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		Implementing the Main Program
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		Implementing the Main Program
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          <th width="60%" align="center">Chapter 2. 
		The Basic Program
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          <div>
            <h2 class="title" style="clear: both"><a id="implementingmain"></a>
		Implementing the Main Program
	</h2>
          </div>
        </div>
        <div></div>
      </div>
      <p>
    The main program opens the environment and databases, stores and retrieves
	objects within a transaction, and finally closes the environment
	databases. This section describes the main program shell, and the
	next section describes how to run transactions for storing and
	retrieving objects.
</p>
      <p>
    The <tt class="classname">Sample</tt> class contains the main program. The skeleton
	for the <tt class="classname">Sample</tt> class follows.
</p>
      <a id="cb_java_sample"></a>
      <pre class="programlisting"><b class="userinput"><tt>import com.sleepycat.db.DatabaseException;
import java.io.FileNotFoundException;

public class Sample
{
    private SampleDatabase db;
    private SampleViews views;

    public static void main(String args)
    {
    }

    private Sample(String homeDir)
        throws DatabaseException, FileNotFoundException
    {
    }

    private void close()
        throws DatabaseException
    {
    }

    private void run()
        throws Exception
    {
    }
}</tt></b> </pre>
      <p>
    The main program uses the <tt class="classname">SampleDatabase</tt> and
	<tt class="classname">SampleViews</tt> classes that were described in the preceding
	sections. The <tt class="methodname">main</tt> method will create an instance of the
	<tt class="classname">Sample</tt> class, and call its <tt class="methodname">run()</tt> and <tt class="methodname">close()</tt>
	methods.
    
</p>
      <p>
    The following statements parse the program's command line
	arguments.
</p>
      <a id="cb_main"></a>
      <pre class="programlisting">    public static void main(String[] args)
    {
<b class="userinput"><tt>        System.out.println("\nRunning sample: " + Sample.class);
        String homeDir = "./tmp";
        for (int i = 0; i &lt; args.length; i += 1)
        {
            String arg = args[i];
            if (args[i].equals("-h") &amp;&amp; i &lt; args.length - 1)
            {
                i += 1;
                homeDir = args[i];
            }
            else
            {
                System.err.println("Usage:\n java " + 
                                   Sample.class.getName() +
                                  "\n  [-h &lt;home-directory&gt;]");
                System.exit(2);
            }
        }</tt></b>
        ...
    } </pre>
      <p>
    The usage command is:
</p>
      <pre class="programlisting"><b class="userinput"><tt>java com.sleepycat.examples.bdb.shipment.basic.Sample
     [-h &lt;home-directory&gt; ]</tt></b> </pre>
      <p>
    The <tt class="literal">-h</tt> command is used to set the <tt class="filename">homeDir</tt>
	variable, which will later be passed to the <tt class="methodname">SampleDatabase()</tt>
	constructor. Normally all Berkeley DB programs should provide a way
	to configure their database environment home directory.
</p>
      <p>
    The default for the home directory is <tt class="filename">./tmp</tt> — the tmp
	subdirectory of the current directory where the sample is run. The
	home directory must exist before running the sample. To re-create
	the sample database from scratch, delete all files in the home
	directory before running the sample.
</p>
      <p>
    The home directory was described previously in
    <a href="opendbenvironment.html">
		Opening and Closing the Database Environment
	</a>.
</p>
      <p>
    Of course, the command line arguments shown are only examples
	and a real-life application may use different techniques for
	configuring these options.
    
</p>
      <p>
    The following statements create an instance of the <tt class="classname">Sample</tt>
	class and call its <tt class="methodname">run()</tt> and <tt class="methodname">close()</tt> methods.
</p>
      <a id="cb_main2"></a>
      <pre class="programlisting">    public static void main(String args)
    {
        ...
<b class="userinput"><tt>        Sample sample = null;
        try
        {
            sample = new Sample(homeDir);
            sample.run();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        finally
        {
            if (sample != null)
            {
                try
                {
                    sample.close();
                }
                catch (Exception e)
                {
                    System.err.println("Exception during database close:");
                    e.printStackTrace();
                }
            }
        }</tt></b>
    } </pre>
      <p>
    The <tt class="methodname">Sample()</tt> constructor will open the environment and
	databases, and the <tt class="methodname">run()</tt> method will run transactions for
	storing and retrieving objects. If either of these throws an
	exception, then the program was unable to run and should normally
	terminate. (Transaction retries are handled at a lower level and
	will be described later.) The first <tt class="literal">catch</tt> statement handles
	such exceptions.
</p>
      <p>
    The <tt class="literal">finally</tt> statement is used to call the <tt class="methodname">close()</tt>
	method since an attempt should always be made to close the environment and
    databases
	cleanly. If an exception is thrown during close and a prior
	exception occurred above, then the exception during close is likely
	a side effect of the prior exception.
</p>
      <p>
    The <tt class="methodname">Sample()</tt> constructor creates the <tt class="literal">SampleDatabase</tt>
	and <tt class="classname">SampleViews</tt> objects.
</p>
      <a id="cb_sample"></a>
      <pre class="programlisting">    private Sample(String homeDir)
        throws DatabaseException, FileNotFoundException
    {
<b class="userinput"><tt>        db = new SampleDatabase(homeDir);
        views = new SampleViews(db);</tt></b>
    } </pre>
      <p>
    Recall that creating the <tt class="classname">SampleDatabase</tt> object will open
	the environment and all databases.
</p>
      <p>
    To close the database the <tt class="methodname">Sample.close()</tt> method simply
	calls <tt class="methodname">SampleDatabase.close()</tt>.
</p>
      <a id="cb_sample-close"></a>
      <pre class="programlisting">     private void close()
        throws DatabaseException
    {
<b class="userinput"><tt>        db.close();</tt></b>
    } </pre>
      <p>
    The <tt class="methodname">run()</tt> method is described in the next section.
</p>
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