Java GroupBy 乘以总和

Question

I'm trying to make group by like in mySQL, I have multiple columns (properties) and I must group by two fields ( socio and idSolicitudEgreso ) and sum another one ( montoPago ). I did:

Map<String, Map<String, Integer>> mymap = santa.stream()
        .collect(Collectors.groupingBy(Santander::getPanSocio,
                 Collectors.groupingBy(Santander::getPanIdsolicitudegreso,
                 Collectors.summingInt(Santander::getPanMontopago))));

mymap.forEach((key, value) -> System.out.println(key + ":" + value));

My class object is:

public class Santander {

    private String panRutbeneficiario;
    private String panNombrebeneficiario;
    private String panEmailbeneficiario;
    private String panMetodopago;
    private String panCodigobancoabono;
    private String panTipocuentaabono;
    private String panNumcuentaabono;
    private String panFechapago;
    private String panCampobanco1;
    private String panCampobanco2;
    private int panMontopago;
    private String panTipocuentacargodet;
    private String panNumcuentacargodet;
    private String panCodigosucursal;
    private String panReferenciacliente;
    private String panRetencionfactura;
    private String panAbonovalesvistalinea;
    private String panCantidaddocumentos;
    private String panSocio;
    private String panIdsolicitudegreso;
}

I getting this result with this code:

BANCO DEL ESTADO:{35113=3026882}

As you can see I get the group very well, ( socio , id and sum as well), but I need to get all the objects or list of object. I just get 3 of 20 fields. What change I must do in my Java stream code to get the list of objects (grouped)? Please?

Thanks

PS: the output I expect is:

{  panRutbeneficiario=146174558, panNombrebeneficiario=No Definido,
   panEmailbeneficiario=, panMetodopago=CAT_CSH_TRANSFER, panCodigobancoabono=12,
   panTipocuentaabono=Ahorro, panNumcuentaabono=8275301, panFechapago=2020-07-30,
   panCampobanco1=, panCampobanco2=, panMontopago=111960,
   panTipocuentacargodet=CAT_CSH_CCTE, panNumcuentacargodet=null,
   panCodigosucursal=, panReferenciacliente=, panRetencionfactura=,
   panAbonovalesvistalinea=null, panCantidaddocumentos=null, 
   panSocio=BANCO DEL ESTADO, panIdsolicitudegreso=35113
}

Answer 1

You may need to prepare an object to hold the grouping result for example:

public class Summary {
    private final String panSocio;
    private final String panSolicitude;
    private final int total;

    public Summary(String socio, String solicitude, int total) {
        this.panSocio = socio;
        this.panSolicitude = solicitude;
        this.total = total;
    }

    public String getPanSocio() { return this.panSocio; }
    public String getPanSolicitude() { return this.panSolicitude; }
    public int getTotal() { return this.total; }

    public String toString() {
        return String.format("{ socio=\"%s\", solicitude=\"%s\", total=%d}%n",
                panSocio, panSolicitude, total);
    }
}

Then it is possible to iterate over the entries of mymap , use flatMap to transform the entries of the inner map into Stream<Summary> therefore collecting into the list of Summary objects (sorted if necessary):

List<Summary> remap = mymap.entrySet()
        .stream()
        .flatMap(e -> e.getValue().entrySet()  // e.getKey() -> panSocio
                       .stream()               // ee.getKey() -> solicitude, ee.getValue() -> total
                       .map(ee -> new Summary(e.getKey(), ee.getKey(), ee.getValue()))
        )
        .sorted(Comparator.comparing(Summary::getPanSocio)
                          .thenComparing(Summary::getPanSolicitude))
        .collect(Collectors.toList());

Update

Of course, it is possibe to reuse existing Santander class to collect the results providing that Santander has a constructor or builder allowing to populate at least the three relevant fields panSocio , panSolicitude , panMontopago :

List<Santander> grouped = mymap.entrySet()
        .stream()
        .flatMap(e -> e.getValue().entrySet()  // e.getKey() -> panSocio
                       .stream()               // ee.getKey() -> solicitude, ee.getValue() -> total
                       .map(ee -> new Santander(e.getKey(), ee.getKey(), ee.getValue())) // the rest of the fields set to some default values
        )
        .collect(Collectors.toList());

However, the rest of Santander fields will be undefined / default upon applying summarizingInt collector by Santander::getMontopago .