原因：springcloud的版本和springboot的版本对应不上，可能因为springboot版本过低或者springcloud版本过高，去springcloud官网查看对应springboot版本重新依赖即可解决
报错版本：springcloud：Greenwich.SR5 springboot：2.1.4
调整后版本：springcloud：Greenwich.SR5 springboot：2.1.8（如果springboot版本大于等于2.2.0还是会报错）
: Failed to introspect Class [$NettyConfiguration] from ClassLoader [$AppClassLoader@7b1d7fff]
at (:507) ~[spring-core-5.1.:5.1.]
at (:404) ~[spring-core-5.1.:5.1.]
at (:389) ~[spring-core-5.1.:5.1.]
at (:447) ~[spring-core-5.1.:5.1.]
at /(:1705) ~[na:na]
at (:738) ~[spring-beans-5.1.:5.1.]
at (:679) ~[spring-beans-5.1.:5.1.]
at (:647) ~[spring-beans-5.1.:5.1.]
at (:1518) ~[spring-beans-5.1.:5.1.]
at (:507) ~[spring-beans-5.1.:5.1.]
at (:477) ~[spring-beans-5.1.:5.1.]
at (:598) ~[spring-beans-5.1.:5.1.]
at (:590) ~[spring-beans-5.1.:5.1.]
at (:1226) ~[spring-context-5.1.:5.1.]
at (:905) ~[spring-boot-2.1.:2.1.]
at (:891) ~[spring-boot-2.1.:2.1.]
at (:877) ~[spring-boot-2.1.:2.1.]
at (:826) ~[spring-boot-2.1.:2.1.]
at (:327) ~[spring-boot-2.1.:2.1.]
at (:1260) ~[spring-boot-2.1.:2.1.]
at (:1248) ~[spring-boot-2.1.:2.1.]
at (:15) ~[classes/:na]
at /.invoke0(Native Method) ~[na:na]
at /(:62) ~[na:na]
at /(:43) ~[na:na]
at /(:566) ~[na:na]
at (:49) ~[spring-boot-devtools-2.1.:2.1.]
Caused by: : reactor/netty/http/client/HttpResponseDecoderSpec
at /.getDeclaredMethods0(Native Method) ~[na:na]
at /(:3167) ~[na:na]
at /(:2310) ~[na:na]
at (:489) ~[spring-core-5.1.:5.1.]
... 26 common frames omitted
Caused by: :
at /(:583) ~[na:na]
at /$(:178) ~[na:na]
at /(:521) ~[na:na]
... 30 common frames omitted
Process finished with exit code 0