A more elegant solution to creating an array from comma sep list of properties?

Question

In my properties file I have one property, which contains a comma separated list of values

In my code, I would like to load that property in, split it from the commas, and add each value into an array. I also want to make sure I don't have values in the array due to whitespace etc

example property :

prop_allowed_extensions = .jpeg,tiff, .txt 

I have come up with this so far, but it feels dirty, is there a more elegant solution?

String test = classProperties.getProperty("prop_allowed_extensions", "txt, jpeg");
String[] splitString = StringUtils.split(test, ',');
String[] newString = new String[splitString.length];             
for (int i = 0; i < splitString.length; i++)
{
   newString[i] = StringUtils.trim(splitString[i]);                
}

I just want the text of the file extension, would it be appropriate to use a regular expression to remove whitespace/non-letters?

Answer 1

Given your use case, it seems like a more elegant solution would be to not use the properties file format at all, and instead go with something that supports arrays such as YAML or JSON.

You will find links to Java libraries on each of those pages; the transition should be painless.

Answer 2

Following your pattern, you can do it like this:

String test = classProperties.getProperty("prop_allowed_extensions", "txt, jpeg");
List<String> extensions = new ArrayList<String>();         
for (String part:test.split(",")) {
   extensions.add(part.trim());               
}

The difference is that the result is in a list now. test.split(",") will be called only once, so there is no performance issue.

Answer 3

String test = classProperties.getProperty("prop_allowed_extensions", "txt, jpeg");
String[] splitString = StringUtils.split(test, ',');
for(String s : splitString) {
    s = StringUtils.trim(s);
}

would be slightly more elegant, but Java does not support LINQ like .net where you would be able to avoid the explicit loop altogether.

Answer 4

String[] allowedFormats = classProperties
                           .getProperty("prop_allowed_extensions", "txt, jpeg")
                           .replaceAll("[ \\.]","")
                           .split(",");

With Java 1.5 or superior, in Array format.

Answer 5

You can do it in two steps:

String[] allowedExtensions = str.replaceAll("[^\\w,_]", "").split(",")

(First kill anything that is not either a comma, an underscore or a word character (letter or digit), then split the resulting string

Answer 6

I'd personally just reduce it to the following (keeping in mind that String.split() takes a regular expression), but I don't know whether or not you'd consider it more elegant:

String test = classProperties.getProperty("prop_allowed_extensions",
        "txt, jpeg");
String[] extensions = test.trim().split("\\s*,\\s*");

Edit: You can remove the leading dot on each extension too, if it is present (this, or one of several other ways):

String[] test = classProperties.getProperty("prop_allowed_extensions",
        "txt, jpeg").trim().split("^\\.", 2);
String[] extensions = test[test.length - 1].split("\\s*,\\s*.?");

Answer 7

It's much more simple:

String test = classProperties.getProperty("prop_allowed_extensions", "txt, jpeg");
String[] splitString = test.trim().split("\\s*,\\s*");

(needs Java 5)

Answer 8

Apache Jakarta Commons Configuration handles properties file in a clean way, allowing you to specify lists in different formats:

colors.pie = #FF0000, #00FF00, #0000FF

OR

colors.pie = #FF0000;
colors.pie = #00FF00;
colors.pie = #0000FF;

And get the list like this:

String[] colors = config.getStringArray("colors.pie");
List colorList = config.getList("colors.pie");

See the How-to