How to fix [ERROR] Hint: Check that your module inherits 'com.google.gwt.core.Core'

Question

I want to start a Web Development project with GWT in Eclipse. For that I am following the tutorial on http://www.gwtproject.org/doc/latest/tutorial/create.html

The form to create the Project does not exactly look like they explain. For example I cannot make a checkmark at "Use Google App Engine" since it does not exist. To get the build.xml I checkmarked the "Generate an Ant Project" field.

When I try to run the generated code, the following error occurs:

Turning off precompile in incremental mode.
Super Dev Mode starting up
workDir: /tmp/gwt-codeserver-9585554490549923267.tmp
2019-02-03 18:36:10.619:INFO::main: Logging initialized @879ms
Loading Java files in com.google.gwt.sample.stockwatcher.StockWatcher.
[ERROR] Hint: Check that your module inherits 'com.google.gwt.core.Core'      either directly or indirectly (most often by inheriting module 'com.google.gwt.user.User')

When I try to use the command line version of their tutorial, I get an 503 Error:

HTTP ERROR: 503

Problem accessing /StockWatcher.html. Reason:

    Service Unavailable

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I use GWT SDK 2.8.1 and Java 10

I installed already lots of plugins for Eclipse, so that I am quite sure to have all plugins I need. Maybe this could be something with the Java version? Does anyone has an idea?

Hellbent

The Eclipse plugin has been updated. Take a look here: youtube.com/watch?v=x04sufQce-Y The "Use Google App Engine" has been removed (use Google Cloud Plugin instead). And, as the error message suggest: check, if you added the "com.google.gwt.user.User" module inside the moduel descriptor. – Kunkel

If you just want a minimal starting-guide with gwt, I have created this tutorial which is updated to last best-practices (dev.to/ibaca/modern-gwt-first-steps-509k) but it is for client only app (minimal example!). Otherwise, I recommend using the tbroyer archetype (github.com/tbroyer/gwt-maven-archetypes). – Bethina

Make sure you name your gwt tests like GwtTest___ to avoid them being picked up by the surefire plugin. The gwt plugin will run them in a separate test step (if you use GwtTestSuites). – Creaturely

Answer 1

1. Check that your gwt.xml really inherits "com.google.gwt.user.User"
2. Check java sdk. Some gwt versions work only with java 1.8
3. If you use Idea, there was a bug, which also causes this error: https://youtrack.jetbrains.com/issue/IDEA-218731?_ga=2.120118728.1133270638.1599566675-1712334692.1566210515

Crossroads

Answer 2

Use 1.8.0 JRE to compile the GWT application. You can setup this in eclipse as shown below.

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Then try to compile the application you will get the following output in console.

Compiling module com.somshine.miniproject.MiniProject Compiling 5 permutations Compiling permutation 0... Compiling permutation 1... Compiling permutation 2... Compiling permutation 3... Compiling permutation 4... Compile of permutations succeeded Compilation succeeded -- 21.193s Linking into D:\Java\gwtProject\miniProject\war\miniproject Link succeeded Linking succeeded -- 0.426s

Aphotic

Answer 3

Make sure your JAVA_HOME is pointing to a JDK 1.8 version folder, as ant will use that to compile your sources

Rosetterosewall

Answer 4

On Eclipse when you get this error, you should navigate to Windows->Preferences->Java->Installed JREs and make sure that whichever item is selected, is actually a JDK.

If it's not, change it to your JDK and make sure it's working with Java 1.8 SDK.

Composure