Better way to represent array in java properties file

Didn't exactly get your intent. Do check Apache Commons configuration library http://commons.apache.org/configuration/

You can have multiple values against a key as in key=value1,value2 and you can read this into an array as configuration.getAsStringArray("key")

Either define a delimiter that will not be a potential value or learn to use XML.

If you still insist on using properties use one of the methods that will return a list of all keys. Your key appears to have three parts a group identifier (foo, bar) an index (1, 2) and then an element name (filename, expire). Get all the keys break them into their component parts. Create a List for each type of identifier, when processing the list use the identifier to determine which List to add to. Create you paired elements as you said and simply add to the list! If the index order is important either add that as a field to your paired elements or sort the keys before processing.

I can suggest using delimiters and using the

String.split(delimiter)

Example properties file:

MON=0800#Something#Something1, Something2

prop.load(new FileInputStream("\\\\Myseccretnetwork\\Project\\props.properties"));
String[]values = prop.get("MON").toString().split("#");

Hope that helps

Use YAML files for properties, this supports properties as an array.

Quick glance about YAML:

A superset of JSON, it can do everything JSON can + more

1. Simple to read
2. Long properties into multiline values
3. Supports comments
4. Properties as Array
5. YAML Validation