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#9428·deeplearning4j

Receiving a NullPointerException when accessing the UI Server

Author: jfarjonaCreated Aug 18, 2021Updated Apr 24, 2025

Issue Description

Getting a Nullpointer Exception from netty/vertx, when trying to access the running UI Server:

java.lang.NullPointerException: cause at io.netty.util.internal.ObjectUtil.checkNotNull(ObjectUtil.java:39) ~[netty-common-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.invokeExceptionCaught(AbstractChannelHandlerContext.java:278) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.DefaultChannelPipeline.fireExceptionCaught(DefaultChannelPipeline.java:907) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.vertx.core.net.impl.VertxHandler.fail(VertxHandler.java:97) ~[vertx-core-3.9.0.jar:3.9.0] at io.vertx.core.net.impl.ConnectionBase.fail(ConnectionBase.java:86) ~[vertx-core-3.9.0.jar:3.9.0] at io.vertx.core.http.impl.Http1xServerConnection.handleError(Http1xServerConnection.java:480) ~[vertx-core-3.9.0.jar:3.9.0] at io.vertx.core.http.impl.Http1xServerConnection.handleMessage(Http1xServerConnection.java:121) ~[vertx-core-3.9.0.jar:3.9.0] at io.vertx.core.impl.ContextImpl.executeTask(ContextImpl.java:369) ~[vertx-core-3.9.0.jar:3.9.0] at io.vertx.core.impl.EventLoopContext.execute(EventLoopContext.java:43) ~[vertx-core-3.9.0.jar:3.9.0] at io.vertx.core.impl.ContextImpl.executeFromIO(ContextImpl.java:232) ~[vertx-core-3.9.0.jar:3.9.0] at io.vertx.core.net.impl.VertxHandler.channelRead(VertxHandler.java:173) ~[vertx-core-3.9.0.jar:3.9.0] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.ChannelInboundHandlerAdapter.channelRead(ChannelInboundHandlerAdapter.java:93) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.handler.codec.http.websocketx.extensions.WebSocketServerExtensionHandler.channelRead(WebSocketServerExtensionHandler.java:99) ~[netty-codec-http-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.vertx.core.http.impl.Http1xUpgradeToH2CHandler.channelRead(Http1xUpgradeToH2CHandler.java:109) ~[vertx-core-3.9.0.jar:3.9.0] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:324) ~[netty-codec-4.1.66.Final.jar:4.1.66.Final] at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:296) ~[netty-codec-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.vertx.core.http.impl.Http1xOrH2CHandler.end(Http1xOrH2CHandler.java:61) ~[vertx-core-3.9.0.jar:3.9.0] at io.vertx.core.http.impl.Http1xOrH2CHandler.channelRead(Http1xOrH2CHandler.java:38) ~[vertx-core-3.9.0.jar:3.9.0] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:719) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:655) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:581) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final] at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:986) ~[netty-common-4.1.66.Final.jar:4.1.66.Final] at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[netty-common-4.1.66.Final.jar:4.1.66.Final] at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) ~[netty-common-4.1.66.Final.jar:4.1.66.Final] at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na] It seems to be an Exception raised by Vertx on line 

io.vertx.core.impl.ContextImpl.executeTask(ContextImpl.java:369)

I think it may be a problem on the websocket handler, which is throwing a Nullpointer exception. The code in Vertx, is:

try {
      setContext(current, this);
      hTask.handle(arg);
      return true;
    } catch (Throwable t) {
      reportException(t);
      return false;
    } finally {

Which means that hTask is null, or somewhere inside the execution of hTask a Nullpointer Exception takes place. I would assume that hTask is responding to websocket requests, see the trace:

at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final]
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final]
	at io.netty.channel.ChannelInboundHandlerAdapter.channelRead(ChannelInboundHandlerAdapter.java:93) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final]
-->	at io.netty.handler.codec.http.websocketx.extensions.WebSocketServerExtensionHandler.channelRead(WebSocketServerExtensionHandler.java:99) ~[netty-codec-http-4.1.66.Final.jar:4.1.66.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.66.Final.jar:4.1.66.Final]

My guess is that somewhere (I don't know the DL4J UIServer inner workings) in the websocket task implementation a null pointer is happening, or, hTask is null (perhaps failed to set the task at initialization?). Or perhaps I am missing a class in my dependencies that initializes the websocket task and sets it to null because it doesn't find the class... I don't see any ClassNotFoundException in the logs or stdout.

My code:

public NetRunner() { super(); // Set the tunning UI uiServer = UIServer.getInstance(); statsStorage = new InMemoryStatsStorage(); uiServer.attach(statsStorage);

int listenerFrequency = 1;

listener = new StatsListener(statsStorage, listenerFrequency);

}

... MultiLayerNetwork net = new MultiLayerNetwork(conf);

net.setListeners(listener); net.init();

...

My dependencies:

<dependencies> <dependency> <groupId>com.google.guava</groupId> <artifactId>guava</artifactId> <version>30.1.1-jre</version> </dependency> <dependency> <groupId>nz.ac.waikato.cms.weka</groupId> <artifactId>weka-dev</artifactId> <version>3.9.5</version> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-math3</artifactId> <version>3.6.1</version> </dependency> <dependency> <groupId>org.deeplearning4j</groupId> <artifactId>deeplearning4j-core</artifactId> <version>1.0.0-M1.1</version> </dependency> <dependency> <groupId>org.deeplearning4j</groupId> <artifactId>deeplearning4j-ui</artifactId> <version>1.0.0-M1.1</version> <exclusions> <exclusion> <groupId>com.google.guava</groupId> <artifactId>guava</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.nd4j</groupId> <artifactId>nd4j-api</artifactId> <version>1.0.0-M1.1</version> </dependency> <dependency> <groupId>org.nd4j</groupId> <artifactId>nd4j-native-platform</artifactId> <version>1.0.0-M1.1</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>log4j-over-slf4j</artifactId> <version>1.7.32</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> <version>1.7.32</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-configuration-processor</artifactId> <optional>true</optional> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> <exclusions> <exclusion> <groupId>org.junit.vintage</groupId> <artifactId>junit-vintage-engine</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web-services</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-webflux</artifactId> </dependency> <dependency> <groupId>org.springframework.security</groupId> <artifactId>spring-security-crypto</artifactId> </dependency> <dependency> <groupId>tech.tablesaw</groupId> <artifactId>tablesaw-core</artifactId> <version>0.38.3</version> <exclusions> <exclusion> <groupId>com.google.guava</groupId> <artifactId>guava</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>tech.tablesaw</groupId> <artifactId>tablesaw-excel</artifactId> <version>0.38.3</version> </dependency> <dependency> <groupId>tech.tablesaw</groupId> <artifactId>tablesaw-jsplot</artifactId> <version>0.38.3</version> </dependency> </dependencies> More info: see https://community.konduit.ai/t/null-pointer-when-running-the-uiserver/1570

Source: deeplearning4j/deeplearning4j

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