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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<html>
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<head>
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<!--
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Copyright 2000-2006 Sun Microsystems, Inc. All Rights Reserved.
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DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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This code is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License version 2 only, as
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published by the Free Software Foundation. Sun designates this
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particular file as subject to the "Classpath" exception as provided
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by Sun in the LICENSE file that accompanied this code.
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This code is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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version 2 for more details (a copy is included in the LICENSE file that
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accompanied this code).
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You should have received a copy of the GNU General Public License version
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2 along with this work; if not, write to the Free Software Foundation,
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Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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CA 95054 USA or visit www.sun.com if you need additional information or
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have any questions.
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-->
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</head>
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<body bgcolor="white">
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Provides the API for server side data source access and processing from
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the Java<sup><font size=-2>TM</font></sup> programming language.
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This package supplements the <code>java.sql</code>
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package and, as of the version 1.4 release, is included in the
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Java Platform, Standard Edition
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(Java SE<sup><font size=-2>TM</sup></font>).
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It remains an essential part of the Java Platform, Enterprise Edition
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(Java EE<sup><font size=-2>TM</sup></font>).
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<P>
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The <code>javax.sql</code> package provides for the following:
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<OL>
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<LI>The <code>DataSource</code> interface as an alternative to the
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<code>DriverManager</code> for establishing a
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connection with a data source
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<LI>Connection pooling and Statement pooling
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<LI>Distributed transactions
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<LI>Rowsets
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</OL>
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<P>
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Applications use the <code>DataSource</code> and <code>RowSet</code>
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APIs directly, but the connection pooling and distributed transaction
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APIs are used internally by the middle-tier infrastructure.
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<H2>Using a <code>DataSource</code> Object to Make a Connection</H2>
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The <code>javax.sql</code> package provides the preferred
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way to make a connection with a data source. The <code>DriverManager</code>
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class, the original mechanism, is still valid, and code using it will
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continue to run. However, the newer <code>DataSource</code> mechanism
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is preferred because it offers many advantages over the
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<code>DriverManager</code> mechanism.
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<P>
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These are the main advantages of using a <code>DataSource</code> object to
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make a connection:
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<UL>
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<LI>Changes can be made to a data source's properties, which means
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that it is not necessary to make changes in application code when
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something about the data source or driver changes.
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<LI>Connection and Statement pooling and distributed transactions are available
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through a <code>DataSource</code> object that is
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implemented to work with the middle-tier infrastructure.
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Connections made through the <code>DriverManager</code>
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do not have connection and statement pooling or distributed transaction
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capabilities.
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</UL>
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<P>
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Driver vendors provide <code>DataSource</code> implementations. A
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particular <code>DataSource</code> object represents a particular
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physical data source, and each connection the <code>DataSource</code> object
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creates is a connection to that physical data source.
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<P>
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A logical name for the data source is registered with a naming service that
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uses the Java Naming and Directory Interface<sup><font size=-2>TM</font></sup>
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(JNDI) API, usually by a system administrator or someone performing the
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duties of a system administrator. An application can retrieve the
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<code>DataSource</code> object it wants by doing a lookup on the logical
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name that has been registered for it. The application can then use the
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<code>DataSource</code> object to create a connection to the physical data
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source it represents.
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<P>
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A <code>DataSource</code> object can be implemented to work with the
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middle tier infrastructure so that the connections it produces will be
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pooled for reuse. An application that uses such a <code>DataSource</code>
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implementation will automatically get a connection that participates in
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connection pooling.
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A <code>DataSource</code> object can also be implemented to work with the
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middle tier infrastructure so that the connections it produces can be
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used for distributed transactions without any special coding.
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<H2>Connection Pooling and Statement Pooling</H2>
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Connections made via a <code>DataSource</code>
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object that is implemented to work with a middle tier connection pool manager
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will participate in connection pooling. This can improve performance
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dramatically because creating new connections is very expensive.
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Connection pooling allows a connection to be used and reused,
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thus cutting down substantially on the number of new connections
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that need to be created.
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<P>
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Connection pooling is totally transparent. It is done automatically
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in the middle tier of a Java EE configuration, so from an application's
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viewpoint, no change in code is required. An application simply uses
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the <code>DataSource.getConnection</code> method to get the pooled
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connection and uses it the same way it uses any <code>Connection</code>
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object.
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<P>
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The classes and interfaces used for connection pooling are:
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<UL>
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<LI><code>ConnectionPoolDataSource</code>
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<LI><code>PooledConnection</code>
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<LI><code>ConnectionEvent</code>
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<LI><code>ConnectionEventListener</code>
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<LI><code>StatementEvent</code>
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<LI><code>StatementEventListener</code>
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</UL>
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The connection pool manager, a facility in the middle tier of
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a three-tier architecture, uses these classes and interfaces
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behind the scenes. When a <code>ConnectionPoolDataSource</code> object
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is called on to create a <code>PooledConnection</code> object, the
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connection pool manager will register as a <code>ConnectionEventListener</code>
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object with the new <code>PooledConnection</code> object. When the connection
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is closed or there is an error, the connection pool manager (being a listener)
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gets a notification that includes a <code>ConnectionEvent</code> object.
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<p>
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If the connection pool manager supports <code>Statement</code> pooling, for
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<code>PreparedStatements</code>, which can be determined by invoking the method
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<code>DatabaseMetaData.supportsStatementPooling</code>, the
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connection pool manager will register as a <code>StatementEventListener</code>
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object with the new <code>PooledConnection</code> object. When the
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<code>PreparedStatement</code> is closed or there is an error, the connection
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pool manager (being a listener)
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gets a notification that includes a <code>StatementEvent</code> object.
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<p>
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<H2>Distributed Transactions</H2>
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As with pooled connections, connections made via a <code>DataSource</code>
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object that is implemented to work with the middle tier infrastructure
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may participate in distributed transactions. This gives an application
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the ability to involve data sources on multiple servers in a single
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transaction.
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<P>
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The classes and interfaces used for distributed transactions are:
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<UL>
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<LI><code>XADataSource</code>
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<LI><code>XAConnection</code>
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</UL>
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These interfaces are used by the transaction manager; an application does
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not use them directly.
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<P>
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The <code>XAConnection</code> interface is derived from the
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<code>PooledConnection</code> interface, so what applies to a pooled connection
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also applies to a connection that is part of a distributed transaction.
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A transaction manager in the middle tier handles everything transparently.
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The only change in application code is that an application cannot do anything
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that would interfere with the transaction manager's handling of the transaction.
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Specifically, an application cannot call the methods <code>Connection.commit</code>
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or <code>Connection.rollback</code>, and it cannot set the connection to be in
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auto-commit mode (that is, it cannot call
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<code>Connection.setAutoCommit(true)</code>).
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<P>
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An application does not need to do anything special to participate in a
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distributed transaction.
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It simply creates connections to the data sources it wants to use via
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the <code>DataSource.getConnection</code> method, just as it normally does.
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The transaction manager manages the transaction behind the scenes. The
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<code>XADataSource</code> interface creates <code>XAConnection</code> objects, and
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each <code>XAConnection</code> object creates an <code>XAResource</code> object
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that the transaction manager uses to manage the connection.
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<H2>Rowsets</H2>
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The <code>RowSet</code> interface works with various other classes and
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interfaces behind the scenes. These can be grouped into three categories.
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<OL>
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<LI>Event Notification
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<UL>
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<LI><code>RowSetListener</code><br>
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A <code>RowSet</code> object is a JavaBeans<sup><font size=-2>TM</font></sup>
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component because it has properties and participates in the JavaBeans
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event notification mechanism. The <code>RowSetListener</code> interface
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is implemented by a component that wants to be notified about events that
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occur to a particular <code>RowSet</code> object. Such a component registers
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itself as a listener with a rowset via the <code>RowSet.addRowSetListener</code>
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method.
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<P>
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When the <code>RowSet</code> object changes one of its rows, changes all of
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it rows, or moves its cursor, it also notifies each listener that is registered
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with it. The listener reacts by carrying out its implementation of the
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notification method called on it.
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<P>
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<LI><code>RowSetEvent</code><br>
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As part of its internal notification process, a <code>RowSet</code> object
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creates an instance of <code>RowSetEvent</code> and passes it to the listener.
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The listener can use this <code>RowSetEvent</code> object to find out which rowset
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had the event.
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</UL>
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<P>
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<LI>Metadata
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<UL>
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<LI><code>RowSetMetaData</code><br>
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This interface, derived from the
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<code>ResultSetMetaData</code> interface, provides information about
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the columns in a <code>RowSet</code> object. An application can use
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<code>RowSetMetaData</code> methods to find out how many columns the
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rowset contains and what kind of data each column can contain.
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<P>
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The <code>RowSetMetaData</code> interface provides methods for
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setting the information about columns, but an application would not
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normally use these methods. When an application calls the <code>RowSet</code>
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method <code>execute</code>, the <code>RowSet</code> object will contain
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a new set of rows, and its <code>RowSetMetaData</code> object will have been
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internally updated to contain information about the new columns.
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<P>
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</UL>
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<LI>The Reader/Writer Facility<br>
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A <code>RowSet</code> object that implements the <code>RowSetInternal</code>
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interface can call on the <code>RowSetReader</code> object associated with it
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to populate itself with data. It can also call on the <code>RowSetWriter</code>
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object associated with it to write any changes to its rows back to the
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data source from which it originally got the rows.
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A rowset that remains connected to its data source does not need to use a
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reader and writer because it can simply operate on the data source directly.
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<UL>
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<LI><code>RowSetInternal</code><br>
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By implementing the <code>RowSetInternal</code> interface, a
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<code>RowSet</code> object gets access to
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its internal state and is able to call on its reader and writer. A rowset
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keeps track of the values in its current rows and of the values that immediately
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preceded the current ones, referred to as the <i>original</i> values. A rowset
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also keeps track of (1) the parameters that have been set for its command and
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(2) the connection that was passed to it, if any. A rowset uses the
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<code>RowSetInternal</code> methods behind the scenes to get access to
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this information. An application does not normally invoke these methods directly.
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<P>
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<LI><code>RowSetReader</code><br>
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A disconnected <code>RowSet</code> object that has implemented the
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<code>RowSetInternal</code> interface can call on its reader (the
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<code>RowSetReader</code> object associated with it) to populate it with
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data. When an application calls the <code>RowSet.execute</code> method,
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that method calls on the rowset's reader to do much of the work. Implementations
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can vary widely, but generally a reader makes a connection to the data source,
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reads data from the data source and populates the rowset with it, and closes
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the connection. A reader may also update the <code>RowSetMetaData</code> object
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for its rowset. The rowset's internal state is also updated, either by the
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reader or directly by the method <code>RowSet.execute</code>.
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<LI><code>RowSetWriter</code><br>
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A disconnected <code>RowSet</code> object that has implemented the
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<code>RowSetInternal</code> interface can call on its writer (the
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<code>RowSetWriter</code> object associated with it) to write changes
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back to the underlying data source. Implementations may vary widely, but
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generally, a writer will do the following:
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<P>
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<UL>
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<LI>Make a connection to the data source
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<LI>Check to see whether there is a conflict, that is, whether
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a value that has been changed in the rowset has also been changed
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in the data source
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<LI>Write the new values to the data source if there is no conflict
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<LI>Close the connection
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</UL>
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</UL>
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</OL>
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<P>
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The <code>RowSet</code> interface may be implemented in any number of
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ways, and anyone may write an implementation. Developers are encouraged
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to use their imaginations in coming up with new ways to use rowsets.
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<P>
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<B>IMPORTANT NOTE:</B> Code that uses API marked "Since 1.6" must be run using a
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JDBC technology driver that implements the JDBC 4.0 API.
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You must check your driver documentation to be sure that it implements
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the particular features you want to use.
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<P>
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<h2>Package Specification</h2>
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<ul>
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<li><a href="http://java.sun.com/products/jdbc/download.html">Specification of the
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JDBC 4.0 API</a>
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</ul>
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<h2>Related Documentation</h2>
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The Java Series book published by Addison-Wesley Longman provides detailed
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information about the classes and interfaces in the <code>javax.sql</code>
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package:
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<ul>
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<li><a href="http://java.sun.com/docs/books/jdbc"><i>JDBC<sup><font size=-2>TM</font></sup>
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API Tutorial and Reference, Third Edition:</i></a>
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</ul>
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<P>
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@since 1.4
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</body>
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</html>
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