Dockerfile special escape symbol

When I use the command with '--build-arg' to build the docker-image,the spaces in incoming parameters are replaced with a plus sign.

My maven pom.xml:

<plugin>
   <groupId>com.spotify</groupId>
    <artifactId>dockerfile-maven-plugin</artifactId>
    <version>1.4.13</version>
    <configuration>
      <repository>192.168.1.200/library/${project.artifactId}</repository>
      <tag>${project.version}</tag>
      <buildArgs>
         <JAR_FILE>${project.build.finalName}.jar</JAR_FILE>
         <JVM_OPTS>-Xms300m -Xmx300m</JVM_OPTS>
      </buildArgs>
    </configuration>
</plugin>

My Dockerfile:

FROM 192.168.1.200/library/openjdk:8-jdk-alpine
MAINTAINER gaojiayiner@163.com
LABEL version="1.0.0"
RUN mkdir -p /project && mkdir -p /data
ENV workdir /project
WORKDIR $workdir
ARG JAR_FILE
ARG JVM_OPTS
ENV jvm $JVM_OPTS
COPY target/${JAR_FILE} /project/demo.jar
EXPOSE 8080
ENTRYPOINT ["sh","-c","java -jar /project/demo.jar $0 $@"]

Terminal execution record:

[root@localhost docker-java]# mvn clean package dockerfile:build
[root@localhost docker-java]# docker images
REPOSITORY                      TAG                 IMAGE ID            CREATED             SIZE
192.168.1.200/library/demo      0.0.1-SNAPSHOT      13373a4761a1        3 seconds ago       131MB
192.168.1.200/library/openjdk   8-jdk-alpine        a3562aa0b991        14 months ago       105MB
[root@localhost docker-java]# docker run -d  13373a4761a1
d0b5ce9392b12505419d5648332f204dc3d59327efd389c27a950aa0d1daba35
[root@localhost docker-java]# docker ps
CONTAINER ID        IMAGE                    COMMAND                  CREATED             STATUS              PORTS                                            NAMES
d0b5ce9392b1        13373a4761a1             "sh -c 'java -jar /p…"   4 seconds ago       Up 4 seconds        8080/tcp                                         reverent_kirch
[root@localhost docker-java]# docker exec -it d0b5ce9392b1 sh
/project # env
jvm=-Xms300m+-Xmx300m
JAVA_ALPINE_VERSION=8.212.04-r0
HOSTNAME=d0b5ce9392b1

You can see the code jvm=-Xms300m+-Xmx300m. How can I solve this?

You would need to recompile the spotify/dockerfile-maven yourself, because the pull request which fixes this bug is not yet merged/accepted.

See "spotify/dockerfile-maven PR 350"

It points out to the culprit: plugin/dockerfile/BuildMojo.java#encodeBuildParam

  private static String encodeBuildParam(Object buildParam) throws MojoExecutionException {
    try {
      return URLEncoder.encode(new Gson().toJson(buildParam), "utf-8");
    } catch (UnsupportedEncodingException e) {
      throw new MojoExecutionException("Could not build image", e);
    }
  }

> Indeed, we can read here (class URLEncoder) that URLEncoder replaces the space character " " with a plus sign "+".
>
> After the encoding, I added a replace to substitute the + sign with a space: after the encoding all the plus signs will be already encoded to /0x2B, so the ones left are the ones are coming from spaces.

The fix would include:

      return URLEncoder.encode(
               new Gson().toJson(buildParam), StandardCharsets.UTF_8.toString()
             ).replace('+', ' ');
              ^^^^^^^^^^^^^^^^^^^