GWT 2.8 with App Engine on Java 7

[Paul Mazzuca]

Using the maven gwt and appengine plugins, is it possible to compile GWT 2.8 in Java 8, and then app engine related files using Java 7?  I realize the managed VMs support Java 8, but it would be nice to stick with the app engine environment which currently only support Java 7?  

I am wondering if there exists some maven configuration that would first compile all the GWT files in Java 8, thereby converting them to javascript, and then use java 7 for all the server files.

[Michael Joyner]

Is there any reason you can't split the project up into two projects? A java8 => js frontend, and the java7 backend?

On 03/09/2016 02:57 PM, Paul Mazzuca wrote:

Using the maven gwt and appengine plugins, is it possible to compile GWT 2.8 in Java 8, and then app engine related files using Java 7?  I realize the managed VMs support Java 8, but it would be nice to stick with the app engine environment which currently only support Java 7?  

I am wondering if there exists some maven configuration that would first compile all the GWT files in Java 8, thereby converting them to javascript, and then use java 7 for all the server files.

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[Paul Mazzuca]

"mvn appengine:update" abstracts most of the packaging and compiling, so I am unsure where that separation would need to be implemented.  I will check it out though. Thanks.

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[Thomas Broyer]

GWT 2.8 should support JDK 7, but if you want to use Java 8 features then indeed you need to use a JDK 8 to JavaC your classes.

You could possibly exclude your client code from being compiled with JavaC, and only processed by GWT.

Alternatives I can think of are:
- use Maven Toolchains to use JDK 7 and JDK 8 in the same build;
- use JDK 8 and retrolambda: https://github.com/orfjackal/retrolambda
- split your code into 2 projects/modules, compiled in 2 phases: mvn install the client code with JDK8, then mvn appengine:update the server code with JDK7, which has a dependency in the client code (resolved from local Maven repo).

The cleaner solution IMO is to use separate JDKs (or proper cross-compilation, with bootclasspath et al); either with toolchains or separate build phases. Retrolambda would need some testing in a Java 7 environment to confirm the transformation went well.

Also, Animal Sniffer on your server code would help, in case you don't compile it with a JDK7.

[Paul Mazzuca]

Thanks as alway for the prompt response.  I went ahead and reverted to Java 7  (while still using GWT 2.8) as the quick solution, with Google Guava for some more advanced Java 8 like APIs.  After some cursory research, I believe the GAE sandbox will be supporting Java 8 at some point this year, so hopefully the wait won't be too long, at which point I will use Java 8 across the board. 

I am still going to explore the Toolchains option though.  Having more of a clear separation between the client and server may make things easier, at least in my case.  If I get it working, I will share the pom.   Thanks again for all the GWT support.

[Drew Spencer]

I've had the same problem - was using GWT 2.8 and playing with a few lambdas and such in my GWT code, and even though there was no Java 8 code in my /server package, something (probably the target version in the pom.xml) stopped the maven plugin from deploying, so I had to revert.

Fingers crossed they get round to Java 8 sooner rather than later!

On Thursday, 10 March 2016 16:06:47 UTC, Paul Mazzuca wrote:

Thanks as alway for the prompt response.  I went ahead and reverted to Java 7  (while still using GWT 2.8) as the quick solution, with Google Guava for some more advanced Java 8 like APIs.  After some cursory research, I believe the GAE sandbox will be supporting Java 8 at some point this year, so hopefully the wait won't be too long, at which point I will use Java 8 across the board. 

I am still going to explore the Toolchains option though.  Having more of a clear separation between the client and server may make things easier, at least in my case.  If I get it working, I will share the pom.   Thanks again for all the GWT support.

On Thu, Mar 10, 2016 at 12:41 AM, Thomas Broyer <t.br...@gmail.com> wrote:

GWT 2.8 should support JDK 7, but if you want to use Java 8 features then indeed you need to use a JDK 8 to JavaC your classes.

You could possibly exclude your client code from being compiled with JavaC, and only processed by GWT.

Alternatives I can think of are:
 - use Maven Toolchains to use JDK 7 and JDK 8 in the same build;
 - use JDK 8 and retrolambda: https://github.com/orfjackal/retrolambda
 - split your code into 2 projects/modules, compiled in 2 phases: mvn install the client code with JDK8, then mvn appengine:update the server code with JDK7, which has a dependency in the client code (resolved from local Maven repo).

The cleaner solution IMO is to use separate JDKs (or proper cross-compilation, with bootclasspath et al); either with toolchains or separate build phases. Retrolambda would need some testing in a Java 7 environment to confirm the transformation went well.

Also, Animal Sniffer on your server code would help, in case you don't compile it with a JDK7.

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