java 8 List<Object[]> to Map<String, Map<String, BigDecimal>>

Question

The list contains Arrays of ( String , String , BigDecimal ). I want to convert the List to Map<String, Map<String, BigDecimal>> grouped by the first String using java 8 Stream class.

List<Object[]> list = ss.createCriteria(PayrollDeduction.class)
                .createAlias("payroll", "pay")
                .add(Restrictions.le("pay.paymentDate", atDate))
                .createAlias("payroll.employee", "employee")
                .add(Restrictions.in("employee.id", Arrays.asList(empId)))
                .setProjection(Projections.projectionList()
                        .add(Projections.property("gouvAgencyCode"))
                        .add(Projections.property("code"))
                        .add(Projections.sum("amount"))
                        .add(Projections.groupProperty("gouvAgencyCode"))
                        .add(Projections.groupProperty("code")))
                .setReadOnly(true)
                .list();
                 list.stream().collect(Collectors.groupingBy(r->r[0], Collectors.mapping(mapper, downstream)));

Answer 1

Do it like this:

List<Object[]> list = Arrays.asList(
        new Object[] { "A", "X", new BigDecimal("1") },
        new Object[] { "A", "Y", new BigDecimal("2.0") },
        new Object[] { "B", "X", new BigDecimal("3.00") },
        new Object[] { "C", "Z", new BigDecimal("4.000") }
);

Map<String, Map<String, BigDecimal>> map = list.stream()
        .collect(Collectors.groupingBy(r -> (String) r[0],
                                       Collectors.toMap(r -> (String) r[1],
                                                        r -> (BigDecimal) r[2])));

System.out.println(map);

Output

{A={X=1, Y=2.0}, B={X=3.00}, C={Z=4.000}}

Answer 2

To me, it looks like a XY Problem :

• You seem to be using Hibernate;
• You want to transform the results from your projection into some other format.

Hibernate's own ResultTransformer could have solved your problem in a cleaner way.