java.sqlpackage and, as of the version 1.4 release, is included in the Java Platform, Standard Edition (Java SE™). It remains an essential part of the Java Platform, Enterprise Edition (Java EE™).
javax.sql package provides for the following:
DataSourceinterface as an alternative to the
DriverManagerfor establishing a connection with a data source
- Connection pooling and Statement pooling
- Distributed transactions
Applications use the
RowSet APIs directly, but the connection pooling and distributed transaction APIs are used internally by the middle-tier infrastructure.
DataSource Object to Make a Connection
javax.sql package provides the preferred way to make a connection with a data source. The
DriverManager class, the original mechanism, is still valid, and code using it will continue to run. However, the newer
DataSource mechanism is preferred because it offers many advantages over the
These are the main advantages of using a
DataSource object to make a connection:
- Changes can be made to a data source's properties, which means that it is not necessary to make changes in application code when something about the data source or driver changes.
- Connection and Statement pooling and distributed transactions are available through a
DataSourceobject that is implemented to work with the middle-tier infrastructure. Connections made through the
DriverManagerdo not have connection and statement pooling or distributed transaction capabilities.
Driver vendors provide
DataSource implementations. A particular
DataSource object represents a particular physical data source, and each connection the
DataSource object creates is a connection to that physical data source.
A logical name for the data source is registered with a naming service that uses the Java Naming and Directory Interface™ (JNDI) API, usually by a system administrator or someone performing the duties of a system administrator. An application can retrieve the
DataSource object it wants by doing a lookup on the logical name that has been registered for it. The application can then use the
DataSource object to create a connection to the physical data source it represents.
DataSource object can be implemented to work with the middle tier infrastructure so that the connections it produces will be pooled for reuse. An application that uses such a
DataSource implementation will automatically get a connection that participates in connection pooling. A
DataSource object can also be implemented to work with the middle tier infrastructure so that the connections it produces can be used for distributed transactions without any special coding.
Connection Pooling and Statement Pooling
Connections made via a
DataSource object that is implemented to work with a middle tier connection pool manager will participate in connection pooling. This can improve performance dramatically because creating new connections is very expensive. Connection pooling allows a connection to be used and reused, thus cutting down substantially on the number of new connections that need to be created.
Connection pooling is totally transparent. It is done automatically in the middle tier of a Java EE configuration, so from an application's viewpoint, no change in code is required. An application simply uses the
DataSource.getConnection method to get the pooled connection and uses it the same way it uses any
The classes and interfaces used for connection pooling are:
ConnectionPoolDataSourceobject is called on to create a
PooledConnectionobject, the connection pool manager will register as a
ConnectionEventListenerobject with the new
PooledConnectionobject. When the connection is closed or there is an error, the connection pool manager (being a listener) gets a notification that includes a
If the connection pool manager supports
Statement pooling, for
PreparedStatements, which can be determined by invoking the method
DatabaseMetaData.supportsStatementPooling, the connection pool manager will register as a
StatementEventListener object with the new
PooledConnection object. When the
PreparedStatement is closed or there is an error, the connection pool manager (being a listener) gets a notification that includes a
As with pooled connections, connections made via a
DataSource object that is implemented to work with the middle tier infrastructure may participate in distributed transactions. This gives an application the ability to involve data sources on multiple servers in a single transaction.
The classes and interfaces used for distributed transactions are:
XAConnection interface is derived from the
PooledConnection interface, so what applies to a pooled connection also applies to a connection that is part of a distributed transaction. A transaction manager in the middle tier handles everything transparently. The only change in application code is that an application cannot do anything that would interfere with the transaction manager's handling of the transaction. Specifically, an application cannot call the methods
Connection.rollback, and it cannot set the connection to be in auto-commit mode (that is, it cannot call
An application does not need to do anything special to participate in a distributed transaction. It simply creates connections to the data sources it wants to use via the
DataSource.getConnection method, just as it normally does. The transaction manager manages the transaction behind the scenes. The
XADataSource interface creates
XAConnection objects, and each
XAConnection object creates an
XAResource object that the transaction manager uses to manage the connection.
RowSetinterface works with various other classes and interfaces behind the scenes. These can be grouped into three categories.
- Event Notification
RowSetobject is a JavaBeans™ component because it has properties and participates in the JavaBeans event notification mechanism. The
RowSetListenerinterface is implemented by a component that wants to be notified about events that occur to a particular
RowSetobject. Such a component registers itself as a listener with a rowset via the
RowSetobject changes one of its rows, changes all of it rows, or moves its cursor, it also notifies each listener that is registered with it. The listener reacts by carrying out its implementation of the notification method called on it.
As part of its internal notification process, a
RowSetobject creates an instance of
RowSetEventand passes it to the listener. The listener can use this
RowSetEventobject to find out which rowset had the event.
This interface, derived from the
ResultSetMetaDatainterface, provides information about the columns in a
RowSetobject. An application can use
RowSetMetaDatamethods to find out how many columns the rowset contains and what kind of data each column can contain.
RowSetMetaDatainterface provides methods for setting the information about columns, but an application would not normally use these methods. When an application calls the
RowSetobject will contain a new set of rows, and its
RowSetMetaDataobject will have been internally updated to contain information about the new columns.
- The Reader/Writer Facility
RowSetobject that implements the
RowSetInternalinterface can call on the
RowSetReaderobject associated with it to populate itself with data. It can also call on the
RowSetWriterobject associated with it to write any changes to its rows back to the data source from which it originally got the rows. A rowset that remains connected to its data source does not need to use a reader and writer because it can simply operate on the data source directly.
By implementing the
RowSetobject gets access to its internal state and is able to call on its reader and writer. A rowset keeps track of the values in its current rows and of the values that immediately preceded the current ones, referred to as the original values. A rowset also keeps track of (1) the parameters that have been set for its command and (2) the connection that was passed to it, if any. A rowset uses the
RowSetInternalmethods behind the scenes to get access to this information. An application does not normally invoke these methods directly.
RowSetobject that has implemented the
RowSetInternalinterface can call on its reader (the
RowSetReaderobject associated with it) to populate it with data. When an application calls the
RowSet.executemethod, that method calls on the rowset's reader to do much of the work. Implementations can vary widely, but generally a reader makes a connection to the data source, reads data from the data source and populates the rowset with it, and closes the connection. A reader may also update the
RowSetMetaDataobject for its rowset. The rowset's internal state is also updated, either by the reader or directly by the method
RowSetobject that has implemented the
RowSetInternalinterface can call on its writer (the
RowSetWriterobject associated with it) to write changes back to the underlying data source. Implementations may vary widely, but generally, a writer will do the following:
- Make a connection to the data source
- Check to see whether there is a conflict, that is, whether a value that has been changed in the rowset has also been changed in the data source
- Write the new values to the data source if there is no conflict
- Close the connection
RowSet interface may be implemented in any number of ways, and anyone may write an implementation. Developers are encouraged to use their imaginations in coming up with new ways to use rowsets.
The Java Series book published by Addison-Wesley Longman provides detailed information about the classes and interfaces in the
Interface Summary Interface Description CommonDataSourceInterface that defines the methods which are common between
ConnectionEventListenerAn object that registers to be notified of events generated by a
ConnectionPoolDataSourceA factory for
DataSourceA factory for connections to the physical data source that this
PooledConnectionAn object that provides hooks for connection pool management. PooledConnectionBuilderA builder created from a
ConnectionPoolDataSourceobject, used to establish a connection to the database that the
data sourceobject represents.
RowSetThe interface that adds support to the JDBC API for the JavaBeans™ component model. RowSetInternalThe interface that a
RowSetobject implements in order to present itself to a
RowSetListenerAn interface that must be implemented by a component that wants to be notified when a significant event happens in the life of a
RowSetMetaDataAn object that contains information about the columns in a
RowSetReaderThe facility that a disconnected
RowSetobject calls on to populate itself with rows of data.
RowSetWriterAn object that implements the
RowSetWriterinterface, called a writer.
StatementEventListenerAn object that registers to be notified of events that occur on PreparedStatements that are in the Statement pool. XAConnectionAn object that provides support for distributed transactions. XAConnectionBuilderA builder created from a
XADataSourceobject, used to establish a connection to the database that the
data sourceobject represents.
XADataSourceA factory for
XAConnectionobjects that is used internally.
Class Summary Class Description ConnectionEventAn
Eventobject that provides information about the source of a connection-related event.
Eventobject generated when an event occurs to a
StatementEventis sent to all
StatementEventListeners which were registered with a