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 * Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 * <p>
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 * <p>
 * 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).
 * <p>
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 * <p>
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 */


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:

    

  1. The DataSource interface as an alternative to the
DriverManager for establishing a
connection with a data source

  2. Connection pooling and Statement pooling

  3. Distributed transactions

  4. Rowsets




Applications use the DataSource and RowSet
APIs directly, but the connection pooling and distributed transaction
APIs are used internally by the middle-tier infrastructure.

Using a 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:

    

  • 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 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.

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 Connection
object.


The classes and interfaces used for connection pooling are:

    

  • ConnectionPoolDataSource

  • PooledConnection

  • ConnectionEvent

  • ConnectionEventListener

  • StatementEvent

  • StatementEventListener


The connection pool manager, a facility in the middle tier of
a three-tier architecture, uses these classes and interfaces
behind the scenes.  When a 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.

Distributed Transactions



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


These interfaces are used by the transaction manager; an application does
not use them directly.


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.

Rowsets

The RowSet interface works with various other classes and
interfaces behind the scenes. These can be grouped into three categories.

    

  1. Event Notification

      

    • RowSetListener
      
A 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
      
As part of its internal notification process, a 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.

    

  2. Metadata

      

    • RowSetMetaData
      
This interface, derived from the
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.

    

  3. The Reader/Writer Facility
    
A 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
      
By implementing the 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
      
A disconnected 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
      
A disconnected 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:

        

      • 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

      

    




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.

Package Specification



Related Documentation



The Java Series book published by Addison-Wesley Longman provides detailed
information about the classes and interfaces in the javax.sql
package:



/**
 * Provides the API for server side data source access and processing from
 * the Java&trade; programming language.
 * This package supplements the <code>java.sql</code>
 * package and, as of the version 1.4 release, is included in the
 * Java Platform, Standard Edition (Java SE&trade;).
 * It remains an essential part of the Java Platform, Enterprise Edition
 * (Java EE&trade;).
 * <p>
 * The <code>javax.sql</code> package provides for the following:
 * <OL>
 * <LI>The <code>DataSource</code> interface as an alternative to the
 * <code>DriverManager</code> for establishing a
 * connection with a data source
 * <LI>Connection pooling and Statement pooling
 * <LI>Distributed transactions
 * <LI>Rowsets
 * </OL>
 * <p>
 * Applications use the <code>DataSource</code> and <code>RowSet</code>
 * APIs directly, but the connection pooling and distributed transaction
 * APIs are used internally by the middle-tier infrastructure.
 *
 * <H2>Using a <code>DataSource</code> Object to Make a Connection</H2>
 * <p>
 * The <code>javax.sql</code> package provides the preferred
 * way to make a connection with a data source.  The <code>DriverManager</code>
 * class, the original mechanism, is still valid, and code using it will
 * continue to run.  However, the newer <code>DataSource</code> mechanism
 * is preferred because it offers many advantages over the
 * <code>DriverManager</code> mechanism.
 * <p>
 * These are the main advantages of using a <code>DataSource</code> object to
 * make a connection:
 * <UL>
 *
 * <LI>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.
 * <LI>Connection  and Statement pooling and distributed transactions are available
 * through a <code>DataSource</code> object that is
 * implemented to work with the middle-tier infrastructure.
 * Connections made through the <code>DriverManager</code>
 * do not have connection and statement pooling or distributed transaction
 * capabilities.
 * </UL>
 * <p>
 * Driver vendors provide <code>DataSource</code> implementations. A
 * particular <code>DataSource</code> object represents a particular
 * physical data source, and each connection the <code>DataSource</code> object
 * creates is a connection to that physical data source.
 * <p>
 * A logical name for the data source is registered with a naming service that
 * uses the Java Naming and Directory Interface&trade;
 * (JNDI) API, usually by a system administrator or someone performing the
 * duties of a system administrator. An application can retrieve the
 * <code>DataSource</code> object it wants by doing a lookup on the logical
 * name that has been registered for it.  The application can then use the
 * <code>DataSource</code> object to create a connection to the physical data
 * source it represents.
 * <p>
 * A <code>DataSource</code> 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 <code>DataSource</code>
 * implementation will automatically get a connection that participates in
 * connection pooling.
 * A <code>DataSource</code> 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.
 *
 * <H2>Connection Pooling and Statement Pooling</H2>
 * <p>
 * Connections made via a <code>DataSource</code>
 * 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.
 * <p>
 * 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 <code>DataSource.getConnection</code> method to get the pooled
 * connection and uses it the same way it uses any <code>Connection</code>
 * object.
 * <p>
 * The classes and interfaces used for connection pooling are:
 * <UL>
 * <LI><code>ConnectionPoolDataSource</code>
 * <LI><code>PooledConnection</code>
 * <LI><code>ConnectionEvent</code>
 * <LI><code>ConnectionEventListener</code>
 * <LI><code>StatementEvent</code>
 * <LI><code>StatementEventListener</code>
 * </UL>
 * The connection pool manager, a facility in the middle tier of
 * a three-tier architecture, uses these classes and interfaces
 * behind the scenes.  When a <code>ConnectionPoolDataSource</code> object
 * is called on to create a <code>PooledConnection</code> object, the
 * connection pool manager will register as a <code>ConnectionEventListener</code>
 * object with the new <code>PooledConnection</code> object.  When the connection
 * is closed or there is an error, the connection pool manager (being a listener)
 * gets a notification that includes a <code>ConnectionEvent</code> object.
 * <p>
 * If the connection pool manager supports <code>Statement</code> pooling, for
 * <code>PreparedStatements</code>, which can be determined by invoking the method
 * <code>DatabaseMetaData.supportsStatementPooling</code>,  the
 * connection pool manager will register as a <code>StatementEventListener</code>
 * object with the new <code>PooledConnection</code> object.  When the
 * <code>PreparedStatement</code> is closed or there is an error, the connection
 * pool manager (being a listener)
 * gets a notification that includes a <code>StatementEvent</code> object.
 *
 * <H2>Distributed Transactions</H2>
 * <p>
 * As with pooled connections, connections made via a <code>DataSource</code>
 * 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.
 * <p>
 * The classes and interfaces used for distributed transactions are:
 * <UL>
 * <LI><code>XADataSource</code>
 * <LI><code>XAConnection</code>
 * </UL>
 * These interfaces are used by the transaction manager; an application does
 * not use them directly.
 * <p>
 * The <code>XAConnection</code> interface is derived from the
 * <code>PooledConnection</code> 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 <code>Connection.commit</code>
 * or <code>Connection.rollback</code>, and it cannot set the connection to be in
 * auto-commit mode (that is, it cannot call
 * <code>Connection.setAutoCommit(true)</code>).
 * <p>
 * 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 <code>DataSource.getConnection</code> method, just as it normally does.
 * The transaction manager manages the transaction behind the scenes.  The
 * <code>XADataSource</code> interface creates <code>XAConnection</code> objects, and
 * each <code>XAConnection</code> object creates an <code>XAResource</code> object
 * that the transaction manager uses to manage the connection.
 *
 *
 * <H2>Rowsets</H2>
 * The <code>RowSet</code> interface works with various other classes and
 * interfaces behind the scenes. These can be grouped into three categories.
 * <OL>
 * <LI>Event Notification
 * <UL>
 * <LI><code>RowSetListener</code><br>
 * A <code>RowSet</code> object is a JavaBeans&trade;
 * component because it has properties and participates in the JavaBeans
 * event notification mechanism. The <code>RowSetListener</code> interface
 * is implemented by a component that wants to be notified about events that
 * occur to a particular <code>RowSet</code> object.  Such a component registers
 * itself as a listener with a rowset via the <code>RowSet.addRowSetListener</code>
 * method.
 * <p>
 * When the <code>RowSet</code> 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.
 * <LI><code>RowSetEvent</code><br>
 * As part of its internal notification process, a <code>RowSet</code> object
 * creates an instance of <code>RowSetEvent</code> and passes it to the listener.
 * The listener can use this <code>RowSetEvent</code> object to find out which rowset
 * had the event.
 * </UL>
 * <LI>Metadata
 * <UL>
 * <LI><code>RowSetMetaData</code><br>
 * This interface, derived from the
 * <code>ResultSetMetaData</code> interface, provides information about
 * the columns in a <code>RowSet</code> object.  An application can use
 * <code>RowSetMetaData</code> methods to find out how many columns the
 * rowset contains and what kind of data each column can contain.
 * <p>
 * The <code>RowSetMetaData</code> interface provides methods for
 * setting the information about columns, but an application would not
 * normally use these methods.  When an application calls the <code>RowSet</code>
 * method <code>execute</code>, the <code>RowSet</code> object will contain
 * a new set of rows, and its <code>RowSetMetaData</code> object will have been
 * internally updated to contain information about the new columns.
 * </UL>
 * <LI>The Reader/Writer Facility<br>
 * A <code>RowSet</code> object that implements the <code>RowSetInternal</code>
 * interface can call on the <code>RowSetReader</code> object associated with it
 * to populate itself with data.  It can also call on the <code>RowSetWriter</code>
 * 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.
 *
 * <UL>
 * <LI><code>RowSetInternal</code><br>
 * By implementing the <code>RowSetInternal</code> interface, a
 * <code>RowSet</code> 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 <i>original</i> 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
 * <code>RowSetInternal</code> methods behind the scenes to get access to
 * this information.  An application does not normally invoke these methods directly.
 *
 * <LI><code>RowSetReader</code><br>
 * A disconnected <code>RowSet</code> object that has implemented the
 * <code>RowSetInternal</code> interface can call on its reader (the
 * <code>RowSetReader</code> object associated with it) to populate it with
 * data.  When an application calls the <code>RowSet.execute</code> 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 <code>RowSetMetaData</code> object
 * for its rowset.  The rowset's internal state is also updated, either by the
 * reader or directly by the method <code>RowSet.execute</code>.
 *
 *
 * <LI><code>RowSetWriter</code><br>
 * A disconnected <code>RowSet</code> object that has implemented the
 * <code>RowSetInternal</code> interface can call on its writer (the
 * <code>RowSetWriter</code> 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:
 *
 * <UL>
 * <LI>Make a connection to the data source
 * <LI>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
 * <LI>Write the new values to the data source if there is no conflict
 * <LI>Close the connection
 * </UL>
 *
 *
 * </UL>
 * </OL>
 * <p>
 * The <code>RowSet</code> 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.
 *
 *
 * <h2>Package Specification</h2>
 *
 * <ul>
 * <li><a href="https://jcp.org/en/jsr/detail?id=221">JDBC 4.3 Specification</a>
 * </ul>
 *
 * <h2>Related Documentation</h2>
 * <p>
 * The Java Series book published by Addison-Wesley Longman provides detailed
 * information about the classes and interfaces in the <code>javax.sql</code>
 * package:
 *
 * <ul>
 * <li><a href="http://www.oracle.com/technetwork/java/index-142838.html">
 * <i>JDBC&#8482;API Tutorial and Reference, Third Edition</i></a>
 * </ul>
 */
package javax.sql;