Docker Build Example

An example of how one can build a docker image from a small java project. The project has resource file in a sub folder which should be copied to the docker image.

The project was created to find a workaround to the Unable to prepare context-error sometimes encountered when building docker images in a OneDrive path.

Build steps

The script docker-build.sh will compile the java project in indicated when starting the script and package it into a jar-file. This application uses files from the /resource-folder. The jar-file and resources are copied to the docker image.

In order to circumvent the Unable to prepare context-error the files which the docker build command needs to access cannot be located in a folder locked by other processes (OneDrive). It seems creating a new folder in OneDrive is enough. If not, I recommend a temporary folder in the home directory (e.g. c:/Users/the_user/).

The build script will, by default, create two temporary folders. One target path ("./TEMP_TARGET") for the java build and one path for the creating docker context ("./DOCKER_BUILD_TEMP/"). The folder paths can be changed when running the script.

!!! NOTE: THE TEMPORARY FOLDERS WILL BE REMOVED AFTER THE SCRIPT IS FINISHED !!!

Running the example

The docker-build.sh script has been run in git-bash/docker quick start terminal on Windows 10.

From the project's root folder run:

$ ./docker-build.sh Main.java
$ docker run java_app

For building a simple application residing in the project root, together with a manifest.txt in the same folder, or:

$ ./docker-build.sh -s ./src -p com.custom_docker_context -m ./src/manifest_w_package.txt Main.java

For a project where the main *.java is located in a sub path as well as the manifest file, omitting -m will have the script look for manifest.txt in the project's root path.

$ ./docker-build.sh -h

Will reveal the options where one can change the name of the application, and thereby the docker image. It is also possible to change the name and/or paths of the temporary folders, manifest file, source path, main package, and the resource path.