ClassCastException inside devtools with Java 9

[juergenzimmermann]

I'm using Spring Boot 1.5.3.RELEASE with Spring Framework 5.0.0.RC1 and Spring Cloud Dalston.SR1. Because of Spring Cloud I cannot upgrade to Spring Boot 2.0.0.M1.
Now I tried to upgrade from JDK 8 to JDK 9 build 171, but get the following stacktrace:

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.invokeListener(SimpleApplicationEventMulticaster.java:167)
        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:68)
        at org.springframework.boot.SpringApplicationRunListeners.starting(SpringApplicationRunListeners.java:48)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:303)
        at org.springframework.boot.builder.SpringApplicationBuilder.run(SpringApplicationBuilder.java:134)
        at de.hska.kunde.Microservice.main(Microservice.java:58)

[snicoll]

@java 9 isn't supported yet (including Spring Boot 2.0.0.M1), and there is no official support of Spring 5 with Spring Boot 1.x

Duplicates #7226

[molzb]

[Spring Boot 1.5.6, JDK 9 build 181]
I would be very grateful, if this can be fixed in Spring Boot 1.x.

[bclozel]

@molzb This issue is closed and Stéphane already pointed out that this won't happen. Note: this is not just a case of Spring Boot 1.x supporting JDK9, all managed dependencies should be compatible with it - something that requires a lot of upgrades.