solve
1. Eclipse compiles to solve the version problem
http://crunchify.com/exception-in-thread-main-java-lang-unsupportedclassversionerror-comcrunchifymain-unsupported-major-minor-version-51-0/
2. When eclipse imports projects elsewhere, an error is reported, and there is nothing wrong with seeing the java file. The solution is to replace all places with the unified jdk version 1.7. For details, see
http://jingyan.baidu.com/article/95c9d20da3ec5fec4e756186.html