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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   *
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   *
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  *
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  *
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  *
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 occurred 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 pertinent 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 }