Reading from a file but getting null in java

I want to read from a file and store it in a string.

This is my method:

public static String createJsonFileFromNode(String filename, JsonNode root)  {
    String dirName = "src/test/resources/json/";
    File dir = new File (dirName);
    File actualFile = new File (dir, filename);
    try (Writer writer = new BufferedWriter(new OutputStreamWriter (
            new FileOutputStream(actualFile), "utf-8")))
    {
        writer.write(String.valueOf(root));
        log.info(actualFile.getPath());
        String updatedJson = FileUtils.readFileToString(actualFile, "UTF-8");
        return updatedJson;
    }
    catch (UnsupportedEncodingException e) {
         e.printStackTrace();
         return "";
    } catch (FileNotFoundException e) {
        e.printStackTrace();
        return "";
    } catch (IOException e) {
        e.printStackTrace();
        return "";
    }
}

I have two problems in the above method:

1. In String dirName = "src/test/resources/json/" I am passing an entire path, which I dont want to. I want to pass it as "/json/"
2. updatedJson is retuning null even though the file is getting saved to the particular direction. Not sure what is going on. Can someone please help me?

Thank you.