@Override
    public Reader getRankingExpression(String name) {
        try {
            return IOUtils.createReader(expressionFileNameToFile(name), "utf-8");
        }
        catch (IOException e) {
            throw new IllegalArgumentException("Could not read ranking expression file '" + name + "'", e);
        }
    }
Reads a ranking expression from file to a string and returns it.

@param name the name of the file to return,
            relative to the search definition directory in the application package
@return the content of a ranking expression file
@throws IllegalArgumentException if the file was not found or could not be read
config-application-package/src/main/java/com/yahoo/config/model/application/provider/FilesApplicationPackage.java