Maven suddenly wants src/ instead of src/main/java - eclipse

Question

I'm using Maven 3.3.3 together with Eclipse Mars and m2e. Yesterday, I created a new Java project and converted it into a Maven one.
Afterwards, the classpath contained only src instead of the standard src/main/java. I was surprised but I simply created the missing folders and ran m2e's "Update Project". This didn't solve the problem; m2e still insisted on using only src.
So I edited the classpath manually to end up with with the usual
src/test/java
src/test/resources
src/main/java
src/main/resources
When I try m2e's "Update Project" now, I get this error:
Cannot nest 'foo/src/test/java' inside 'foo/src'. To enable the nesting, exclude 'test/' from 'foo/src'
sigh I went to the command line next and ran mvn eclipse:eclipse to get this classpath:
src/test/java
src/test/resources
src
src/main/resources
Now, I'm completely stumped. Why is that happening?

Answer 1

Open your POM in the POM editor and click on the "Effective POM" tab. Search for sourceDirectory. You'll probably see something like this:
<sourceDirectory>src</sourceDirectory>
When you first converted the Java project to Maven, m2e tried to keep the classpath the same. Eclipse Java projects have a different layout by default. They use src/ instead of src/main/java/. There is no test folder since Eclipse projects usually put their tests into a different project.
To fix the issue:
Delete the sourceDirectory element from the POM (Note: It might be in a parent POM).
Go to the project
Select all the source folders
Remove them from the build path (context menu -> Build Path -> Remove From Build Path).
Update the project
The error should now be gone and the classpath should be correct.

Answer 2

There are two types of folders that you can create: 1) Package 2) Source Folder
1) A package looks like this
To create a package, right click on the folder you want (in my example, I right clicked on Java Resources) --> New --> Package
A pop up window that looks like this should appear
“Source folder:” That is where you choose your project. If you don’t see anything there, click on “Browse…” and find your project. If I click “Browse…” it shows this:
“Name:” is the name you will give your package.
Note: Packages should be within Source Folders. Source Folders are the parent folder.
2) Source Folders look like this:
To create a Source Folder, right click on the folder you want (in my example, I right clicked on Java Resources) --> New --> Source Folder
Under “Project name:” write your project’s name. If you need help, click “Browse…”
Under “Folder name:” write the folder name you want.
Error: If you’re trying to create a “src/main/resources” folder and you’re running into this error “Cannot nest ‘ProjectName’ inside ‘ProjectName’. To enable the nesting exclude ‘main/’ from
Solution: