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）
java.lang.IllegalStateException: Failed to introspect Class [org.springframework.cloud.gateway.config.GatewayAutoConfiguration$NettyConfiguration] from ClassLoader [jdk.internal.loader.ClassLoaders$AppClassLoader@7b1d7fff]
at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:507) ~[spring-core-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.util.ReflectionUtils.doWithMethods(ReflectionUtils.java:404) ~[spring-core-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.util.ReflectionUtils.doWithMethods(ReflectionUtils.java:389) ~[spring-core-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.util.ReflectionUtils.getUniqueDeclaredMethods(ReflectionUtils.java:447) ~[spring-core-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1705) ~[na:na]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.getTypeForFactoryMethod(AbstractAutowireCapableBeanFactory.java:738) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.determineTargetType(AbstractAutowireCapableBeanFactory.java:679) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.predictBeanType(AbstractAutowireCapableBeanFactory.java:647) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.isFactoryBean(AbstractBeanFactory.java:1518) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doGetBeanNamesForType(DefaultListableBeanFactory.java:507) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanNamesForType(DefaultListableBeanFactory.java:477) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeansOfType(DefaultListableBeanFactory.java:598) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeansOfType(DefaultListableBeanFactory.java:590) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.getBeansOfType(AbstractApplicationContext.java:1226) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
at org.springframework.boot.SpringApplication.getExitCodeFromMappedException(SpringApplication.java:905) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at org.springframework.boot.SpringApplication.getExitCodeFromException(SpringApplication.java:891) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at org.springframework.boot.SpringApplication.handleExitCode(SpringApplication.java:877) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at org.springframework.boot.SpringApplication.handleRunFailure(SpringApplication.java:826) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
at com.changgou.GatewayWebApplication.main(GatewayWebApplication.java:15) ~[classes/:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) ~[spring-boot-devtools-2.1.4.RELEASE.jar:2.1.4.RELEASE]
Caused by: java.lang.NoClassDefFoundError: reactor/netty/http/client/HttpResponseDecoderSpec
at java.base/java.lang.Class.getDeclaredMethods0(Native Method) ~[na:na]
at java.base/java.lang.Class.privateGetDeclaredMethods(Class.java:3167) ~[na:na]
at java.base/java.lang.Class.getDeclaredMethods(Class.java:2310) ~[na:na]
at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:489) ~[spring-core-5.1.6.RELEASE.jar:5.1.6.RELEASE]
... 26 common frames omitted
Caused by: java.lang.ClassNotFoundException: reactor.netty.http.client.HttpResponseDecoderSpec
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:583) ~[na:na]
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178) ~[na:na]
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521) ~[na:na]
... 30 common frames omitted
Process finished with exit code 0