在dubbo官网克隆了dubbo-admin-backend项目，打包成war包放到tomcat下启动，启动时报错，错误信息如下：

stack: java.lang.NoClassDefFoundError: javassist/ClassPool

java.lang.NoClassDefFoundError: javassist/ClassPool
	at org.apache.dubbo.common.compiler.support.JavassistCompiler.doCompile(JavassistCompiler.java:54)
	at org.apache.dubbo.common.compiler.support.AbstractCompiler.compile(AbstractCompiler.java:59)

	......

	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:759)
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:395)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:327)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1255)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1243)
	at org.apache.dubbo.admin.DubboAdminApplication.main(DubboAdminApplication.java:30)
Caused by: java.lang.ClassNotFoundException: javassist.ClassPool
	at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	... 64 more

	at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:729) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
	at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:192) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
	
    ......

	at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) [spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1255) [spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1243) [spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
	at org.apache.dubbo.admin.DubboAdminApplication.main(DubboAdminApplication.java:30) [classes/:na]

经过一番探索，终于找到解决办法，即在pom文件中加上如下依赖：

...

		<dependency>
			<groupId>org.javassist</groupId>
			<artifactId>javassist</artifactId>
			<version>3.20.0-GA</version>
		</dependency>

...

重新打包，在tomcat8.5下成功启动项目。