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 * Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * 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.

 * 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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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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/**

 * Provides the API for server side data source access and processing from

 * the Java™ 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™).

 * It remains an essential part of the Java Platform, Enterprise Edition

 * (Java EE™).

 * <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™

 * (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>&ldquo;<i>JDBC&#8482;API Tutorial and Reference, Third Edition</i>&rdquo;

 * </ul>

 */

package javax.sql;