存在 java 类时在运行时出现 ClassNotFoundException

Question

我在向 Flink 运行时提交 JAR 时遇到了一个特殊问题。我有一个 Flink Streaming JAR 可以运行。当我提交 JAR 时，出现以下异常。

org.apache.flink.streaming.runtime.tasks.StreamTaskException: Could not instantiate outputs in order.
    at org.apache.flink.streaming.api.graph.StreamConfig.getOutEdgesInOrder(StreamConfig.java:470)
    at org.apache.flink.streaming.runtime.tasks.StreamTask.createRecordWriters(StreamTask.java:1138)
    at org.apache.flink.streaming.runtime.tasks.StreamTask.createRecordWriterDelegate(StreamTask.java:1122)
    at org.apache.flink.streaming.runtime.tasks.StreamTask.<init>(StreamTask.java:290)
    at org.apache.flink.streaming.runtime.tasks.StreamTask.<init>(StreamTask.java:277)
    at org.apache.flink.streaming.runtime.tasks.SourceStreamTask.<init>(SourceStreamTask.java:73)
    at org.apache.flink.streaming.runtime.tasks.SourceStreamTask.<init>(SourceStreamTask.java:69)
    at sun.reflect.GeneratedConstructorAccessor58.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at org.apache.flink.runtime.taskmanager.Task.loadAndInstantiateInvokable(Task.java:1373)
    at org.apache.flink.runtime.taskmanager.Task.doRun(Task.java:700)
    at org.apache.flink.runtime.taskmanager.Task.run(Task.java:547)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.ClassNotFoundException: com.rdata.watcher.streaming.Selector
    at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
    at org.apache.flink.util.FlinkUserCodeClassLoader.loadClassWithoutExceptionHandling(FlinkUserCodeClassLoader.java:63)
    at org.apache.flink.util.ChildFirstClassLoader.loadClassWithoutExceptionHandling(ChildFirstClassLoader.java:72)
    at org.apache.flink.util.FlinkUserCodeClassLoader.loadClass(FlinkUserCodeClassLoader.java:49)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
    at org.apache.flink.runtime.execution.librarycache.FlinkUserCodeClassLoaders$SafetyNetWrapperClassLoader.loadClass(FlinkUserCodeClassLoaders.java:168)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:348)
    at org.apache.flink.util.InstantiationUtil$ClassLoaderObjectInputStream.resolveClass(InstantiationUtil.java:78)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1986)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1850)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2160)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1667)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2405)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2329)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2187)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1667)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2405)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2329)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2187)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1667)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:503)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:461)
    at java.util.ArrayList.readObject(ArrayList.java:799)
    at sun.reflect.GeneratedMethodAccessor18.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:1184)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2296)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2187)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1667)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:503)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:461)
    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.getOutEdgesInOrder(StreamConfig.java:467)
    ... 13 more

当我展开 JAR 时，我确实看到了异常所涉及的 Java 类。我该如何解决这个问题？任何指针都有帮助！

我尝试将类移动到不同的包中，结果仍然相同。

Answer 1

我能够找出问题所在。显然，当使用 maven-shade-plugin 解决问题时，我使用的是 spring-boot-maven-plugin。

仍然不确定为什么这解决了我的问题。