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我在ProviderConfig.setDispatcher()里面发现了如下代码：
I found the following code in ProviderConfig.setDispatcher()：

    public void setDispatcher(String dispatcher) {
        checkExtension(Dispatcher.class, Constants.DISPATCHER_KEY, exchanger);
        checkExtension(Dispatcher.class, "dispather", exchanger);
        this.dispatcher = dispatcher;
    }

我不明白为什么需要在这里做这个检查。
I don't understand why this method needs to do this check here.