1 /*
2 * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 * questions.
24 */
25
26 package javax.sql.rowset.spi;
27
28 import javax.sql.RowSet;
29 import java.sql.SQLException;
30
31 /**
32 * Defines a framework that allows applications to use a manual decision tree
33 * to decide what should be done when a synchronization conflict occurs.
34 * Although it is not mandatory for
35 * applications to resolve synchronization conflicts manually, this
36 * framework provides the means to delegate to the application when conflicts
37 * arise.
38 * <p>
39 * Note that a conflict is a situation where the <code>RowSet</code> object's original
40 * values for a row do not match the values in the data source, which indicates that
41 * the data source row has been modified since the last synchronization. Note also that
42 * a <code>RowSet</code> object's original values are the values it had just prior to the
43 * the last synchronization, which are not necessarily its initial values.
44 * <p>
45 *
46 * <H2>Description of a <code>SyncResolver</code> Object</H2>
47 *
48 * A <code>SyncResolver</code> object is a specialized <code>RowSet</code> object
49 * that implements the <code>SyncResolver</code> interface.
50 * It <b>may</b> operate as either a connected <code>RowSet</code> object (an
51 * implementation of the <code>JdbcRowSet</code> interface) or a connected
52 * <code>RowSet</code> object (an implementation of the
53 * <code>CachedRowSet</code> interface or one of its subinterfaces). For information
54 * on the subinterfaces, see the
55 * <a href="../package-summary.html"><code>javax.sql.rowset</code></a> package
56 * description. The reference implementation for <code>SyncResolver</code> implements
57 * the <code>CachedRowSet</code> interface, but other implementations
58 * may choose to implement the <code>JdbcRowSet</code> interface to satisfy
59 * particular needs.
60 * <P>
61 * After an application has attempted to synchronize a <code>RowSet</code> object with
62 * the data source (by calling the <code>CachedRowSet</code>
63 * method <code>acceptChanges</code>), and one or more conflicts have been found,
64 * a rowset's <code>SyncProvider</code> object creates an instance of
65 * <code>SyncResolver</code>. This new <code>SyncResolver</code> object has
66 * the same number of rows and columns as the
67 * <code>RowSet</code> object that was attempting the synchronization. The
68 * <code>SyncResolver</code> object contains the values from the data source that caused
69 * the conflict(s) and <code>null</code> for all other values.
70 * In addition, it contains information about each conflict.
71 * <P>
72 *
73 * <H2>Getting and Using a <code>SyncResolver</code> Object</H2>
74 *
75 * When the method <code>acceptChanges</code> encounters conflicts, the
76 * <code>SyncProvider</code> object creates a <code>SyncProviderException</code>
77 * object and sets it with the new <code>SyncResolver</code> object. The method
78 * <code>acceptChanges</code> will throw this exception, which
79 * the application can then catch and use to retrieve the
80 * <code>SyncResolver</code> object it contains. The following code snippet uses the
81 * <code>SyncProviderException</code> method <code>getSyncResolver</code> to get
82 * the <code>SyncResolver</code> object <i>resolver</i>.
83 * <PRE>
84 * {@code
85 * } catch (SyncProviderException spe) {
86 * SyncResolver resolver = spe.getSyncResolver();
87 * ...
88 * }
89 *
90 * }
91 * </PRE>
92 * <P>
93 * With <i>resolver</i> in hand, an application can use it to get the information
94 * it contains about the conflict or conflicts. A <code>SyncResolver</code> object
95 * such as <i>resolver</i> keeps
96 * track of the conflicts for each row in which there is a conflict. It also places a
97 * lock on the table or tables affected by the rowset's command so that no more
98 * conflicts can occur while the current conflicts are being resolved.
99 * <P>
100 * The following kinds of information can be obtained from a <code>SyncResolver</code>
101 * object:
102 * <P>
103 * <h3>What operation was being attempted when a conflict occurred</h3>
104 * The <code>SyncProvider</code> interface defines four constants
105 * describing states that may occur. Three
106 * constants describe the type of operation (update, delete, or insert) that a
107 * <code>RowSet</code> object was attempting to perform when a conflict was discovered,
108 * and the fourth indicates that there is no conflict.
109 * These constants are the possible return values when a <code>SyncResolver</code> object
110 * calls the method <code>getStatus</code>.
111 * <PRE>
112 * {@code int operation = resolver.getStatus(); }
113 * </PRE>
114 * <P>
115 * <h3>The value in the data source that caused a conflict</h3>
116 * A conflict exists when a value that a <code>RowSet</code> object has changed
117 * and is attempting to write to the data source
118 * has also been changed in the data source since the last synchronization. An
119 * application can call the <code>SyncResolver</code> method
120 * <code>getConflictValue</code > to retrieve the
121 * value in the data source that is the cause of the conflict because the values in a
122 * <code>SyncResolver</code> object are the conflict values from the data source.
123 * <PRE>
124 * java.lang.Object conflictValue = resolver.getConflictValue(2);
125 * </PRE>
126 * Note that the column in <i>resolver</i> can be designated by the column number,
127 * as is done in the preceding line of code, or by the column name.
128 * <P>
129 * With the information retrieved from the methods <code>getStatus</code> and
130 * <code>getConflictValue</code>, the application may make a determination as to
131 * which value should be persisted in the data source. The application then calls the
132 * <code>SyncResolver</code> method <code>setResolvedValue</code>, which sets the value
133 * to be persisted in the <code>RowSet</code> object and also in the data source.
134 * <PRE>
135 * resolver.setResolvedValue("DEPT", 8390426);
136 * </PRE>
137 * In the preceding line of code,
138 * the column name designates the column in the <code>RowSet</code> object
139 * that is to be set with the given value. The column number can also be used to
140 * designate the column.
141 * <P>
142 * An application calls the method <code>setResolvedValue</code> after it has
143 * resolved all of the conflicts in the current conflict row and repeats this process
144 * for each conflict row in the <code>SyncResolver</code> object.
145 * <P>
146 *
147 * <H2>Navigating a <code>SyncResolver</code> Object</H2>
148 *
149 * Because a <code>SyncResolver</code> object is a <code>RowSet</code> object, an
150 * application can use all of the <code>RowSet</code> methods for moving the cursor
151 * to navigate a <code>SyncResolver</code> object. For example, an application can
152 * use the <code>RowSet</code> method <code>next</code> to get to each row and then
153 * call the <code>SyncResolver</code> method <code>getStatus</code> to see if the row
154 * contains a conflict. In a row with one or more conflicts, the application can
155 * iterate through the columns to find any non-null values, which will be the values
156 * from the data source that are in conflict.
157 * <P>
158 * To make it easier to navigate a <code>SyncResolver</code> object, especially when
159 * there are large numbers of rows with no conflicts, the <code>SyncResolver</code>
160 * interface defines the methods <code>nextConflict</code> and
161 * <code>previousConflict</code>, which move only to rows
162 * that contain at least one conflict value. Then an application can call the
163 * <code>SyncResolver</code> method <code>getConflictValue</code>, supplying it
164 * with the column number, to get the conflict value itself. The code fragment in the
165 * next section gives an example.
166 *
167 * <H2>Code Example</H2>
168 *
169 * The following code fragment demonstrates how a disconnected <code>RowSet</code>
170 * object <i>crs</i> might attempt to synchronize itself with the
171 * underlying data source and then resolve the conflicts. In the <code>try</code>
172 * block, <i>crs</i> calls the method <code>acceptChanges</code>, passing it the
173 * <code>Connection</code> object <i>con</i>. If there are no conflicts, the
174 * changes in <i>crs</i> are simply written to the data source. However, if there
175 * is a conflict, the method <code>acceptChanges</code> throws a
176 * <code>SyncProviderException</code> object, and the
177 * <code>catch</code> block takes effect. In this example, which
178 * illustrates one of the many ways a <code>SyncResolver</code> object can be used,
179 * the <code>SyncResolver</code> method <code>nextConflict</code> is used in a
180 * <code>while</code> loop. The loop will end when <code>nextConflict</code> returns
181 * <code>false</code>, which will occur when there are no more conflict rows in the
182 * <code>SyncResolver</code> object <i>resolver</i>. In This particular code fragment,
183 * <i>resolver</i> looks for rows that have update conflicts (rows with the status
184 * <code>SyncResolver.UPDATE_ROW_CONFLICT</code>), and the rest of this code fragment
185 * executes only for rows where conflicts occurred because <i>crs</i> was attempting an
186 * update.
187 * <P>
188 * After the cursor for <i>resolver</i> has moved to the next conflict row that
189 * has an update conflict, the method <code>getRow</code> indicates the number of the
190 * current row, and
191 * the cursor for the <code>CachedRowSet</code> object <i>crs</i> is moved to
192 * the comparable row in <i>crs</i>. By iterating
193 * through the columns of that row in both <i>resolver</i> and <i>crs</i>, the conflicting
194 * values can be retrieved and compared to decide which one should be persisted. In this
195 * code fragment, the value in <i>crs</i> is the one set as the resolved value, which means
196 * that it will be used to overwrite the conflict value in the data source.
197 *
198 * <PRE>
199 * {@code
200 * try {
201 *
202 * crs.acceptChanges(con);
203 *
204 * } catch (SyncProviderException spe) {
205 *
206 * SyncResolver resolver = spe.getSyncResolver();
207 *
208 * Object crsValue; // value in the RowSet object
209 * Object resolverValue: // value in the SyncResolver object
210 * Object resolvedValue: // value to be persisted
211 *
212 * while(resolver.nextConflict()) {
213 * if(resolver.getStatus() == SyncResolver.UPDATE_ROW_CONFLICT) {
214 * int row = resolver.getRow();
215 * crs.absolute(row);
216 *
217 * int colCount = crs.getMetaData().getColumnCount();
218 * for(int j = 1; j <= colCount; j++) {
219 * if (resolver.getConflictValue(j) != null) {
220 * crsValue = crs.getObject(j);
221 * resolverValue = resolver.getConflictValue(j);
222 * . . .
223 * // compare crsValue and resolverValue to determine
224 * // which should be the resolved value (the value to persist)
225 * resolvedValue = crsValue;
226 *
227 * resolver.setResolvedValue(j, resolvedValue);
228 * }
229 * }
230 * }
231 * }
232 * }
233 * }</PRE>
234 * @author Jonathan Bruce
235 */
236
237 public interface SyncResolver extends RowSet {
238 /**
239 * Indicates that a conflict occurred while the <code>RowSet</code> object was
240 * attempting to update a row in the data source.
241 * The values in the data source row to be updated differ from the
242 * <code>RowSet</code> object's original values for that row, which means that
243 * the row in the data source has been updated or deleted since the last
244 * synchronization.
245 */
246 public static int UPDATE_ROW_CONFLICT = 0;
247
248 /**
249 * Indicates that a conflict occurred while the <code>RowSet</code> object was
250 * attempting to delete a row in the data source.
251 * The values in the data source row to be updated differ from the
252 * <code>RowSet</code> object's original values for that row, which means that
253 * the row in the data source has been updated or deleted since the last
254 * synchronization.
255 */
256 public static int DELETE_ROW_CONFLICT = 1;
257
258 /**
259 * Indicates that a conflict occurred while the <code>RowSet</code> object was
260 * attempting to insert a row into the data source. This means that a
261 * row with the same primary key as the row to be inserted has been inserted
262 * into the data source since the last synchronization.
263 */
264 public static int INSERT_ROW_CONFLICT = 2;
265
266 /**
267 * Indicates that <b>no</b> conflict occured while the <code>RowSet</code> object
268 * was attempting to update, delete or insert a row in the data source. The values in
269 * the <code>SyncResolver</code> will contain <code>null</code> values only as an indication
270 * that no information in pertitent to the conflict resolution in this row.
271 */
272 public static int NO_ROW_CONFLICT = 3;
273
274 /**
275 * Retrieves the conflict status of the current row of this <code>SyncResolver</code>,
276 * which indicates the operation
277 * the <code>RowSet</code> object was attempting when the conflict occurred.
278 *
279 * @return one of the following constants:
280 * <code>SyncResolver.UPDATE_ROW_CONFLICT</code>,
281 * <code>SyncResolver.DELETE_ROW_CONFLICT</code>,
282 * <code>SyncResolver.INSERT_ROW_CONFLICT</code>, or
283 * <code>SyncResolver.NO_ROW_CONFLICT</code>
284 */
285 public int getStatus();
286
287 /**
288 * Retrieves the value in the designated column in the current row of this
289 * <code>SyncResolver</code> object, which is the value in the data source
290 * that caused a conflict.
291 *
292 * @param index an <code>int</code> designating the column in this row of this
293 * <code>SyncResolver</code> object from which to retrieve the value
294 * causing a conflict
295 * @return the value of the designated column in the current row of this
296 * <code>SyncResolver</code> object
297 * @throws SQLException if a database access error occurs
298 */
299 public Object getConflictValue(int index) throws SQLException;
300
301 /**
302 * Retrieves the value in the designated column in the current row of this
303 * <code>SyncResolver</code> object, which is the value in the data source
304 * that caused a conflict.
305 *
306 * @param columnName a <code>String</code> object designating the column in this row of this
307 * <code>SyncResolver</code> object from which to retrieve the value
308 * causing a conflict
309 * @return the value of the designated column in the current row of this
310 * <code>SyncResolver</code> object
311 * @throws SQLException if a database access error occurs
312 */
313 public Object getConflictValue(String columnName) throws SQLException;
314
315 /**
316 * Sets <i>obj</i> as the value in column <i>index</i> in the current row of the
317 * <code>RowSet</code> object that is being synchronized. <i>obj</i>
318 * is set as the value in the data source internally.
319 *
320 * @param index an <code>int</code> giving the number of the column into which to
321 * set the value to be persisted
322 * @param obj an <code>Object</code> that is the value to be set in the
323 * <code>RowSet</code> object and persisted in the data source
324 * @throws SQLException if a database access error occurs
325 */
326 public void setResolvedValue(int index, Object obj) throws SQLException;
327
328 /**
329 * Sets <i>obj</i> as the value in column <i>columnName</i> in the current row of the
330 * <code>RowSet</code> object that is being synchronized. <i>obj</i>
331 * is set as the value in the data source internally.
332 *
333 * @param columnName a <code>String</code> object giving the name of the column
334 * into which to set the value to be persisted
335 * @param obj an <code>Object</code> that is the value to be set in the
336 * <code>RowSet</code> object and persisted in the data source
337 * @throws SQLException if a database access error occurs
338 */
339 public void setResolvedValue(String columnName, Object obj) throws SQLException;
340
341 /**
342 * Moves the cursor down from its current position to the next row that contains
343 * a conflict value. A <code>SyncResolver</code> object's
344 * cursor is initially positioned before the first conflict row; the first call to the
345 * method <code>nextConflict</code> makes the first conflict row the current row;
346 * the second call makes the second conflict row the current row, and so on.
347 * <p>
348 * A call to the method <code>nextConflict</code> will implicitly close
349 * an input stream if one is open and will clear the <code>SyncResolver</code>
350 * object's warning chain.
351 *
352 * @return <code>true</code> if the new current row is valid; <code>false</code>
353 * if there are no more rows
354 * @throws SQLException if a database access error occurs or the result set type
355 * is <code>TYPE_FORWARD_ONLY</code>
356 *
357 */
358 public boolean nextConflict() throws SQLException;
359
360 /**
361 * Moves the cursor up from its current position to the previous conflict
362 * row in this <code>SyncResolver</code> object.
363 * <p>
364 * A call to the method <code>previousConflict</code> will implicitly close
365 * an input stream if one is open and will clear the <code>SyncResolver</code>
366 * object's warning chain.
367 *
368 * @return <code>true</code> if the cursor is on a valid row; <code>false</code>
369 * if it is off the result set
370 * @throws SQLException if a database access error occurs or the result set type
371 * is <code>TYPE_FORWARD_ONLY</code>
372 */
373 public boolean previousConflict() throws SQLException;
374
375 }