务启动失败！
启动异常信息：

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'testController': Unsatisfied dependency expressed through field 'testBoolean'; nested exception is org.springframework.beans.TypeMismatchException: Failed to convert value of type 'java.lang.String' to required type 'boolean'; nested exception is java.lang.IllegalArgumentException: Invalid boolean value []
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:596) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:374) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1411) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:592) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:845) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:877) ~[spring-context-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549) ~[spring-context-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.1.8.RELEASE.jar:2.1.8.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:744) [spring-boot-2.1.8.RELEASE.jar:2.1.8.RELEASE]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:391) [spring-boot-2.1.8.RELEASE.jar:2.1.8.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:312) [spring-boot-2.1.8.RELEASE.jar:2.1.8.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) [spring-boot-2.1.8.RELEASE.jar:2.1.8.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1204) [spring-boot-2.1.8.RELEASE.jar:2.1.8.RELEASE]
	at com.example.demo.DemoApplication.main(DemoApplication.java:17) [classes/:na]
Caused by: org.springframework.beans.TypeMismatchException: Failed to convert value of type 'java.lang.String' to required type 'boolean'; nested exception is java.lang.IllegalArgumentException: Invalid boolean value []
	at org.springframework.beans.TypeConverterSupport.convertIfNecessary(TypeConverterSupport.java:79) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1199) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1171) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:593) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	... 19 common frames omitted
Caused by: java.lang.IllegalArgumentException: Invalid boolean value []
	at org.springframework.beans.propertyeditors.CustomBooleanEditor.setAsText(CustomBooleanEditor.java:154) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.TypeConverterDelegate.doConvertTextValue(TypeConverterDelegate.java:429) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.TypeConverterDelegate.doConvertValue(TypeConverterDelegate.java:402) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:155) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.beans.TypeConverterSupport.convertIfNecessary(TypeConverterSupport.java:73) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	... 22 common frames omitted

@Value原理

搜索了一大堆资料，关于Spring @Value原理描述最清楚的应该是这篇博客:springboot中@Value的工作原理，非常感谢作者。看了这篇博客，基本上对@Value的原理和过程有个大概理解。因为我的示例中使用到了类型转换，从异常堆栈看，是String到boolean的类型转换抛出异常了。
直接查看Spring framework社区的CustomBooleanEditor.java源码，输入text为空字符串的情况下，如果allowEmpty是true，则可以转换成null，否则抛出IllegalArgumentException异常。

	@Override
	public void setAsText(@Nullable String text) throws IllegalArgumentException {
   
   
		String input = (text != null ? text.trim() : null)