In maven how can I include non-java src files in the same place in the output jar?

You could add the following in your pom indicating that the resources are available in src/main/java and including the type of resources.

<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.properties</include>
            </includes>
        </resource>
    </resources>
</build>

With this pom fragment you include anything that is not a java file for both main and test artifact:

<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <excludes>
                <exclude>**/*.java</exclude>
            </excludes>
        </resource>
    </resources>
    <testResources>
        <testResource>
            <directory>src/test/java</directory>
            <excludes>
                <exclude>**/*.java</exclude>
            </excludes>
        </testResource>
    </testResources>
</build>