Support Java 9

[snicoll]

Spring Boot master (2.0.0.BUILD-SNAPSHOT) doesn't currently build with JDK9, see the dedicated job

• AgentAttacher does not work on JDK9 AgentAttacher does not work on JDK9 #9139
• Antlib support is broken with JDK9 Antlib support is broken with Java 9 #9140
• ModifiedClassPathRunner is broken with JDK9 ModifiedClassPathRunner is broken with Java 9 #9142

[snicoll]

The current build doesn't exhibit the same issue. I'll investigate that a bit more.

[snicoll]

We need to find a different way to extract the default values for the meta-data as we're using a proprietary API.

java.lang.IllegalAccessException: class org.springframework.boot.configurationprocessor.fieldvalues.javac.Trees cannot access class com.sun.tools.javac.api.JavacTrees (in module jdk.compiler) because module jdk.compiler does not export com.sun.tools.javac.api to unnamed module @5a7fe64f

[snicoll]

[ERROR] /Users/snicoll/workspace/pivotal/spring-boot/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/tunnel/server/RemoteDebugPortProvider.java:[51,43] cannot find symbol
  symbol:   class VMSupport
  location: package sun.misc

[philwebb]

java.lang.IllegalAccessException: class org.springframework.boot.configurationprocessor.fieldvalues.javac.Trees cannot access class com.sun.tools.javac.api.JavacTrees (in module jdk.compiler) because module jdk.compiler does not export com.sun.tools.javac.api to unnamed module @5a7fe64f

Yikes, this might be an issue. It might be worth asking on the JDK mailing list if there's any official way to do this.

[snicoll]

I've created a thread on jigsaw-dev about this.