Using Array Values In IN Clause Of Select Query?

I have some issues in passing array values to IN clause.

I am passing a String Array from Java to PL\SQL and want to use the Array values in the IN CLAUSE of Select Query

cust_array is the Array
search_id VARCHAR2(1000);
search_id := '';
FOR j IN 1 .. cust_array.count
LOOP
IF (j != 1) THEN
search_id := search_id || ''',''' || cust_array(j) || ''';
ELSE
search_id := search_id || '''' || cust_array(j) || '''';
END IF;
END LOOP;

trying to form a string of below form: search_id '3211335201','3211335209','3211335279','3211335509'

and use the string search_id in the IN clause of the search Query select * from DPP_EMP where empl in (search_id)

but the query does not returns any result

When I try to hardcode the values in the query as below, its returing 4 rows

select * from DPP_EMP where empl in ('3211335201','3211335209','3211335279','3211335509')

How to achieve this (String to the IN clause) or is there a better way of passing the Array values to the IN clause