Error: Java compiler level does not match the version of the installed Java project facet.

问题现象：项目图标报错“Java compiler level does not match the version of the installed Java project facet.”。

分析原因：这个是因为Project Facets中的Java版本设定与项目的Java版本设定不一致。

解决方法：（依据ECLIPSE自带的帮助）

Changing the version of a facet

You can change the version of a facet in a J2EE project by editing the facets for the project.

Changing the Java compiler version of a J2EE project involves
changing the version of the Java facet. See Changing the Java compiler
version for a J2EE project.

1. In the Project Explorer view, right-click the project and then click "Properties".

2. In the Properties window, click "Project Facets". The Project Facets page lists the facets in the project.

3. Click "java" option, and select the version is your java compiler version(1.6).

4. Click OK.