Properties in java - can we have comma-separated keys with single value?

Question

I want to have multiple keys (>1) for a single value in a properties file in my java application. One simple way of doing the define each key in separate line in property file and the same value to all these keys. This approach increases the maintainability of property file. The other way (which I think could be smart way) is define comma separated keys with the value in single line. e.g.

  key1,key2,key3=value

Java.util.properties doesn't support this out of box. Does anybody did simillar thing before? I did google but didn't find anything.

--manish

Answer 1

Since java.util.Properties extends java.util.Hashtable, you could use Properties to load the data, then post-process the data.

The advantage to using java.util.Properties to load the data instead of rolling your own is that the syntax for properties is actually fairly robust, already supporting many of the useful features you might end up having to re-implement (such as splitting values across multiple lines, escapes, etc.).

Answer 2

My advice would be rather than java.util.properties use a hashmap/hashtable on its own and implement your own properties methods - this way using a hashmap for multiple values you can have many keys point to the same value. The only problem is the duplication of the value and I don't see how you can get around this.

You'd get:

Key1=Value Key2=Value Key3=Value

You can parse the string using string.split("=") and split again on commas both sides to get some clever assignment options.

Answer 3

One of the nice things about properties files is that they are simple. No complex syntax to learn, and they are easy on the eye.

Want to know what the value of the property foo is? Quickly scan the left column until you see "foo".

Personally, I would find it confusing if I saw a properties file like that.

If that's what you really want, it should be simple to implement. A quick first stab might look like this:

• Open file
• For each line:
  • trim() whitespace
  • If the line is empty or starts with a #, move on
  • Split on "=" (with limit set to 2), leaving you with key and value
  • Split key on ","
  • For each key, trim() it and add it to the map, along with the trim()'d value

That's it.

Answer 4

I'm not aware of an existing solution, but it should be quite straightforward to implement:

String key = "key1,key2,key3", val = "value";
Map<String, String> map = new HashMap<String, String>();
for(String k : key.split(",")) map.put(k, val); 
System.out.println(map);