@Override
    public void onApplicationEvent(final PluginHandlerEvent event) {
        PluginHandlerEventEnum stateEnums = event.getPluginStateEnums();
        PluginData pluginData = (PluginData) event.getSource();
        switch (stateEnums) {
            case ENABLED:
                onPluginEnabled(pluginData);
                break;
            case DELETE:
            case DISABLED:
                // disable or removed plugin.
                onPluginRemoved(pluginData);
                break;
            case SORTED:
                // copy a new one, or there will be concurrency problems
                this.plugins = sortPlugins(new ArrayList<>(this.plugins));
                break;
            default:
                throw new IllegalStateException("Unexpected value: " + event.getPluginStateEnums());
        }
    }
listen plugin handler event and handle plugin.

@param event sort plugin event
shenyu-web/src/main/java/org/apache/shenyu/web/handler/ShenyuWebHandler.java