Persistent Storage I: MIDP Record Store - Beginning J2ME: From Novice to Professional - page 110

// Now save the preferences records.
Enumeration keys = mHashtable.keys();
while (keys.hasMoreElements()) {
String key = (String)keys.nextElement();
String value = get(key);
String pref = key + "|" + value;
byte[] raw = pref.getBytes();
rs.addRecord(raw, 0, raw.length);
}
}
finally {
if (re != null) re.destroy();
if (rs != null) rs.closeRecordStore();
}
}
}
RecordMIDlet saves the updated values back to the RecordStore in its destroyApp() method. It
saves the user name and password from the user interface in the Preferences object, then calls
the save() method to write the new values out to the RecordStore . The save() method removes
all records from the record store, and then adds each key and value pair.
To test out the MIDlet, enter some text into the user name and password fields. Then exit
the MIDlet and restart it. You will see the same values loaded into the text fields.
Note that Preferences only deals with String values, but records can contain any data
packed into a byte array. By using stream classes from the java.io package, it's possible to
store complex data types in records. For example, you could use a DataOutputStream wrapped
around a ByteArrayOutputStream to generate data to be written into the record store. To extract
data values, you would use a DataInputStream wrapped around a ByteArrayInputStream based
on the record data.
Listening for Record Changes
RecordStore s support a JavaBeans-style listener mechanism. Interested objects can listen for
changes to a record store by registering themselves as listeners.
The listener interface is javax.microedition.rms.RecordListener . You can manage a
RecordStore 's listeners with the following two methods:
public void addRecordListener(RecordListener listener)
public void removeRecordListener(RecordListener listener)
The RecordListener interface has three methods: recordAdded() , recordChanged() , and
recordDeleted() . These are called whenever a record is added, changed, or deleted. Each method
is passed the RecordStore involved and the ID of the record in question.