|
|
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 Sleepycat 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