|Home > Documentation > User's guide > Connectors and Transaction Management (JDBC, JMS, J2CA, DataSource, Connection Pool, EIS)|
Inbound and outbound connections in Geronimo are managed through the J2CA connector framework. This covers JDBC, JMS, DataSources, EIS connectivity, and connection pools. JDBC connectivity is implemented by wrapping JDBC XADataSource, ConnectionPoolDataSource, DataSource, or Driver implementations in J2CA connector wrappers. The wrappers we use are from the codehaus Tranql project.
Applications can delegate transaction management to the server infrastructure through application managed UserTransactions or for ejbs container manager transactions. The server uses a transaction manager to coordinate this application view of transaction boundaries with the resource manager view of work done on specific data stores within particular transactions. Geronimo uses a JTA TransactionManager implementation that is extended in three ways:
The J2CA connector spec provides a reasonable approach to configuring and pooling outbound connections and configuring and managing inbound message delivery. Geronimo uses this for jdbc connection support by wrapping jdbc artifacts in the required J2CA artifacts, using the tranql project wrappers.
Often connections to legacy EIS systems and databases have connections that are extremely expensive to set up. Rather than creating a new connection to the external system every time one is needed, normally you use a connection pool: when a connection is needed an unused connection is supplied from the pool, and when the application is done with it the connection is put back in the pool. The J2CA spec supports this idea with these components:
A connection factory (e.g. DataSource) is a component used by an application to get "connections" it can use. These connections are short lived, lightweight handles or wrappers to underlying "physical" managed connections. When an application calls datasource.getConnection(), the connection factory routes the request to the connection manager, which supplies a suitable connection handle from a cached, pooled, or new connection.
The connection manager received connection requests from the connection factory and figures out how to accomodate them. It also receives notification of transaction events and transfer of control between application components such as ejbs.
Generally, if there is a cached ManagedConnection in the environment, the connection manager returns a new handle to the cached ManagedConnection. Otherwise it looks for a suitable ManagedConnection in the pool, and returns a handle to such a connection if it exists. Otherwise it creates a new connection.
Connection managers in geronimo can be configured with xa, local, or no transaction support.
No Transaction support means that connections are never enrolled in jta transactions and committing such a jta transaction has no effect on any connections managed by the connection manager. In this case the connection manager does no caching and each connection request is handled independently.
Local transaction support relies on the connector support of j2ca local transaction control. This maps to such things as non-xa jdbc Driver, DataSource, and ConnectionPoolDataSource implementations. In this case geronimo constructs a "fake" XAResource that enables the JTA transaction manager to control the local transaction, however xa features such as separation of prepare and commit phases and recovery are not implemented. Since the resource manager has no transaction identifier that lets it distinguish which transaction work is being done on, the connection manager has to keep track of this by caching all the connections enrolled in a jta transaction. Whenever your application requests a connection while in a jta transaction, the connection manager checks for an existing connection enrolled in this transaction and if found supplies an additional handle to it. If no connection is associated, one is fetched from the pool (or created anew) and cached with the transaction. Furthermore, closing one or all of these connection handles will not result in returning the connection to the pool. The connection is returned to the pool only when all the handles have been closed and the jta transaction completes.
XA transaction support should theoretically not require caching connections with transactions but in practice usually does. The XA spec indicates that any connection should be able to handle work in any transaction at any time, but few if any XA capable resource managers actually implement this. Normally you must do all work in a JTA transaction against a given resource manager over the same physical connection. Setting transaction-caching on will assure that this caching takes place.
The intent of the enlist/delist methods on XAResource appears to be to support reusing a connection in a thread as it enters and leaves "Requires New" transaction boundaries. By default geronimo does not attempt to reuse connections in this way: the connections associated with the previous transaction are left associated with it and new connection requests get new ManagedConnections from the pool. There is an experimental configuration to reuse the connections already associated with the thread.
In the J2CA 1.5 spec security considerations are confined to providing the credentials for outbound connections. There is no provision for credential inflow for inbound messaging. This hole is being addressed in the next spec revision.
There are three possible sources for credentials for outbound connections:
TODO container managed security example
Effective connection pooling relies on all the connections in a pool being effectively identical. We won't discuss the impact of reauthentication support here: the only place I know it is available is in some Oracle connectors, and only through using some special packages. Geronimo allows you to set up pooling for a single connection manager/ManagedConnectionFactory with either one pool or multiple pools. Multiple pools are distinguished by credentials, either from application managed security or container managed security. Given a request geronimo looks for a pool with matching credentials and creates one if there is none. In particular this means that pool size is per credential set, so with 10 distinct users and a pool size of 10, you may have 100 connections in the multiple pools.
Within a single pool, you can specify how hard geronimo works to assure that a connection matches the request.
An outbound connector includes ManagedConnectionFactory and ManagedConnection implementations. The ManagedConnection represents an actual "physical" connection to the resource manager (database). The ManagedConnectionFactory contains configuration for the desired ManagedConnections such as the location of the resource manager. It also contains matching code to select a connection matching a request from a set of connections. The ManagedConnection also can provide connection handles that the connection factory can return.
In geronimo we wrap the ManagedConnectionFactory with a gbean so it can be configured like other geronimo components.
JDBC support is generally provided through wrapping JDBC artifacts in J2CA artifacts from the codehaus tranql project. Some databases such as Firebird also provide J2CA implementations that can be deployed directly. Tranql provides a framework for constructing outbound resource adapters and a variety of published adapters.
All JDBC implementations provide at least a Driver implementation. Tranql provides a generic connector org.tranql:tranql-connector-ra:1.4:rar that can be used with any Driver implementation. This provides only local transaction support and requires that you encode any specific connection properties in the jdbc url.
Most JDBC implementations also provide DataSource, ConnectionPoolDataSource, or XADataSource implementations. The tranql framework is designed to make it easy to write database specific wrappers for these classes. With such wrappers properties that can be set on these connection factories or "managed connection factories" are exposed as ManagedConnectionFactory config-properties and can be documented in the ra.xml. Currently tranql provides wrappers for DB2 (xa), Derby (local and xa, embedded and client), mysql (local and xa), oracle (local and xa), and postgres (local and xa).
As of J2EE 1.4 JMS implementations are expected to provide a J2CA resource adapter for use in EE environments. Geronimo relies on this for JMS support. Geronimo provides ActiveMQ as the default JMS provider.
The J2CA spec envisages connection between EE servers and EIS through J2CA connectors. J2CA provides for outbound connections as already described and inbound connections to MDBs. Along with JMS style asynchronous inbound messaging, in which the message may be delivered in a container controlled transaction, message delivery may be performed in an adapter provided transaction. Currently there are no facilities for security context import but this is expected in the next J2CA spec revision.