端口被占用时，打印出提醒日志

broker/src/main/java/io/moquette/server/netty/NettyAcceptor.java

@@ -49,6 +49,7 @@ import org.slf4j.LoggerFactory;
 import javax.net.ssl.SSLContext;
 import javax.net.ssl.SSLEngine;
 import java.io.IOException;
+import java.net.BindException;
 import java.util.List;
 import java.util.Optional;
 import java.util.concurrent.TimeUnit;
@@ -187,6 +188,13 @@ public class NettyAcceptor implements ServerAcceptor {
             f.sync().addListener(FIRE_EXCEPTION_ON_FAILURE);
         } catch (InterruptedException ex) {
             LOG.error("An interruptedException was caught while initializing server. Protocol={}", protocol, ex);
+        } catch (Exception e) {
+            if(e instanceof BindException) {
+                e.printStackTrace();
+                LOG.error("端口 {} 已经被占用。请检查该端口被那个程序占用，找到程序停掉。\n查找端口被那个程序占用的命令是: netstat -tunlp | grep {}", port, port);
+                System.out.println("端口 " + port + " 已经被占用。请检查该端口被那个程序占用，找到程序停掉。\n查找端口被那个程序占用的命令是: netstat -tunlp | grep " + port);
+            }
+            throw e;
         }
     }