Maven not working with Java SE 9 but Java SE-1.8, why?

Question

I am trying to write something with websockets but got the Problem of unresolvable imports.

After a few tries, I created two identical Projects. One with Java SE9 and one with JAVA SE-1.8.

The import works with the 1.8 but not the 9 Can someone explain me what I am doing wrong in 9?

At first I thought it was because of using the default package in 9 (only difference i can tell), but even after creating a new package it still does not work in 9

Has it something to do with modules? The "bin" folder is different with both projects

Here are some Screenshots:

Answer 1

you have missed the group id

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.7.0</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
        </plugin>
    </plugins>
</build>