JanusGraph启动ES报错：Unable to determine Elasticsearch server version. Default to FIVE.

问题描述：启动janusgraph连接elasticsearch报错

1360 [main] INFO  org.janusgraph.diskstorage.Backend  - Configuring index [search]
4351 [main] WARN  org.janusgraph.diskstorage.es.rest.RestElasticSearchClient  - Unable to determine Elasticsearch server version. Default to FIVE.
java.net.UnknownHostException: elasticsearch
        at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
        at java.net.InetAddress$2.lookupAllHostAddr(Unknown Source)
        at java.net.InetAddress.getAddressesFromNameService(Unknown Source)
        at java.net.InetAddress.getAllByName0(Unknown Source)
        at java.net.InetAddress.getAllByName(Unknown Source)
        at java.net.InetAddress.getAllByName(Unknown Source)
        at org.apache.http.impl.conn.SystemDefaultDnsResolver.resolve(SystemDefaultDnsResolver.java:45)
        at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager$InternalAddressResolver.resolveRemoteAddress(PoolingNHttpClientConnectionManager.java:609)
        at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager$InternalAddressResolver.resolveRemoteAddress(PoolingNHttpClientConnectionManager.java:580)
        at org.apache.http.nio.pool.AbstractNIOConnPool.processPendingRequest(AbstractNIOConnPool.java:427)
        at org.apache.http.nio.pool.AbstractNIOConnPool.lease(AbstractNIOConnPool.java:276)
        at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager.requestConnection(PoolingNHttpClientConnectionManager.java:266)
        at org.apache.http.impl.nio.client.AbstractClientExchangeHandler.requestConnection(AbstractClientExchangeHandler.java:363)
        at org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl.start(DefaultClientExchangeHandlerImpl.java:125)
        at org.apache.http.impl.nio.client.InternalHttpAsyncClient.execute(InternalHttpAsyncClient.java:141)
        at org.elasticsearch.client.RestClient.performRequestAsync(RestClient.java:344)
        at org.elasticsearch.client.RestClient.performRequestAsync(RestClient.java:326)
        at org.elasticsearch.client.RestClient.performRequest(RestClient.java:219)
        at org.elasticsearch.client.RestClient.performRequest(RestClient.java:192)
        at org.elasticsearch.client.RestClient.performRequest(RestClient.java:154)
        at org.janusgraph.diskstorage.es.rest.RestElasticSearchClient.getMajorVersion(RestElasticSearchClient.java:118)
        at org.janusgraph.diskstorage.es.rest.RestElasticSearchClient.<init>(RestElasticSearchClient.java:101)
        at org.janusgraph.diskstorage.es.rest.RestClientSetup.getElasticSearchClient(RestClientSetup.java:107)
        at org.janusgraph.diskstorage.es.rest.RestClientSetup.connect(RestClientSetup.java:74)
        at org.janusgraph.diskstorage.es.ElasticSearchSetup$1.connect(ElasticSearchSetup.java:50)
        at org.janusgraph.diskstorage.es.ElasticSearchIndex.interfaceConfiguration(ElasticSearchIndex.java:391)
        at org.janusgraph.diskstorage.es.ElasticSearchIndex.<init>(ElasticSearchIndex.java:297)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
        at java.lang.reflect.Constructor.newInstance(Unknown Source)
        at org.janusgraph.util.system.ConfigurationUtil.instantiate(ConfigurationUtil.java:58)
        at org.janusgraph.diskstorage.Backend.getImplementationClass(Backend.java:476)
        at org.janusgraph.diskstorage.Backend.getIndexes(Backend.java:463)
        at org.janusgraph.diskstorage.Backend.<init>(Backend.java:148)
        at org.janusgraph.graphdb.configuration.GraphDatabaseConfiguration.getBackend(GraphDatabaseConfiguration.java:1840)
        at org.janusgraph.graphdb.database.StandardJanusGraph.<init>(StandardJanusGraph.java:138)
        at org.janusgraph.core.JanusGraphFactory.open(JanusGraphFactory.java:160)
        at org.janusgraph.core.JanusGraphFactory.open(JanusGraphFactory.java:131)
        at org.janusgraph.core.JanusGraphFactory.open(JanusGraphFactory.java:111)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at org.apache.tinkerpop.gremlin.structure.util.GraphFactory.open(GraphFactory.java:78)
        at org.apache.tinkerpop.gremlin.structure.util.GraphFactory.open(GraphFactory.java:70)
        at org.apache.tinkerpop.gremlin.structure.util.GraphFactory.open(GraphFactory.java:104)
        at org.apache.tinkerpop.gremlin.server.util.DefaultGraphManager.lambda$new$0(DefaultGraphManager.java:57)
        at java.util.LinkedHashMap$LinkedEntrySet.forEach(Unknown Source)
        at org.apache.tinkerpop.gremlin.server.util.DefaultGraphManager.<init>(DefaultGraphManager.java:55)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
        at java.lang.reflect.Constructor.newInstance(Unknown Source)
        at org.apache.tinkerpop.gremlin.server.util.ServerGremlinExecutor.<init>(ServerGremlinExecutor.java:80)
        at org.apache.tinkerpop.gremlin.server.GremlinServer.<init>(GremlinServer.java:120)
        at org.apache.tinkerpop.gremlin.server.GremlinServer.<init>(GremlinServer.java:84)
        at org.apache.tinkerpop.gremlin.server.GremlinServer.main(GremlinServer.java:343)
4404 [main] WARN  org.apache.tinkerpop.gremlin.server.GremlinServer  - Graph [graph] configured at [conf/gremlin-server/janusgraph-berkeleyje-es-server.properties] could not be instantiated and will not be available in Gremlin Server.  GraphFactory message: GraphFactory could not instantiate this Graph implementation [class org.janusgraph.core.JanusGraphFactory]

解决方法：

找到启动时读取的配置文件conf/gremlin-server/janusgraph-berkeleyje-er-server.properties，修改配置文件中的index.search.hostname。
index.search.hostname=127.0.0.1