Properties file : Use key as variable

Question

I want to use a key defined in properties file as a variable like this :

key1= value1
key2= value2
key3= key1

I try :

key3= {key1}

or

key3= ${key1}

But it dosn't work !

Any idea please ?

Answer 1

Java's built-in Properties class doesn't do what you're looking for.

But there are third-party libraries out there that do. Commons Configuration is one that I have used with some success. The PropertiesConfiguration class does exactly what you're looking for.

So you might have a file named my.properties that looks like this:

key1=value1
key2=Something and ${key1}

Code that uses this file might look like this:

CompositeConfiguration config = new CompositeConfiguration();
config.addConfiguration(new SystemConfiguration());
config.addConfiguration(new PropertiesConfiguration("my.properties"));

String myValue = config.getString("key2");

myValue will be "Something and value1".