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Santiago Pericas-Geertsen's BlogDeveloping MEP Connectors - Part IIIPosted by spericas on October 01, 2008 at 07:09 AM | Comments (4)In the two installments of this series we've looked at the architecture of a MEP connector, discussed the main abstractions of the ECBO (Enterprise Connector Business Object) API and showed an example of a MusicAlbum business object. In this third part, we'll focus on the MusicAlbumProvider class which is needed to complete the implementation of the connector to access music albums from a JDBC database. The complete source code for the MusicDB enterprise connector is included in the MEP client bundle available for download here. In the directory where you unzipped the client bundle, look for it under sjsmep-client-1_0-fcs/samples/ecbo/. As explained earlier in this series, the ECBO API provides two essential abstractions: BusinessObject and BusinessObjectProvider. Due to the nature of the synchronization process, every enterprise connector must provide the ability to CRUD (create, retrieve, update and delete) business objects. The BusinessObject abstraction provides support for CUD, i.e. each object provides the ability to create, update and delete itself as shown in Part II. The R operation, or retrieve, is implemented by the BusinessObjectProvider. Here is the implementation of the R operation in MusicAlbumProvider, a class extending BusinessObjectProvider.
@Override
public List<MusicAlbum> getBusinessObjects() {
Statement stmt = null;
List<MusicAlbum> albums = null;
try {
stmt = sqlConnection.createStatement();
// Read all music albums and store them in array
albums = new ArrayList<MusicAlbum>();
ResultSet rs = stmt.executeQuery(
"SELECT * FROM album WHERE username = '" + username + "'");
while (rs.next()) {
MusicAlbum album = new MusicAlbum(this);
album.setName(rs.getString(1));
album.setArtist(rs.getString(2));
album.setDatePublished(rs.getString(3).replace("-", ""));
album.setRating(rs.getInt(4));
albums.add(album);
}
rs.close();
} catch (Exception ex) {
throw new RuntimeException(ex);
} finally {
if (stmt != null) {
try { stmt.close(); } catch (Exception e) { /* ignore !*/ }
}
}
return albums;
}
The getBusinessObjects() method simply queries the database for all albums that are owned by the user that logged in into the connector and returns them as a List<MusicAlbum>. In addition to providing support for the R operation, a business object provider being the entry point to the connector, should also provide implementations for the lifecycle methods initialize() and terminate(). These methods are called at the beginning and at the end of a synchronization session. In most connectors, these methods are used to connect to and disconnect from an enterprise system; in the MusicDB connector, in particular, they are used to connect and disconnect from the database as shown below.
@Override
public void initialize() {
try {
Context jndiContext = new InitialContext();
DataSource ds = (DataSource) jndiContext.lookup(MUSICDB_JNDI_DATASOURCE);
sqlConnection = ds.getConnection();
} catch (Exception ex) {
throw new RuntimeException(ex);
}
}
@Override
public void terminate() {
try {
if (sqlConnection != null) {
sqlConnection.close();
}
} catch (Exception e) {
throw new RuntimeException(e);
}
}
Contextual information related to the active synchronization session (e.g., session id or user logged in) can be access via calling getSessionContext(). Finally, each connector may define its own transaction manager by overriding the method getTransactionManager(). For more information on these features, the reader is referred to the MEP online documentation. If you're interested in developing a MEP connector, I suggest that you start by using Maven's MEP Connector Archetype (JAR). If you're a Netbeans user, simply go to File -> New Project -> Maven -> Maven Project and select it from the list. Happy synching! Bookmark blog post:  del.icio.us  Digg  DZone  Furl  Reddit
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