Jar file is not executed in with Dockerfile - scala

Question

I am building docker image of my application. And I would like to run jar file when I run my docker image. However, I get this error:
Could not find or load main class
Main class is set in the manifest file of the jar file. If I run my jar file from terminal or bash script it works fine. So this error is only observed while running docker:
docker run -v my-volume:/workdir container-name
Are there some configurations missing in my Dockerfile or jar file should be copied/added?
Here is my Dockerfile:
FROM java:8
ENV SCALA_VERSION 2.11.8
ENV SBT_VERSION 1.1.1
ENV SPARK_VERSION 2.2.0
ENV SPARK_DIST spark-$SPARK_VERSION-bin-hadoop2.6
ENV SPARK_ARCH $SPARK_DIST.tgz
WORKDIR /opt
# Install Scala
RUN \
cd /root && \
curl -o scala-$SCALA_VERSION.tgz http://downloads.typesafe.com/scala/$SCALA_VERSION/scala-$SCALA_VERSION.tgz && \
tar -xf scala-$SCALA_VERSION.tgz && \
rm scala-$SCALA_VERSION.tgz && \
echo >> /root/.bashrc && \
echo 'export PATH=~/scala-$SCALA_VERSION/bin:$PATH' >> /root/.bashrc
# Install SBT
RUN \
curl -L -o sbt-$SBT_VERSION.deb https://dl.bintray.com/sbt/debian/sbt-$SBT_VERSION.deb && \
dpkg -i sbt-$SBT_VERSION.deb && \
rm sbt-$SBT_VERSION.deb
# Install Spark
RUN \
cd /opt && \
curl -o $SPARK_ARCH http://d3kbcqa49mib13.cloudfront.net/$SPARK_ARCH && \
tar xvfz $SPARK_ARCH && \
rm $SPARK_ARCH && \
echo 'export PATH=$SPARK_DIST/bin:$PATH' >> /root/.bashrc
EXPOSE 9851 9852 4040 9092 9200 9300 5601 7474 7687 7473
VOLUME /workdir
CMD java -cp "target/scala-2.11/demo_consumer.jar" consumer.SparkConsumer

Answer 1

I believe this is because the command you execute from the Docker container are not in the right folder. You could try to execute the commands from the workdir:
docker run -v my-volume:/workdir -w /workdir container_name
If that does not work, you could inspect what's inside the container. Either with a ls:
docker run -v my-volume:/workdir -w /workdir container_name bash -c 'ls -lah'
Or by accessing its bash session:
docker run -v my-volume:/workdir -w /workdir container_name bash
p.s: if bash does not work, try with sh.