| author | darcy |
| Thu, 01 Nov 2018 20:37:45 -0700 | |
| changeset 52380 | 6b31efbf833e |
| parent 47216 | 71c04702a3d5 |
| permissions | -rw-r--r-- |
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> |
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<!-- |
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Copyright (c) 2000, 2017, Oracle and/or its affiliates. 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. Oracle designates this |
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particular file as subject to the "Classpath" exception as provided |
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by Oracle 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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327690766109
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Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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6956202: Fix a few missed rebranding issues, please contact lines etc.
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parents:
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or visit www.oracle.com if you need additional information or have any |
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6956202: Fix a few missed rebranding issues, please contact lines etc.
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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™ 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 (Java SE™). |
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It remains an essential part of the Java Platform, Enterprise Edition |
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(Java EE™). |
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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™ |
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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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<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™ |
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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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<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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<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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</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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<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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<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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<h2>Package Specification</h2> |
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<ul> |
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<li><a href="https://jcp.org/en/jsr/detail?id=221">JDBC 4.3 Specification</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://www.oracle.com/technetwork/java/index-142838.html"> |
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<i>JDBC™API Tutorial and Reference, Third Edition</i></a> |
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</ul> |
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</body> |
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</html> |