String regex = // Puts a double quoted field into group(1), an unquoted field into group(2).
    "  \\G(?:^|,)                                    \n"+
    "  (?:\n"+
    "       # Either a double-quoted field . . . \n"+
    "       \" # field's opening quote\n"+
    "        (   [^\"]*+  (?: \"\" [^\"]*+ )*+  )\n"+
    "       \" # field's closing quote\n"+
    "   |# . . . or . . . \n"+
    "       # some non-quote/non-comma text . . . \n"+
    "       ( [^\",]*+ )\n"+
    "  )\n";

// Create a matcher for the CSV line of text, using the regex above.
Matcher mMain = Pattern.compile(regex, Pattern.COMMENTS).matcher(line);

// Create a matcher for  「"" , with dummy text for the time being.
Matcher mQuote = Pattern.compile("\"\"").matcher("");

while (mMain.find())
{
    String field;
    if (mMain.start(2) >= 0)
        field = mMain.group(2); // The field is unquoted, so we can use it as is.
    else
        // The field is quoted, so we must replace paired double quotes with one double quote.
        field = mQuote.reset(mMain.group(1)).replaceAll("\"");

    // We can now work with field . . . 
    System.out.println("Field [" + field + "]");
}