Retrieving Database Items
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## Retrieving Database Items

Retrieving information from the database is accomplished via the standard Java collections API. In the example, the Set.iterator method is used to iterate all Map.Entry objects for each store. All standard Java methods for retrieving objects from a collection may be used with the Java Collections API.

The `PrintDatabase.doWork()` method calls `printEntries()` to print the map entries for each database store. It is called via the TransactionRunner class and was outlined in the previous section.

    import com.sleepycat.collections.StoredIterator;
    import java.util.Iterator;
    ...
    public class Sample
    {
        ...
        private SampleViews views;
        ...
        private class PrintDatabase implements TransactionWorker
        {
            public void doWork()
                throws Exception
            {
                printEntries("Parts",
                              views.getPartEntrySet().iterator());
                printEntries("Suppliers",
                              views.getSupplierEntrySet().iterator());
                printEntries("Shipments",
                              views.getShipmentEntrySet().iterator());
            }
        }
        ...

        private void printEntries(String label, Iterator iterator)
        {
        }
        ...
    }

The Set of Map.Entry objects for each store is obtained from the `SampleViews` object. This set can also be obtained by calling the Map.entrySet method of a stored map.

The `printEntries()` prints the map entries for any stored map. The Object.toString method of each key and value is called to obtain a printable representation of each object.

        private void printEntries(String label, Iterator iterator)
        {
            System.out.println("\n--- " + label + " ---");
            try
            {
                while (iterator.hasNext())
                {
                    Map.Entry entry = (Map.Entry) iterator.next();
                    System.out.println(entry.getKey().toString());
                    System.out.println(entry.getValue().toString());
                }
            }
            finally
            {
                StoredIterator.close(iterator);
            }
        }

It is very important that all iterators for stored collections are explicitly closed. To ensure they are closed, a `finally` clause should be used as shown above. If the iterator is not closed, the underlying Berkeley DB cursor is not closed either and the store may become unusable.

If the iterator is cast to StoredIterator then its StoredIterator.close() method can be called. Or, as shown above, the static StoredIterator.close() method can be called to avoid casting. The static form of this method can be called safely for any Iterator. If an iterator for a non-stored collection is passed, it is simply ignored.

This is one of a small number of behavioral differences between standard Java collections and stored collections. For a complete list see Using Stored Collections .

The output of the example program is shown below.

    Adding Suppliers
    Adding Parts
    Adding Shipments

    --- Parts ---
    PartKey: number=P1
    PartData: name=Nut color=Red weight=[12.0 grams] city=London
    PartKey: number=P2
    PartData: name=Bolt color=Green weight=[17.0 grams] city=Paris
    PartKey: number=P3
    PartData: name=Screw color=Blue weight=[17.0 grams] city=Rome
    PartKey: number=P4
    PartData: name=Screw color=Red weight=[14.0 grams] city=London
    PartKey: number=P5
    PartData: name=Cam color=Blue weight=[12.0 grams] city=Paris
    PartKey: number=P6
    PartData: name=Cog color=Red weight=[19.0 grams] city=London

    --- Suppliers ---
    SupplierKey: number=S1
    SupplierData: name=Smith status=20 city=London
    SupplierKey: number=S2
    SupplierData: name=Jones status=10 city=Paris
    SupplierKey: number=S3
    SupplierData: name=Blake status=30 city=Paris
    SupplierKey: number=S4
    SupplierData: name=Clark status=20 city=London
    SupplierKey: number=S5
    SupplierData: name=Adams status=30 city=Athens

    --- Shipments ---
    ShipmentKey: supplier=S1 part=P1
    ShipmentData: quantity=300
    ShipmentKey: supplier=S2 part=P1
    ShipmentData: quantity=300
    ShipmentKey: supplier=S1 part=P2
    ShipmentData: quantity=200
    ShipmentKey: supplier=S2 part=P2
    ShipmentData: quantity=400
    ShipmentKey: supplier=S3 part=P2
    ShipmentData: quantity=200
    ShipmentKey: supplier=S4 part=P2
    ShipmentData: quantity=200
    ShipmentKey: supplier=S1 part=P3
    ShipmentData: quantity=400
    ShipmentKey: supplier=S1 part=P4
    ShipmentData: quantity=200
    ShipmentKey: supplier=S4 part=P4
    ShipmentData: quantity=300
    ShipmentKey: supplier=S1 part=P5
    ShipmentData: quantity=100
    ShipmentKey: supplier=S4 part=P5
    ShipmentData: quantity=400
    ShipmentKey: supplier=S1 part=P6
    ShipmentData: quantity=100

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