qq_42554719的博客

报错原因：编译出来的class文件和运行时中所使用的的JDK版本号不一致，大概率是复用别人的项目，但是前后的编译环境不一致。JDK版本和Java编译器内部的版本号J2SE 8 = 52,J2SE 7 = 51,J2SE 6.0 = 50,J2SE 5.0 = 49,JDK 1.4 = 48,JDK 1.3 = 47,JDK 1.2 = 46,JDK 1.1 = 45解决办法：1、cmd，查看本地配置的JDK版本2、配置IDEA中项目的运行环境2.1、点击file–Project

报错信息：java.sql.SQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failurejava.sql.SQLNonTransientCon