CachedRowSet must implement.
The reference implementation of the CachedRowSet interface provided
by Sun Microsystems is a standard implementation. Developers may use this implementation
just as it is, they may extend it, or they may choose to write their own implementations
of this interface.
A CachedRowSet object is a container for rows of data
that caches its rows in memory, which makes it possible to operate without always being
connected to its data source. Further, it is a
JavaBeansTM component and is scrollable,
updatable, and serializable. A CachedRowSet object typically
contains rows from a result set, but it can also contain rows from any file
with a tabular format, such as a spread sheet. The reference implementation
supports getting data only from a ResultSet object, but
developers can extend the SyncProvider implementations to provide
access to other tabular data sources.
An application can modify the data in a CachedRowSet object, and
those modifications can then be propagated back to the source of the data.
A CachedRowSet object is a disconnected rowset, which means
that it makes use of a connection to its data source only briefly. It connects to its
data source while it is reading data to populate itself with rows and again
while it is propagating changes back to its underlying data source. The rest
of the time, a CachedRowSet object is disconnected, including
while its data is being modified. Being disconnected makes a RowSet
object much leaner and therefore much easier to pass to another component. For
example, a disconnected RowSet object can be serialized and passed
over the wire to a thin client such as a personal digital assistant (PDA).
CachedRowSet ObjectCachedRowSet
supplied in the reference implementation (RI) to create a default
CachedRowSet object.
CachedRowSetImpl crs = new CachedRowSetImpl();
This new CachedRowSet object will have its properties set to the
default properties of a BaseRowSet object, and, in addition, it will
have an RIOptimisticProvider object as its synchronization provider.
RIOptimisticProvider, one of two SyncProvider
implementations included in the RI, is the default provider that the
SyncFactory singleton will supply when no synchronization
provider is specified.
A SyncProvider object provides a CachedRowSet object
with a reader (a RowSetReader object) for reading data from a
data source to populate itself with data. A reader can be implemented to read
data from a ResultSet object or from a file with a tabular format.
A SyncProvider object also provides
a writer (a RowSetWriter object) for synchronizing any
modifications to the CachedRowSet object's data made while it was
disconnected with the data in the underlying data source.
A writer can be implemented to exercise various degrees of care in checking
for conflicts and in avoiding them.
(A conflict occurs when a value in the data source has been changed after
the rowset populated itself with that value.)
The RIOptimisticProvider implementation assumes there will be
few or no conflicts and therefore sets no locks. It updates the data source
with values from the CachedRowSet object only if there are no
conflicts.
Other writers can be implemented so that they always write modified data to
the data source, which can be accomplished either by not checking for conflicts
or, on the other end of the spectrum, by setting locks sufficient to prevent data
in the data source from being changed. Still other writer implementations can be
somewhere in between.
A CachedRowSet object may use any
SyncProvider implementation that has been registered
with the SyncFactory singleton. An application
can find out which SyncProvider implementations have been
registered by calling the following line of code.
java.util.Enumeration providers = SyncFactory.getRegisteredProviders();
There are two ways for a CachedRowSet object to specify which
SyncProvider object it will use.
The following line of code creates the CachedRowSet
object crs2 that is initialized with default values except that its
SyncProvider object is the one specified.
CachedRowSetImpl crs2 = new CachedRowSetImpl(
"com.fred.providers.HighAvailabilityProvider");
SyncProvider using the CachedRowSet
method setSyncProvider
The following line of code resets the SyncProvider object
for crs, the CachedRowSet object created with the
default constructor.
crs.setSyncProvider("com.fred.providers.HighAvailabilityProvider");
SyncProvider for
more details.
CachedRowSet ObjectCachedRowSet object by using the
getter methods inherited from the ResultSet
interface. The following examples, in which crs is a
CachedRowSet
object, demonstrate how to iterate through the rows, retrieving the column
values in each row. The first example uses the version of the
getter methods that take a column number; the second example
uses the version that takes a column name. Column numbers are generally
used when the RowSet object's command
is of the form SELECT * FROM TABLENAME; column names are most
commonly used when the command specifies columns by name.
while (crs.next()) {
String name = crs.getString(1);
int id = crs.getInt(2);
Clob comment = crs.getClob(3);
short dept = crs.getShort(4);
System.out.println(name + " " + id + " " + comment + " " + dept);
}
while (crs.next()) {
String name = crs.getString("NAME");
int id = crs.getInt("ID");
Clob comment = crs.getClob("COM");
short dept = crs.getShort("DEPT");
System.out.println(name + " " + id + " " + comment + " " + dept);
}
RowSetMetaDataCachedRowSet
object by calling ResultSetMetaData and RowSetMetaData
methods on a RowSetMetaData object. The following code fragment,
in which crs is a CachedRowSet object, illustrates the process.
The first line creates a RowSetMetaData object with information
about the columns in crs. The method getMetaData,
inherited from the ResultSet interface, returns a
ResultSetMetaData object, which is cast to a
RowSetMetaData object before being assigned to the variable
rsmd. The second line finds out how many columns jrs has, and
the third line gets the JDBC type of values stored in the second column of
jrs.
RowSetMetaData rsmd = (RowSetMetaData)crs.getMetaData();
int count = rsmd.getColumnCount();
int type = rsmd.getColumnType(2);
The RowSetMetaData interface differs from the
ResultSetMetaData interface in two ways.
setter methods: A RowSet
object uses these methods internally when it is populated with data from a
different ResultSet object.
getter methods: Some
ResultSetMetaData methods to not apply to a RowSet
object. For example, methods retrieving whether a column value is writable
or read only do not apply because all of a RowSet object's
columns will be writable or read only, depending on whether the rowset is
updatable or not.
RowSetMetaData object, implementations must
override the getMetaData() method defined in
java.sql.ResultSet and return a RowSetMetaData object.
CachedRowSet ObjectCachedRowSet object is similar to updating a
ResultSet object, but because the rowset is not connected to
its data source while it is being updated, it must take an additional step
to effect changes in its underlying data source. After calling the method
updateRow or insertRow, a
CachedRowSet
object must also call the method acceptChanges to have updates
written to the data source. The following example, in which the cursor is
on a row in the CachedRowSet object crs, shows
the code required to update two column values in the current row and also
update the RowSet object's underlying data source.
crs.updateShort(3, 58);
crs.updateInt(4, 150000);
crs.updateRow();
crs.acceptChanges();
The next example demonstrates moving to the insert row, building a new
row on the insert row, inserting it into the rowset, and then calling the
method acceptChanges to add the new row to the underlying data
source. Note that as with the getter methods, the updater methods may take
either a column index or a column name to designate the column being acted upon.
crs.moveToInsertRow();
crs.updateString("Name", "Shakespeare");
crs.updateInt("ID", 10098347);
crs.updateShort("Age", 58);
crs.updateInt("Sal", 150000);
crs.insertRow();
crs.moveToCurrentRow();
crs.acceptChanges();
NOTE: Where the insertRow() method inserts the contents of a
CachedRowSet object's insert row is implementation-defined.
The reference implementation for the CachedRowSet interface
inserts a new row immediately following the current row, but it could be
implemented to insert new rows in any number of other places.
Another thing to note about these examples is how they use the method
acceptChanges. It is this method that propagates changes in
a CachedRowSet object back to the underlying data source,
calling on the RowSet object's writer internally to write
changes to the data source. To do this, the writer has to incur the expense
of establishing a connection with that data source. The
preceding two code fragments call the method acceptChanges
immediately after calling updateRow or insertRow.
However, when there are multiple rows being changed, it is more efficient to call
acceptChanges after all calls to updateRow
and insertRow have been made. If acceptChanges
is called only once, only one connection needs to be established.
acceptChanges is executed, the
CachedRowSet object's writer, a RowSetWriterImpl
object, is called behind the scenes to write the changes made to the
rowset to the underlying data source. The writer is implemented to make a
connection to the data source and write updates to it.
A writer is made available through an implementation of the
SyncProvider interface, as discussed in section 1,
"Creating a CachedRowSet Object."
The default reference implementation provider, RIOptimisticProvider,
has its writer implemented to use an optimistic concurrency control
mechanism. That is, it maintains no locks in the underlying database while
the rowset is disconnected from the database and simply checks to see if there
are any conflicts before writing data to the data source. If there are any
conflicts, it does not write anything to the data source.
The reader/writer facility
provided by the SyncProvider class is pluggable, allowing for the
customization of data retrieval and updating. If a different concurrency
control mechanism is desired, a different implementation of
SyncProvider can be plugged in using the method
setSyncProvider.
In order to use the optimistic concurrency control routine, the
RIOptismisticProvider maintains both its current
value and its original value (the value it had immediately preceding the
current value). Note that if no changes have been made to the data in a
RowSet object, its current values and its original values are the same,
both being the values with which the RowSet object was initially
populated. However, once any values in the RowSet object have been
changed, the current values and the original values will be different, though at
this stage, the original values are still the initial values. With any subsequent
changes to data in a RowSet object, its original values and current
values will still differ, but its original values will be the values that
were previously the current values.
Keeping track of original values allows the writer to compare the RowSet
object's original value with the value in the database. If the values in
the database differ from the RowSet object's original values, which means that
the values in the database have been changed, there is a conflict.
Whether a writer checks for conflicts, what degree of checking it does, and how
it handles conflicts all depend on how it is implemented.
BaseRowSet class. A listener for a
CachedRowSet object is a component that wants to be notified
whenever there is a change in the rowset. For example, if a
CachedRowSet object contains the results of a query and
those
results are being displayed in, say, a table and a bar graph, the table and
bar graph could be registered as listeners with the rowset so that they can
update themselves to reflect changes. To become listeners, the table and
bar graph classes must implement the RowSetListener interface.
Then they can be added to the CachedRowSet object's list of
listeners, as is illustrated in the following lines of code.
crs.addRowSetListener(table);
crs.addRowSetListener(barGraph);
Each CachedRowSet method that moves the cursor or changes
data also notifies registered listeners of the changes, so
table and barGraph will be notified when there is
a change in crs.
CachedRowSet object is to
pass data between different components of an application. Because it is
serializable, a CachedRowSet object can be used, for example,
to send the result of a query executed by an enterprise JavaBeans component
running in a server environment over a network to a client running in a
web browser.
While a CachedRowSet object is disconnected, it can be much
leaner than a ResultSet object with the same data.
As a result, it can be especially suitable for sending data to a thin client
such as a PDA, where it would be inappropriate to use a JDBC driver
due to resource limitations or security considerations.
Thus, a CachedRowSet object provides a means to "get rows in"
without the need to implement the full JDBC API.
CachedRowSet objects is to provide
scrolling and updating for ResultSet objects that
do not provide these capabilities themselves. In other words, a
CachedRowSet object can be used to augment the
capabilities of a JDBC technology-enabled driver (hereafter called a
"JDBC driver") when the DBMS does not provide full support for scrolling and
updating. To achieve the effect of making a non-scrollble and read-only
ResultSet object scrollable and updatable, a programmer
simply needs to create a CachedRowSet object populated
with that ResultSet object's data. This is demonstrated
in the following code fragment, where stmt is a
Statement object.
ResultSet rs = stmt.executeQuery("SELECT * FROM EMPLOYEES");
CachedRowSetImpl crs = new CachedRowSetImpl();
crs.populate(rs);
The object crs now contains the data from the table
EMPLOYEES, just as the object rs does.
The difference is that the cursor for crs can be moved
forward, backward, or to a particular row even if the cursor for
rs can move only forward. In addition, crs is
updatable even if rs is not because by default, a
CachedRowSet object is both scrollable and updatable.
In summary, a CachedRowSet object can be thought of as simply
a disconnected set of rows that are being cached outside of a data source.
Being thin and serializable, it can easily be sent across a wire,
and it is well suited to sending data to a thin client. However, a
CachedRowSet object does have a limitation: It is limited in
size by the amount of data it can store in memory at one time.
CachedRowSet class is that it makes it
possible to retrieve and store data from sources other than a relational
database. The reader for a rowset can be implemented to read and populate
its rowset with data from any tabular data source, including a spreadsheet
or flat file.
Because both a CachedRowSet object and its metadata can be
created from scratch, a component that acts as a factory for rowsets
can use this capability to create a rowset containing data from
non-SQL data sources. Nevertheless, it is expected that most of the time,
CachedRowSet objects will contain data that was fetched
from an SQL database using the JDBC API.
ResultSet object need to
set the properties that are required for making a database connection.
If a rowset uses the DriverManager facility to make a
connection, it needs to set a property for the JDBC URL that identifies
the appropriate driver, and it needs to set the properties that give the
user name and password.
If, on the other hand, the rowset uses a DataSource object
to make the connection, which is the preferred method, it does not need to
set the property for the JDBC URL. Instead, it needs to set
properties for the logical name of the data source, for the user name,
and for the password.
NOTE: In order to use a DataSource object for making a
connection, the DataSource object must have been registered
with a naming service that uses the Java Naming and Directory
InterfaceTM (JNDI) API. This registration
is usually done by a person acting in the capacity of a system
administrator.
In order to be able to populate itself with data from a database, a rowset
needs to set a command property. This property is a query that is a
PreparedStatement object, which allows the query to have
parameter placeholders that are set at run time, as opposed to design time.
To set these placeholder parameters with values, a rowset provides
setter methods for setting values of each data type,
similar to the setter methods provided by the PreparedStatement
interface.
The following code fragment illustrates how the CachedRowSet
object crs might have its command property set. Note that if a
tool is used to set properties, this is the code that the tool would use.
crs.setCommand("SELECT FIRST_NAME, LAST_NAME, ADDRESS FROM CUSTOMERS " +
"WHERE CREDIT_LIMIT > ? AND REGION = ?");
The values that will be used to set the command's placeholder parameters are
contained in the RowSet object's params field, which is a
Vector object.
The CachedRowSet class provides a set of setter
methods for setting the elements in its params field. The
following code fragment demonstrates setting the two parameters in the
query from the previous example.
crs.setInt(1, 5000);
crs.setString(2, "West");
The params field now contains two elements, each of which is
an array two elements long. The first element is the parameter number;
the second is the value to be set.
In this case, the first element of params is
1, 5000, and the second element is 2,
"West". When an application calls the method
execute, it will in turn call on this RowSet object's reader,
which will in turn invoke its readData method. As part of
its implementation, readData will get the values in
params and use them to set the command's placeholder
parameters.
The following code fragment gives an idea of how the reader
does this, after obtaining the Connection object
con.
PreparedStatement pstmt = con.prepareStatement(crs.getCommand());
reader.decodeParams();
// decodeParams figures out which setter methods to use and does something
// like the following:
// for (i = 0; i < params.length; i++) {
// pstmt.setObject(i + 1, params[i]);
// }
At this point, the command for crs is the query "SELECT
FIRST_NAME, LAST_NAME, ADDRESS FROM CUSTOMERS WHERE CREDIT_LIMIT > 5000
AND REGION = "West". After the readData method executes
this command with the following line of code, it will have the data from
rs with which to populate crs.
ResultSet rs = pstmt.executeQuery();
The preceding code fragments give an idea of what goes on behind the
scenes; they would not appear in an application, which would not invoke
methods like readData and decodeParams.
In contrast, the following code fragment shows what an application might do.
It sets the rowset's command, sets the command's parameters, and executes
the command. Simply by calling the execute method,
crs populates itself with the requested data from the
table CUSTOMERS.
crs.setCommand("SELECT FIRST_NAME, LAST_NAME, ADDRESS FROM CUSTOMERS" +
"WHERE CREDIT_LIMIT > ? AND REGION = ?");
crs.setInt(1, 5000);
crs.setString(2, "West");
crs.execute();
CachedRowSet object stores data in memory,
the amount of data that it can contain at any one
time is determined by the amount of memory available. To get around this limitation,
a CachedRowSet object can retrieve data from a ResultSet
object in chunks of data, called pages. To take advantage of this mechanism,
an application sets the number of rows to be included in a page using the method
setPageSize. In other words, if the page size is set to five, a chunk
of five rows of
data will be fetched from the data source at one time. An application can also
optionally set the maximum number of rows that may be fetched at one time. If the
maximum number of rows is set to zero, or no maximum number of rows is set, there is
no limit to the number of rows that may be fetched at a time.
After properties have been set,
the CachedRowSet object must be populated with data
using either the method populate or the method execute.
The following lines of code demonstrate using the method populate.
Note that this version of the method takes two parameters, a ResultSet
handle and the row in the ResultSet object from which to start
retrieving rows.
CachedRowSet crs = new CachedRowSetImpl();
crs.setMaxRows(20);
crs.setPageSize(4);
crs.populate(rsHandle, 10);
When this code runs, crs will be populated with four rows from
rsHandle starting with the tenth row.
The next code fragment shows populating a CachedRowSet object using the
method execute, which may or may not take a Connection
object as a parameter. This code passes execute the Connection
object conHandle.
Note that there are two differences between the following code
fragment and the previous one. First, the method setMaxRows is not
called, so there is no limit set for the number of rows that crs may contain.
(Remember that crs always has the overriding limit of how much data it can
store in memory.) The second difference is that the you cannot pass the method
execute the number of the row in the ResultSet object
from which to start retrieving rows. This method always starts with the first row.
CachedRowSet crs = new CachedRowSetImpl();
crs.setPageSize(5);
crs.execute(conHandle);
After this code has run, crs will contain five rows of data from the
ResultSet object produced by the command for crs. The writer
for crs will use conHandle to connect to the data source and
execute the command for crs. An application is then able to operate on the
data in crs in the same way that it would operate on data in any other
CachedRowSet object.
To access the next page (chunk of data), an application calls the method
nextPage. This method creates a new CachedRowSet object
and fills it with the next page of data. For example, assume that the
CachedRowSet object's command returns a ResultSet object
rs with 1000 rows of data. If the page size has been set to 100, the first
call to the method nextPage will create a CachedRowSet object
containing the first 100 rows of rs. After doing what it needs to do with the
data in these first 100 rows, the application can again call the method
nextPage to create another CachedRowSet object
with the second 100 rows from rs. The data from the first CachedRowSet
object will no longer be in memory because it is replaced with the data from the
second CachedRowSet object. After the tenth call to the method nextPage,
the tenth CachedRowSet object will contain the last 100 rows of data from
rs, which are stored in memory. At any given time, the data from only one
CachedRowSet object is stored in memory.
The method nextPage returns true as long as the current
page is not the last page of rows and false when there are no more pages.
It can therefore be used in a while loop to retrieve all of the pages,
as is demonstrated in the following lines of code.
CachedRowSet crs = CachedRowSetImpl();
crs.setPageSize(100);
crs.execute(conHandle);
while(crs.next() {
. . . // operate on first chunk of 100 rows in crs, row by row
}
while(crs.nextPage()) {
while(crs.next()) {
. . . // operate on the subsequent chunks (of 100 rows each) in crs,
// row by row
}
}
After this code fragment has been run, the application will have traversed all
1000 rows, but it will have had no more than 100 rows in memory at a time.
The CachedRowSet interface also defines the method previousPage.
Just as the method nextPage is analogous to the ResultSet
method next, the method previousPage is analogous to
the ResultSet method previous. Similar to the method
nextPage, previousPage creates a CachedRowSet
object containing the number of rows set as the page size. So, for instance, the
method previousPage could be used in a while loop at
the end of the preceding code fragment to navigate back through the pages from the last
page to the first page.
The method previousPage is also similar to nextPage
in that it can be used in a while
loop, except that it returns true as long as there is another page
preceding it and false when there are no more pages ahead of it.
By positioning the cursor after the last row for each page,
as is done in the following code fragment, the method previous
navigates from the last row to the first row in each page.
The code could also have left the cursor before the first row on each page and then
used the method next in a while loop to navigate each page
from the first row to the last row.
The following code fragment assumes a continuation from the previous code fragment,
meaning that the cursor for the tenth CachedRowSet object is on the
last row. The code moves the cursor to after the last row so that the first
call to the method previous will put the cursor back on the last row.
After going through all of the rows in the last page (the CachedRowSet
object crs), the code then enters
the while loop to get to the ninth page, go through the rows backwards,
go to the eighth page, go through the rows backwards, and so on to the first row
of the first page.
crs.afterLast();
while(crs.previous()) {
. . . // navigate through the rows, last to first
{
while(crs.previousPage()) {
crs.afterLast();
while(crs.previous()) {
. . . // go from the last row to the first row of each page
}
}
CachedRowSet object's SyncProvider
to commit the changes when acceptChanges() is called. If
set to false, the changes will not be committed until one of the
CachedRowSet interface transaction methods is called.CachedRowSet object to the underlying data source.
This method calls on this CachedRowSet object's writer
to do the work behind the scenes.
Standard CachedRowSet implementations should use the
SyncFactory singleton
to obtain a SyncProvider instance providing a
RowSetWriter object (writer). The writer will attempt
to propagate changes made in this CachedRowSet object
back to the data source.
When the method acceptChanges executes successfully, in
addition to writing changes to the data source, it
makes the values in the current row be the values in the original row.
Depending on the synchronization level of the SyncProvider
implementation being used, the writer will compare the original values
with those in the data source to check for conflicts. When there is a conflict,
the RIOptimisticProvider implementation, for example, throws a
SyncProviderException and does not write anything to the
data source.
An application may choose to catch the SyncProviderException
object and retrieve the SyncResolver object it contains.
The SyncResolver object lists the conflicts row by row and
sets a lock on the data source to avoid further conflicts while the
current conflicts are being resolved.
Further, for each conflict, it provides methods for examining the conflict
and setting the value that should be persisted in the data source.
After all conflicts have been resolved, an application must call the
acceptChanges method again to write resolved values to the
data source. If all of the values in the data source are already the
values to be persisted, the method acceptChanges does nothing.
Some provider implementations may use locks to ensure that there are no
conflicts. In such cases, it is guaranteed that the writer will succeed in
writing changes to the data source when the method acceptChanges
is called. This method may be called immediately after the methods
updateRow, insertRow, or deleteRow
have been called, but it is more efficient to call it only once after
all changes have been made so that only one connection needs to be
established.
Note: The acceptChanges() method will determine if the
COMMIT_ON_ACCEPT_CHANGES is set to true or not. If it is set
to true, all updates in the synchronization are committed to the data
source. Otherwise, the application must explicity call the
commit() or rollback() methods as appropriate.
CachedRowSet object
using the specified Connection object to establish a
connection to the data source.
The other version of the acceptChanges method is not passed
a connection because it uses
the Connection object already defined within the RowSet
object, which is the connection used for populating it initially.
This form of the method acceptChanges is similar to the
form that takes no arguments; however, unlike the other form, this form
can be used only when the underlying data source is a JDBC data source.
The updated Connection properties must be used by the
SyncProvider to reset the RowSetWriter
configuration to ensure that the contents of the CachedRowSet
object are synchronized correctly.
When the method acceptChanges executes successfully, in
addition to writing changes to the data source, it
makes the values in the current row be the values in the original row.
Depending on the synchronization level of the SyncProvider
implementation being used, the writer will compare the original values
with those in the data source to check for conflicts. When there is a conflict,
the RIOptimisticProvider implementation, for example, throws a
SyncProviderException and does not write anything to the
data source.
An application may choose to catch the SyncProviderException
object and retrieve the SyncResolver object it contains.
The SyncResolver object lists the conflicts row by row and
sets a lock on the data source to avoid further conflicts while the
current conflicts are being resolved.
Further, for each conflict, it provides methods for examining the conflict
and setting the value that should be persisted in the data source.
After all conflicts have been resolved, an application must call the
acceptChanges method again to write resolved values to the
data source. If all of the values in the data source are already the
values to be persisted, the method acceptChanges does nothing.
Some provider implementations may use locks to ensure that there are no
conflicts. In such cases, it is guaranteed that the writer will succeed in
writing changes to the data source when the method acceptChanges
is called. This method may be called immediately after the methods
updateRow, insertRow, or deleteRow
have been called, but it is more efficient to call it only once after
all changes have been made so that only one connection needs to be
established.
Note: The acceptChanges() method will determine if the
COMMIT_ON_ACCEPT_CHANGES is set to true or not. If it is set
to true, all updates in the synchronization are committed to the data
source. Otherwise, the application must explicity call the
commit or rollback methods as appropriate.
RowSet object.RowSet object's command.
In general, parameter values remain in force for repeated use of a
RowSet object. Setting a parameter value automatically clears its
previous value. However, in some cases it is useful to immediately
release the resources used by the current parameter values, which can
be done by calling the method clearParameters.
CachedRowSet object has been updated.CachedRowSet object has been updated.CachedRowSet object's SyncProvider contains
a Connection object from the ResultSet or JDBC
properties passed to it's constructors. This method wraps the
Connection commit method to allow flexible
auto commit or non auto commit transactional control support.
Makes all changes that are performed by the acceptChanges()
method since the previous commit/rollback permanent. This method should
be used only when auto-commit mode has been disabled.
RowSet object that is a deep copy of the data in
this CachedRowSet object. In contrast to
the RowSet object generated from a createShared
call, updates made to the copy of the original RowSet object
must not be visible to the original RowSet object. Also, any
event listeners that are registered with the original
RowSet must not have scope over the new
RowSet copies. In addition, any constraint restrictions
established must be maintained.CachedRowSet object that is a deep copy of
this CachedRowSet object's data but is independent of it.
In contrast to
the RowSet object generated from a createShared
method call, updates made to a copy of this CachedRowSet object
must not be visible to it. Also, any
event listeners that are registered with this
CachedRowSet object must not have scope over the new
RowSet object. In addition, any constraint restrictions
established for this CachedRowSet object must not be maintained
in the copy.CachedRowSet object that is an empty copy of this
CachedRowSet object. The copy
must not contain any contents but only represent the table
structure of the original CachedRowSet object. In addition, primary
or foreign key constraints set in the originating CachedRowSet object must
be equally enforced in the new empty CachedRowSet object.
In contrast to
the RowSet object generated from a createShared method
call, updates made to a copy of this CachedRowSet object with the
createCopySchema method must not be visible to it.
Applications can form a WebRowSet object from the CachedRowSet
object returned by this method in order
to export the RowSet schema definition to XML for future use.
RowSet object backed by the same data as
that of this CachedRowSet object. In effect, both
CachedRowSet objects have a cursor over the same data.
As a result, any changes made by a duplicate are visible to the original
and to any other duplicates, just as a change made by the original is visible
to all of its duplicates. If a duplicate calls a method that changes the
underlying data, the method it calls notifies all registered listeners
just as it would when it is called by the original CachedRowSet
object.
In addition, any RowSet object
created by this method will have the same properties as this
CachedRowSet object. For example, if this CachedRowSet
object is read-only, all of its duplicates will also be read-only. If it is
changed to be updatable, the duplicates also become updatable.
NOTE: If multiple threads access RowSet objects created from
the createShared() method, the following behavior is specified
to preserve shared data integrity: reads and writes of all
shared RowSet objects should be made serially between each
object and the single underlying tabular structure.
RowSet object with data.
The execute method may use the following properties
to create a connection for reading data: url, data source name,
user name, password, transaction isolation, and type map.
The execute method may use the following properties
to create a statement to execute a command:
command, read only, maximum field size,
maximum rows, escape processing, and query timeout.
If the required properties have not been set, an exception is thrown. If this method is successful, the current contents of the rowset are discarded and the rowset's metadata is also (re)set. If there are outstanding updates, they are ignored.
If this RowSet object does not maintain a continuous connection
with its source of data, it may use a reader (a RowSetReader
object) to fill itself with data. In this case, a reader will have been
registered with this RowSet object, and the method
execute will call on the reader's readData
method as part of its implementation.
CachedRowSet object with data, using the
given connection to produce the result set from which the data will be read.
This method should close any database connections that it creates to
ensure that this CachedRowSet object is disconnected except when
it is reading data from its data source or writing data to its data source.
The reader for this CachedRowSet object
will use conn to establish a connection to the data source
so that it can execute the rowset's command and read data from the
the resulting ResultSet object into this
CachedRowSet object. This method also closes conn
after it has populated this CachedRowSet object.
If this method is called when an implementation has already been
populated, the contents and the metadata are (re)set. Also, if this method is
called before the method acceptChanges has been called
to commit outstanding updates, those updates are lost.
RowSet object's command property.
The command property contains a command string, which must be an SQL
query, that can be executed to fill the rowset with data.
The default value is null.RowSet object. Users should set
either the url property or the data source name property. The rowset will use
the property that was set more recently to get a connection.RowSet object.
If escape scanning is enabled, which is the default, the driver will do
escape substitution before sending an SQL statement to the database.CachedRowSet object.RowSet object with the method
setMatchColumn(int[] columnIdxes).RowSet object with the method
setMatchColumn(String [] columnNames).BINARY,
VARBINARY, LONGVARBINARYBINARY, CHAR,
VARCHAR, and LONGVARCHAR columns.
If the limit is exceeded, the excess data is silently discarded.RowSet
object can contain.
If the limit is exceeded, the excess rows are silently dropped.ResultSet object containing the original value of this
CachedRowSet object.
The cursor for the ResultSet
object should be positioned before the first row.
In addition, the returned ResultSet object should have the following
properties:
The original value for a RowSet object is the value it had before
the last synchronization with the underlying data source. If there have been
no synchronizations, the original value will be the value with which the
RowSet object was populated. This method is called internally
when an aplication calls the method acceptChanges and the
SyncProvider object has been implemented to check for conflicts.
If this is the case, the writer compares the original value with the value
currently in the data source to check for conflicts.
ResultSet object containing the original value for the
current row only of this CachedRowSet object.
The cursor for the ResultSet
object should be positioned before the first row.
In addition, the returned ResultSet object should have the following
properties:
CachedRowSet objectexecute. It is not usually part of the serialized state
of a RowSet object.SQLException is thrown.RowSet object.
Subsequent warnings on this RowSet object will be chained to the
RowSetWarning object that this method returns.
The warning chain is automatically cleared each time a new row is read.
This method may not be called on a RowSet object that has been closed;
doing so will cause a SQLException to be thrown.boolean indicating whether rows marked
for deletion appear in the set of current rows. If true is
returned, deleted rows are visible with the current rows. If
false is returned, rows are not visible with the set of
current rows. The default value is false.
Standard rowset implementations may choose to restrict this behavior due to security considerations or to better fit certain deployment scenarios. This is left as implementation defined and does not represent standard behavior.
Note: Allowing deleted rows to remain visible complicates the behavior
of some standard JDBC RowSet Implementations methods.
However, most rowset users can simply ignore this extra detail because
only very specialized applications will likely want to take advantage of
this feature.
SyncProvider implementation for this
CachedRowSet object. Internally, this method is used by a rowset
to trigger read or write actions between the rowset
and the data source. For example, a rowset may need to get a handle
on the the rowset reader (RowSetReader object) from the
SyncProvider to allow the rowset to be populated.
RowSetReader rowsetReader = null;
SyncProvider provider =
SyncFactory.getInstance("javax.sql.rowset.provider.RIOptimisticProvider");
if (provider instanceof RIOptimisticProvider) {
rowsetReader = provider.getRowSetReader();
}
Assuming rowsetReader is a private, accessible field within
the rowset implementation, when an application calls the execute
method, it in turn calls on the reader's readData method
to populate the RowSet object.
rowsetReader.readData((RowSetInternal)this);
In addition, an application can use the SyncProvider object
returned by this method to call methods that return information about the
SyncProvider object, including information about the
vendor, version, provider identification, synchronization grade, and locks
it currently has set.
CachedRowSet object. This name may be set on multiple occasions,
and the specification imposes no limits on how many times this
may occur or whether standard implementations should keep track
of previous table names.RowSet object.Map object associated with this
RowSet object, which specifies the custom mapping
of SQL user-defined types, if any. The default is for the
type map to be empty.RowSet object will use to
create a connection if it uses the DriverManager
instead of a DataSource object to establish the connection.
The default value is null.RowSet object.
The username property is set at run time before calling the method
execute. It is
not usually part of the serialized state of a RowSet object.RowSet object is read-only.
If updates are possible, the default is for a rowset to be
updatable.
Attempts to update a read-only rowset will result in an
SQLException being thrown.
CachedRowSet. This causes
the CachedRowSet implementation to fetch the next page-size
rows and populate the RowSet, if remaining rows remain within scope of the
original SQL query used to populated the RowSet.CachedRowSet object with data from
the given ResultSet object.
This method can be used as an alternative to the execute method when an
application has a connection to an open ResultSet object.
Using the method populate can be more efficient than using
the version of the execute method that takes no parameters
because it does not open a new connection and re-execute this
CachedRowSet object's command. Using the populate
method is more a matter of convenience when compared to using the version
of execute that takes a ResultSet object.
CachedRowSet object with data from
the given ResultSet object. While related to the populate(ResultSet)
method, an additional parameter is provided to allow starting position within
the ResultSet from where to populate the CachedRowSet
instance.
This method can be used as an alternative to the execute method when an
application has a connection to an open ResultSet object.
Using the method populate can be more efficient than using
the version of the execute method that takes no parameters
because it does not open a new connection and re-execute this
CachedRowSet object's command. Using the populate
method is more a matter of convenience when compared to using the version
of execute that takes a ResultSet object.
CachedRowSet. This causes
the CachedRowSet implementation to fetch the previous page-size
rows and populate the RowSet. The amount of rows returned in the previous
page must always remain within scope of the original SQL query used to
populate the RowSet.CachedRowSet
object and sends a rowSetChanged event to all
registered listeners. Any outstanding updates are discarded and
the rowset contains no rows after this method is called. There
are no interactions with the underlying data source, and any rowset
content, metadata, and content updates should be non-recoverable.
This CachedRowSet object should lock until its contents and
associated updates are fully cleared, thus preventing 'dirty' reads by
other components that hold a reference to this RowSet object.
In addition, the contents cannot be released
until all all components reading this CachedRowSet object
have completed their reads. This CachedRowSet object
should be returned to normal behavior after firing the
rowSetChanged event.
The metadata, including JDBC properties and Synchronization SPI
properties, are maintained for future use. It is important that
properties such as the command property be
relevant to the originating data source from which this CachedRowSet
object was originally established.
This method empties a rowset, as opposed to the close method,
which marks the entire rowset as recoverable to allow the garbage collector
the rowset's Java VM resources.
RowSet object.CachedRowSet object to its original
value, that is, its value before the last set of changes. If there
have been no changes to the rowset or only one set of changes,
the original value is the value with which this CachedRowSet object
was populated; otherwise, the original value is
the value it had immediately before its current value.
When this method is called, a CachedRowSet implementation
must ensure that all updates, inserts, and deletes to the current
rowset instance are replaced by the previous values. In addition,
the cursor should be
reset to the first row and a rowSetChanged event
should be fired to notify all registered listeners.
CachedRowSet object's SyncProvider contains
a Connection object from the original ResultSet
or JDBC properties passed to it.
Undoes all changes made in the current transaction. This method should be used only when auto-commit mode has been disabled.
CachedRowSet object's SyncProvider contains
a Connection object from the original ResultSet
or JDBC properties passed to it.
Undoes all changes made in the current transaction back to the last
Savepoint transaction marker. This method should be used only
when auto-commit mode has been disabled.
numRows parameter
ensures that this event will only be fired every numRow.
The source of the event can be retrieved with the method event.getSource.
RowSet object's command
with the given Array value. The driver will convert this
to the ARRAY value that the Array object
represents before sending it to the database.RowSet object's command
to the given java.io.InputStream value.
It may be more practical to send a very large ASCII value via a
java.io.InputStream rather than as a LONGVARCHAR
parameter. The driver will read the data from the stream
as needed until it reaches end-of-file.
Note: This stream object can either be a standard Java stream object or your own subclass that implements the standard interface.
RowSet object's command
to the given java.math.BigDeciaml value.
The driver converts this to
an SQL NUMERIC value before sending it to the database.RowSet object's command
to the given java.io.InputStream value.
It may be more practical to send a very large binary value via a
java.io.InputStream rather than as a LONGVARBINARY
parameter. The driver will read the data from the stream
as needed until it reaches end-of-file.
Note: This stream object can either be a standard Java stream object or your own subclass that implements the standard interface.
RowSet object's command
with the given Blob value. The driver will convert this
to the BLOB value that the Blob object
represents before sending it to the database.RowSet object's command
to the given Java boolean value. The driver converts this to
an SQL BIT value before sending it to the database.RowSet object's command
to the given Java byte value. The driver converts this to
an SQL TINYINT value before sending it to the database.RowSet object's command
to the given Java array of byte values. Before sending it to the
database, the driver converts this to an SQL VARBINARY or
LONGVARBINARY value, depending on the argument's size relative
to the driver's limits on VARBINARY values.RowSet object's command
to the given java.io.Reader value.
It may be more practical to send a very large UNICODE value via a
java.io.Reader rather than as a LONGVARCHAR
parameter. The driver will read the data from the stream
as needed until it reaches end-of-file.
Note: This stream object can either be a standard Java stream object or your own subclass that implements the standard interface.
RowSet object's command
with the given Clob value. The driver will convert this
to the CLOB value that the Clob object
represents before sending it to the database.RowSet object's command property to the given
SQL query.
This property is optional
when a rowset gets its data from a data source that does not support
commands, such as a spreadsheet.RowSet object to the given
concurrency level. This method is used to change the concurrency level
of a rowset, which is by default ResultSet.CONCUR_READ_ONLYRowSet object to the
given String.
The value of the data source name property can be used to do a lookup of
a DataSource object that has been registered with a naming
service. After being retrieved, the DataSource object can be
used to create a connection to the data source that it represents.
RowSet object's command
to the given java.sql.Date value. The driver converts this to
an SQL DATE value before sending it to the database, using the
default java.util.Calendar to calculate the date.RowSet object's command
with the given java.sql.Date value. The driver will convert this
to an SQL DATE value, using the given java.util.Calendar
object to calculate the date.RowSet object's command
to the given Java double value. The driver converts this to
an SQL DOUBLE value before sending it to the database.RowSet object on or
off. If escape scanning is on (the default), the driver will do
escape substitution before sending an SQL statement to the database.RowSet object's command
to the given Java float value. The driver converts this to
an SQL REAL value before sending it to the database.RowSet object's command
to the given Java int value. The driver converts this to
an SQL INTEGER value before sending it to the database.CachedRowSet object's keyCols
field with the given array of column numbers, which forms a key
for uniquely identifying a row in this CachedRowSet object.
If a CachedRowSet object becomes part of a JoinRowSet
object, the keys defined by this method and the resulting constraints are
maintained if the columns designated as key columns also become match
columns.
RowSet object's command
to the given Java long value. The driver converts this to
an SQL BIGINT value before sending it to the database.RowSet
object. A JoinRowSet object can now add this RowSet
object based on the match column.
Sub-interfaces such as the CachedRowSetTM
interface define the method CachedRowSet.setKeyColumns, which allows
primary key semantics to be enforced on specific columns.
Implementations of the setMatchColumn(int columnIdx) method
should ensure that the constraints on the key columns are maintained when
a CachedRowSet object sets a primary key column as a match column.
RowSet
object. A JoinRowSet object can now add this RowSet
object based on the match column.RowSet
object. A JoinRowSet object can now add this RowSet
object based on the match column.
Subinterfaces such as the CachedRowSet interface define
the method CachedRowSet.setKeyColumns, which allows
primary key semantics to be enforced on specific columns.
Implementations of the setMatchColumn(String columnIdx) method
should ensure that the constraints on the key columns are maintained when
a CachedRowSet object sets a primary key column as a match column.
RowSet
object. A JoinRowSet object can now add this RowSet
object based on the match column.BINARY,
VARBINARY, LONGVARBINARYBINARY, CHAR,
VARCHAR, and LONGVARCHAR columns.
If the limit is exceeded, the excess data is silently discarded.
For maximum portability, use values greater than 256.RowSet
object can contain to the specified number.
If the limit is exceeded, the excess rows are silently dropped.CachedRowSet object with
the given RowSetMetaData object. When a
RowSetReader object is reading the contents of a rowset,
it creates a RowSetMetaData object and initializes
it using the methods in the RowSetMetaData implementation.
The reference implementation uses the RowSetMetaDataImpl
class. When the reader has completed reading the rowset contents,
this method is called internally to pass the RowSetMetaData
object to the rowset.RowSet object's SQL
command to SQL NULL.
Note: You must specify the parameter's SQL type.
RowSet object's SQL
command to SQL NULL. This version of the method setNull
should be used for SQL user-defined types (UDTs) and REF type
parameters. Examples of UDTs include: STRUCT, DISTINCT,
JAVA_OBJECT, and named array types.
Note: To be portable, applications must give the
SQL type code and the fully qualified SQL type name when specifying
a NULL UDT or REF parameter. In the case of a UDT,
the name is the type name of the parameter itself. For a REF
parameter, the name is the type name of the referenced type. If
a JDBC driver does not need the type code or type name information,
it may ignore it.
Although it is intended for UDT and REF parameters,
this method may be used to set a null parameter of any JDBC type.
If the parameter does not have a user-defined or REF type,
the typeName parameter is ignored.
RowSet object's command
with a Java Object. For integral values, the
java.lang equivalent objects should be used.
The JDBC specification provides a standard mapping from Java Object types to SQL types. The driver will convert the given Java object to its standard SQL mapping before sending it to the database.
Note that this method may be used to pass datatabase-specific
abstract data types by using a driver-specific Java type.
If the object is of a class implementing SQLData,
the rowset should call the method SQLData.writeSQL
to write the object to an SQLOutput data stream.
If the object is an instance of a class implementing the Ref,
Struct, Array, Blob,
or Clob interfaces,
the driver uses the default mapping to the corresponding SQL type.
An exception is thrown if there is an ambiguity, for example, if the object is of a class implementing more than one of these interfaces.
RowSet object's command
with a Java Object. For integral values, the
java.lang equivalent objects should be used.
This method is like setObject above, but the scale used is the scale
of the second parameter. Scalar values have a scale of zero. Literal
values have the scale present in the literal.
Even though it is supported, it is not recommended that this method be called with floating point input values.
RowSet object's command
with the given Java Object. For integral values, the
java.lang equivalent objects should be used (for example,
an instance of the class Integer for an int).
The given Java object will be converted to the targetSqlType before being sent to the database.
If the object is of a class implementing SQLData,
the rowset should call the method SQLData.writeSQL
to write the object to an SQLOutput data stream.
If the object is an instance of a class implementing the Ref,
Struct, Array, Blob,
or Clob interfaces,
the driver uses the default mapping to the corresponding SQL type.
Note that this method may be used to pass datatabase-specific abstract data types.
CachedRowSet object as the original
row.
This method is called internally after the any modified values in the current row have been synchronized with the data source. The current row must be tagged as no longer inserted, deleted or updated.
A call to setOriginalRow is irreversible.
CachedRowSet object's page-size. A CachedRowSet
may be configured to populate itself in page-size sized batches of rows. When
either populate() or execute() are called, the
CachedRowSet fetches an additional page according to the
original SQL query used to populate the RowSet.RowSet object to
the given String.SQLException is thrown.RowSet object is read-only to the
given boolean.RowSet object's command
with the given Ref value. The driver will convert this
to the appropriate REF(<structured-type>) value.RowSet object's command
to the given Java short value. The driver converts this to
an SQL SMALLINT value before sending it to the database.showDeleted to the given
boolean value, which determines whether
rows marked for deletion appear in the set of current rows.
If the value is set to true, deleted rows are immediately
visible with the set of current rows. If the value is set to
false, the deleted rows are set as invisible with the
current set of rows.
Standard rowset implementations may choose to restrict this behavior due to security considerations or to better fit certain deployment scenarios. This is left as implementations defined and does not represent standard behavior.
RowSet object's command
to the given Java String value. Before sending it to the
database, the driver converts this to an SQL VARCHAR or
LONGVARCHAR value, depending on the argument's size relative
to the driver's limits on VARCHAR values.SyncProvider objec for this CachedRowSet
object to the one specified. This method
allows the SyncProvider object to be reset.
A CachedRowSet implementation should always be instantiated
with an available SyncProvider mechanism, but there are
cases where resetting the SyncProvider object is desirable
or necessary. For example, an application might want to use the default
SyncProvider object for a time and then choose to use a provider
that has more recently become available and better fits its needs.
Resetting the SyncProvider object causes the
RowSet object to request a new SyncProvider implementation
from the SyncFactory. This has the effect of resetting
all previous connections and relationships with the originating
data source and can potentially drastically change the synchronization
behavior of a disconnected rowset.
CachedRowSet
object was derived to the given table name. The writer uses this name to
determine which table to use when comparing the values in the data source with the
CachedRowSet object's values during a synchronization attempt.
The table identifier also indicates where modified values from this
CachedRowSet object should be written.
The implementation of this CachedRowSet object may obtain the
the name internally from the RowSetMetaDataImpl object.
RowSet object's command
to the given java.sql.Time value. The driver converts this to
an SQL TIME value before sending it to the database, using the
default java.util.Calendar to calculate it.RowSet object's command
with the given java.sql.Time value. The driver will convert this
to an SQL TIME value, using the given java.util.Calendar
object to calculate it, before sending it to the database.RowSet object's command
to the given java.sql.Timestamp value. The driver converts this to
an SQL TIMESTAMP value before sending it to the database, using the
default java.util.Calendar to calculate it.RowSet object's command
with the given java.sql.Timestamp value. The driver will
convert this to an SQL TIMESTAMP value, using the given
java.util.Calendar object to calculate it, before sending it to the
database.RowSet obejct.RowSet object to the given type.
This method is used to change the type of a rowset, which is by
default read-only and non-scrollable.java.util.Map object as the default
type map for this RowSet object. This type map will be
used unless another type map is supplied as a method parameter.RowSet object will use when it uses the
DriverManager to create a connection.
Setting this property is optional. If a URL is used, a JDBC driver
that accepts the URL must be loaded by the application before the
rowset is used to connect to a database. The rowset will use the URL
internally to create a database connection when reading or writing
data. Either a URL or a data source name is used to create a
connection, whichever was specified most recently.RowSet object to the
given String.CachedRowSet
object.CachedRowSet object to a Collection
object that contains all of this CachedRowSet object's data.
Implementations have some latitude in
how they can represent this Collection object because of the
abstract nature of the Collection framework.
Each row must be fully represented in either a
general purpose Collection implementation or a specialized
Collection implementation, such as a TreeMap
object or a Vector object.
An SQL NULL column value must be represented as a null
in the Java programming language.
The standard reference implementation for the CachedRowSet
interface uses a TreeMap object for the rowset, with the
values in each row being contained in Vector objects. It is
expected that most implementations will do the same.
The TreeMap type of collection guarantees that the map will be in
ascending key order, sorted according to the natural order for the
key's class.
Each key references a Vector object that corresponds to one
row of a RowSet object. Therefore, the size of each
Vector object must be exactly equal to the number of
columns in the RowSet object.
The key used by the TreeMap collection is determined by the
implementation, which may choose to leverage a set key that is
available within the internal RowSet tabular structure by
virtue of a key already set either on the RowSet object
itself or on the underlying SQL data.
CachedRowSet object
to a Collection object. Implementations have some latitude in
how they can represent this Collection object because of the
abstract nature of the Collection framework.
Each column value should be fully represented in either a
general purpose Collection implementation or a specialized
Collection implementation, such as a Vector object.
An SQL NULL column value must be represented as a null
in the Java programming language.
The standard reference implementation uses a Vector object
to contain the column values, and it is expected
that most implementations will do the same. If a Vector object
is used, it size must be exactly equal to the number of rows
in this CachedRowSet object.
CachedRowSet object
to a Collection object. Implementations have some latitude in
how they can represent this Collection object because of the
abstract nature of the Collection framework.
Each column value should be fully represented in either a
general purpose Collection implementation or a specialized
Collection implementation, such as a Vector object.
An SQL NULL column value must be represented as a null
in the Java programming language.
The standard reference implementation uses a Vector object
to contain the column values, and it is expected
that most implementations will do the same. If a Vector object
is used, it size must be exactly equal to the number of rows
in this CachedRowSet object.
In addition, multiple cancellations of row deletions can be made by adjusting the position of the cursor using any of the cursor position control methods such as:
CachedRowSet.absolute
CachedRowSet.first
CachedRowSet.last
CachedRowSet
object if the row has been inserted, and also notifies listeners that a
row has changed. This method can be called at any time during the
lifetime of a rowset and assuming the current row is within
the exception limitations (see below), it cancels the row insertion
of the current row.
In addition, multiple cancellations of row insertions can be made by adjusting the position of the cursor using any of the cursor position control methods such as:
CachedRowSet.absolute
CachedRowSet.first
CachedRowSet.last
acceptChanges) or population. This method may also be called
while performing updates to the insert row.
undoUpdate
RowSet
object.
RowSet objects that implement the Joinable interface
must ensure that a key-like constraint continues to be enforced until the
method CachedRowSet.unsetKeyColumns has been called on the
designated column.
RowSet
object.RowSet
object.
RowSet objects that implement the Joinable interface
must ensure that a key-like constraint continues to be enforced until the
method CachedRowSet.unsetKeyColumns has been called on the
designated column.
RowSet
object.