暴露监听扩展

<!-- 暴露服务监听 -->
<dubbo:service listener="xxx,yyy" />
<!-- 暴露服务缺省监听器 -->
<dubbo:provider listener="xxx,yyy" />

src
 |-main
    |-java
        |-com
            |-xxx
                |-XxxExporterListener.java (实现ExporterListener接口)
    |-resources
        |-META-INF
            |-dubbo
                |-org.apache.dubbo.rpc.ExporterListener (纯文本文件，内容为：xxx=com.xxx.XxxExporterListener)

package com.xxx;
 
import org.apache.dubbo.rpc.ExporterListener;
import org.apache.dubbo.rpc.Exporter;
import org.apache.dubbo.rpc.RpcException;
 
 
public class XxxExporterListener implements ExporterListener {
    public void exported(Exporter<?> exporter) throws RpcException {
        // ...
    }
    public void unexported(Exporter<?> exporter) throws RpcException {
        // ...
    }
}

xxx=com.xxx.XxxExporterListener