private void addPropertiesFromFile(String envPropsFile, Properties envProps) {
        // External properties override internally specified properties
        try {
            FileReader reader = new FileReader(envPropsFile);
            envProps.load(reader);
        } catch (FileNotFoundException e) {
            throw new IllegalArgumentException(String.format("Cannot find environment property file '%s'", envPropsFile));
        } catch (IOException e) {
            throw new IllegalArgumentException(String.format("Error while loading environment properties: %s", e.getMessage()), e);
        }
    }
Get JSON which is used for <em>creating</em> a container

@return string representation for JSON representing creating a container
src/main/java/io/fabric8/maven/docker/access/ContainerCreateConfig.java