【Azure Spring Cloud】Java Spring Cloud 應用部署到Azure上後，發現大量的 java.lang.NullPointerException: null at io.lettuce.core.protocol.CommandHandler.writeSingleCommand(CommandHandler.java:426) at ... 異常

Azure Spring Cloud 是什麼？

借助 Azure Spring Cloud，可以輕松地将 Spring Boot 微服務應用程式部署到 Azure，不需更改任何代碼。 該服務管理 Spring Cloud 應用程式的基礎結構，是以開發人員可以專注于其代碼。 Azure Spring Cloud 可以通過以下方法提供生命周期管理：綜合性監視和診斷、配置管理、服務發現、CI/CD 內建、藍綠部署等。 Link: https://docs.azure.cn/zh-cn/spring-cloud/overview

問題描述

在本地運作正常的Spring Cloud項目，部署在Azure Spring Cloud服務後，在日志中，發現大量的null pointer exception

java.lang.NullPointerException: null 
at io.lettuce.core.protocol.CommandHandler.writeSingleCommand(CommandHandler.java:426) 
at io.lettuce.core.protocol.CommandHandler.write(CommandHandler.java:378) 
at io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:717) 
at io.netty.channel.AbstractChannelHandlerContext.invokeWriteAndFlush(AbstractChannelHandlerContext.java:764) 
at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:790) 
at io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:758) 
at io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:808) 
at io.netty.channel.DefaultChannelPipeline.writeAndFlush(DefaultChannelPipeline.java:1025) 
at io.netty.channel.AbstractChannel.writeAndFlush(AbstractChannel.java:294) 
at io.lettuce.core.protocol.DefaultEndpoint.channelWriteAndFlush(DefaultEndpoint.java:392) 
at io.lettuce.core.protocol.DefaultEndpoint.writeToChannelAndFlush(DefaultEndpoint.java:332) 
at io.lettuce.core.protocol.DefaultEndpoint.write(DefaultEndpoint.java:162) 
at io.lettuce.core.protocol.DefaultEndpoint$RetryListener.requeueCommands(DefaultEndpoint.java:1002) 
at io.lettuce.core.protocol.DefaultEndpoint$RetryListener.lambda$potentiallyRequeueCommands$0(DefaultEndpoint.java:989) 
at io.netty.util.concurrent.PromiseTask.runTask(PromiseTask.java:98) 
at io.netty.util.concurrent.PromiseTask.run(PromiseTask.java:106) 
at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:164)       

問題解決

根據在Github和stackoverflow中檢視到的資訊，判斷這是一個和sleuth版本相關，在新的版本中，預設啟用了redis配置。通過 spring.sleuth.redis.enabled=false 來關閉預設配置， Null Point Exception問題解決。

StackOverflow ：

I use spring-session-data-redis to manage sessions. It will get session data from redis before every request. But it throws a NPE when get session from redis. And if I remove spring-cloud-starter-sleuth dependency, it won't happend.

springboot version: 2.3.8.RELEASE

springcloud version: Hoxton.SR10

Here is the exception information:

java.lang.NullPointerException: null
    at io.lettuce.core.protocol.CommandHandler.writeSingleCommand(CommandHandler.java:426) ~[lettuce-core-5.3.6.RELEASE.jar:5.3.6.RELEASE]
    at io.lettuce.core.protocol.CommandHandler.write(CommandHandler.java:378) ~[lettuce-core-5.3.6.RELEASE.jar:5.3.6.RELEASE]
    at io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:717) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.channel.AbstractChannelHandlerContext.invokeWriteAndFlush(AbstractChannelHandlerContext.java:764) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:790) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:758) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:808) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.channel.DefaultChannelPipeline.writeAndFlush(DefaultChannelPipeline.java:1025) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.channel.AbstractChannel.writeAndFlush(AbstractChannel.java:294) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
    at io.lettuce.core.protocol.DefaultEndpoint.channelWriteAndFlush(DefaultEndpoint.java:392) ~[lettuce-core-5.3.6.RELEASE.jar:5.3.6.RELEASE]
    at io.lettuce.core.protocol.DefaultEndpoint.writeToChannelAndFlush(DefaultEndpoint.java:332) ~[lettuce-core-5.3.6.RELEASE.jar:5.3.6.RELEASE]
    at io.lettuce.core.protocol.DefaultEndpoint.write(DefaultEndpoint.java:162) ~[lettuce-core-5.3.6.RELEASE.jar:5.3.6.RELEASE]
    at io.lettuce.core.protocol.DefaultEndpoint$RetryListener.requeueCommands(DefaultEndpoint.java:1002) ~[lettuce-core-5.3.6.RELEASE.jar:5.3.6.RELEASE]
    at io.lettuce.core.protocol.DefaultEndpoint$RetryListener.lambda$potentiallyRequeueCommands$0(DefaultEndpoint.java:989) ~[lettuce-core-5.3.6.RELEASE.jar:5.3.6.RELEASE]
    at io.netty.util.concurrent.PromiseTask.runTask(PromiseTask.java:98) [netty-common-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.util.concurrent.PromiseTask.run(PromiseTask.java:106) [netty-common-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.util.concurrent.AbstractEventExecutor.safeExecute$$$capture(AbstractEventExecutor.java:164) [netty-common-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java) [netty-common-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:472) [netty-common-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:497) [netty-transport-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989) [netty-common-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) [netty-common-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) [netty-common-4.1.58.Final.jar:4.1.58.Final]
      

Answer：

I have resolved this problem. It seems that there are some bugs in this sleuth version. I compare this new version with the old version we used, the old version sleuth doesn't intercept the redis request, but this new version will. If I disable this configuration, it won't happen. I use 'spring.sleuth.redis.enabled=false' to disable redis sleuth configuration. It is enabled by default. 

GitHub: https://githubmemory.com/repo/spring-cloud/spring-cloud-sleuth/issues/1992

當在複雜的環境中面臨問題，格物之道需：濁而靜之徐清，安以動之徐生。 雲中，恰是如此!