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* This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). *
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*/
/**
* Provides the API for server side data source access and processing from
* the Java™ programming language.
* This package supplements the java.sql
* package 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™).
*
* The javax.sql
package provides for the following:
*
DataSource
interface as an alternative to the
* DriverManager
for establishing a
* connection with a data source
*
* Applications use the DataSource
and 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
* The 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
* DriverManager
mechanism.
*
* These are the main advantages of using a DataSource
object to
* make a connection:
*
DataSource
object that is
* implemented to work with the middle-tier infrastructure.
* Connections made through the DriverManager
* do 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.
*
* A 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.
*
*
* 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 Connection
* object.
*
* The classes and interfaces used for connection pooling are: *
ConnectionPoolDataSource
* PooledConnection
* ConnectionEvent
* ConnectionEventListener
* StatementEvent
* StatementEventListener
* ConnectionPoolDataSource
object
* is called on to create a PooledConnection
object, the
* connection pool manager will register as a ConnectionEventListener
* object with the new PooledConnection
object. When the connection
* is closed or there is an error, the connection pool manager (being a listener)
* gets a notification that includes a ConnectionEvent
object.
*
* 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 StatementEvent
object.
*
*
* 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: *
XADataSource
* XAConnection
*
* The 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.commit
* or Connection.rollback
, and it cannot set the connection to be in
* auto-commit mode (that is, it cannot call
* Connection.setAutoCommit(true)
).
*
* 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.
*
*
*
RowSet
interface works with various other classes and
* interfaces behind the scenes. These can be grouped into three categories.
* RowSetListener
RowSet
object is a JavaBeans™
* component because it has properties and participates in the JavaBeans
* event notification mechanism. The RowSetListener
interface
* is implemented by a component that wants to be notified about events that
* occur to a particular RowSet
object. Such a component registers
* itself as a listener with a rowset via the RowSet.addRowSetListener
* method.
*
* When the RowSet
object 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.
*
RowSetEvent
RowSet
object
* creates an instance of RowSetEvent
and passes it to the listener.
* The listener can use this RowSetEvent
object to find out which rowset
* had the event.
* RowSetMetaData
ResultSetMetaData
interface, provides information about
* the columns in a RowSet
object. An application can use
* RowSetMetaData
methods to find out how many columns the
* rowset contains and what kind of data each column can contain.
*
* The RowSetMetaData
interface provides methods for
* setting the information about columns, but an application would not
* normally use these methods. When an application calls the RowSet
* method execute
, the RowSet
object will contain
* a new set of rows, and its RowSetMetaData
object will have been
* internally updated to contain information about the new columns.
*
RowSet
object that implements the RowSetInternal
* interface can call on the RowSetReader
object associated with it
* to populate itself with data. It can also call on the RowSetWriter
* object 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.
*
* RowSetInternal
RowSetInternal
interface, a
* RowSet
object 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
* RowSetInternal
methods behind the scenes to get access to
* this information. An application does not normally invoke these methods directly.
*
* RowSetReader
RowSet
object that has implemented the
* RowSetInternal
interface can call on its reader (the
* RowSetReader
object associated with it) to populate it with
* data. When an application calls the RowSet.execute
method,
* 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 RowSetMetaData
object
* for its rowset. The rowset's internal state is also updated, either by the
* reader or directly by the method RowSet.execute
.
*
*
* RowSetWriter
RowSet
object that has implemented the
* RowSetInternal
interface can call on its writer (the
* RowSetWriter
object associated with it) to write changes
* back to the underlying data source. Implementations may vary widely, but
* generally, a writer will do the following:
*
*
* The 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 javax.sql
* package:
*
*