This is the solution to my problem:

public List searchReadModelfields(String modelName, List domain, List<String> fields, Integer uid) throws XmlRpcException {
        return (List)Arrays.asList((Object[])models.execute("execute_kw", Arrays.asList(
                db, uid, password,
                modelName,
                "search_read",
                Arrays.asList(domain),
                new HashMap() {{
                    put("fields", fields);
                }}
        )));
    }

 List<String> fields = new ArrayList<>();
 
  fields.add("product_tmpl_ids");
 
  List domain = Arrays.asList(Arrays.asList("name", "=", "A - Administration / Office"));
 
// return list of hashmaps)
List result = (List)service.searchReadModelfields("product.public.category", domain, fields, uid);

HashMap values;
Integer partner_id;
Object[] category_ids;
for(Object partner_data: result) {
    values  = (HashMap)partner_data;
    partner_id = (Integer) values.get("id");
    category_ids = (Object [])values.get("product_tmpl_ids");

    System.out.printf("{partner_id: %s, ", partner_id);
    System.out.print("category_ids:[");
    for(Object category_id: category_ids) {
        System.out.printf("%s,",
                category_id
        );
    }
    System.out.println("]}");
}