Interface SyncResolver
- All Superinterfaces:
-
AutoCloseable
,ResultSet
,RowSet
,Wrapper
public interface SyncResolver extends RowSet
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.
Note that a conflict is a situation where the RowSet
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 RowSet
object's original values are the values it had just prior to the the last synchronization, which are not necessarily its initial values.
Description of a SyncResolver
Object
A SyncResolver
object is a specialized RowSet
object that implements the SyncResolver
interface. It may operate as either a connected RowSet
object (an implementation of the JdbcRowSet
interface) or a connected RowSet
object (an implementation of the CachedRowSet
interface or one of its subinterfaces). For information on the subinterfaces, see the javax.sql.rowset
package description. The reference implementation for SyncResolver
implements the CachedRowSet
interface, but other implementations may choose to implement the JdbcRowSet
interface to satisfy particular needs. After an application has attempted to synchronize a RowSet
object with the data source (by calling the CachedRowSet
method acceptChanges
), and one or more conflicts have been found, a rowset's SyncProvider
object creates an instance of SyncResolver
. This new SyncResolver
object has the same number of rows and columns as the RowSet
object that was attempting the synchronization. The SyncResolver
object contains the values from the data source that caused the conflict(s) and null
for all other values. In addition, it contains information about each conflict.
Getting and Using a SyncResolver
Object
When the method acceptChanges
encounters conflicts, the SyncProvider
object creates a SyncProviderException
object and sets it with the new SyncResolver
object. The method acceptChanges
will throw this exception, which the application can then catch and use to retrieve the SyncResolver
object it contains. The following code snippet uses the SyncProviderException
method getSyncResolver
to get the SyncResolver
object resolver. catch (SyncProviderException spe) { SyncResolver resolver = spe.getSyncResolver(); ... } }
With resolver in hand, an application can use it to get the information it contains about the conflict or conflicts. A SyncResolver
object such as resolver 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.
The following kinds of information can be obtained from a SyncResolver
object:
What operation was being attempted when a conflict occurred
TheSyncProvider
interface defines four constants describing states that may occur. Three constants describe the type of operation (update, delete, or insert) that a RowSet
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 SyncResolver
object calls the method getStatus
. int operation = resolver.getStatus();
The value in the data source that caused a conflict
A conflict exists when a value that aRowSet
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 SyncResolver
method getConflictValue
to retrieve the value in the data source that is the cause of the conflict because the values in a SyncResolver
object are the conflict values from the data source. java.lang.Object conflictValue = resolver.getConflictValue(2);Note that the column in resolver can be designated by the column number, as is done in the preceding line of code, or by the column name.
With the information retrieved from the methods getStatus
and getConflictValue
, the application may make a determination as to which value should be persisted in the data source. The application then calls the SyncResolver
method setResolvedValue
, which sets the value to be persisted in the RowSet
object and also in the data source.
resolver.setResolvedValue("DEPT", 8390426);In the preceding line of code, the column name designates the column in the
RowSet
object that is to be set with the given value. The column number can also be used to designate the column. An application calls the method setResolvedValue
after it has resolved all of the conflicts in the current conflict row and repeats this process for each conflict row in the SyncResolver
object.
Navigating a SyncResolver
Object
Because a SyncResolver
object is a RowSet
object, an application can use all of the RowSet
methods for moving the cursor to navigate a SyncResolver
object. For example, an application can use the RowSet
method next
to get to each row and then call the SyncResolver
method getStatus
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. To make it easier to navigate a SyncResolver
object, especially when there are large numbers of rows with no conflicts, the SyncResolver
interface defines the methods nextConflict
and previousConflict
, which move only to rows that contain at least one conflict value. Then an application can call the SyncResolver
method getConflictValue
, supplying it with the column number, to get the conflict value itself. The code fragment in the next section gives an example.
Code Example
The following code fragment demonstrates how a disconnectedRowSet
object crs might attempt to synchronize itself with the underlying data source and then resolve the conflicts. In the try
block, crs calls the method acceptChanges
, passing it the Connection
object con. If there are no conflicts, the changes in crs are simply written to the data source. However, if there is a conflict, the method acceptChanges
throws a SyncProviderException
object, and the catch
block takes effect. In this example, which illustrates one of the many ways a SyncResolver
object can be used, the SyncResolver
method nextConflict
is used in a while
loop. The loop will end when nextConflict
returns false
, which will occur when there are no more conflict rows in the SyncResolver
object resolver. In This particular code fragment, resolver looks for rows that have update conflicts (rows with the status SyncResolver.UPDATE_ROW_CONFLICT
), and the rest of this code fragment executes only for rows where conflicts occurred because crs was attempting an update. After the cursor for resolver has moved to the next conflict row that has an update conflict, the method getRow
indicates the number of the current row, and the cursor for the CachedRowSet
object crs is moved to the comparable row in crs. By iterating through the columns of that row in both resolver and crs, the conflicting values can be retrieved and compared to decide which one should be persisted. In this code fragment, the value in crs is the one set as the resolved value, which means that it will be used to overwrite the conflict value in the data source.
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); } } } } }
- Since:
- 1.5
Field Summary
Modifier and Type | Field | Description |
---|---|---|
static int | DELETE_ROW_CONFLICT | Indicates that a conflict occurred while the |
static int | INSERT_ROW_CONFLICT | Indicates that a conflict occurred while the |
static int | NO_ROW_CONFLICT | Indicates that no conflict occurred while the |
static int | UPDATE_ROW_CONFLICT | Indicates that a conflict occurred while the |
Fields declared in interface java.sql.ResultSet
CLOSE_CURSORS_AT_COMMIT, CONCUR_READ_ONLY, CONCUR_UPDATABLE, FETCH_FORWARD, FETCH_REVERSE, FETCH_UNKNOWN, HOLD_CURSORS_OVER_COMMIT, TYPE_FORWARD_ONLY, TYPE_SCROLL_INSENSITIVE, TYPE_SCROLL_SENSITIVE
Method Summary
Modifier and Type | Method | Description |
---|---|---|
Object | getConflictValue(int index) | Retrieves the value in the designated column in the current row of this |
Object | getConflictValue(String columnName) | Retrieves the value in the designated column in the current row of this |
int | getStatus() | Retrieves the conflict status of the current row of this |
boolean | nextConflict() | Moves the cursor down from its current position to the next row that contains a conflict value. |
boolean | previousConflict() | Moves the cursor up from its current position to the previous conflict row in this |
void | setResolvedValue(int index,
Object obj) | Sets obj as the value in column index in the current row of the |
void | setResolvedValue(String columnName,
Object obj) | Sets obj as the value in column columnName in the current row of the |
Methods declared in interface java.sql.ResultSet
absolute, afterLast, beforeFirst, cancelRowUpdates, clearWarnings, close, deleteRow, findColumn, first, getArray, getArray, getAsciiStream, getAsciiStream, getBigDecimal, getBigDecimal, getBigDecimal, getBigDecimal, getBinaryStream, getBinaryStream, getBlob, getBlob, getBoolean, getBoolean, getByte, getByte, getBytes, getBytes, getCharacterStream, getCharacterStream, getClob, getClob, getConcurrency, getCursorName, getDate, getDate, getDate, getDate, getDouble, getDouble, getFetchDirection, getFetchSize, getFloat, getFloat, getHoldability, getInt, getInt, getLong, getLong, getMetaData, getNCharacterStream, getNCharacterStream, getNClob, getNClob, getNString, getNString, getObject, getObject, getObject, getObject, getObject, getObject, getRef, getRef, getRow, getRowId, getRowId, getShort, getShort, getSQLXML, getSQLXML, getStatement, getString, getString, getTime, getTime, getTime, getTime, getTimestamp, getTimestamp, getTimestamp, getTimestamp, getType, getUnicodeStream, getUnicodeStream, getURL, getURL, getWarnings, insertRow, isAfterLast, isBeforeFirst, isClosed, isFirst, isLast, last, moveToCurrentRow, moveToInsertRow, next, previous, refreshRow, relative, rowDeleted, rowInserted, rowUpdated, setFetchDirection, setFetchSize, updateArray, updateArray, updateAsciiStream, updateAsciiStream, updateAsciiStream, updateAsciiStream, updateAsciiStream, updateAsciiStream, updateBigDecimal, updateBigDecimal, updateBinaryStream, updateBinaryStream, updateBinaryStream, updateBinaryStream, updateBinaryStream, updateBinaryStream, updateBlob, updateBlob, updateBlob, updateBlob, updateBlob, updateBlob, updateBoolean, updateBoolean, updateByte, updateByte, updateBytes, updateBytes, updateCharacterStream, updateCharacterStream, updateCharacterStream, updateCharacterStream, updateCharacterStream, updateCharacterStream, updateClob, updateClob, updateClob, updateClob, updateClob, updateClob, updateDate, updateDate, updateDouble, updateDouble, updateFloat, updateFloat, updateInt, updateInt, updateLong, updateLong, updateNCharacterStream, updateNCharacterStream, updateNCharacterStream, updateNCharacterStream, updateNClob, updateNClob, updateNClob, updateNClob, updateNClob, updateNClob, updateNString, updateNString, updateNull, updateNull, updateObject, updateObject, updateObject, updateObject, updateObject, updateObject, updateObject, updateObject, updateRef, updateRef, updateRow, updateRowId, updateRowId, updateShort, updateShort, updateSQLXML, updateSQLXML, updateString, updateString, updateTime, updateTime, updateTimestamp, updateTimestamp, wasNull
Methods declared in interface javax.sql.RowSet
addRowSetListener, clearParameters, execute, getCommand, getDataSourceName, getEscapeProcessing, getMaxFieldSize, getMaxRows, getPassword, getQueryTimeout, getTransactionIsolation, getTypeMap, getUrl, getUsername, isReadOnly, removeRowSetListener, setArray, setAsciiStream, setAsciiStream, setAsciiStream, setAsciiStream, setBigDecimal, setBigDecimal, setBinaryStream, setBinaryStream, setBinaryStream, setBinaryStream, setBlob, setBlob, setBlob, setBlob, setBlob, setBlob, setBoolean, setBoolean, setByte, setByte, setBytes, setBytes, setCharacterStream, setCharacterStream, setCharacterStream, setCharacterStream, setClob, setClob, setClob, setClob, setClob, setClob, setCommand, setConcurrency, setDataSourceName, setDate, setDate, setDate, setDate, setDouble, setDouble, setEscapeProcessing, setFloat, setFloat, setInt, setInt, setLong, setLong, setMaxFieldSize, setMaxRows, setNCharacterStream, setNCharacterStream, setNCharacterStream, setNCharacterStream, setNClob, setNClob, setNClob, setNClob, setNClob, setNClob, setNString, setNString, setNull, setNull, setNull, setNull, setObject, setObject, setObject, setObject, setObject, setObject, setPassword, setQueryTimeout, setReadOnly, setRef, setRowId, setRowId, setShort, setShort, setSQLXML, setSQLXML, setString, setString, setTime, setTime, setTime, setTime, setTimestamp, setTimestamp, setTimestamp, setTimestamp, setTransactionIsolation, setType, setTypeMap, setUrl, setURL, setUsername
Methods declared in interface java.sql.Wrapper
isWrapperFor, unwrap
Field Detail
UPDATE_ROW_CONFLICT
static final int UPDATE_ROW_CONFLICT
Indicates that a conflict occurred while the RowSet
object was attempting to update a row in the data source. The values in the data source row to be updated differ from the RowSet
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.
- See Also:
- Constant Field Values
DELETE_ROW_CONFLICT
static final int DELETE_ROW_CONFLICT
Indicates that a conflict occurred while the RowSet
object was attempting to delete a row in the data source. The values in the data source row to be updated differ from the RowSet
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.
- See Also:
- Constant Field Values
INSERT_ROW_CONFLICT
static final int INSERT_ROW_CONFLICT
Indicates that a conflict occurred while the RowSet
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.
- See Also:
- Constant Field Values
NO_ROW_CONFLICT
static final int NO_ROW_CONFLICT
Indicates that no conflict occurred while the RowSet
object was attempting to update, delete or insert a row in the data source. The values in the SyncResolver
will contain null
values only as an indication that no information in pertinent to the conflict resolution in this row.
- See Also:
- Constant Field Values
Method Detail
getStatus
int getStatus()
Retrieves the conflict status of the current row of this SyncResolver
, which indicates the operation the RowSet
object was attempting when the conflict occurred.
- Returns:
- one of the following constants:
SyncResolver.UPDATE_ROW_CONFLICT
,SyncResolver.DELETE_ROW_CONFLICT
,SyncResolver.INSERT_ROW_CONFLICT
, orSyncResolver.NO_ROW_CONFLICT
getConflictValue
Object getConflictValue(int index) throws SQLException
Retrieves the value in the designated column in the current row of this SyncResolver
object, which is the value in the data source that caused a conflict.
- Parameters:
-
index
- anint
designating the column in this row of thisSyncResolver
object from which to retrieve the value causing a conflict - Returns:
- the value of the designated column in the current row of this
SyncResolver
object - Throws:
-
SQLException
- if a database access error occurs
getConflictValue
Object getConflictValue(String columnName) throws SQLException
Retrieves the value in the designated column in the current row of this SyncResolver
object, which is the value in the data source that caused a conflict.
- Parameters:
-
columnName
- aString
object designating the column in this row of thisSyncResolver
object from which to retrieve the value causing a conflict - Returns:
- the value of the designated column in the current row of this
SyncResolver
object - Throws:
-
SQLException
- if a database access error occurs
setResolvedValue
void setResolvedValue(int index, Object obj) throws SQLException
Sets obj as the value in column index in the current row of the RowSet
object that is being synchronized. obj is set as the value in the data source internally.
- Parameters:
-
index
- anint
giving the number of the column into which to set the value to be persisted -
obj
- anObject
that is the value to be set in theRowSet
object and persisted in the data source - Throws:
-
SQLException
- if a database access error occurs
setResolvedValue
void setResolvedValue(String columnName, Object obj) throws SQLException
Sets obj as the value in column columnName in the current row of the RowSet
object that is being synchronized. obj is set as the value in the data source internally.
- Parameters:
-
columnName
- aString
object giving the name of the column into which to set the value to be persisted -
obj
- anObject
that is the value to be set in theRowSet
object and persisted in the data source - Throws:
-
SQLException
- if a database access error occurs
nextConflict
boolean nextConflict() throws SQLException
Moves the cursor down from its current position to the next row that contains a conflict value. A SyncResolver
object's cursor is initially positioned before the first conflict row; the first call to the method nextConflict
makes the first conflict row the current row; the second call makes the second conflict row the current row, and so on.
A call to the method nextConflict
will implicitly close an input stream if one is open and will clear the SyncResolver
object's warning chain.
- Returns:
-
true
if the new current row is valid;false
if there are no more rows - Throws:
-
SQLException
- if a database access error occurs or the result set type isTYPE_FORWARD_ONLY
previousConflict
boolean previousConflict() throws SQLException
Moves the cursor up from its current position to the previous conflict row in this SyncResolver
object.
A call to the method previousConflict
will implicitly close an input stream if one is open and will clear the SyncResolver
object's warning chain.
- Returns:
-
true
if the cursor is on a valid row;false
if it is off the result set - Throws:
-
SQLException
- if a database access error occurs or the result set type isTYPE_FORWARD_ONLY