How do I convert a String to Double in Java using a specific locale?

Try java.text.NumberFormat. From the Javadocs:

To format a number for a different Locale, specify it in the call to getInstance.

NumberFormat nf = NumberFormat.getInstance(Locale.FRENCH);

You can also use a NumberFormat to parse numbers:

myNumber = nf.parse(myString);

parse() returns a Number; so to get a double, you must call myNumber.doubleValue():

    double myNumber = nf.parse(myString).doubleValue();

Note that parse() will never return null, so this cannot cause a NullPointerException. Instead, parse throws a checked ParseException if it fails.

Edit: I originally said that there was another way to convert to double: cast the result to Double and use unboxing. I thought that since a general-purpose instance of NumberFormat was being used (per the Javadocs for getInstance), it would always return a Double. But DJClayworth points out that the Javadocs for parse(String, ParsePosition) (which is called by parse(String)) say that a Long is returned if possible. Therefore, casting the result to Double is unsafe and should not be tried!
Thanks, DJClayworth!

NumberFormat is the way to go, but you should be aware of its peculiarities which crop up when your data is less than 100% correct.

I found the following usefull:

http://www.ibm.com/developerworks/java/library/j-numberformat/index.html

If your input can be trusted then you don't have to worry about it.

You use a NumberFormat. Here is one example, which I think looks correct.

This should be no problem using java.text.DecimalFormat.

Use NumberFormat.getNumberInstance(Locale)

Do you know which locale it is? Then you can use

DecimalFormat format = DecimalFormat.getInstance(theLocale);
format.parse(yourString);

this will even work for scientific notations, strings with percentage signs or strings with currency symbols.