@GetMapping("/roman-validate")
public static String RomanNumerals(int num)   
{  
LinkedHashMap<String, Integer> romanNumerals = new LinkedHashMap<String, Integer>();  
//storing roman letters and corresponding decimal values in HashMap  
romanNumerals.put("M", 1000);  
romanNumerals.put("CM", 900);  
romanNumerals.put("D", 500);  
romanNumerals.put("CD", 400);  
romanNumerals.put("C", 100);  
romanNumerals.put("XC", 90);  
romanNumerals.put("L", 50);  
romanNumerals.put("XL", 40);  
romanNumerals.put("X", 10);  
romanNumerals.put("IX", 9);  
romanNumerals.put("V", 5);  
romanNumerals.put("IV", 4);  
romanNumerals.put("I", 1);  
//variable for string the result  
String result = "";  
//loop iterate over Map  
for(Map.Entry<String, Integer> entry : romanNumerals.entrySet())  
{  
int matches = num/entry.getValue();  
result = result+repeat(entry.getKey(), matches);  
num = num % entry.getValue();  
}  
return result;  
}  
public static String repeat(String s, int n)   
{  
if(s == null)   
{  
return null;  
}  
final StringBuilder sb = new StringBuilder();  
for(int i = 0; i < n; i++)   
{  
sb.append(s);  
}  
//converts into string  
return sb.toString();  
}  
//driver code  
public static void main(String args[])   
{  
//prints roman numerals from 1 to 200 
	 Integer a[] = new Integer[] { 1, 4, 9, 90, 900, 1903, 1997, 4000, 0, -1 };
	 
     // Getting the list view of Array
     List<Object> list = Arrays.asList(a);
	
for (int i = 1;i<=list.size();i++)   
{  
	if(a[i]==0&& a[i]==-1)
	throw new RomenNumeralException("Romen numeral exception"+a[i]);
System.out.println("i="+a[i]+" -> "+RomanNumerals(a[i]));  
}  
}  

after that i have tried in rest api  define controller,service class as below:
1.RomanNumeralToDigitController

@GetMapping("/roman-validate")
public static void romenValidate()
{

rs.validateRomen();
  
	
}
2.RomenValidateService

 Integer a[] = new Integer[] { 1, 4, 9, 90, 900, 1903, 1997, 4000, 0, -1 };
 
 // Getting the list view of Array
 List<Object> list = Arrays.asList(a);
public void validateRomen() {