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package javax.sql.rowset.spi;
import javax.sql.RowSet;
import java.sql.SQLException;
/**
* Defines a framework that allows applications to use a manual decision tree
* to decide what should be done when a synchronization conflict occurs.
* Although it is not mandatory for
* applications to resolve synchronization conflicts manually, this
* framework provides the means to delegate to the application when conflicts
* arise.
* <p>
* Note that a conflict is a situation where the <code>RowSet</code> object's original
* values for a row do not match the values in the data source, which indicates that
* the data source row has been modified since the last synchronization. Note also that
* a <code>RowSet</code> object's original values are the values it had just prior to the
* the last synchronization, which are not necessarily its initial values.
*
*
* <H2>Description of a <code>SyncResolver</code> Object</H2>
*
* A <code>SyncResolver</code> object is a specialized <code>RowSet</code> object
* that implements the <code>SyncResolver</code> interface.
* It <b>may</b> operate as either a connected <code>RowSet</code> object (an
* implementation of the <code>JdbcRowSet</code> interface) or a connected
* <code>RowSet</code> object (an implementation of the
* <code>CachedRowSet</code> interface or one of its subinterfaces). For information
* on the subinterfaces, see the
* <a href="../package-summary.html"><code>javax.sql.rowset</code></a> package
* description. The reference implementation for <code>SyncResolver</code> implements
* the <code>CachedRowSet</code> interface, but other implementations
* may choose to implement the <code>JdbcRowSet</code> interface to satisfy
* particular needs.
* <P>
* After an application has attempted to synchronize a <code>RowSet</code> object with
* the data source (by calling the <code>CachedRowSet</code>
* method <code>acceptChanges</code>), and one or more conflicts have been found,
* a rowset's <code>SyncProvider</code> object creates an instance of
* <code>SyncResolver</code>. This new <code>SyncResolver</code> object has
* the same number of rows and columns as the
* <code>RowSet</code> object that was attempting the synchronization. The
* <code>SyncResolver</code> object contains the values from the data source that caused
* the conflict(s) and <code>null</code> for all other values.
* In addition, it contains information about each conflict.
*
*
* <H2>Getting and Using a <code>SyncResolver</code> Object</H2>
*
* When the method <code>acceptChanges</code> encounters conflicts, the
* <code>SyncProvider</code> object creates a <code>SyncProviderException</code>
* object and sets it with the new <code>SyncResolver</code> object. The method
* <code>acceptChanges</code> will throw this exception, which
* the application can then catch and use to retrieve the
* <code>SyncResolver</code> object it contains. The following code snippet uses the
* <code>SyncProviderException</code> method <code>getSyncResolver</code> to get
* the <code>SyncResolver</code> object <i>resolver</i>.
* <PRE>
* {@code
* } catch (SyncProviderException spe) {
* SyncResolver resolver = spe.getSyncResolver();
* ...
* }
*
* }
* </PRE>
* <P>
* With <i>resolver</i> in hand, an application can use it to get the information
* it contains about the conflict or conflicts. A <code>SyncResolver</code> object
* such as <i>resolver</i> keeps
* track of the conflicts for each row in which there is a conflict. It also places a
* lock on the table or tables affected by the rowset's command so that no more
* conflicts can occur while the current conflicts are being resolved.
* <P>
* The following kinds of information can be obtained from a <code>SyncResolver</code>
* object:
*
* <h3>What operation was being attempted when a conflict occurred</h3>
* The <code>SyncProvider</code> interface defines four constants
* describing states that may occur. Three
* constants describe the type of operation (update, delete, or insert) that a
* <code>RowSet</code> object was attempting to perform when a conflict was discovered,
* and the fourth indicates that there is no conflict.
* These constants are the possible return values when a <code>SyncResolver</code> object
* calls the method <code>getStatus</code>.
* <PRE>
* {@code int operation = resolver.getStatus(); }
* </PRE>
*
* <h3>The value in the data source that caused a conflict</h3>
* A conflict exists when a value that a <code>RowSet</code> object has changed
* and is attempting to write to the data source
* has also been changed in the data source since the last synchronization. An
* application can call the <code>SyncResolver</code> method
* <code>getConflictValue</code > to retrieve the
* value in the data source that is the cause of the conflict because the values in a
* <code>SyncResolver</code> object are the conflict values from the data source.
* <PRE>
* java.lang.Object conflictValue = resolver.getConflictValue(2);
* </PRE>
* Note that the column in <i>resolver</i> can be designated by the column number,
* as is done in the preceding line of code, or by the column name.
* <P>
* With the information retrieved from the methods <code>getStatus</code> and
* <code>getConflictValue</code>, the application may make a determination as to
* which value should be persisted in the data source. The application then calls the
* <code>SyncResolver</code> method <code>setResolvedValue</code>, which sets the value
* to be persisted in the <code>RowSet</code> object and also in the data source.
* <PRE>
* resolver.setResolvedValue("DEPT", 8390426);
* </PRE>
* In the preceding line of code,
* the column name designates the column in the <code>RowSet</code> object
* that is to be set with the given value. The column number can also be used to
* designate the column.
* <P>
* An application calls the method <code>setResolvedValue</code> after it has
* resolved all of the conflicts in the current conflict row and repeats this process
* for each conflict row in the <code>SyncResolver</code> object.
*
*
* <H2>Navigating a <code>SyncResolver</code> Object</H2>
*
* Because a <code>SyncResolver</code> object is a <code>RowSet</code> object, an
* application can use all of the <code>RowSet</code> methods for moving the cursor
* to navigate a <code>SyncResolver</code> object. For example, an application can
* use the <code>RowSet</code> method <code>next</code> to get to each row and then
* call the <code>SyncResolver</code> method <code>getStatus</code> to see if the row
* contains a conflict. In a row with one or more conflicts, the application can
* iterate through the columns to find any non-null values, which will be the values
* from the data source that are in conflict.
* <P>
* To make it easier to navigate a <code>SyncResolver</code> object, especially when
* there are large numbers of rows with no conflicts, the <code>SyncResolver</code>
* interface defines the methods <code>nextConflict</code> and
* <code>previousConflict</code>, which move only to rows
* that contain at least one conflict value. Then an application can call the
* <code>SyncResolver</code> method <code>getConflictValue</code>, supplying it
* with the column number, to get the conflict value itself. The code fragment in the
* next section gives an example.
*
* <H2>Code Example</H2>
*
* The following code fragment demonstrates how a disconnected <code>RowSet</code>
* object <i>crs</i> might attempt to synchronize itself with the
* underlying data source and then resolve the conflicts. In the <code>try</code>
* block, <i>crs</i> calls the method <code>acceptChanges</code>, passing it the
* <code>Connection</code> object <i>con</i>. If there are no conflicts, the
* changes in <i>crs</i> are simply written to the data source. However, if there
* is a conflict, the method <code>acceptChanges</code> throws a
* <code>SyncProviderException</code> object, and the
* <code>catch</code> block takes effect. In this example, which
* illustrates one of the many ways a <code>SyncResolver</code> object can be used,
* the <code>SyncResolver</code> method <code>nextConflict</code> is used in a
* <code>while</code> loop. The loop will end when <code>nextConflict</code> returns
* <code>false</code>, which will occur when there are no more conflict rows in the
* <code>SyncResolver</code> object <i>resolver</i>. In This particular code fragment,
* <i>resolver</i> looks for rows that have update conflicts (rows with the status
* <code>SyncResolver.UPDATE_ROW_CONFLICT</code>), and the rest of this code fragment
* executes only for rows where conflicts occurred because <i>crs</i> was attempting an
* update.
* <P>
* After the cursor for <i>resolver</i> has moved to the next conflict row that
* has an update conflict, the method <code>getRow</code> indicates the number of the
* current row, and
* the cursor for the <code>CachedRowSet</code> object <i>crs</i> is moved to
* the comparable row in <i>crs</i>. By iterating
* through the columns of that row in both <i>resolver</i> and <i>crs</i>, the conflicting
* values can be retrieved and compared to decide which one should be persisted. In this
* code fragment, the value in <i>crs</i> is the one set as the resolved value, which means
* that it will be used to overwrite the conflict value in the data source.
*
* <PRE>
* {@code
* try {
*
* crs.acceptChanges(con);
*
* } catch (SyncProviderException spe) {
*
* SyncResolver resolver = spe.getSyncResolver();
*
* Object crsValue; // value in the RowSet object
* Object resolverValue: // value in the SyncResolver object
* Object resolvedValue: // value to be persisted
*
* while(resolver.nextConflict()) {
* if(resolver.getStatus() == SyncResolver.UPDATE_ROW_CONFLICT) {
* int row = resolver.getRow();
* crs.absolute(row);
*
* int colCount = crs.getMetaData().getColumnCount();
* for(int j = 1; j <= colCount; j++) {
* if (resolver.getConflictValue(j) != null) {
* crsValue = crs.getObject(j);
* resolverValue = resolver.getConflictValue(j);
* . . .
* // compare crsValue and resolverValue to determine
* // which should be the resolved value (the value to persist)
* resolvedValue = crsValue;
*
* resolver.setResolvedValue(j, resolvedValue);
* }
* }
* }
* }
* }
* }</PRE>
*
* @author Jonathan Bruce
* @since 1.5
*/
public interface SyncResolver extends RowSet {
/**
* Indicates that a conflict occurred while the <code>RowSet</code> object was
* attempting to update a row in the data source.
* The values in the data source row to be updated differ from the
* <code>RowSet</code> object's original values for that row, which means that
* the row in the data source has been updated or deleted since the last
* synchronization.
*/
public static int UPDATE_ROW_CONFLICT = 0;
/**
* Indicates that a conflict occurred while the <code>RowSet</code> object was
* attempting to delete a row in the data source.
* The values in the data source row to be updated differ from the
* <code>RowSet</code> object's original values for that row, which means that
* the row in the data source has been updated or deleted since the last
* synchronization.
*/
public static int DELETE_ROW_CONFLICT = 1;
/**
* Indicates that a conflict occurred while the <code>RowSet</code> object was
* attempting to insert a row into the data source. This means that a
* row with the same primary key as the row to be inserted has been inserted
* into the data source since the last synchronization.
*/
public static int INSERT_ROW_CONFLICT = 2;
/**
* Indicates that <b>no</b> conflict occurred while the <code>RowSet</code> object
* was attempting to update, delete or insert a row in the data source. The values in
* the <code>SyncResolver</code> will contain <code>null</code> values only as an indication
* that no information in pertinent to the conflict resolution in this row.
*/
public static int NO_ROW_CONFLICT = 3;
/**
* Retrieves the conflict status of the current row of this <code>SyncResolver</code>,
* which indicates the operation
* the <code>RowSet</code> object was attempting when the conflict occurred.
*
* @return one of the following constants:
* <code>SyncResolver.UPDATE_ROW_CONFLICT</code>,
* <code>SyncResolver.DELETE_ROW_CONFLICT</code>,
* <code>SyncResolver.INSERT_ROW_CONFLICT</code>, or
* <code>SyncResolver.NO_ROW_CONFLICT</code>
*/
public int getStatus();
/**
* Retrieves the value in the designated column in the current row of this
* <code>SyncResolver</code> object, which is the value in the data source
* that caused a conflict.
*
* @param index an <code>int</code> designating the column in this row of this
* <code>SyncResolver</code> object from which to retrieve the value
* causing a conflict
* @return the value of the designated column in the current row of this
* <code>SyncResolver</code> object
* @throws SQLException if a database access error occurs
*/
public Object getConflictValue(int index) throws SQLException;
/**
* Retrieves the value in the designated column in the current row of this
* <code>SyncResolver</code> object, which is the value in the data source
* that caused a conflict.
*
* @param columnName a <code>String</code> object designating the column in this row of this
* <code>SyncResolver</code> object from which to retrieve the value
* causing a conflict
* @return the value of the designated column in the current row of this
* <code>SyncResolver</code> object
* @throws SQLException if a database access error occurs
*/
public Object getConflictValue(String columnName) throws SQLException;
/**
* Sets <i>obj</i> as the value in column <i>index</i> in the current row of the
* <code>RowSet</code> object that is being synchronized. <i>obj</i>
* is set as the value in the data source internally.
*
* @param index an <code>int</code> giving the number of the column into which to
* set the value to be persisted
* @param obj an <code>Object</code> that is the value to be set in the
* <code>RowSet</code> object and persisted in the data source
* @throws SQLException if a database access error occurs
*/
public void setResolvedValue(int index, Object obj) throws SQLException;
/**
* Sets <i>obj</i> as the value in column <i>columnName</i> in the current row of the
* <code>RowSet</code> object that is being synchronized. <i>obj</i>
* is set as the value in the data source internally.
*
* @param columnName a <code>String</code> object giving the name of the column
* into which to set the value to be persisted
* @param obj an <code>Object</code> that is the value to be set in the
* <code>RowSet</code> object and persisted in the data source
* @throws SQLException if a database access error occurs
*/
public void setResolvedValue(String columnName, Object obj) throws SQLException;
/**
* Moves the cursor down from its current position to the next row that contains
* a conflict value. A <code>SyncResolver</code> object's
* cursor is initially positioned before the first conflict row; the first call to the
* method <code>nextConflict</code> makes the first conflict row the current row;
* the second call makes the second conflict row the current row, and so on.
* <p>
* A call to the method <code>nextConflict</code> will implicitly close
* an input stream if one is open and will clear the <code>SyncResolver</code>
* object's warning chain.
*
* @return <code>true</code> if the new current row is valid; <code>false</code>
* if there are no more rows
* @throws SQLException if a database access error occurs or the result set type
* is <code>TYPE_FORWARD_ONLY</code>
*
*/
public boolean nextConflict() throws SQLException;
/**
* Moves the cursor up from its current position to the previous conflict
* row in this <code>SyncResolver</code> object.
* <p>
* A call to the method <code>previousConflict</code> will implicitly close
* an input stream if one is open and will clear the <code>SyncResolver</code>
* object's warning chain.
*
* @return <code>true</code> if the cursor is on a valid row; <code>false</code>
* if it is off the result set
* @throws SQLException if a database access error occurs or the result set type
* is <code>TYPE_FORWARD_ONLY</code>
*/
public boolean previousConflict() throws SQLException;
}