In this blog post, we are going to understand the method for overriding basic file attributes while Skill creation/editing on SUSI Server. The need for this arose, when the creationTime for the Skill file that is stored on the server gets changed when the skill was edited.

Need for the implementation

As briefly explained above, the creationTime for the Skill file that is stored on the server gets changed when the skill is edited. Also, the need to override the lastModifiedTime was done, so that the Skills based on metrics gives correct results. Currently, we have two metrics for the SUSI Skills – Recently updated skills and Newest Skills. The former is determined by the lastModifiedTime and the later is determined by the creationTime. Due, to inconsistencies of these attributes, the skills that were shown were out of order. The lastModifiedTime was overridden to save the epoch date during Skill creation, so that the newly created skills don’t show up on the Recently Updated Skills section, whereas the creationTime was overridden to maintain the correct the time.

Going through the implementation

Let us first have a look on how the creationTime was overridden in the ModifySkillService.java file.

….
BasicFileAttributes attr = null;
Path p = Paths.get(skill.getPath());
try {
    attr = Files.readAttributes(p, BasicFileAttributes.class);
} catch (IOException e) {
    e.printStackTrace();
}
FileTime skillCreationTime = null;
if( attr != null ) {
    skillCreationTime = attr.creationTime();
}

if (model_name.equals(modified_model_name) &&
    group_name.equals(modified_group_name) &&
    language_name.equals(modified_language_name) &&
    skill_name.equals(modified_skill_name)) {
    // Writing to File
    try (FileWriter file = new FileWriter(skill)) {
        file.write(content);
        json.put("message", "Skill updated");
        json.put("accepted", true);

    } catch (IOException e) {
        e.printStackTrace();
        json.put("message", "error: " + e.getMessage());
    }
    // Keep the creation time same as previous
    if(attr!=null) {
        try {
            Files.setAttribute(p, "creationTime", skillCreationTime);
        } catch (IOException e) {
            System.err.println("Cannot persist the creation time. " + e);
        }
    }
    ….
}
.
.
.

• Firstly, we get the BasicFileAttributes of the Skill file and store it in the attr variable.

• Next, we initialise the variable skillCreationTime of type FileTime to null and set the value to the existing creationTime.

• The new Skill file is saved on the path using the FileWriter instance, which changes the creationTime, lastModifiedTime to the time of editing of the skill.

• The above behaviour is not desired and hence, we want to override the creationTIme with the FileTime saved in skillCreationTIme. This ensures that the creation time of the skill is persisted, even after editing the skill.

• Now we are going to see how the lastModifiedTime was overridden in the CreateSkillService.java file.

….
Path newPath = Paths.get(path);
// Override modified date to an older date so that the recently updated metrics works fine
// Set is to the epoch time
try {
  Files.setAttribute(newPath, "lastModifiedTime", FileTime.fromMillis(0));
} catch (IOException e) {
  System.err.println("Cannot override the modified time. " + e);
}
.
.
.

• For this, we get the newPath of the Skill file and then the lastModifiedTime for the Skill File is explicitly set to a particular time.

• We set it to FileTime.fromMillis(0) i.e, the epoch time.

I hope that I was able to convey my learnings and implementation of the code properly and it proved to be helpful for your understanding.

Resources

Documentation for BasicFileAttributes Interface – https://docs.oracle.com/javase/8/docs/api/java/nio/file/attribute/BasicFileAttributes.html