eclipse  使用 jdk8 编译出来的jar 
Exception in thread "main" java.lang.UnsupportedClassVersionError: LogDemoTest : Unsupported major.minor version 52.0

Unsupported major.minor version 52.0
 
不同 JDK 版本，编译出的class文件是不同的 class文件前几个字节 

jdk9  53
jdk8  52
J2SE 7 = 51 (0x33 hex)
J2SE 6.0 = 50 (0x32 hex)
J2SE 5.0 = 49 (0x31 hex)
JDK 1.4 = 48 (0x30 hex)
JDK 1.3 = 47 (0x2F hex)
JDK 1.2 = 46 (0x2E hex)
JDK 1.1 = 45 (0x2D hex)

javap -verbose LogBackUtil.class 
Classfile /Users/dugang/work/logdemo/target/classes/dyyx/LogBackUtil.class
  Last modified 2019-11-7; size 906 bytes
  MD5 checksum 7149e19b5e8285b2abf79336ccb546c2
  Compiled from "LogBackUtil.java"
public class dyyx.LogBackUtil
  minor version: 0
  major version: 52

  
工程  JRE System Library 使用 jdk7

右键 / 属性 / Java build path / JRE System Library 
修改 选择 jdk8