异常信息：
Exception in thread "main" java.lang.ClassCastException: java.base/jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to java.base/java.net.URLClassLoader
at org.springframework.boot.devtools.restart.DefaultRestartInitializer.getUrls(DefaultRestartInitializer.java:93)
at org.springframework.boot.devtools.restart.DefaultRestartInitializer.getInitialUrls(DefaultRestartInitializer.java:56)
at org.springframework.boot.devtools.restart.Restarter.<init>(Restarter.java:140)
at org.springframework.boot.devtools.restart.Restarter.initialize(Restarter.java:546)
at org.springframework.boot.devtools.restart.RestartApplicationListener.onApplicationStartingEvent(RestartApplicationListener.java:67)
at org.springframework.boot.devtools.restart.RestartApplicationListener.onApplicationEvent(RestartApplicationListener.java:45)
at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)
at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)
at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)
at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:122)
at org.springframework.boot.context.event.EventPublishingRunListener.starting(EventPublishingRunListener.java:69)
at org.springframework.boot.SpringApplicationRunListeners.starting(SpringApplicationRunListeners.java:48)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:292)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1118)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1107)
at com.asofdate.AsofdateMain.main(AsofdateMain.java:18)
出现这个异常的主要原因是：
当JDK是1.9时，jdk.internal.loader.ClassLoaders类型转换失败，哪一行代码导致的呢？
spring-boot中引入热部署后，出现了这个异常。
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<optional>true</optional>
</dependency>
两种简单的解决办法：
- 降低JDK版本到1.8
- 删除热部署依赖
