COMP 405	Java EE Tips and Traps

"Cannot get the System Java Compiler. Please use a JDK, not a JRE" error

First, try changing the default JRE that Eclipse uses (Preferences/Java/Installed JREs) to be a JDK, not a JRE.   If that doesn't work, try the following:

Edit the eclipse.ini file  (must start your ASCII editor "As Administrator" in Windows)  and add the following lines, right above the  "-vmargs" line:

-vm
[java executable location]      e.g. C:\Program Files\Java\jdk1.7.0_17\bin\javaw.exe

Ref:  http://wiki.eclipse.org/Eclipse.ini

Upgrading Eclipse with GWT and GAE plugins

Sooner or later you will need to upgrade Eclipse and/or its GAE and GWT plugins.    Unfortunately, the upgrade process may not be as smooth as one wishes.  Here are some issues to be aware of:

• Commit your code before doing any upgrades!
• The main Eclipse application update may require that Eclipse be "Run As Administrator".  The indication is that Eclipse will not allow you to select this particular upgrade because it says that you have insufficient privileges to perform that update.
• After an AppEngine SDK update, the project may be using an incorrect and possibly now invalid GAE SDK.
  • Go to Preferences/Google/App Engine to select the updated SDK and remove any old, invalid SDKs.
  • Check to make sure that your project's settings:
    • Java Build path has been updated to use the updated SDK (Project/Properties/Java Build Path/Libraries)
    •  The appengine-api-x.x-sdk-y.y.y.jar file in the war/WEB-INF/lib folder has been updated to the new version.
• After an Google Web Toolkit update, the project may be using an incorrect and possibly now invalid GWT SDK.
  • Go to Preferences/Google/Web Toolkit to select the updated SDK and remove any old, invalid SDKs.
  • Check to make sure that your project's settings:
    • Java Build path has been updated to use the updated GWT SDK (Project/Properties/Java Build Path/Libraries)
•  Make sure that all team members perform the update right away so that incorrect versions of SDK JAR files aren't committed into the repository which could cause problems on other people's machines.
• Be sure to clean the project (Project/Clean...) and to redo the GWT compile  (make sure that the Development Mode server is not running when you do this!).
  • If the GWT compile fails, try deleting the gwt-unitCache folder.  This will force the GWT compiler to recompile everything and hopefully get rid of any cross-version inconsistencies.

© 2013 by Stephen Wong