How to change the Properties.store() divider symbol from “=” to “:”?

Question

I recently found out about java.util.Properties, which allows me to write and read from a config without writing my own function for it.

I was excited since it is so easy to use, but later noticed a flaw when I stored the modified config file.

Here is my code, quite simple for now:

FileWriter writer = null;
Properties configFile = new Properties();
configFile.load(ReadFileTest.class.getClassLoader().getResourceAsStream("config.txt"));

String screenwidth = configFile.getProperty("screenwidth");
String screenheight = configFile.getProperty("screenheight");
System.out.println(screenwidth);
System.out.println(screenheight);
configFile.setProperty("screenwidth", "1024");
configFile.setProperty("screenheight", "600");
try {
    writer = new FileWriter("config.txt" );
    configFile.store(writer, null);
} catch (IOException e) {
    e.printStackTrace();
}
writer.flush();
writer.close();

The problem I noticed was that the config file I try to edit is stored like this:

foo: bar
bar: foo
foobar: barfoo

However, the output after properties.store(writer, null) is this:

foo=bar
bar=foo
foobar=barfoo

The config file I edit is not for my program, it is for an other application that needs the config file to be in the format shown above with : as divider or else it will reset the configuration to default.

Does anybody know how to easily change this?

I searched through the first 5 Google pages now but found noone with a similar problem. I also checked the Javadoc and found no function that allows me to change it without writing a class for myself. I would like to use Properties for now since it is there and quite easy to use. I also got the idea of just replacing all = with : after I saved the file but maybe someone got a better suggestion?

Answer 1

Don't use a tool that isn't designed for the task - don't use Properties here. Instead, I'd just write your own - should be easy enough.

You can still use a Properties instance as your "store", but don't use it for serializing the properties to text. Instead, just use a FileWriter, iterate through the properties, and write the lines yourself - as key + ": " + value.

Answer 2

New idea here

Your comment about converting the = to : got me thinking: Properties.store() writes to a Stream. You could use an in-memory ByteArrayOutputStream, convert as appropriate in memory before you write to a file, then write the file. Likewise for Properties.load(). Or you could insert FilterXXXs instead. (I'd probably do it in memory).

---

I was looking into how hard it would be to subclass. It's nearly impossible. :-(

If you look at the source code for Properties, (I'm looking at Java 6) store() calls store0(). Now, unfortunately, store0 is private, not protected, and the "=" is given as a magic constant, not something read from a property. And it calls another private method called saveConvert() that also has a lot of magic constants.

Overall, I rate this code as D- quality. It breaks almost all the rules of good code and good style.

But, it's open source, so, theoretically, you could copy and paste (and improve!) a bunch of code into your own BetterProperties class.