rocketMQ启动时出现 找不到或无法加载主类 org.apache.rocketmq.namesrv.NamesrvStartup

错误如下：

Java HotSpot(TM) 64-Bit Server VM warning: Using the DefNew young collector with the CMS collector is deprecated and will likely be removed in a future release
Java HotSpot(TM) 64-Bit Server VM warning: UseCMSCompactAtFullCollection is deprecated and will likely be removed in a future release.
错误: 找不到或无法加载主类 org.apache.rocketmq.namesrv.NamesrvStartup

原因：

1、确保你配置了ROCKET_HOME环境变量
2、如果你是按照官网的那套教程，配置ROCKET_HOME时需要配置的地址不是你下载下来的源码的位置，而是编译后的位置

编译前：
D:\rocketMQ\rocketmq-release-4.2.0
编译后配置的地址：
D:\rocketMQ\rocketmq-release-4.2.0\distribution\target\apache-rocketmq