project facet java version 1.7 is not supported

1. Project --> properties --> compiler
                          --> server --> Runtime Environment

   or valid for the entire eclipse
   Window --> preferences --> compiler
                           --> server --> Runtime Environment


2. Modify the configuration file, Change the
   file org.eclipse.wst.common.project.facet.core.xml

<installed facet="java" version="1.7"/> to: <installed facet="java" version=" in the navigator view of the project to which it belongs . 1.6"/>

Sometimes after recompiling or even rebooting, the file is not updated