[23/07/19 05:30:24:024 CST] main ERROR integration.MetadataReportService:  [DUBBO] publishProvider getServiceDescriptor error. providerUrl: dubbo://30.5.121.125:20880/org.apache.dubbo.samples.generic.call.api.HelloService?anyhost=true&application=generic-impl-provider&deprecated=false&dubbo=2.0.2&dynamic=true&generic=true&interface=org.apache.dubbo.samples.generic.call.api.HelloService&methods=*&register=true&release=2.7.3&side=provider, dubbo version: 2.7.3, current host: 30.5.121.125
java.lang.ClassNotFoundException: org.apache.dubbo.samples.generic.call.api.HelloService
	at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at org.apache.dubbo.metadata.integration.MetadataReportService.publishProvider(MetadataReportService.java:97)
	at org.apache.dubbo.config.ServiceConfig.doExportUrlsFor1Protocol(ServiceConfig.java:623)
	at org.apache.dubbo.config.ServiceConfig.doExportUrls(ServiceConfig.java:457)
	at org.apache.dubbo.config.ServiceConfig.doExport(ServiceConfig.java:415)
	at org.apache.dubbo.config.ServiceConfig.export(ServiceConfig.java:378)
	at org.apache.dubbo.samples.generic.call.GenericImplProvider.main(GenericImplProvider.java:48)

Reproduce by running dubbo-samples-generic-impl
protected final Logger logger = LoggerFactory.getLogger(getClass());
    private static volatile MetadataReportService metadataReportService;
    private static Object lock = new Object();
    private MetadataReportFactory metadataReportFactory = ExtensionLoader.getExtensionLoader(MetadataReportFactory.class).getAdaptiveExtension();
    MetadataReport metadataReport;
    URL metadataReportUrl;
    MetadataReportService(URL metadataReportURL) {
        if (METADATA_REPORT_KEY.equals(metadataReportURL.getProtocol())) {
            String protocol = metadataReportURL.getParameter(METADATA_REPORT_KEY, DEFAULT_DIRECTORY);
            metadataReportURL = URLBuilder.from(metadataReportURL)
                    .setProtocol(protocol)
                    .removeParameter(METADATA_REPORT_KEY)
                    .build();
        }
        this.metadataReportUrl = metadataReportURL;
        metadataReport = metadataReportFactory.getMetadataReport(this.metadataReportUrl);
    }
    public static MetadataReportService instance(Supplier<URL> metadataReportUrl) {
        if (metadataReportService == null) {
            synchronized (lock) {
                if (metadataReportService == null) {
                    URL metadataReportURLTmp = metadataReportUrl.get();
                    if (metadataReportURLTmp == null) {
                        return null;
                    }
                    metadataReportService = new MetadataReportService(metadataReportURLTmp);
                }
            }
        }
        return metadataReportService;