GWT compilation error with JDK 11

[Ying Jin]

Hello,

I tried to compile our GWT 2.9 project with JDK 11, but encountered the following error:

Error: Could not find or load main class com.google.gwt.dev.Compiler

Caused by: java.lang.ClassNotFoundException: com.google.gwt.dev.Compiler

BTW, the Eclipse version is  Version: 2020-06 (4.16.0). 

Please help shed some lights on this issue.

thanks,

Jenny

[Colin Alworth]

GWT 2.9 should support running on Java 11, both running on JDK 11 and compiling Java 11 sources.

Without other information, it sounds like there is a problem with your copy of gwt-dev.jar - the jar might be corrupt, or somehow not on your classpath?

Can you verify that the jar is present and correct, and share more specifics of how you are building?

[Ying Jin]

Thanks for your reply. Please see attached for the GWT lib specified in the java build path in Eclipse. I tried to compile it with JDK 8 and it didn't work either. 

The same project configuration in Eclipse worked in my old laptop, but not in my new laptop. The Eclipse in the new laptop is a copy of the Eclipse installed in the old laptop.

In addition, I also tried to  copy the "gwt-dev.jar" from the old laptop to the new one, but the compilation still gave me the following error.

Error: Could not find or load main class com.google.gwt.dev.Compiler

The project was compiled by using GWT->Compile option provided by the GWT Plugin installed in Eclipse.

Version: 2020-06 (4.16.0)

GWT Plugin version: 3.0

Your help is greatly appreciated!

thanks,

Jenny

[Ying Jin]

I tried to reinstall Eclipse again and GWT 3 plugin again from Eclipse market, downloaded and reinstalled gwt 2.9 for the project, however, I still encountered the error below.
It is so weird, the project configuration in eclipse works in my old laptop, not in the new one though it both has windows 10 installed.

Error: Could not find or load main class com.google.gwt.dev.Compiler

eclipse-jee-2020-06-R-win32-x86_64

GWT Plugin 3.0

gwt-2.9.0

Please see attached for the java build path dialog in eclipse.

Any idea about resolving this error? Please help shed some light on this problem.

Your help is much appreciated!

Jenny

[Colin Alworth]

If the class can't be found, something is wrong with your gwt-dev, or the gwt-dev isn't on the classpath, or more details from the error message will indicate why the Compiler class couldn't be loaded.

Please file a bug with more details (logs, full error message, other details about differences between the working computer and non-working computer) at https://github.com/gwt-plugins/gwt-eclipse-plugin/ so contributors there can take a closer look?

[Ying Jin]

Hi Colin,

I posted this issue on the gwt plugin site below, but there is no reply yet.

https://github.com/gwt-plugins/gwt-eclipse-plugin/issues/470

In addition, I've tried to install other version of Eclipse such as Eclipse 4.18 (2020-12) with a new workspace. After I installed GWT plugin 3 from market place and tried to create a sample gwt web application project 

as described below in gwt site, I got the error " Invocation of com.google.gwt.user.tools.WebAppCreator failed. See the error log for more details."  It seems to me this current market place gwt plugin didn't work as I didn't use our project at all

and followed the tutorial below.

https://www.gwtproject.org/usingeclipse.html

Is there a way to get a working GWT plugin for Eclipse which can work with JDK 11?

Your help is much appreciated!

Jenny

[Ralph Fiergolla]

Hi Jenny!

With all these issues related to out-dated Eclipse plug-ins I would strongly suggest switching to the new GWT Maven plug-in instead. Follow the instructions https://github.com/tbroyer/gwt-maven-archetypes/ to create a project that you can easily import into the most recent Eclipse (or any other IDE) subsequently. I don’t see much support for Eclipse plug-ins coming… I learned it the hard way too but am now happily working the Maven way. 

Bon courage!

Ralph 

[Ying Jin]

Ralph,

Thanks for your suggestion. However, one of our GWT project in production was developed long time ago and has very big codebase. I'm not sure how hard to convert it to Maven oriented project. It seems that we have to do lots of code refactoring 

in order to separate client side and server side code and other configuraitons. 

thanks,

Jenny

[Ralph Fiergolla]

It should not be that hard actually: you probably have separated client, shared and server side classes following the standard package naming convention. That is, basically it will be sufficient to copy your source code to the according client/shared/server sub projects and you are done. Okay, devil is in the details, but I did the same with some legacy project and happily live ever after. Give it a try. Definitely better than spending more time on installing different eclipse versions and plug-ins.

Cheers

Ralph 

[Ying Jin]

Ralph, thanks very much for your suggestion. I'll look into more of the approach to convert our gwt project to maven project.

BTW, I've found the solution to make the GWT plugin work again in my laptop to compile the GWT project.

I came across the following post when searching for the error related to webappcreator.

After I removed the "classpath" system variable from my new laptop and moved the GWT SDK to the top of the build path, the GWT Compiler starts working to compile the GWT project.

https://topic.alibabacloud.com/a/exception-invocation-of-font-colorredcomfont-font-colorredgooglefont-gwt-user-font-colorredtoolsfont-webappcreator-failed-see-the-error-log-for-more-details_8_8_31771273.html

Cheers ,
Jenny

[RobW]

I can't comment on the Eclipse plugin side of things, because we don't use those. But I can confirm that basic GWT 2.9/2.10 compilation works fine under Java 11 - that's our main Java platform now. I do recall some migration notes in the GWT 2.9 or 2.10 release notes we had to take care over, but I don't think those were Java version specific. More a case of changes in GWT packaging.

[Ying Jin]

Thanks for the information. The compilation problem has already been resolved. thanks, Jenny