/* * Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * 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. * * 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). * * 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. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ /** * * Repository for the RowSet reference implementations of the * SyncProvider abstract class. These implementations provide a * disconnected RowSet * object with the ability to synchronize the data in the underlying data * source with its data. These implementations are provided as * the default SyncProvider implementations and are accessible via the * SyncProvider SPI managed by the SyncFactory. * *

1.0 SyncProvider Reference Implementations

* The main job of a SyncProvider implementation is to manage * the reader and writer mechanisms. * The SyncProvider SPI, as specified in the javax.sql.rowset.spi * package, provides a pluggable mechanism by which javax.sql.RowSetReader * and javax.sql.RowSetWriter implementations can be supplied to a disconnected * RowSet object. *

* A reader, a javax.sql.RowSetReader * object, does the work necessary to populate a RowSet object with data. * A writer, a javax.sql.RowSetWriter object, does the work necessary for * synchronizing a RowSet object's data with the data in the originating * source of data. Put another way, a writer writes a RowSet * object's data back to the data source. *

* Generally speaking, the course of events is this. The reader makes a connection to * the data source and reads the data from a ResultSet object into its * RowSet object. Then it closes the connection. While * the RowSet object is disconnected, an application makes some modifications * to the data and calls the method acceptChanges. At this point, the * writer is called to write the changes back to the database table or view * from which the original data came. This is called synchronization. *

* If the data in the originating data source has not changed, there is no problem * with just writing the RowSet object's new data to the data source. * If it has changed, however, there is a conflict that needs to be resolved. One * way to solve the problem is not to let the data in the data source be changed in * the first place, which can be done by setting locks on a row, a table, or the * whole data source. Setting locks is a way to avoid conflicts, but it can be * very expensive. Another approach, which is at the other end of the spectrum, * is simply to assume that no conflicts will occur and thus do nothing to avoid * conflicts. * Different SyncProvider implementations may handle synchronization in * any of these ways, varying from doing no checking for * conflicts, to doing various levels of checking, to guaranteeing that there are no * conflicts. *

* The SyncProvider class offers methods to help a RowSet * object discover and manage how a provider handles synchronization. * The method getProviderGrade returns the * grade of synchronization a provider offers. An application can * direct the provider to use a particular level of locking by calling * the method setDataSourceLock and specifying the level of locking desired. * If a RowSet object's data came from an SQL VIEW, an * application may call the method supportsUpdatableView to * find out whether the VIEW can be updated. *

* Synchronization is done completely behind the scenes, so it is third party vendors of * synchronization provider implementations who have to take care of this complex task. * Application programmers can decide which provider to use and the level of locking to * be done, but they are free from having to worry about the implementation details. *

* The JDBC RowSet Implementations reference implementation provides two * implementations of the SyncProvider class: * *

* *

2.0 Basics in RowSet Population & Synchronization

* A rowset's first task is to populate itself with rows of column values. * Generally, these rows will come from a relational database, so a rowset * has properties that supply what is necessary for making a connection to * a database and executing a query. A rowset that does not need to establish * a connection and execute a command, such as one that gets its data from * a tabular file instead of a relational database, does not need to have these * properties set. The vast majority of RowSets, however, do need to set these * properties. The general rule is that a RowSet is required to set only the * properties that it uses.
*
* The command property contains the query that determines what * data a RowSet will contain. Rowsets have methods for setting a query's * parameter(s), which means that a query can be executed multiple times with * different parameters to produce different result sets. Or the query can be * changed to something completely new to get a new result set. *

Once a rowset contains the rows from a ResultSet object or some * other data source, its column values can be updated, and its rows can be * inserted or deleted. Any method that causes a change in the rowset's values * or cursor position also notifies any object that has been registered as * a listener with the rowset. So, for example, a table that displays the rowset's * data in an applet can be notified of changes and make updates as they * occur.
*
* The changes made to a rowset can be propagated back to the original data * source to keep the rowset and its data source synchronized. Although this * involves many operations behind the scenes, it is completely transparent * to the application programmer and remains the concern of the RowSet provider * developer. All an application has to do is invoke the method acceptChanges, * and the data source backing the rowset will be updated to match the current * values in the rowset.

* *

A disconnected rowset, such as a CachedRowSet or WebRowSet * object, establishes a connection to populate itself with data from a database * and then closes the connection. The RowSet object will remain * disconnected until it wants to propagate changes back to its database table, * which is optional. To write its changes back to the database (synchronize with * the database), the rowset establishes a connection, write the changes, and then * once again disconnects itself.
*

* *

3.0 Other Possible Implementations

* There are many other possible implementations of the SyncProvider abstract * class. One possibility is to employ a more robust synchronization model, which * would give a RowSet object increased trust in the provider's * ability to get any updates back to the original data source. Another possibility * is a more formal synchronization mechanism such as SyncML * (http://www.syncml.org/)
*/ package com.sun.rowset.providers;