elasticseach Java API报错的问题

Question

使用elasticsearch 6.6版本的JavaAPI去多次查询数据，jar包放在服务器上运行，先是没有报错，查询几次后再查询，出现了报错。想请教下大家这个问题的原因？
报错结果如下

no modules loaded
loaded plugin [org.elasticsearch.index.reindex.ReindexPlugin]
loaded plugin [org.elasticsearch.join.ParentJoinPlugin]
loaded plugin [org.elasticsearch.percolator.PercolatorPlugin]
loaded plugin [org.elasticsearch.script.mustache.MustachePlugin]
loaded plugin [org.elasticsearch.transport.Netty4Plugin]
Exception in thread "elasticsearch[_client_][generic][T#1]" java.lang.NullPointerException
    at org.elasticsearch.transport.netty4.Netty4Transport.lambda$stopInternal$2(Netty4Transport.java:255)
    at org.elasticsearch.core.internal.io.IOUtils.close(IOUtils.java:103)
    at org.elasticsearch.core.internal.io.IOUtils.close(IOUtils.java:85)
    at org.elasticsearch.common.lease.Releasables.close(Releasables.java:36)
    at org.elasticsearch.common.lease.Releasables.close(Releasables.java:46)
    at org.elasticsearch.common.lease.Releasables.close(Releasables.java:51)
    at org.elasticsearch.transport.netty4.Netty4Transport.stopInternal(Netty4Transport.java:254)
    at org.elasticsearch.transport.TcpTransport.lambda$doStop$11(TcpTransport.java:591)
    at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingRunnable.run(ThreadContext.java:660)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
java.lang.IllegalStateException: failed to create a child event loop
    at io.netty.util.concurrent.MultithreadEventExecutorGroup.<init>(MultithreadEventExecutorGroup.java:88)
    at io.netty.util.concurrent.MultithreadEventExecutorGroup.<init>(MultithreadEventExecutorGroup.java:58)
    at io.netty.util.concurrent.MultithreadEventExecutorGroup.<init>(MultithreadEventExecutorGroup.java:47)
    at io.netty.channel.MultithreadEventLoopGroup.<init>(MultithreadEventLoopGroup.java:58)
    at io.netty.channel.nio.NioEventLoopGroup.<init>(NioEventLoopGroup.java:77)
    at io.netty.channel.nio.NioEventLoopGroup.<init>(NioEventLoopGroup.java:72)
    at io.netty.channel.nio.NioEventLoopGroup.<init>(NioEventLoopGroup.java:59)
    at org.elasticsearch.transport.netty4.Netty4Transport.doStart(Netty4Transport.java:131)
    at org.elasticsearch.common.component.AbstractLifecycleComponent.start(AbstractLifecycleComponent.java:65)
    at org.elasticsearch.transport.TransportService.doStart(TransportService.java:229)
    at org.elasticsearch.common.component.AbstractLifecycleComponent.start(AbstractLifecycleComponent.java:65)
    at org.elasticsearch.client.transport.TransportClient.buildTemplate(TransportClient.java:227)
    at org.elasticsearch.client.transport.TransportClient.<init>(TransportClient.java:288)
    at org.elasticsearch.transport.client.PreBuiltTransportClient.<init>(PreBuiltTransportClient.java:128)
    at org.elasticsearch.transport.client.PreBuiltTransportClient.<init>(PreBuiltTransportClient.java:114)
    at org.elasticsearch.transport.client.PreBuiltTransportClient.<init>(PreBuiltTransportClient.java:104)
    at ClusterManagement.ClusterManagerment.getAllAliases2(ClusterManagerment.java:155)
    at NettyServer.HealthServerHandler.channelRead(HealthServerHandler.java:131)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:373)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:359)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:351)
    at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:373)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:359)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:351)
    at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:435)
    at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:293)
    at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:267)
    at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:250)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:373)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:359)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:351)
    at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1334)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:373)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:359)
    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:926)
    at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:129)
    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:651)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:574)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:488)
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:450)
    at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:873)
    at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:144)
    at java.lang.Thread.run(Thread.java:745)
Caused by: io.netty.channel.ChannelException: failed to open a new selector
    at io.netty.channel.nio.NioEventLoop.openSelector(NioEventLoop.java:157)
    at io.netty.channel.nio.NioEventLoop.<init>(NioEventLoop.java:148)
    at io.netty.channel.nio.NioEventLoopGroup.newChild(NioEventLoopGroup.java:126)
    at io.netty.channel.nio.NioEventLoopGroup.newChild(NioEventLoopGroup.java:36)
    at io.netty.util.concurrent.MultithreadEventExecutorGroup.<init>(MultithreadEventExecutorGroup.java:84)
    ... 43 more
Caused by: java.io.IOException: Too many open files
    at sun.nio.ch.IOUtil.makePipe(Native Method)
    at sun.nio.ch.EPollSelectorImpl.<init>(EPollSelectorImpl.java:65)
    at sun.nio.ch.EPollSelectorProvider.openSelector(EPollSelectorProvider.java:36)
    at io.netty.channel.nio.NioEventLoop.openSelector(NioEventLoop.java:155)
    ... 47 more

Answer 1

java.io.IOException: Too many open files这个错误提示创建了太多连接，比如可能是数据库或es未及时关闭连接，导致内存被耗尽，检查下代码是否有类似es连接的代码。
参考下：https://blog.csdn.net/qq_33581278/article/details/87966154