In Database Usage Example we wrote an
application that loaded two Database objects with vendor
and inventory information. In this example, we will use those databases to
display all of the items in the inventory database. As a part of showing
any given inventory item, we will look up the vendor who can provide the
item and show the vendor's contact information.
To do this, we create the ExampleDatabaseRead
application. This application reads and displays all inventory records by:
Opening the inventory, vendor, and
class catalog Database objects. We do this using the
MyDbs class. See Stored Class Catalog Management with MyDbs
for a description of this class.
Obtaining a cursor from the inventory Database.
Steps through the Database, displaying
each record as it goes.
To display the Inventory record, the custom tuple binding that we created in InventoryBinding.java is used.
Database.get() is used to obtain the vendor that corresponds to
the inventory item.
A serial binding is used to convert the
DatabaseEntry returned
by the get() to a Vendor object.
The contents of the Vendor object are displayed.
We implemented the Vendor class in Vendor.java. We implemented the
Inventory class in Inventory.java.
The full implementation of ExampleDatabaseRead
can be found in:
DB_INSTALL/examples_java/db/GettingStarted
where DB_INSTALL is the location where you
placed your DB distribution.
Example 9.1 ExampleDatabaseRead.java
To begin, we import the necessary classes:
// file ExampleDatabaseRead.java package db.GettingStarted; import java.io.File; import java.io.IOException; import com.sleepycat.bind.EntryBinding; import com.sleepycat.bind.serial.SerialBinding; import com.sleepycat.bind.tuple.TupleBinding; import com.sleepycat.db.Cursor; import com.sleepycat.db.DatabaseEntry; import com.sleepycat.db.DatabaseException; import com.sleepycat.db.LockMode; import com.sleepycat.db.OperationStatus;
Next we declare our class and set up some global variables. Note a
MyDbs object is instantiated here. We can do
this because its constructor never throws an exception. See Database Example for its implementation
details.
public class ExampleDatabaseRead {
private static String myDbsPath = "./";
// Encapsulates the database environment and databases.
private static MyDbs myDbs = new MyDbs();
private static TupleBinding inventoryBinding;
private static EntryBinding vendorBinding;
Next we create the ExampleDatabaseRead.usage() and
ExampleDatabaseRead.main() methods.
We perform almost all of our exception handling from ExampleDatabaseRead.main(), and so we
must catch DatabaseException because the com.sleepycat.db.*
APIs throw them.
private static void usage() {
System.out.println("ExampleDatabaseRead [-h <env directory>]" +
"[-s <item to locate>]");
System.exit(-1);
}
public static void main(String args[]) {
ExampleDatabaseRead edr = new ExampleDatabaseRead();
try {
edr.run(args);
} catch (DatabaseException dbe) {
System.err.println("ExampleDatabaseRead: " + dbe.toString());
dbe.printStackTrace();
} finally {
myDbs.close();
}
System.out.println("All done.");
}
In ExampleDatabaseRead.run(), we call MyDbs.setup() to
open our databases. Then we create the bindings that we need for using our data objects with
DatabaseEntry objects.
private void run(String args[])
throws DatabaseException {
// Parse the arguments list
parseArgs(args);
myDbs.setup(myDbsPath);
// Setup our bindings.
inventoryBinding = new InventoryBinding();
vendorBinding =
new SerialBinding(myDbs.getClassCatalog(),
Vendor.class);
showAllInventory();
}
Now we write the loop that displays the Inventory
records. We do this by opening a cursor on the inventory database and
iterating over all its contents, displaying each as we go.
private void showAllInventory()
throws DatabaseException {
// Get a cursor
Cursor cursor = myDbs.getInventoryDB().openCursor(null, null);
// DatabaseEntry objects used for reading records
DatabaseEntry foundKey = new DatabaseEntry();
DatabaseEntry foundData = new DatabaseEntry();
try { // always want to make sure the cursor gets closed
while (cursor.getNext(foundKey, foundData,
LockMode.DEFAULT) == OperationStatus.SUCCESS) {
Inventory theInventory =
(Inventory)inventoryBinding.entryToObject(foundData);
displayInventoryRecord(foundKey, theInventory);
}
} catch (Exception e) {
System.err.println("Error on inventory cursor:");
System.err.println(e.toString());
e.printStackTrace();
} finally {
cursor.close();
}
}
We use ExampleDatabaseRead.displayInventoryRecord()
to actually show the record. This
method first displays all the relevant information from the retrieved
Inventory object. It then uses the vendor database to retrieve and
display the vendor. Because the vendor database is keyed by vendor name,
and because each inventory object contains this key, it is trivial to
retrieve the appropriate vendor record.
private void displayInventoryRecord(DatabaseEntry theKey,
Inventory theInventory)
throws DatabaseException {
String theSKU = new String(theKey.getData(), "UTF-8");
System.out.println(theSKU + ":");
System.out.println("\t " + theInventory.getItemName());
System.out.println("\t " + theInventory.getCategory());
System.out.println("\t " + theInventory.getVendor());
System.out.println("\t\tNumber in stock: " +
theInventory.getVendorInventory());
System.out.println("\t\tPrice per unit: " +
theInventory.getVendorPrice());
System.out.println("\t\tContact: ");
DatabaseEntry searchKey = null;
try {
searchKey =
new DatabaseEntry(theInventory.getVendor().getBytes("UTF-8"));
} catch (IOException willNeverOccur) {}
DatabaseEntry foundVendor = new DatabaseEntry();
if (myDbs.getVendorDB().get(null, searchKey, foundVendor,
LockMode.DEFAULT) != OperationStatus.SUCCESS) {
System.out.println("Could not find vendor: " +
theInventory.getVendor() + ".");
System.exit(-1);
} else {
Vendor theVendor =
(Vendor)vendorBinding.entryToObject(foundVendor);
System.out.println("\t\t " + theVendor.getAddress());
System.out.println("\t\t " + theVendor.getCity() + ", " +
theVendor.getState() + " " + theVendor.getZipcode());
System.out.println("\t\t Business Phone: " +
theVendor.getBusinessPhoneNumber());
System.out.println("\t\t Sales Rep: " +
theVendor.getRepName());
System.out.println("\t\t " +
theVendor.getRepPhoneNumber());
}
}
The remainder of this application provides a utility method used to parse the command line options. From the perspective of this document, this is relatively uninteresting. You can see how this is implemented by looking at:
DB_INSTALL/examples_java/db/GettingStarted
where DB_INSTALL is the location where you
placed your DB distribution.