1

My aim is to debug this code to see it live as suggested in the tutorial.

My IDE is Visual Studio Code and the language of this example is Java. I am running a Flink Datastream API tutorial.

When I put a breakpoint at any of the line, I get the following error:

Cannot find a class with the main method in the folder 'frauddetection'.

I was hinted towards created a launch.json file and so, this is what I created:

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "type": "java",
            "name": "Debug (Launch) - Current File",
            "request": "launch",
            "mainClass": "FraudDetectionJob"
        }
    ]
}

Even after configuring the above file and specifying the mainClass, I am getting the same error in the debugger terminal:

Error: Could not find or load main class FraudDetectionJob

The code that I am trying to execute is as follows:

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package spendreport;

import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.walkthrough.common.sink.AlertSink;
import org.apache.flink.walkthrough.common.entity.Alert;
import org.apache.flink.walkthrough.common.entity.Transaction;
import org.apache.flink.walkthrough.common.source.TransactionSource;

/**
 * Skeleton code for the datastream walkthrough
 */
public class FraudDetectionJob {
    public static void main(String[] args) throws Exception {
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

        DataStream<Transaction> transactions = env
            .addSource(new TransactionSource())
            .name("transactions");

        DataStream<Alert> alerts = transactions
            .keyBy(Transaction::getAccountId)
            .process(new FraudDetector())
            .name("fraud-detector");

        alerts
            .addSink(new AlertSink())
            .name("send-alerts");

        env.execute("Fraud Detection");
    }
}

How do I debug this file?

Aviral Srivastava
  • 4,058
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  • 81

2 Answers2

1

I believe you are not able to compile and run the application. In your pom.xml, this is causing the issue

<dependency>
    <groupId>org.apache.flink</groupId>
    <artifactId>flink-streaming-java_${scala.binary.version}</artifactId>
    <version>${flink.version}</version>
    <scope>provided</scope>
</dependency>

Change the scope to compile in order to resolve this issue. Also, more technical info here.

-- How I went about finding the issue--

I tried running the example in the tutorial (in Intellij IDEA) and got this error similar to you:

Error: Unable to initialize main class spendreport.FraudDetectionJob
Caused by: java.lang.NoClassDefFoundError: org/apache/flink/streaming/api/functions/source/SourceFunction

On searching further I found this answer which is similar.

Shubham Arora
  • 26
  • 3
0

Reprint:

Seems a bug in eclipse maven importer not work with lifecycle-mapping plugin, to solve your problem temporarily, try to

  1. close vscode and eclipse
  2. delete .project file and .classpath file(if the root folder has)
  3. run mvn eclipse:eclipse at the root folder
  4. open the root folder in vscode, F5 and you will be able to debug

or remove the lifecycle-mapping plugin in pluginManagement->plugins

more detail see in Flink official demo debug will get error :Cannot find a class with the main method

liurundong
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  • 1