| JavaTM 2 Platform Std. Ed. v1.5.0
javax.sql.rowset.spi
Interface SyncResolver
- All Superinterfaces:
- ResultSet, RowSet
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
The SyncProvider 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 a RowSet 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 disconnected RowSet
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);
}
}
}
}
}
|
Field Summary |
static int |
DELETE_ROW_CONFLICT
Indicates that a conflict occurred while the RowSet object was
attempting to delete a row in the data source. |
static int |
INSERT_ROW_CONFLICT
Indicates that a conflict occurred while the RowSet object was
attempting to insert a row into the data source. |
static int |
NO_ROW_CONFLICT
Indicates that no conflict occured while the RowSet object
was attempting to update, delete or insert a row in the data source. |
static int |
UPDATE_ROW_CONFLICT
Indicates that a conflict occurred while the RowSet object was
attempting to update a row in the data source. |
|
Method Summary |
Object |
getConflictValue(int index)
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. |
Object |
getConflictValue(String columnName)
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. |
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. |
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 SyncResolver object. |
void |
setResolvedValue(int index,
Object obj)
Sets obj as the value in column index in the current row of the
RowSet object that is being synchronized. |
void |
setResolvedValue(String columnName,
Object obj)
Sets obj as the value in column columnName in the current row of the
RowSet object that is being synchronized. |
| Methods inherited from interface javax.sql.RowSet |
addRowSetListener, clearParameters, execute, getCommand, getDataSourceName, getEscapeProcessing, getMaxFieldSize, getMaxRows, getPassword, getQueryTimeout, getTransactionIsolation, getTypeMap, getUrl, getUsername, isReadOnly, removeRowSetListener, setArray, setAsciiStream, setBigDecimal, setBinaryStream, setBlob, setBoolean, setByte, setBytes, setCharacterStream, setClob, setCommand, setConcurrency, setDataSourceName, setDate, setDate, setDouble, setEscapeProcessing, setFloat, setInt, setLong, setMaxFieldSize, setMaxRows, setNull, setNull, setObject, setObject, setObject, setPassword, setQueryTimeout, setReadOnly, setRef, setShort, setString, setTime, setTime, setTimestamp, setTimestamp, setTransactionIsolation, setType, setTypeMap, setUrl, setUsername |
| Methods inherited from 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, getInt, getInt, getLong, getLong, getMetaData, getObject, getObject, getObject, getObject, getRef, getRef, getRow, getShort, getShort, getStatement, getString, getString, getTime, getTime, getTime, getTime, getTimestamp, getTimestamp, getTimestamp, getTimestamp, getType, getUnicodeStream, getUnicodeStream, getURL, getURL, getWarnings, insertRow, isAfterLast, isBeforeFirst, isFirst, isLast, last, moveToCurrentRow, moveToInsertRow, next, previous, refreshRow, relative, rowDeleted, rowInserted, rowUpdated, setFetchDirection, setFetchSize, updateArray, updateArray, updateAsciiStream, updateAsciiStream, updateBigDecimal, updateBigDecimal, updateBinaryStream, updateBinaryStream, updateBlob, updateBlob, updateBoolean, updateBoolean, updateByte, updateByte, updateBytes, updateBytes, updateCharacterStream, updateCharacterStream, updateClob, updateClob, updateDate, updateDate, updateDouble, updateDouble, updateFloat, updateFloat, updateInt, updateInt, updateLong, updateLong, updateNull, updateNull, updateObject, updateObject, updateObject, updateObject, updateRef, updateRef, updateRow, updateShort, updateShort, updateString, updateString, updateTime, updateTime, updateTimestamp, updateTimestamp, wasNull |
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 occured 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 pertitent to the conflict resolution in this row.
- See Also:
- Constant Field Values
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, or
SyncResolver.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 - an int designating the column in this row of this
SyncResolver 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 - a String object designating the column in this row of this
SyncResolver 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 - an int giving the number of the column into which to
set the value to be persistedobj - an Object that is the value to be set in the
RowSet 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 - a String object giving the name of the column
into which to set the value to be persistedobj - an Object that is the value to be set in the
RowSet 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
is TYPE_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
is TYPE_FORWARD_ONLY
Copyright 2003 Sun Microsystems, Inc. All rights reserved
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