Records are stored in the database using whatever organization is required by the access method that you have selected. In some cases (such as BTree), records are stored in a sort order that you may want to define (see Setting Comparison Functions for more information).

In any case, the mechanics of putting and getting database records do not change once you have selected your access method, configured your sorting routines (if any), and opened your database. From your code's perspective, a simple database put and get is largely the same no matter what access method you are using.

You can use the following methods to put database records:

When you put database records, you provide both the key and the data as DatabaseEntry objects. This means you must convert your key and data into a Java byte array. For example:

package db.GettingStarted;

import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.Database;

...

// Database opens omitted for clarity.
// Databases must NOT be opened read-only.

String aKey = "myFirstKey";
String aData = "myFirstData";

try {
    DatabaseEntry theKey = new DatabaseEntry(aKey.getBytes("UTF-8"));
    DatabaseEntry theData = new DatabaseEntry(aData.getBytes("UTF-8"));
    myDatabase.put(null, theKey, theData);
} catch (Exception e) {
    // Exception handling goes here
} 

The Database class provides several methods that you can use to retrieve database records. Note that if your database supports duplicate records, then these methods will only ever return the first record in a duplicate set. For this reason, if your database supports duplicates, you should use a cursor to retrieve records from it. Cursors are described in Using Cursors.

You can use either of the following methods to retrieve records from the database:

Both the key and data for a database record are returned as byte arrays in DatabaseEntry objects. These objects are passed as parameter values to the Database.get() method.

In order to retrieve your data once Database.get() has completed, you must retrieve the byte array stored in the DatabaseEntry and then convert that byte array back to the appropriate datatype. For example:

package db.GettingStarted;
      
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.Database;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.OperationStatus;

...

Database myDatabase = null;
// Database opens omitted for clarity.
// Database may be opened read-only.  
  
String aKey = "myFirstKey";

try {
    // Create a pair of DatabaseEntry objects. theKey
    // is used to perform the search. theData is used
    // to store the data returned by the get() operation.
    DatabaseEntry theKey = new DatabaseEntry(aKey.getBytes("UTF-8"));
    DatabaseEntry theData = new DatabaseEntry();
    
    // Perform the get.
    if (myDatabase.get(null, theKey, theData, LockMode.DEFAULT) ==
        OperationStatus.SUCCESS) {

        // Recreate the data String.
        byte[] retData = theData.getData();
        String foundData = new String(retData, "UTF-8");
        System.out.println("For key: '" + aKey + "' found data: '" + 
                            foundData + "'.");
    } else {
        System.out.println("No record found for key '" + aKey + "'.");
    } 
} catch (Exception e) {
    // Exception handling goes here
}

You can use the Database.delete() method to delete a record from the database. If your database supports duplicate records, then all records associated with the provided key are deleted. To delete just one record from a list of duplicates, use a cursor. Cursors are described in Using Cursors.

You can also delete every record in the database by using Environment.truncateDatabase().

For example:

package db.GettingStarted;

import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.Database;

...

Database myDatabase = null;
// Database opens omitted for clarity.
// Database can NOT be opened read-only.  
  
try {
    String aKey = "myFirstKey";
    DatabaseEntry theKey = new DatabaseEntry(aKey.getBytes("UTF-8"));
    
    // Perform the deletion. All records that use this key are
    // deleted.
    myDatabase.delete(null, theKey); 
} catch (Exception e) {
    // Exception handling goes here
}

When you perform a database modification, your modification is made in the in-memory cache. This means that your data modifications are not necessarily flushed to disk, and so your data may not appear in the database after an application restart.

Note that as a normal part of closing a database, its cache is written to disk. However, in the event of an application or system failure, there is no guarantee that your databases will close cleanly. In this event, it is possible for you to lose data. Under extremely rare circumstances, it is also possible for you to experience database corruption.

Therefore, if you care if your data is durable across system failures, and to guard against the rare possibility of database corruption, you should use transactions to protect your database modifications. Every time you commit a transaction, DB ensures that the data will not be lost due to application or system failure. Transaction usage is described in the Berkeley DB Getting Started with Transaction Processing guide.

If you do not want to use transactions, then the assumption is that your data is of a nature that it need not exist the next time your application starts. You may want this if, for example, you are using DB to cache data relevant only to the current application runtime.

If, however, you are not using transactions for some reason and you still want some guarantee that your database modifications are persistent, then you should periodically run environment syncs. Syncs cause any dirty entries in the in-memory cache and the operating system's file cache to be written to disk. As such, they are quite expensive and you should use them sparingly.

Remember that by default a sync is performed any time a non-transactional database is closed cleanly. (You can override this behavior by specifying true on the call to Database.close().) That said, you can manually run a sync by calling Database.sync().