使用Scala 2.12运行Flink 1.9.0并尝试使用flink-connector-kafka将数据发布到Kafka，在本地调试时一切正常。一旦我将作业提交到集群，我在运行时会得到以下java.lang.LinkageError，它无法运行作业：
java.lang.LinkageError: loader constraint violation: loader (instance of org/apache/flink/util/ChildFirstClassLoader) previously initiated loading for a different type with name "org/apache/kafka/clients/producer/ProducerRecord"
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
at org.apache.flink.util.ChildFirstClassLoader.loadClass(ChildFirstClassLoader.java:66)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
at java.lang.Class.getDeclaredMethod(Class.java:2128)
at java.io.ObjectStreamClass.getPrivateMethod(ObjectStreamClass.java:1629)
at java.io.ObjectStreamClass.access$1700(ObjectStreamClass.java:79)
at java.io.ObjectStreamClass$3.run(ObjectStreamClass.java:520)
at java.io.ObjectStreamClass$3.run(ObjectStreamClass.java:494)
at java.security.AccessController.doPrivileged(Native Method)
at java.io.ObjectStreamClass.<init>(ObjectStreamClass.java:494)
at java.io.ObjectStreamClass.lookup(ObjectStreamClass.java:391)
at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:681)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1885)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1751)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2042)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2287)
at java.io.ObjectInputStream.defaultReadObject(ObjectInputStream.java:561)
at org.apache.flink.streaming.connectors.kafka.FlinkKafkaProducer.readObject(FlinkKafkaProducer.java:1202)
at sun.reflect.GeneratedMethodAccessor358.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1170)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2178)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2069)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2287)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2211)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2069)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2287)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2211)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2069)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:431)
at org.apache.flink.util.InstantiationUtil.deserializeObject(InstantiationUtil.java:576)
at org.apache.flink.util.InstantiationUtil.deserializeObject(InstantiationUtil.java:562)
at org.apache.flink.util.InstantiationUtil.deserializeObject(InstantiationUtil.java:550)
at org.apache.flink.util.InstantiationUtil.readObjectFromConfig(InstantiationUtil.java:511)
at org.apache.flink.streaming.api.graph.StreamConfig.getStreamOperatorFactory(StreamConfig.java:235)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createChainedOperator(OperatorChain.java:427)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createOutputCollector(OperatorChain.java:354)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createChainedOperator(OperatorChain.java:418)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createOutputCollector(OperatorChain.java:354)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createChainedOperator(OperatorChain.java:418)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createOutputCollector(OperatorChain.java:354)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createChainedOperator(OperatorChain.java:418)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createOutputCollector(OperatorChain.java:354)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createChainedOperator(OperatorChain.java:418)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createOutputCollector(OperatorChain.java:354)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createChainedOperator(OperatorChain.java:418)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createOutputCollector(OperatorChain.java:354)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createChainedOperator(OperatorChain.java:418)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createOutputCollector(OperatorChain.java:354)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createChainedOperator(OperatorChain.java:418)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.createOutputCollector(OperatorChain.java:354)
at org.apache.flink.streaming.runtime.tasks.OperatorChain.<init>(OperatorChain.java:144)
at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:370)
at org.apache.flink.runtime.taskmanager.Task.doRun(Task.java:705)
at org.apache.flink.runtime.taskmanager.Task.run(Task.java:530)
at java.lang.Thread.run(Thread.java:748)
当使用-verbose:class查看加载的类时，我看到该类被加载了好几次：
taskmanager [Loaded org.apache.kafka.clients.producer.ProducerRecord from file:/tmp/blobStore-8cf95113-e767-4073-9b1b-e579d46c0283/job_f0c3db8b84dd38e83f92ecf1bc61b698/blob_p-c327eb8f4333a638b2b7049049368f23254aeb9c-03045e6d6a9c8f3c7dacdded8cb97d6e]
taskmanager [Loaded org.apache.kafka.clients.producer.ProducerRecord from file:/tmp/blobStore-8cf95113-e767-4073-9b1b-e579d46c0283/job_f0c3db8b84dd38e83f92ecf1bc61b698/blob_p-c327eb8f4333a638b2b7049049368f23254aeb9c-03045e6d6a9c8f3c7dacdded8cb97d6e]
其中类是从我提交给Flink的同一个Uber JAR加载的。此外，加载ProducerRecord时没有多个可传递的依赖项，我的JAR是该依赖项的唯一提供者。
build.sbt:
lazy val flinkVersion = "1.9.0"
libraryDependencies ++= Seq(
"org.apache.flink" %% "flink-table-planner" % flinkVersion,
"org.apache.flink" %% "flink-table-api-scala-bridge" % flinkVersion,
"org.apache.flink" % "flink-s3-fs-hadoop" % flinkVersion,
"org.apache.flink" %% "flink-container" % flinkVersion,
"org.apache.flink" %% "flink-connector-kafka" % flinkVersion,
"org.apache.flink" %% "flink-scala" % flinkVersion % "provided",
"org.apache.flink" %% "flink-streaming-scala" % flinkVersion % "provided",
"org.apache.flink" % "flink-json" % flinkVersion % "provided",
"org.apache.flink" % "flink-avro" % flinkVersion % "provided",
"org.apache.flink" %% "flink-parquet" % flinkVersion % "provided",
"org.apache.flink" %% "flink-runtime-web" % flinkVersion % "provided",
"org.apache.flink" %% "flink-cep" % flinkVersion
)
由于未知原因，如Apache Flink邮件列表中所述，将classloader.resolve-order属性设置为parent-first可以解决此问题。我仍然困惑于为什么它能工作，因为加载该依赖关系的不同版本的子类加载器和父类加载器之间不应该有依赖关系冲突(因为它不是我使用的flink-dist开箱即用的(。
在Flink文档中；调试类加载"；，有一节讲的是这种亲子关系：
在涉及动态类加载的设置中(插件组件，在会话设置中闪烁作业(，通常有两个层次结构ClassLoaders：(1(Java的应用程序类加载器，它具有类路径中的类，以及(2(动态插件/用户代码类加载器。用于从插件或用户代码加载类罐子。动态ClassLoader将应用程序类加载器作为其父母亲
默认情况下，Flink反转类加载顺序，这意味着它会查看首先是动态类加载器，并且只查看父类(应用程序类加载器(如果该类不是加载的代码。
反向类加载的好处是插件和作业可以使用与Flink的核心不同的库版本，这非常当不同版本的库不是可共用的该机制有助于避免常见的依赖关系冲突错误，如IllegalAccessError或NoSuchMethodError。代码的不同部分只是具有类的单独副本(Flink的核心或其依赖项之一可以使用与用户代码或插件代码(。在大多数情况下，这很有效需要来自用户的附加配置。
我还不明白为什么加载ProducerRecord不止一次，或者这是什么"；不同类型的"；在异常消息中指的是(对-verbose:class的结果进行greping仅为ProducerRecord产生单个路径(。