Cleanly starting apps on Java 9 and earlier

[Alan Bateman]

On 01/07/2017 10:18, Mark Thomas wrote:
> Hi,
>
> Apache Tomcat needs to add the following options when running on Java 9:
>
> --add-modules=java.se.ee
> --add-opens=java.base/java.lang=ALL-UNNAMED
> --add-opens=java.rmi/sun.rmi.transport=ALL-UNNAMED
>
> The first is because it depends on javax.xml.ws.WebServiceRef and
> javax.xml.ws.WebServiceRefs.
> We could work around this by shipping our own implementations but that
> sort of duplication should not be necessary.
The java.xml.ws module is deprecated for removal (along with the other 
modules shared with Java EE) so expect these modules to not be included 
in the JDK some day (exactly when is TBD as it depends on when Java SE 
drops them).

In the short term then `--add-modules java.se.ee` will resolve the EE 
modules included in the JDK but it may bring complications, it all 
depends on whether you have the EE java.transaction module or JAR files 
with annotations in the javax.annotation package in your environment. An 
important page for the JDK 9 docs is a page with instructions and 
deployments options for those using these APIs.


>
> The second and third are required by Tomcat's memory leak detection and
> prevention code. In an ideal world, web applications wouldn't have
> memory leaks. Unfortunately, the world isn't ideal and the memory leak
> detection and prevention code has proven immensely valuable over the years.
Both of these packages are open since jdk-9+175 so the hacks to null 
fields will continue to work.

That said, I thought the issue with TCCL in sun.rmi.transport.GC was 
fixed via JDK-8157570. Have you tested that?


> The problem we have is that Tomcat needs to run on Java 9 though 6. If
> the above options aren't provided, Java 6 through 8 are fine but on Java
> 9 at best the users see a bunch of errors and at worst Tomcat won't
> start. If the above options are included, Java 9 is fine but then Tomcat
> fails to start on Java 6 though 8.
>
The launch script could examine the JAVA_VERSION property in the 
`release` file. Another approach is to set the JDK_JAVA_OPTIONS 
environment variable as that is new 9 and so will be ignored by older 
releases. There is also -XX:+IgnoreUnrecognizedVMOptions to ignore 
unrecognized options.

-Alan