Cleanly starting apps on Java 9 and earlier

[Mark Thomas]

On 01/07/17 14:57, Stephen Felts wrote:
> IMO:
> 
> 1. You should avoid `--add-modules java.se.ee' unless you need all of those modules.  You should bring in only those modules that you need.  The choices are java.activation, java.corba, java.transaction, java.xml.bind, java.xml.ws, 
> java.xml.ws.annotation.  So use --add-modules java.xml.ws.

Thanks for the tip.

> 2. You can't use -XX:+IgnoreUnrecognizedVMOptions as a general solution because that isn't available in JDK6 JRockit for example.

Good to know. I was leaning towards JDK_JAVA_OPTIONS anyway. This point
confirms that choice.

> 3. Setting JDK_JAVA_OPTIONS is good because only JDK9 recognizes it and it is inherited by all nested invocations (unless there is an exec that excludes the environment).  You might want to use
> export JDK_JAVA_OPTIONS="-XX:+IgnoreUnrecognizedVMOptions --add-modules java.xml.ws"
> 
> 4. --add-opens is not needed starting in b175 so require that as a base.  It will still be noisy (a 3-line WARNING will be printed to the standard error).

Tomcat won't officially support Java 9 until there is a GA release.
Anything before then is on the basis that is should work, but it might not.

Thanks again for the additional info.

Mark


> 
> 
> -----Original Message-----
> From: Alan Bateman 
> Sent: Saturday, July 1, 2017 5:53 AM
> To: Mark Thomas; jigsaw-dev at openjdk.java.net
> Subject: Re: Cleanly starting apps on Java 9 and earlier
> 
> 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
>