I have created a New Dynamic Project under Eclipse Helios Version, where my JRE Version is set to 1.6. I have added Maven capabilities to the Web Application by clicking on
TK Gospodinov answer is correct even for maven projects. Beware: I do use Maven. The pom was correct and still got this issue. I went to "Project Facets" and actually removed the Java selection which was pointing to 1.6 but my project is using 1.7. On the right in the "Runtimes" tab I had to check the jdk1.7 option. Nothing appeared on the left even after I hit "Apply". The issue went away though which is why I still think this answer is important of the specific "Project Facets" related issue. After you hit OK if you come back to "Project Facets" you will notice Java shows up as version 1.7 so you can now select it to make sure the project is "marked" as a Java project. I also needed to right click on the project and select Maven|Update Project.
If your project is not a Maven project, right-click on your project and choose Properties to open the Project Properties dialog.
There is a Project Facets item on the left, select it, look for the Java facet on the list, choose which version you want to use for the project and apply.
If using eclipse,
Under.settings click on org.eclipse.wst.common.project.facet.core.xml
<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
<installed facet="java" version="1.7"/>
</faceted-project>
Change the version to the correct version.
I found @bigleftie's comment above very helpful: "Four things must match
In my case, in the project properties, Java compiler, the JDK compliance was set to use the workspace settings, which were different from the java version for the project. I clicked on 'Configure Workspace Settings', and changed the workspace Compiler compliance level to what I wanted, and the problem was resolved.
I resolved this problem by setting the java version in Project Facet property of the project properties, Right click the project root folder -> Properties, search for Project Facets, and select compatible java version.
For reference -
I resolved it by Myproject--->java Resource---->libraries-->JRE System Libraries[java-1.6] click on this go to its "property" select "Classpath Container" change the Execution Environment to java-1.8(jdk1.8.0-35) (that is latest)