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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Java API Tutorial - Tuple</dl></h3></td>
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<p>
<h3 align=center>Tuple - Using the tuple format</h3>
<p>Tuples are sequences of primitive Java values that can be written to, and
read from, the raw data bytes of a stored record. The primitive values are
written or read one at a time in sequence, using the Java API
<a href="../../java/com/sleepycat/bdb/bind/tuple/TupleInput.html">TupleInput</a>
and
<a href="../../java/com/sleepycat/bdb/bind/tuple/TupleOutput.html">TupleOutput</a>
classes. These classes
are very similar to the standard Java
<a href="http://java.sun.com/j2se/1.3/docs/api/java/io/DataInput.html">DataInput</a>
and
<a href="http://java.sun.com/j2se/1.3/docs/api/java/io/DataOutput.html">DataOutput</a>
interfaces. The primary difference is the
binary format of the data, which is designed for sorting in the case of
tuples.</p>
<p>For example, to read and write a tuple containing two string values, the
following code snippets could be used.</p>
<blockquote><pre><b>import com.sleepycat.bdb.bind.tuple.TupleInput;
import com.sleepycat.bdb.bind.tuple.TupleOutput;
...
TupleInput input;
TupleOutput output;
...
String partNumber = input.readString();
String supplierNumber = input.readString();
...
output.writeString(partNumber);
output.writeString(supplierNumber);
</b></pre></blockquote>
<p>Since a tuple is defined as an ordered sequence, reading and writing
order must match. If the wrong data type is read (an integer instead of
string, for example), an exception may be thrown or at minimum invalid data
will be read.</p>
<p>When the tuple format is used, bindings and key extractors must read and
write tuples using the tuple API as shown above. This will be illustrated in
the next two sections.</p>
<hr size=1 noshade>
<p>First, the tuple format objects must be created as shown below in the
modified <b>SampleDatabase</b> class.</p>
<blockquote><pre>
<b>import com.sleepycat.bdb.bind.serial.TupleSerialKeyExtractor;
import com.sleepycat.bdb.bind.tuple.TupleFormat;
import com.sleepycat.bdb.bind.tuple.TupleInput;
import com.sleepycat.bdb.bind.tuple.TupleOutput;
...
</b>public class SampleDatabase
{
<b> ...
private TupleFormat partKeyFormat;
</b> private SerialFormat partValueFormat;
<b> private TupleFormat supplierKeyFormat;
</b> private SerialFormat supplierValueFormat;
<b> private TupleFormat shipmentKeyFormat;
</b> private SerialFormat shipmentValueFormat;
<b> private TupleFormat cityKeyFormat;
...
</b> public SampleDatabase(String homeDirectory, boolean runRecovery)
throws DbException, FileNotFoundException
{
<b> ...
partKeyFormat = new TupleFormat();
</b> partValueFormat = new SerialFormat(javaCatalog, PartValue.class);
<b> supplierKeyFormat = new TupleFormat();
</b> supplierValueFormat = new SerialFormat(javaCatalog, SupplierValue.class);
<b> shipmentKeyFormat = new TupleFormat();
</b> shipmentValueFormat = new SerialFormat(javaCatalog, ShipmentValue.class);
<b> cityKeyFormat = new TupleFormat();
...
</b> }
}
</pre></blockquote>
<p>For each key, a
<a href="../../java/com/sleepycat/bdb/bind/tuple/TupleFormat.html">TupleFormat</a>
object is used instead of the
<a href="../../java/com/sleepycat/bdb/bind/serial/SerialFormat.html">SerialFormat</a>
used in the prior examples. The
<a href="../../java/com/sleepycat/bdb/bind/tuple/TupleFormat.html">TupleFormat</a>
constructor has no
parameters.</p>
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