The main program opens the environment and databases, 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.

The Sample class contains the main program. The skeleton for the Sample class follows.

import com.sleepycat.je.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
    {
    }
} 

The main program uses the SampleDatabase and SampleViews classes that were described in the preceding sections. The main method will create an instance of the Sample class, and call its run() and close() methods.

The following statements parse the program's command line arguments.

    public static void main(String[] args)
    {
        System.out.println("\nRunning sample: " + Sample.class);
        String homeDir = "./tmp";
        for (int i = 0; i < args.length; i += 1)
        {
            String arg = args[i];
            if (args[i].equals("-h") && i < args.length - 1)
            {
                i += 1;
                homeDir = args[i];
            }
            else
            {
                System.err.println("Usage:\n java " + 
                                   Sample.class.getName() +
                                  "\n  [-h <home-directory>]");
                System.exit(2);
            }
        }
    } 

The usage command is:

java com.sleepycat.examples.bdb.shipment.basic.Sample
     [-h <home-directory> ] 

The -h command is used to set the homeDir variable, which will later be passed to the SampleDatabase() constructor. Normally all Berkeley DB programs should provide a way to configure their database environment home directory.

The default for the home directory is ./tmp — 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.

The home directory was described previously in Opening and Closing the Database Environment .

Of course, the command line arguments shown are only examples and a real-life application may use different techniques for configuring these options.

The following statements create an instance of the Sample class and call its run() and close() methods.

    public static void main(String args)
    {
        ...
        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();
                }
            }
        }
    } 

The Sample() constructor will open the environment and databases, and the run() 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 catch statement handles such exceptions.

The finally statement is used to call the close() method since an attempt should always be made to close the database 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.

The Sample() constructor creates the SampleDatabase and SampleViews objects.

    private Sample(String homeDir)
        throws DatabaseException, FileNotFoundException
    {
        db = new SampleDatabase(homeDir);
        views = new SampleViews(db);
    } 

Recall that creating the SampleDatabase object will open the environment and all databases.

To close the database the Sample.close() method simply calls SampleDatabase.close().

     private void close()
        throws DatabaseException
    {
        db.close();
    } 

The run() method is described in the next section.