GitHub user i7pacheco edited a discussion: PLC4X Kafka Connect 0.12.0 –
NoClassDefFoundError for PlcDriverManager in Docker
Hello everyone,
I’m integrating PLC4X with Kafka Connect (version 0.12.0, I've tried 0.8.0 and
0.10.0 too) inside a Docker container to collect data from an S7 PLC. I’m
running into persistent issues with plugin dependencies and classpath
resolution, and would appreciate guidance from the community.
### **Environment**
- **Kafka Connect:** 3.6.x (Confluent Platform, Dockerized)
- **PLC4X Kafka Connector:** 0.12.0
- **Docker**: Custom image, plugins in `/usr/share/java/plc4x/`
- **OS:** Linux (containerized)
- **Goal:** Connect to S7 PLC and publish data to a Kafka topic
### **What I’ve Done**
- Placed all PLC4X JARs (including `plc4j-apache-kafka-0.12.0.jar`,
`plc4j-api-0.12.0.jar`, `plc4j-spi-0.12.0.jar`, `plc4j-driver-s7-0.12.0.jar`,
and other dependencies) in `/usr/share/java/plc4x/`.
- Set `plugin.path` to include `/usr/share/java/`.
- Verified that `org.apache.plc4x.kafka.Plc4xSourceConnector` appears in the
`/connector-plugins/` REST API output.
- Used the advanced connector configuration format.
### **Problem**
When I POST the connector config, I get a 500 error and the logs show:
```
Caused by: java.lang.NoClassDefFoundError:
org/apache/plc4x/java/PlcDriverManager
at org.apache.plc4x.kafka.config.Source.validate(Source.java:76)
...
Caused by: java.lang.ClassNotFoundException:
org.apache.plc4x.java.PlcDriverManager
at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:476)
...
```
I also tried running `jdeps -summary plc4j-apache-kafka-0.12.0.jar` in the
container and saw:
```
plc4j-apache-kafka-0.12.0.jar -> java.base
plc4j-apache-kafka-0.12.0.jar -> not found
```
### **What I’ve Checked**
- All JARs are present in `/usr/share/java/plc4x/` (listing below).
- No duplicate or mismatched versions.
- Restarted Kafka Connect after every change.
- The connector config uses the advanced format and references the correct
classes.
### **Questions**
1. **What could cause NoClassDefFoundError for `PlcDriverManager` even when
`plc4j-api-0.12.0.jar` is present?**
2. **Are there any known issues with PLC4X classloading in Dockerized Kafka
Connect?**
3. **Is there a definitive list of all dependencies (including transitive ones)
for the PLC4X Kafka connector 0.12.0?**
4. **Are there best practices for structuring the plugin path or for
troubleshooting classpath issues in this scenario?**
5. **Any tips for debugging further or confirming exactly which JAR is missing
or not being loaded?**
### **Directory Listing**
Here’s what’s in `/usr/share/java/plc4x/`:
```
plc4j-apache-kafka-0.12.0.jar
plc4j-api-0.12.0.jar
plc4j-spi-0.12.0.jar
plc4j-driver-s7-0.12.0.jar
commons-codec-*.jar
commons-lang3-*.jar
jackson-*.jar
bcprov-*.jar
bcpkix-*.jar
bcutil-*.jar
...
```
### **Connector Config (Snippet)**
```json
{
"name": "plc4x-source",
"config": {
"connector.class": "org.apache.plc4x.kafka.Plc4xSourceConnector",
"tasks.max": "1",
"default-topic": "sensor_data",
"sources": "plc1",
"sources.plc1.connectionString": "s7://192.168.1.100/0/1",
"sources.plc1.jobReferences": "jobA",
"sources.plc1.jobReferences.jobA": "sensor_data",
"jobs": "jobA",
"jobs.jobA.interval": "1000",
"jobs.jobA.fields": "tag1,tag2",
"jobs.jobA.fields.tag1": "%DB501.DBD1:REAL",
"jobs.jobA.fields.tag2": "%DB501.DBD5:REAL"
}
}
```
The **docker compose file** is:
```yml
services:
zookeeper:
image: confluentinc/cp-zookeeper:7.6.0
container_name: zookeeper
environment:
ZOOKEEPER_CLIENT_PORT: 2181
ZOOKEEPER_TICK_TIME: 2000
ports:
- "2181:2181"
kafka:
image: confluentinc/cp-kafka:7.6.0
container_name: kafka
depends_on:
- zookeeper
ports:
- "9092:9092"
- "9093:9093"
environment:
KAFKA_BROKER_ID: 1
KAFKA_ZOOKEEPER_CONNECT: zookeeper:2181
KAFKA_LISTENERS: PLAINTEXT://0.0.0.0:9092,PLAINTEXT_HOST://0.0.0.0:9093
KAFKA_ADVERTISED_LISTENERS:
PLAINTEXT://kafka:9092,PLAINTEXT_HOST://localhost:9093
KAFKA_LISTENER_SECURITY_PROTOCOL_MAP:
PLAINTEXT:PLAINTEXT,PLAINTEXT_HOST:PLAINTEXT
KAFKA_INTER_BROKER_LISTENER_NAME: PLAINTEXT
KAFKA_AUTO_CREATE_TOPICS_ENABLE: "true"
KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
volumes:
- ./kafka_data:/var/lib/kafka/data
kafka-connect:
image: confluentinc/cp-kafka-connect:7.6.0
container_name: kafka-connect
depends_on:
- kafka
environment:
CONNECT_BOOTSTRAP_SERVERS: kafka:9092
CONNECT_GROUP_ID: connect-cluster
CONNECT_CONFIG_STORAGE_TOPIC: connect-configs
CONNECT_OFFSET_STORAGE_TOPIC: connect-offsets
CONNECT_STATUS_STORAGE_TOPIC: connect-status
CONNECT_KEY_CONVERTER: org.apache.kafka.connect.json.JsonConverter
CONNECT_VALUE_CONVERTER: org.apache.kafka.connect.json.JsonConverter
CONNECT_PLUGIN_PATH:
"/usr/share/java,/usr/share/confluent-hub-components,/usr/share/java/plc4x"
CONNECT_REST_ADVERTISED_HOST_NAME: kafka-connect
# Only working with a single node
CONNECT_OFFSET_STORAGE_REPLICATION_FACTOR: 1
CONNECT_CONFIG_STORAGE_REPLICATION_FACTOR: 1
CONNECT_STATUS_STORAGE_REPLICATION_FACTOR: 1
ports:
- "8083:8083"
volumes:
- ./plugins:/plugins
- ./timescale-sink.json:/data/timescale-sink.json
```
I prepared some series of bat files that help me set up the connectors:
**Installing the PLC4X plugin:**
```bash
@echo off
REM === CONFIGURATION ===
set "PLC4X_VERSION=0.12.0"
set "CONNECT_CONTAINER=kafka-connect"
REM === Step 1: Download the PLC4X Kafka Connect standalone ZIP ===
echo Downloading PLC4X Kafka Connect standalone ZIP...
curl -L -o plc4x-kafka.zip
https://repo1.maven.org/maven2/org/apache/plc4x/plc4j-apache-kafka/%PLC4X_VERSION%/plc4j-apache-kafka-%PLC4X_VERSION%-standalone.zip
REM === Step 2: Extract the ZIP using PowerShell ===
echo Extracting PLC4X connector files...
powershell -Command "Expand-Archive -Path 'plc4x-kafka.zip' -DestinationPath
'plc4x-kafka' -Force"
REM === Step 3: Copy the connector JAR(s) into the Kafka Connect container ===
echo Copying connector JARs into the container...
docker exec %CONNECT_CONTAINER% mkdir -p /usr/share/java/plc4x
@REM for %%f in (plc4x-kafka\*.jar) do docker cp %%f
%CONNECT_CONTAINER%:/usr/share/java/plc4x/
@REM for /r plc4x-kafka %%f in (*.jar) do docker cp "%%f"
%CONNECT_CONTAINER%:/usr/share/java/
for /r plc4x-kafka %%f in (*.jar) do (
echo Copying "%%f" to %CONNECT_CONTAINER%:/usr/share/java/plc4x/
docker cp "%%f" %CONNECT_CONTAINER%:/usr/share/java/plc4x/
if errorlevel 1 echo ERROR copying "%%f"
)
REM === Step 4: Restart the Kafka Connect container ===
echo Restarting Kafka Connect container...
docker restart %CONNECT_CONTAINER%
REM === Step 5: Wait for Kafka Connect to restart (adjust time if needed) ===
echo Waiting for Kafka Connect to restart...
timeout /t 30
REM === Step 6: Verify the connector is available ===
echo Checking available connector plugins:
docker exec %CONNECT_CONTAINER% curl http://localhost:8083/connector-plugins
REM === Step 7: Clean up temporary files ===
echo Cleaning up...
rmdir /s /q plc4x-kafka
del plc4x-kafka.zip
echo.
echo Done! If you see 'org.apache.plc4x.kafka.Plc4xSourceConnector' above,
installation succeeded.
pause
```
**Registering the plugin:**
```bash
@echo off
REM === CONFIGURATION ===
set "PLC4X_VERSION=0.12.0"
set "CONNECT_CONTAINER=kafka-connect"
echo Registering PLC4X connector...
@REM docker cp plc4x-s7-source.json kafka-connect:/data/
@REM docker exec kafka-connect curl -X POST -H "Content-Type: application/json"
--data @/data/plc4x-s7-source.json http://localhost:8083/connectors
docker cp plc4x-s7-source.json %CONNECT_CONTAINER%:/tmp/plc4x-s7-source.json
docker exec %CONNECT_CONTAINER% curl -X POST -H "Content-Type:
application/json" --data @/tmp/plc4x-s7-source.json
http://localhost:8083/connectors
echo Registered connectors:
docker exec %CONNECT_CONTAINER% curl -s http://localhost:8083/connectors
```
**Updating the plugin:**
```bash
@echo off
REM === CONFIGURATION ===
set "CONNECT_CONTAINER=kafka-connect"
set "CONNECTOR_NAME=plc4x-source"
set "CONFIGURATION_FILENAME=plc4x-s7-source"
set "FULL_JSON=%CONFIGURATION_FILENAME%.json"
set "CONFIG_ONLY_JSON=%CONFIGURATION_FILENAME%-config-only.json"
REM === Extract only the config object using PowerShell ===
echo Extracting config section from %FULL_JSON%...
powershell -Command "Get-Content %FULL_JSON% | ConvertFrom-Json | Select-Object
-ExpandProperty config | ConvertTo-Json | Set-Content %CONFIG_ONLY_JSON%"
REM === Copy the config-only JSON to the container ===
echo Copying config-only JSON to container...
docker cp %CONFIG_ONLY_JSON% %CONNECT_CONTAINER%:/tmp/%CONFIG_ONLY_JSON%
REM === Update the connector using PUT ===
echo Updating PLC4X connector...
docker exec %CONNECT_CONTAINER% curl -X PUT -H "Content-Type: application/json"
--data @/tmp/%CONFIG_ONLY_JSON%
http://localhost:8083/connectors/%CONNECTOR_NAME%/config
REM === Show registered connectors ===
echo Registered connectors:
docker exec %CONNECT_CONTAINER% curl -s http://localhost:8083/connectors
REM === Show connector configuration ===
echo Current configuration of %CONNECTOR_NAME%:
docker exec %CONNECT_CONTAINER% curl -s
http://localhost:8083/connectors/%CONNECTOR_NAME%/config
REM === Optional: Clean up temp file ===
del %CONFIG_ONLY_JSON%
```
### **Any help or troubleshooting suggestions would be greatly appreciated!**
Thanks in advance.
GitHub link: https://github.com/apache/plc4x/discussions/2164
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