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25
26 /**
27 * The standard classes and interfaces that a third party vendor has to
28 * use in its implementation of a synchronization provider. These classes and
29 * interfaces are referred to as the Service Provider Interface (SPI). To make it possible
30 * for a <code>RowSet</code> object to use an implementation, the vendor must register
31 * it with the <code>SyncFactory</code> singleton. (See the class comment for
32 * <code>SyncProvider</code> for a full explanation of the registration process and
33 * the naming convention to be used.)
34 *
35 * <h2>Table of Contents</h2>
36 * <ul>
37 * <li><a href="#pkgspec">1.0 Package Specification</a>
38 * <li><a href="#arch">2.0 Service Provider Architecture</a>
39 * <li><a href="#impl">3.0 Implementer's Guide</a>
40 * <li><a href="#resolving">4.0 Resolving Synchronization Conflicts</a>
41 * <li><a href="#relspec">5.0 Related Specifications</a>
42 * <li><a href="#reldocs">6.0 Related Documentation</a>
43 * </ul>
44 *
45 * <h3><a id="pkgspec">1.0 Package Specification</a></h3>
46 * <P>
47 * The following classes and interfaces make up the <code>javax.sql.rowset.spi</code>
48 * package:
49 * <UL>
50 * <LI><code>SyncFactory</code>
51 * <LI><code>SyncProvider</code>
52 * <LI><code>SyncFactoryException</code>
53 * <LI><code>SyncProviderException</code>
54 * <LI><code>SyncResolver</code>
55 * <LI><code>XmlReader</code>
56 * <LI><code>XmlWriter</code>
57 * <LI><code>TransactionalWriter</code>
58 * </UL>
59 * The following interfaces, in the <code>javax.sql</code> package, are also part of the SPI:
60 * <UL>
61 * <LI><code>RowSetReader</code>
62 * <LI><code>RowSetWriter</code>
63 * </UL>
64 * <P>
65 * A <code>SyncProvider</code> implementation provides a disconnected <code>RowSet</code>
66 * object with the mechanisms for reading data into it and for writing data that has been
67 * modified in it
68 * back to the underlying data source. A <i>reader</i>, a <code>RowSetReader</code> or
69 * <code>XMLReader</code> object, reads data into a <code>RowSet</code> object when the
70 * <code>CachedRowSet</code> methods <code>execute</code> or <code>populate</code>
71 * are called. A <i>writer</i>, a <code>RowSetWriter</code> or <code>XMLWriter</code>
72 * object, writes changes back to the underlying data source when the
73 * <code>CachedRowSet</code> method <code>acceptChanges</code> is called.
74 * <P>
75 * The process of writing changes in a <code>RowSet</code> object to its data source
76 * is known as <i>synchronization</i>. The <code>SyncProvider</code> implementation that a
77 * <code>RowSet</code> object is using determines the level of synchronization that the
78 * <code>RowSet</code> object's writer uses. The various levels of synchronization are
79 * referred to as <i>grades</i>.
80 * <P>
81 * The lower grades of synchronization are
82 * known as <i>optimistic</i> concurrency levels because they optimistically
83 * assume that there will be no conflicts or very few conflicts. A conflict exists when
84 * the same data modified in the <code>RowSet</code> object has also been modified
85 * in the data source. Using the optimistic concurrency model means that if there
86 * is a conflict, modifications to either the data source or the <code>RowSet</code>
87 * object will be lost.
88 * <P>
89 * Higher grades of synchronization are called <i>pessimistic</i> because they assume
90 * that others will be accessing the data source and making modifications. These
91 * grades set varying levels of locks to increase the chances that no conflicts
92 * occur.
93 * <P>
94 * The lowest level of synchronization is simply writing any changes made to the
95 * <code>RowSet</code> object to its underlying data source. The writer does
96 * nothing to check for conflicts.
97 * If there is a conflict and the data
98 * source values are overwritten, the changes other parties have made by to the data
99 * source are lost.
100 * <P>
101 * The <code>RIXMLProvider</code> implementation uses the lowest level
102 * of synchronization and just writes <code>RowSet</code> changes to the data source.
103 *
104 * <P>
105 * For the next level up, the
106 * writer checks to see if there are any conflicts, and if there are,
107 * it does not write anything to the data source. The problem with this concurrency
108 * level is that if another party has modified the corresponding data in the data source
109 * since the <code>RowSet</code> object got its data,
110 * the changes made to the <code>RowSet</code> object are lost. The
111 * <code>RIOptimisticProvider</code> implementation uses this level of synchronization.
112 * <P>
113 * At higher levels of synchronization, referred to as pessimistic concurrency,
114 * the writer take steps to avoid conflicts by setting locks. Setting locks
115 * can vary from setting a lock on a single row to setting a lock on a table
116 * or the entire data source. The level of synchronization is therefore a tradeoff
117 * between the ability of users to access the data source concurrently and the ability
118 * of the writer to keep the data in the <code>RowSet</code> object and its data source
119 * synchronized.
120 * <P>
121 * It is a requirement that all disconnected <code>RowSet</code> objects
122 * (<code>CachedRowSet</code>, <code>FilteredRowSet</code>, <code>JoinRowSet</code>,
123 * and <code>WebRowSet</code> objects) obtain their <code>SyncProvider</code> objects
124 * from the <code>SyncFactory</code> mechanism.
125 * <P>
126 * The reference implementation (RI) provides two synchronization providers.
127 * <UL>
128 * <LI><b><code>RIOptimisticProvider</code></b> <br>
129 * The default provider that the <code>SyncFactory</code> instance will
130 * supply to a disconnected <code>RowSet</code> object when no provider
131 * implementation is specified.<BR>
132 * This synchronization provider uses an optimistic concurrency model,
133 * assuming that there will be few conflicts among users
134 * who are accessing the same data in a database. It avoids
135 * using locks; rather, it checks to see if there is a conflict
136 * before trying to synchronize the <code>RowSet</code> object and the
137 * data source. If there is a conflict, it does nothing, meaning that
138 * changes to the <code>RowSet</code> object are not persisted to the data
139 * source.
140 * <LI><B><code>RIXMLProvider</code></B> <BR>
141 * A synchronization provider that can be used with a
142 * <code>WebRowSet</code> object, which is a rowset that can be written
143 * in XML format or read from XML format. The
144 * <code>RIXMLProvider</code> implementation does no checking at all for
145 * conflicts and simply writes any updated data in the
146 * <code>WebRowSet</code> object to the underlying data source.
147 * <code>WebRowSet</code> objects use this provider when they are
148 * dealing with XML data.
149 * </UL>
150 *
151 * These <code>SyncProvider</code> implementations
152 * are bundled with the reference implementation, which makes them always available to
153 * <code>RowSet</code> implementations.
154 * <code>SyncProvider</code> implementations make themselves available by being
155 * registered with the <code>SyncFactory</code> singleton. When a <code>RowSet</code>
156 * object requests a provider, by specifying it in the constructor or as an argument to the
157 * <code>CachedRowSet</code> method <code>setSyncProvider</code>,
158 * the <code>SyncFactory</code> singleton
159 * checks to see if the requested provider has been registered with it.
160 * If it has, the <code>SyncFactory</code> creates an instance of it and passes it to the
161 * requesting <code>RowSet</code> object.
162 * If the <code>SyncProvider</code> implementation that is specified has not been registered,
163 * the <code>SyncFactory</code> singleton causes a <code>SyncFactoryException</code> object
164 * to be thrown. If no provider is specified,
165 * the <code>SyncFactory</code> singleton will create an instance of the default
166 * provider implementation, <code>RIOptimisticProvider</code>,
167 * and pass it to the requesting <code>RowSet</code> object.
168 *
169 * <P>
170 * If a <code>WebRowSet</code> object does not specify a provider in its constructor, the
171 * <code>SyncFactory</code> will give it an instance of <code>RIOptimisticProvider</code>.
172 * However, the constructor for <code>WebRowSet</code> is implemented to set the provider
173 * to the <code>RIXMLProvider</code>, which reads and writes a <code>RowSet</code> object
174 * in XML format.
175 * <P>
176 * See the <a href="SyncProvider.html">SyncProvider</a> class
177 * specification for further details.
178 * <p>
179 * Vendors may develop a <code>SyncProvider</code> implementation with any one of the possible
180 * levels of synchronization, thus giving <code>RowSet</code> objects a choice of
181 * synchronization mechanisms.
182 *
183 * <h3><a id="arch">2.0 Service Provider Interface Architecture</a></h3>
184 * <b>2.1 Overview</b>
185 * <p>
186 * The Service Provider Interface provides a pluggable mechanism by which
187 * <code>SyncProvider</code> implementations can be registered and then generated when
188 * required. The lazy reference mechanism employed by the <code>SyncFactory</code> limits
189 * unnecessary resource consumption by not creating an instance until it is
190 * required by a disconnected
191 * <code>RowSet</code> object. The <code>SyncFactory</code> class also provides
192 * a standard API to configure logging options and streams that <b>may</b> be provided
193 * by a particular <code>SyncProvider</code> implementation.
194 * <p>
195 * <b>2.2 Registering with the <code>SyncFactory</code></b>
196 * <p>
197 * A third party <code>SyncProvider</code> implementation must be registered with the
198 * <code>SyncFactory</code> in order for a disconnected <code>RowSet</code> object
199 * to obtain it and thereby use its <code>javax.sql.RowSetReader</code> and
200 * <code>javax.sql.RowSetWriter</code>
201 * implementations. The following registration mechanisms are available to all
202 * <code>SyncProvider</code> implementations:
203 * <ul>
204 * <li><b>System properties</b> - Properties set at the command line. These
205 * properties are set at run time and apply system-wide per invocation of the Java
206 * application. See the section <a href="#reldocs">"Related Documentation"</a>
207 * further related information.
208 *
209 * <li><b>Property Files</b> - Properties specified in a standard property file.
210 * This can be specified using a System Property or by modifying a standard
211 * property file located in the platform run-time. The
212 * reference implementation of this technology includes a standard property
213 * file than can be edited to add additional <code>SyncProvider</code> objects.
214 *
215 * <li><b>JNDI Context</b> - Available providers can be registered on a JNDI
216 * context. The <code>SyncFactory</code> will attempt to load <code>SyncProvider</code>
217 * objects bound to the context and register them with the factory. This
218 * context must be supplied to the <code>SyncFactory</code> for the mechanism to
219 * function correctly.
220 * </ul>
221 * <p>
222 * Details on how to specify the system properties or properties in a property file
223 * and how to configure the JNDI Context are explained in detail in the
224 * <a href="SyncFactory.html"><code>SyncFactory</code></a> class description.
225 * <p>
226 * <b>2.3 SyncFactory Provider Instance Generation Policies</b>
227 * <p>
228 * The <code>SyncFactory</code> generates a requested <code>SyncProvider</code>
229 * object if the provider has been correctly registered. The
230 * following policies are adhered to when either a disconnected <code>RowSet</code> object
231 * is instantiated with a specified <code>SyncProvider</code> implementation or is
232 * reconfigured at runtime with an alternative <code>SyncProvider</code> object.
233 * <ul>
234 * <li> If a <code>SyncProvider</code> object is specified and the <code>SyncFactory</code>
235 * contains <i>no</i> reference to the provider, a <code>SyncFactoryException</code> is
236 * thrown.
237 *
238 * <li> If a <code>SyncProvider</code> object is specified and the <code>SyncFactory</code>
239 * contains a reference to the provider, the requested provider is supplied.
240 *
241 * <li> If no <code>SyncProvider</code> object is specified, the reference
242 * implementation provider <code>RIOptimisticProvider</code> is supplied.
243 * </ul>
244 * <p>
245 * These policies are explored in more detail in the <a href="SyncFactory.html">
246 * <code>SyncFactory</code></a> class.
247 *
248 * <h3><a id="impl">3.0 SyncProvider Implementer's Guide</a></h3>
249 *
250 * <b>3.1 Requirements</b>
251 * <p>
252 * A compliant <code>SyncProvider</code> implementation that is fully pluggable
253 * into the <code>SyncFactory</code> <b>must</b> extend and implement all
254 * abstract methods in the <a href="SyncProvider.html"><code>SyncProvider</code></a>
255 * class. In addition, an implementation <b>must</b> determine the
256 * grade, locking and updatable view capabilities defined in the
257 * <code>SyncProvider</code> class definition. One or more of the
258 * <code>SyncProvider</code> description criteria <b>must</b> be supported. It
259 * is expected that vendor implementations will offer a range of grade, locking, and
260 * updatable view capabilities.
261 * <p>
262 * Furthermore, the <code>SyncProvider</code> naming convention <b>must</b> be followed as
263 * detailed in the <a href="SyncProvider.html"><code>SyncProvider</code></a> class
264 * description.
265 * <p>
266 * <b>3.2 Grades</b>
267 * <p>
268 * JSR 114 defines a set of grades to describe the quality of synchronization
269 * a <code>SyncProvider</code> object can offer a disconnected <code>RowSet</code>
270 * object. These grades are listed from the lowest quality of service to the highest.
271 * <ul>
272 * <li><b>GRADE_NONE</b> - No synchronization with the originating data source is
273 * provided. A <code>SyncProvider</code> implementation returning this grade will simply
274 * attempt to write any data that has changed in the <code>RowSet</code> object to the
275 *underlying data source, overwriting whatever is there. No attempt is made to compare
276 * original values with current values to see if there is a conflict. The
277 * <code>RIXMLProvider</code> is implemented with this grade.
278 *
279 * <li><b>GRADE_CHECK_MODIFIED_AT_COMMIT</b> - A low grade of optimistic synchronization.
280 * A <code>SyncProvider</code> implementation returning this grade
281 * will check for conflicts in rows that have changed between the last synchronization
282 * and the current synchronization under way. Any changes in the originating data source
283 * that have been modified will not be reflected in the disconnected <code>RowSet</code>
284 * object. If there are no conflicts, changes in the <code>RowSet</code> object will be
285 * written to the data source. If there are conflicts, no changes are written.
286 * The <code>RIOptimisticProvider</code> implementation uses this grade.
287 *
288 * <li><b>GRADE_CHECK_ALL_AT_COMMIT</b> - A high grade of optimistic synchronization.
289 * A <code>SyncProvider</code> implementation returning this grade
290 * will check all rows, including rows that have not changed in the disconnected
291 * <code>RowSet</code> object. In this way, any changes to rows in the underlying
292 * data source will be reflected in the disconnected <code>RowSet</code> object
293 * when the synchronization finishes successfully.
294 *
295 * <li><b>GRADE_LOCK_WHEN_MODIFIED</b> - A pessimistic grade of synchronization.
296 * <code>SyncProvider</code> implementations returning this grade will lock
297 * the row in the originating data source that corresponds to the row being changed
298 * in the <code>RowSet</code> object to reduce the possibility of other
299 * processes modifying the same data in the data source.
300 *
301 * <li><b>GRADE_LOCK_WHEN_LOADED</b> - A higher pessimistic synchronization grade.
302 * A <code>SyncProvider</code> implementation returning this grade will lock
303 * the entire view and/or table affected by the original query used to
304 * populate a <code>RowSet</code> object.
305 * </ul>
306 * <p>
307 * <b>3.3 Locks</b>
308 * <p>
309 * JSR 114 defines a set of constants that specify whether any locks have been
310 * placed on a <code>RowSet</code> object's underlying data source and, if so,
311 * on which constructs the locks are placed. These locks will remain on the data
312 * source while the <code>RowSet</code> object is disconnected from the data source.
313 * <P>
314 * These constants <b>should</b> be considered complementary to the
315 * grade constants. The default setting for the majority of grade settings requires
316 * that no data source locks remain when a <code>RowSet</code> object is disconnected
317 * from its data source.
318 * The grades <code>GRADE_LOCK_WHEN_MODIFIED</code> and
319 * <code>GRADE_LOCK_WHEN_LOADED</code> allow a disconnected <code>RowSet</code> object
320 * to have a fine-grained control over the degree of locking.
321 * <ul>
322 * <li><b>DATASOURCE_NO_LOCK</b> - No locks remain on the originating data source.
323 * This is the default lock setting for all <code>SyncProvider</code> implementations
324 * unless otherwise directed by a <code>RowSet</code> object.
325 *
326 * <li><b>DATASOURCE_ROW_LOCK</b> - A lock is placed on the rows that are touched by
327 * the original SQL query used to populate the <code>RowSet</code> object.
328 *
329 * <li><b>DATASOURCE_TABLE_LOCK</b> - A lock is placed on all tables that are touched
330 * by the query that was used to populate the <code>RowSet</code> object.
331 *
332 * <li><b>DATASOURCE_DB_LOCK</b>
333 * A lock is placed on the entire data source that is used by the <code>RowSet</code>
334 * object.
335 * </ul>
336 * <p>
337 * <b>3.4 Updatable Views</b>
338 * <p>
339 * A <code>RowSet</code> object may be populated with data from an SQL <code>VIEW</code>.
340 * The following constants indicate whether a <code>SyncProvider</code> object can
341 * update data in the table or tables from which the <code>VIEW</code> was derived.
342 * <ul>
343 * <li><b>UPDATABLE_VIEW_SYNC</b>
344 * Indicates that a <code>SyncProvider</code> implementation supports synchronization
345 * to the table or tables from which the SQL <code>VIEW</code> used to populate
346 * a <code>RowSet</code> object is derived.
347 *
348 * <li><b>NONUPDATABLE_VIEW_SYNC</b>
349 * Indicates that a <code>SyncProvider</code> implementation does <b>not</b> support
350 * synchronization to the table or tables from which the SQL <code>VIEW</code>
351 * used to populate a <code>RowSet</code> object is derived.
352 * </ul>
353 * <p>
354 * <b>3.5 Usage of <code>SyncProvider</code> Grading and Locking</b>
355 * <p>
356 * In the example below, the reference <code>CachedRowSetImpl</code> implementation
357 * reconfigures its current <code>SyncProvider</code> object by calling the
358 * <code>setSyncProvider</code> method.<br>
359 *
360 * <PRE>
361 * CachedRowSetImpl crs = new CachedRowSetImpl();
362 * crs.setSyncProvider("com.foo.bar.HASyncProvider");
363 * </PRE>
364 * An application can retrieve the <code>SyncProvider</code> object currently in use
365 * by a disconnected <code>RowSet</code> object. It can also retrieve the
366 * grade of synchronization with which the provider was implemented and the degree of
367 * locking currently in use. In addition, an application has the flexibility to set
368 * the degree of locking to be used, which can increase the possibilities for successful
369 * synchronization. These operation are shown in the following code fragment.
370 * <PRE>
371 * SyncProvider sync = crs.getSyncProvider();
372 *
373 * switch (sync.getProviderGrade()) {
374 * case: SyncProvider.GRADE_CHECK_ALL_AT_COMMIT
375 * //A high grade of optimistic synchronization
376 * break;
377 * case: SyncProvider.GRADE_CHECK_MODIFIED_AT_COMMIT
378 * //A low grade of optimistic synchronization
379 * break;
380 * case: SyncProvider.GRADE_LOCK_WHEN_LOADED
381 * // A pessimistic synchronization grade
382 * break;
383 * case: SyncProvider.GRADE_LOCK_WHEN_MODIFIED
384 * // A pessimistic synchronization grade
385 * break;
386 * case: SyncProvider.GRADE_NONE
387 * // No synchronization with the originating data source provided
388 * break;
389 * }
390 *
391 * switch (sync.getDataSourcLock() {
392 * case: SyncProvider.DATASOURCE_DB_LOCK
393 * // A lock is placed on the entire datasource that is used by the
394 * // <code>RowSet</code> object
395 * break;
396 *
397 * case: SyncProvider.DATASOURCE_NO_LOCK
398 * // No locks remain on the originating data source.
399 * break;
400 *
401 * case: SyncProvider.DATASOURCE_ROW_LOCK
402 * // A lock is placed on the rows that are touched by the original
403 * // SQL statement used to populate
404 * // the RowSet object that is using the SyncProvider
405 * break;
406 *
407 * case: DATASOURCE_TABLE_LOCK
408 * // A lock is placed on all tables that are touched by the original
409 * // SQL statement used to populated
410 * // the RowSet object that is using the SyncProvider
411 * break;
412 *
413 * </PRE>
414 * It is also possible using the static utility method in the
415 * <code>SyncFactory</code> class to determine the list of <code>SyncProvider</code>
416 * implementations currently registered with the <code>SyncFactory</code>.
417 *
418 * <pre>
419 * Enumeration e = SyncFactory.getRegisteredProviders();
420 * </pre>
421 *
422 *
423 * <h3><a id="resolving">4.0 Resolving Synchronization Conflicts</a></h3>
424 *
425 * The interface <code>SyncResolver</code> provides a way for an application to
426 * decide manually what to do when a conflict occurs. When the <code>CachedRowSet</code>
427 * method <code>acceptChanges</code> finishes and has detected one or more conflicts,
428 * it throws a <code>SyncProviderException</code> object. An application can
429 * catch the exception and
430 * have it retrieve a <code>SyncResolver</code> object by calling the method
431 * <code>SyncProviderException.getSyncResolver()</code>.
432 * <P>
433 * A <code>SyncResolver</code> object, which is a special kind of
434 * <code>CachedRowSet</code> object or
435 * a <code>JdbcRowSet</code> object that has implemented the <code>SyncResolver</code>
436 * interface, examines the conflicts row by row. It is a duplicate of the
437 * <code>RowSet</code> object being synchronized except that it contains only the data
438 * from the data source this is causing a conflict. All of the other column values are
439 * set to <code>null</code>. To navigate from one conflict value to another, a
440 * <code>SyncResolver</code> object provides the methods <code>nextConflict</code> and
441 * <code>previousConflict</code>.
442 * <P>
443 * The <code>SyncResolver</code> interface also
444 * provides methods for doing the following:
445 * <UL>
446 * <LI>finding out whether the conflict involved an update, a delete, or an insert
447 * <LI>getting the value in the data source that caused the conflict
448 * <LI>setting the value that should be in the data source if it needs to be changed
449 * or setting the value that should be in the <code>RowSet</code> object if it needs
450 * to be changed
451 * </UL>
452 * <P>
453 * When the <code>CachedRowSet</code> method <code>acceptChanges</code> is called, it
454 * delegates to the <code>RowSet</code> object's <code>SyncProvider</code> object.
455 * How the writer provided by that <code>SyncProvider</code> object is implemented
456 * determines what level (grade) of checking for conflicts will be done. After all
457 * checking for conflicts is completed and one or more conflicts has been found, the method
458 * <code>acceptChanges</code> throws a <code>SyncProviderException</code> object. The
459 * application can catch the exception and use it to obtain a <code>SyncResolver</code> object.
460 * <P>
461 * The application can then use <code>SyncResolver</code> methods to get information
462 * about each conflict and decide what to do. If the application logic or the user
463 * decides that a value in the <code>RowSet</code> object should be the one to
464 * persist, the application or user can overwrite the data source value with it.
465 * <P>
466 * The comment for the <code>SyncResolver</code> interface has more detail.
467 *
468 * <h3><a id="relspec">5.0 Related Specifications</a></h3>
469 * <ul>
470 * <li><a href="http://docs.oracle.com/javase/jndi/tutorial/index.html">JNDI</a>
471 * <li><a href="{@docRoot}/java.logging/java/util/logging/package-summary.html">Java Logging
472 * APIs</a>
473 * </ul>
474 * <h3><a id="reldocs">6.0 Related Documentation</a></h3>
475 * <ul>
476 * <li><a href="http://docs.oracle.com/javase/tutorial/jdbc/">DataSource for JDBC
477 * Connections</a>
478 * </ul>
479 */
480 package javax.sql.rowset.spi;