No need for regular expressions. Simply match any string where the first seven characters are "mailto:".
If you insist on using regular expressions, the expression would be "mailto:.*". If you only want to keep what is after the "mailto:", it would be "mailto:(.*)"
For first you can use String.startsWith(String prefix)
And second maybe trim string for "?" then use String.split("&|="); and you hav array with [ subject, Indian, body, hello]
http://java.sun.com/javase/6/docs/api/java/lang/String.html#split(java.lang.String)
Regex really isn't necessary for this. A simple String.startsWith would suffice for the first match and you could use the URL class to extract the query.
String string = "mailto:[email protected]?subject=Indian&body=hello";
if (string.startsWith("mailto:")) {
try {
URL url = new URL(string);
String query = url.getQuery(); // Here is your query string.
} catch (MalformedURLException e) {
throw new AssertionError("This should not happen: " + e);
}
}