Java now has a pretty good built-in date library, java.time bundled with Java 8.
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
public class Foo {
public static void main(String[] args) {
DateTimeFormatter format =
DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss'Z'");
LocalDateTime now = LocalDateTime.now();
LocalDateTime then = now.minusDays(7);
System.out.println(String.format(
"Now: %s\nThen: %s",
now.format(format),
then.format(format)
));
/*
Example output:
Now: 2014-05-09T14:51:48Z
Then: 2014-05-02T14:51:48Z
*/
}
}