01-Api.java

package bulk;

import javaslang.Tuple2;
import javaslang.collection.List;

public class Api {
    public static void main(String[] args) {
        String ids = List.of("id-1", "id-2", "id-3", "id-4", "id-5", "id-6", "id-7").mkString("\n");

        List<Tuple2<String, String>> found = DB.find(List.of(ids.split("\n")));

        System.out.println("result:");
        System.out.println(
                found.map(t -> t._1 + ", " + t._2).mkString("\n")
        );

        /*
        out
            select * from xxx where xxx in (id-1, id-2)
            select * from xxx where xxx in (id-3, id-4)
            select * from xxx where xxx in (id-5, id-6)
            select * from xxx where xxx in (id-7)

            result:
            en-1, id-1
            en-2, id-2
            en-3, id-3
            en-4, id-4
            en-5, id-5
            en-6, id-6
            en-7, id-7

         */
    }
}

02-DB.java

package bulk;

import javaslang.Tuple2;
import javaslang.collection.List;

class DB {
    static List<Tuple2<String, String>> find(List<String> ids) {
        return chunk(ids, List.empty()).flatMap(DB::_find);
    }

    private static List<List<String>> chunk(List<String> xs, List<List<String>> acc) {
        if (xs.nonEmpty()) {
            Tuple2<List<String>, List<String>> sp = xs.splitAt(2);

            return chunk(sp._2, acc.append(sp._1));
        } else {
            return acc;
        }
    }

    static private List<Tuple2<String, String>> _find(List<String> ids) {
        System.out.println("select * from xxx where xxx in (" + ids.mkString(", ") + ")");
        // sql in fact
        return ids.map(id -> "en-" + id.split("-")[1]).zip(ids);
    }
}