Apache Flink error java.lang.ClassNotFoundException

Question

Can anybody help me with the following error? I think there are some problems with versions, but I have no idea on how to fix it. I'm trying to run Apache Flink, I use Kafka topic as an input to this I'm getting the following error when trying to run Flink:

Error:

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/flink/util/Preconditions at org.apache.flink.cep.pattern.Pattern.where(Pattern.java:130) at hes.cs63.CEPMonitor.CEPMonitoring.main(CEPMonitoring.java:55) Caused by: java.lang.ClassNotFoundException: org.apache.flink.util.Preconditions at java.net.URLClassLoader.findClass(URLClassLoader.java:381) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ... 2 more

pom.xml:

<dependencies>
    <dependency>
        <groupId>org.apache.flink</groupId>
        <artifactId>flink-streaming-java_2.10</artifactId>
        <version>1.0.2</version>
    </dependency>
    <dependency>
        <groupId>org.apache.flink</groupId>
        <artifactId>flink-cep_2.11</artifactId>
        <version>1.3.2</version>
    </dependency>
    <dependency>
        <groupId>org.apache.kafka</groupId>
        <artifactId>kafka-clients</artifactId>
        <version>0.9.0.1</version>
    </dependency>
    <dependency>
        <groupId>org.apache.flink</groupId>
        <artifactId>flink-connector-kafka-0.9_2.10</artifactId>
        <version>1.0.2</version>
    </dependency>
    <dependency>
        <groupId>com.google.code.gson</groupId>
        <artifactId>gson</artifactId>
        <version>2.6.2</version>
    </dependency>
</dependencies>

From InteliJ IDEA with there parameters: '--topic CEP --bootstrap.servers localhost:9092 --group.id SBG --out file:///home/user/' — David
– David, Commented Nov 21, 2017 at 0:41
As you mentioned earlier, it might be related to conflicting dependencies. Can you run the following command mvn dependency:tree -Dverbose to verify if there are any conflicts. — Srikanth Anusuri
– Srikanth Anusuri, Commented Nov 21, 2017 at 1:03

David Anderson · Accepted Answer · 2017-11-21 10:06:44Z

1

You should update the flink-streaming-java_2.10 and flink-connector-kafka-0.9_2.10 dependencies to version 1.3.2, to the match the version of the CEP library. And be consistent about scala versions -- pick either 2.10 or 2.11 for all dependencies.

CEP is much improved since 1.0.2, so I wouldn't recommend downgrading CEP.

edited Nov 21, 2017 at 10:06

answered Nov 21, 2017 at 9:50

David Anderson

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gjoranv · Accepted Answer · 2017-11-21 21:51:26Z

Your dependency flink-cep_2.11 uses scala 2.11 and flink 1.3.2, while flink-streaming-java_2.10 and flink-connector-kafka-0.9_2.10 use scala 2.10 and flink 1.0.2.

You can downgrade flink-cep to get scala 2.10 and flink 1.0.2 for all deps:

<dependency>
    <groupId>org.apache.flink</groupId>
    <artifactId>flink-cep_2.10</artifactId>
    <version>1.0.2</version>
</dependency>

This will give the minimal diff in your pom.xml, but you'll be using libraries from early 2016. Hence, a better solution is to upgrade the two other deps to version 1.3.2 and scala 2.11:

<dependencies>
  <dependency>
    <groupId>org.apache.flink</groupId>
    <artifactId>flink-streaming-java_2.11</artifactId>
    <version>1.3.2</version>
  </dependency>
  <dependency>
    <groupId>org.apache.flink</groupId>
    <artifactId>flink-cep_2.11</artifactId>
    <version>1.3.2</version>
  </dependency>
  <dependency>
    <groupId>org.apache.kafka</groupId>
    <artifactId>kafka-clients</artifactId>
    <version>0.9.0.1</version>
  </dependency>
  <dependency>
    <groupId>org.apache.flink</groupId>
    <artifactId>flink-connector-kafka-0.9_2.11</artifactId>
    <version>1.3.2</version>
  </dependency>
  <dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.6.2</version>
  </dependency>
</dependencies>

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