/* package whatever; // don't place package name! */
 
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		final String regex = "^(?!.*\\bvencimiento\\b).*\\b([0-3]?\\d[-/][01]?\\d[-/]\\d{4})\\b";
		final String texto = "fecha vencimiento 20-12-2017\nfecha 20-12-2017\notra: 12/05/2016";
 
		final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE);
		final Matcher matcher = pattern.matcher(texto);
 
		if (matcher.find()) {
		    do {
		        System.out.println("Fecha: " + matcher.group(1));
		    } while (matcher.find());
		} else {
		    System.out.println("No se encontró ninguna fecha");
		}
	}
}

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