MigrationRuleListener类中有以下缺陷

1、
```java
    public synchronized void process(ConfigChangedEvent event) {
        // 如果有其他Reference未调用onRefer方法，此时配置中心传入空配置，会导致后续onRefer方法调用失败
        rawRule = event.getContent();
        if (StringUtils.isEmpty(rawRule)) {
            logger.warn("Received empty migration rule, will ignore.");
            return;
        }

        logger.info("Using the following migration rule to migrate:");
        logger.info(rawRule);

        rule = parseRule(rawRule);

        if (CollectionUtils.isNotEmptyMap(handlers)) {
            handlers.forEach((_key, handler) -> handler.doMigrate(rule));
        }
    }

    @Override
    public synchronized void onRefer(RegistryProtocol registryProtocol, ClusterInvoker<?> invoker, URL consumerUrl, URL registryURL) {
        MigrationRuleHandler<?> migrationRuleHandler = handlers.computeIfAbsent((MigrationInvoker<?>) invoker, _key -> {
            ((MigrationInvoker<?>) invoker).setMigrationRuleListener(this);
            return new MigrationRuleHandler<>((MigrationInvoker<?>) invoker, consumerUrl);
        });

        rule = parseRule(rawRule);

        migrationRuleHandler.doMigrate(rule);
    }
```

2、
```java
    public synchronized void process(ConfigChangedEvent event) {
        rawRule = event.getContent();
        if (StringUtils.isEmpty(rawRule)) {
            logger.warn("Received empty migration rule, will ignore.");
            return;
        }

        logger.info("Using the following migration rule to migrate:");
        logger.info(rawRule);

        rule = parseRule(rawRule);

        if (CollectionUtils.isNotEmptyMap(handlers)) {
            handlers.forEach((_key, handler) -> handler.doMigrate(rule));
        }
    }

    @Override
    public synchronized void onRefer(RegistryProtocol registryProtocol, ClusterInvoker<?> invoker, URL consumerUrl, URL registryURL) {
        MigrationRuleHandler<?> migrationRuleHandler = handlers.computeIfAbsent((MigrationInvoker<?>) invoker, _key -> {
            ((MigrationInvoker<?>) invoker).setMigrationRuleListener(this);
            return new MigrationRuleHandler<>((MigrationInvoker<?>) invoker, consumerUrl);
        });

        // 该方法在有大量Reference场景下会调用多次yaml反序列化操作
        rule = parseRule(rawRule);

        migrationRuleHandler.doMigrate(rule);
    }
```
if (this.configuration != null) {
            logger.info("Listening for migration rules on dataId " + RULE_KEY + ", group " + DUBBO_SERVICEDISCOVERY_MIGRATION);
            configuration.addListener(RULE_KEY, DUBBO_SERVICEDISCOVERY_MIGRATION, this);
            String rawRule = configuration.getConfig(RULE_KEY, DUBBO_SERVICEDISCOVERY_MIGRATION);
            if (StringUtils.isEmpty(rawRule)) {
                rawRule = INIT;
            }
            this.rawRule = rawRule;
        } else {
            if (logger.isWarnEnabled()) {
                logger.warn("Using default configuration rule because config center is not configured!");
            }
            rawRule = INIT;
        }
        String localRawRule = ApplicationModel.getEnvironment().getLocalMigrationRule();
        if (!StringUtils.isEmpty(localRawRule)) {
            Executors.newSingleThreadScheduledExecutor(new NamedThreadFactory("DubboMigrationRuleDelayWorker", true))
                .schedule(() -> {
                    if (this.rawRule.equals(INIT)) {
                        this.process(new ConfigChangedEvent(null, null, localRawRule));
                    }
                }, getDelay(), TimeUnit.MILLISECONDS);
        }
    }
    private int getDelay() {
        int delay = 60000;
        String delayStr = ConfigurationUtils.getProperty(MIGRATION_DELAY_KEY);
        if (StringUtils.isEmpty(delayStr)) {
            return delay;
        }