12:15:49 WARN  org.janusgraph.diskstorage.es.rest.RestElasticSearchClient 
 - Unable to determine Elasticsearch server version. Default to FIVE.
java.net.ConnectException: Connection refused
    at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
    at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
    at org.apache.http.impl.nio.reactor.DefaultConnectingIOReactor.processEvent(DefaultConnectingIOReactor.java:171)
    at org.apache.http.impl.nio.reactor.DefaultConnectingIOReactor.processEvents(DefaultConnectingIOReactor.java:145)
    at org.apache.http.impl.nio.reactor.AbstractMultiworkerIOReactor.execute(AbstractMultiworkerIOReactor.java:348)
    at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager.execute(PoolingNHttpClientConnectionManager.java:192)
    at org.apache.http.impl.nio.client.CloseableHttpAsyncClientBase$1.run(CloseableHttpAsyncClientBase.java:64)
    at java.lang.Thread.run(Thread.java:748)
 

 原因：

1.es沒有啟動

2.我遇到的：janusgraph-cassandra-es-server.properties 中es的埠配置錯誤，配置檔案中是9201，但es服務配置的是9200。