plugin/src/main/java/io/fabric8/maven/plugin/mojo/build/ResourceMojo.java
private Date getBuildReferenceDate() throws MojoExecutionException {
        // Pick up an existing build date created by fabric8:build previously
        File tsFile = new File(project.getBuild().getDirectory(), AbstractDockerMojo.DOCKER_BUILD_TIMESTAMP);
        if (!tsFile.exists()) {
            return new Date();
        }
        try {
            return EnvUtil.loadTimestamp(tsFile);
        } catch (IOException e) {
            throw new MojoExecutionException("Cannot read timestamp from " + tsFile, e);
        }
    }
private Date getBuildReferenceDate() throws MojoExecutionException {
        // Pick up an existing build date created by fabric8:build previously
        File tsFile = new File(project.getBuild().getDirectory(), AbstractDockerMojo.DOCKER_BUILD_TIMESTAMP);
        if (!tsFile.exists()) {
            return new Date();
        }
        try {
            return EnvUtil.loadTimestamp(tsFile);
        } catch (IOException e) {
            throw new MojoExecutionException("Cannot read timestamp from " + tsFile, e);
        }
    }
get a reference date