I encountered this problem recently, and the solutions found on the Internet are basically the following:
1. Right-click the project, properties, project facets, and change the version of java to 1.7.
2. window, properties, java, compiler, change the compiler compliance level to 1.7.
3, window, properties, java, installed jres, add a 1.7, and select it.
However, none of the above solved my problem. Later, in the configuration of tomcat, it was found that the jre version was wrong, and the path was as follows:
window, properties, server, runtime environments, select Apache tomcat7, click edit on the right, and change jre to version 1.7.