如何在Eclipse中更改“已安装的项目方面”的Java版本？

Question

I just installed Eclipse 3.7 and the Google Plugin for Eclipse because I want to teach myself how to use Google App Engine.

When I create a new web application and run, I got an error that noted that annotations were not allowed in my JRE version (1.4). Hence, I set my JRE to 1.6 and my compiler compliance level to 1.6.

However, I now get this new error.

Description Resource    Path    Location    Type
Java compiler level does not match the version of the installed Java project facet.
Myprojectname       Unknown Faceted Project Problem (Java Version Mismatch)

How do I change "the version of the installed Java project facet"?

There is no item called "Project Facet" to the left of my project's properties menu.

Answer 1

If you are getting that validation message, you should be able to find "Project Facets" under your project's properties. You should see a screen like this one, where you will be able to change Java facet version:

If you are not seeing this page, then the project you created is likely corrupted somehow. How did you create it? Did you use a wizard provided by Google Plugin for Eclipse? If so, you will need to file a bug report with Google as they are not creating a valid project.

Regardless of the above, you should be able to resolve this problem by right clicking on the problem in the problems view and selecting "quick fix", where you will be guided in aligning your java facet and java compliance settings.

Answer 2

In case you have not yet found a solution or somebody else is facing this problem:

I had the same problem with the "Project facet" and not having the "Project Facets" page in the project properties when switching from 1.7 down to 1.6. I was able to fix it with editing the file org.eclipse.wst.common.project.facet.core.xml in the project folder .settings .

In this file I had the following code, in which the 1.7 was replaced by 1.6 and the error went away:

    <?xml version="1.0" encoding="UTF-8"?>
    <faceted-project>
    <installed facet="java" version="1.7"/>
    </faceted-project>

EDIT: I forgot to mention that you have to edit the filters on the "Package Explorer" to show .* resources: Select "View Menu" (the down-facing arrow) -> Filters... -> uncheck ".* resources" -> click "Ok" and you should see the .settings folder.

Answer 3

If you are using Eclipse IDE for Java EE Developers , you should have the Project Facets property section.

It is possible that your Eclipse 3.7 is the Eclipse IDE for Java Developers . In that case you need to add the ability to have facets by installing the EE goodies...

use the Help -> Install New Software... -> Work with: (choose Indigo) and then turn down "Web, XML, Java EE and OSGi Enterprise Development" and check Eclipse Java EE Developer Tools

Allowing Eclipse to be restarted should now add the Project Facets property section visibility.