How to retain exported file in docker image

I am migrating a java standalone maven project in docker. As of now we create a jar file for this maven project and it runs with public static void main method.

java -cp app.jar com.xxx.ExportManager db.properties

After completion of this code it exports a file in its current directory.

Dockerfile

FROM centos:7

RUN yum install -y 
   java-1.8.0-openjdk 
   java-1.8.0-openjdk-devel

ENV JAVA_HOME /usr/lib/jvm/java-1.8.0-openjdk/

ENV echo $JAVA_HOME

RUN  java -version

ARG JAR_FILE=target/manager.jar
ARG JAR_LIB_FILE=target/lib/

WORKDIR /opt/manager/app/

COPY ${JAR_FILE} app.jar

COPY conf/db.properties /opt/manager/app/db.properties

ADD ${JAR_LIB_FILE} lib/

ENTRYPOINT ["java","-jar","app.jar"]

==============================================================================================

Commands:
Building image: docker build -t pc .
Run the main method : docker run -t pc /opt/manager/app/db.properties

After run it’s exporting file inside image (I am sure coz i have checked it through loggers) to /opt/manager/app/. But when i see the contents of image using command

docker run -it –entrypoint sh pc
cd /opt/manager/app

the directory doesn’t have exported file however it contains all other project files.

How to retain the exported file in the image. Please suggest.

PS: I’m new in docker, pls forgive for any mistakes.
Thanks.

Source: Docker Questions