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<h2 class="title" style="clear: both"><a id="CoreJavaUsage"></a>Database Example</h2>
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<p>
Throughout this book we will build a couple of applications that load
and retrieve inventory data from DB databases. While we are not yet ready to
begin reading from or writing to our databases, we can at least create
the class that we will use to manage our databases.
</p>
<p>
Note that subsequent examples in this book will build on this code to
perform the more interesting work of writing to and reading from the
databases.
</p>
<p>
Note that you can find the complete implementation of these functions
in:
</p>
<pre class="programlisting"><span class="emphasis"><em>DB_INSTALL</em></span>/examples_java/db/GettingStarted</pre>
<p>
where <tt class="literal"><span class="emphasis"><em>DB_INSTALL</em></span></tt> is the location where you
placed your DB distribution.
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<div class="example">
<a id="MyDb"></a>
<p class="title">
<b>Example 7.1 MyDbs Class</b>
</p>
<p>
To manage our database open and close activities, we encapsulate them
in the <tt class="classname">MyDbs</tt> class. There are several good reasons
to do this, the most important being that we can ensure our databases are
closed by putting that activity in the <tt class="classname">MyDbs</tt>
class destructor.
</p>
<p>
To begin, we import some needed classes:
</p>
<a id="java_db12"></a>
<pre class="programlisting">// File: MyDbs.java
package db.GettingStarted;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseConfig;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.DatabaseType;
import java.io.FileNotFoundException; </pre>
<p>
And then we write our class declaration and provided some necessary private data members:
</p>
<a id="java_db13"></a>
<pre class="programlisting">public class MyDbs {
// The databases that our application uses
private Database vendorDb = null;
private Database inventoryDb = null;
private String vendordb = "VendorDB.db";
private String inventorydb = "InventoryDB.db";
// Our constructor does nothing
public MyDbs() {} </pre>
<p>
Next we need a <tt class="methodname">setup()</tt> method. This is where
we configure and open our databases.
</p>
<a id="java_db14"></a>
<pre class="programlisting"> // The setup() method opens all our databases
// for us.
public void setup(String databasesHome)
throws DatabaseException {
DatabaseConfig myDbConfig = new DatabaseConfig();
myDbConfig.setErrorStream(System.err);
myDbConfig.setErrorPrefix("MyDbs");
myDbConfig.setType(DatabaseType.BTREE);
myDbConfig.setAllowCreate(true);
// Now open, or create and open, our databases
// Open the vendors and inventory databases
try {
vendordb = databasesHome + "/" + vendordb;
vendorDb = new Database(vendordb,
null,
myDbConfig);
inventorydb = databasesHome + "/" + inventorydb;
inventoryDb = new Database(inventorydb,
null,
myDbConfig);
} catch(FileNotFoundException fnfe) {
System.err.println("MyDbs: " + fnfe.toString());
System.exit(-1);
}
} </pre>
<p>
Finally, we provide some getter methods, and our <tt class="methodname">close()</tt> method.
</p>
<a id="java_db15"></a>
<pre class="programlisting"> // getter methods
public Database getVendorDB() {
return vendorDb;
}
public Database getInventoryDB() {
return inventoryDb;
}
// Close the databases
public void close() {
try {
if (vendorDb != null) {
vendorDb.close();
}
if (inventoryDb != null) {
inventoryDb.close();
}
} catch(DatabaseException dbe) {
System.err.println("Error closing MyDbs: " +
dbe.toString());
System.exit(-1);
}
}
} </pre>
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