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Java™ Platform Standard Ed. 6 |
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See:
Description
Interface Summary | |
---|---|
SyncResolver | Defines a framework that allows applications to use a manual decision tree to decide what should be done when a synchronization conflict occurs. |
TransactionalWriter | A specialized interface that facilitates an extension of the standard
SyncProvider abstract class so that it has finer grained
transaction control. |
XmlReader | A specialized interface that facilitates an extension of the
SyncProvider abstract class for XML orientated
synchronization providers. |
XmlWriter | A specialized interface that facilitates an extension of the
SyncProvider abstract class for XML orientated
synchronization providers. |
Class Summary | |
---|---|
SyncFactory | The Service Provider Interface (SPI) mechanism that generates SyncProvider
instances to be used by disconnected RowSet objects. |
SyncProvider | The synchronization mechanism that provides reader/writer capabilities for
disconnected RowSet objects. |
Exception Summary | |
---|---|
SyncFactoryException | Indicates an error with SyncFactory mechanism. |
SyncProviderException | Indicates an error with the SyncProvider mechanism. |
The standard classes and interfaces that a third party vendor has to
use in its implementation of a synchronization provider. These classes and
interfaces are referred to as the Service Provider Interface (SPI). A vendor may
have its implementation included on the JDBC web page that lists available
SyncProvider
implementations by sending email to jdbc@sun.com
.
Doing this helps make developers aware of the implementation. To make it possible
for a RowSet
object to use an implementation, the vendor must register
it with the SyncFactory
singleton. (See the class comment for
SyncProvider
for a full explanation of the registration process and
the naming convention to be used.)
The following classes and interfaces make up the javax.sql.rowset.spi
package:
SyncFactory
SyncProvider
SyncFactoryException
SyncProviderException
SyncResolver
XmlReader
XmlWriter
TransactionalWriter
javax.sql
package, are also part of the SPI:
RowSetReader
RowSetWriter
A SyncProvider
implementation provides a disconnected RowSet
object with the mechanisms for reading data into it and for writing data that has been
modified in it
back to the underlying data source. A reader, a RowSetReader
or
XMLReader
object, reads data into a RowSet
object when the
CachedRowSet
methods execute
or populate
are called. A writer, a RowSetWriter
or XMLWriter
object, writes changes back to the underlying data source when the
CachedRowSet
method acceptChanges
is called.
The process of writing changes in a RowSet
object to its data source
is known as synchronization. The SyncProvider
implementation that a
RowSet
object is using determines the level of synchronization that the
RowSet
object's writer uses. The various levels of synchronization are
referred to as grades.
The lower grades of synchronization are
known as optimistic concurrency levels because they optimistically
assume that there will be no conflicts or very few conflicts. A conflict exists when
the same data modified in the RowSet
object has also been modified
in the data source. Using the optimistic concurrency model means that if there
is a conflict, modifications to either the data source or the RowSet
object will be lost.
Higher grades of synchronization are called pessimistic because they assume that others will be accessing the data source and making modifications. These grades set varying levels of locks to increase the chances that no conflicts occur.
The lowest level of synchronization is simply writing any changes made to the
RowSet
object to its underlying data source. The writer does
nothing to check for conflicts.
If there is a conflict and the data
source values are overwritten, the changes other parties have made by to the data
source are lost.
The RIXMLProvider
implementation uses the lowest level
of synchronization and just writes RowSet
changes to the data source.
This is true because typically XML data sources do not enable transaction
techniques for maintaining the integrity of data. However, specific standards
groups have considered offering XML-based synchronization. For details, see
http://www.syncml.org
For the the next level up, the
writer checks to see if there are any conflicts, and if there are,
it does not write anything to the data source. The problem with this concurrency
level is that if another party has modified the corresponding data in the data source
since the RowSet
object got its data,
the changes made to the RowSet
object are lost. The
RIOptimisticProvider
implementation uses this level of synchronization.
At higher levels of synchronization, referred to as pessimistic concurrency,
the writer take steps to avoid conflicts by setting locks. Setting locks
can vary from setting a lock on a single row to setting a lock on a table
or the entire data source. The level of synchronization is therefore a tradeoff
between the ability of users to access the data source concurrently and the ability
of the writer to keep the data in the RowSet
object and its data source
synchronized.
It is a requirement that all disconnected RowSet
objects
(CachedRowSet
, FilteredRowSet
, JoinRowSet
,
and WebRowSet
objects) obtain their SyncProvider
objects
from the SyncFactory
mechanism.
The reference implementation (RI) provides two synchronization providers.
SyncFactory
instance will
supply to a disconnected RowSet
object when no provider
implementation is specified.RowSet
object and the
data source. If there is a conflict, it does nothing, meaning that
changes to the RowSet
object are not persisted to the data
source.
WebRowSet
object, which is a rowset that can be written
in XML format or read from XML format. The
RIXMLProvider
implementation does no checking at all for
conflicts and simply writes any updated data in the
WebRowSet
object to the underlying data source.
WebRowSet
objects use this provider when they are
dealing with XML data.
SyncProvider
implementations
are bundled with the reference implementation, which makes them always available to
RowSet
implementations.
SyncProvider
implementations make themselves available by being
registered with the SyncFactory
singleton. When a RowSet
object requests a provider, by specifying it in the constructor or as an argument to the
CachedRowSet
method setSyncProvider
,
the SyncFactory
singleton
checks to see if the requested provider has been registered with it.
If it has, the SyncFactory
creates an instance of it and passes it to the
requesting RowSet
object.
If the SyncProvider
implementation that is specified has not been registered,
the SyncFactory
singleton causes a SyncFactoryException
object
to be thrown. If no provider is specified,
the SyncFactory
singleton will create an instance of the default
provider implementation, RIOptimisticProvider
,
and pass it to the requesting RowSet
object.
If a WebRowSet
object does not specify a provider in its constructor, the
SyncFactory
will give it an instance of RIOptimisticProvider
.
However, the constructor for WebRowSet
is implemented to set the provider
to the RIXMLProvider
, which reads and writes a RowSet
object
in XML format.
See the SyncProvider class specification for further details.
Vendors may develop a SyncProvider implementation with any one of the possible
levels of synchronization, thus giving RowSet
objects a choice of
synchronization mechanisms. A vendor can make its implementation available by
registering the fully qualified class name with Sun Microsystems at
jdbc@sun.com
. This process is discussed in further detail below.
The Service Provider Interface provides a pluggable mechanism by which
2.2 Registering with the
A third party
Details on how to specify the system properties or properties in a property file
and how to configure the JNDI Context are explained in detail in the
2.3 SyncFactory Provider Instance Generation Policies
The
These policies are explored in more detail in the
A compliant
Furthermore, the
3.2 Grades
JSR 114 defines a set of grades to describe the quality of synchronization
a
3.3 Locks
JSR 114 defines a set of constants that specify whether any locks have been
placed on a
These constants should be considered complementary to the
grade constants. The default setting for the majority of grade settings requires
that no data source locks remain when a
3.4 Updatable Views
A
3.5 Usage of
In the example below, the reference CachedRowSetImpl implementation
reconfigures its current SyncProvider object by calling the
setSyncProvider method.
A
The
When the
The application can then use
The comment for the
Copyright © 1993, 2015, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy. Scripting on this page tracks web page traffic, but does not change the content in any way.2.0 Service Provider Interface Architecture
2.1 Overview
SyncProvider
implementations can be registered and then generated when
required. The lazy reference mechanism employed by the SyncFactory
limits
unnecessary resource consumption by not creating an instance until it is
required by a disconnected
RowSet
object. The SyncFactory
class also provides
a standard API to configure logging options and streams that may be provided
by a particular SyncProvider
implementation.
SyncFactory
SyncProvider
implementation must be registered with the
SyncFactory
in order for a disconnected RowSet
object
to obtain it and thereby use its javax.sql.RowSetReader
and
javax.sql.RowSetWriter
implementations. The following registration mechanisms are available to all
SyncProvider
implementations:
SyncProvider
objects.
SyncFactory
for the mechanism to
function correctly.
SyncFactory
class description.
SyncFactory
generates a requested SyncProvider
object if the provider has been correctly registered. The
following policies are adhered to when either a disconnected RowSet
object
is instantiated with a specified SyncProvider
implementation or is
reconfigured at runtime with an alternative SyncProvider
object.
SyncProvider
object is specified and the SyncFactory
contains no reference to the provider, a SyncFactoryException
is
thrown.
SyncProvider
object is specified and the SyncFactory
contains a reference to the provider, the requested provider is supplied.
SyncProvider
object is specified, the reference
implementation provider RIOptimisticProvider
is supplied.
SyncFactory
class.
3.0 SyncProvider Implementer's Guide
3.1 Requirements
SyncProvider
implementation that is fully pluggable
into the SyncFactory
must extend and implement all
abstract methods in the SyncProvider
class. In addition, an implementation must determine the
grade, locking and updatable view capabilities defined in the
SyncProvider
class definition. One or more of the
SyncProvider
description criteria must be supported. It
is expected that vendor implementations will offer a range of grade, locking, and
updatable view capabilities.
SyncProvider
naming convention must be followed as
detailed in the SyncProvider
class
description.
SyncProvider
object can offer a disconnected RowSet
object. These grades are listed from the lowest quality of service to the highest.
SyncProvider
implementation returning this grade will simply
attempt to write any data that has changed in the RowSet
object to the
underlying data source, overwriting whatever is there. No attempt is made to compare
original values with current values to see if there is a conflict. The
RIXMLProvider
is implemented with this grade.
SyncProvider
implementation returning this grade
will check for conflicts in rows that have changed between the last synchronization
and the current synchronization under way. Any changes in the originating data source
that have been modified will not be reflected in the disconnected RowSet
object. If there are no conflicts, changes in the RowSet
object will be
written to the data source. If there are conflicts, no changes are written.
The RIOptimisticProvider
implementation uses this grade.
SyncProvider
implementation returning this grade
will check all rows, including rows that have not changed in the disconnected
RowSet
object. In this way, any changes to rows in the underlying
data source will be reflected in the disconnected RowSet
object
when the synchronization finishes successfully.
SyncProvider
implementations returning this grade will lock
the row in the originating data source that corresponds to the row being changed
in the RowSet
object to reduce the possibility of other
processes modifying the same data in the data source.
SyncProvider
implementation returning this grade will lock
the entire view and/or table affected by the original query used to
populate a RowSet
object.
RowSet
object's underlying data source and, if so,
on which constructs the locks are placed. These locks will remain on the data
source while the RowSet
object is disconnected from the data source.
RowSet
object is disconnected
from its data source.
The grades GRADE_LOCK_WHEN_MODIFIED
and
GRADE_LOCK_WHEN_LOADED
allow a disconnected RowSet
object
to have a fine-grained control over the degree of locking.
SyncProvider
implementations
unless otherwise directed by a RowSet
object.
RowSet
object.
RowSet
object.
RowSet
object.
RowSet
object may be populated with data from an SQL VIEW
.
The following constants indicate whether a SyncProvider
object can
update data in the table or tables from which the VIEW
was derived.
SyncProvider
implementation supports synchronization
to the table or tables from which the SQL VIEW
used to populate a
a RowSet
object is derived.
SyncProvider
implementation does not support
synchronization to the table or tables from which the SQL VIEW
used to populate a RowSet
object is derived.
SyncProvider
Grading and Locking
CachedRowSetImpl crs = new CachedRowSetImpl();
crs.setSyncProvider("com.foo.bar.HASyncProvider");
An application can retrieve the SyncProvider object currently in use
by a disconnected RowSet
object. It can also retrieve the
grade of synchronization with which the provider was implemented and the degree of
locking currently in use. In addition, an application has the flexibility to set
the degree of locking to be used, which can increase the possibilities for successful
synchronization. These operation are shown in the following code fragment.
SyncProvider sync = crs.getSyncProvider();
switch (sync.getProviderGrade()) {
case: SyncProvider.GRADE_CHECK_ALL_AT_COMMIT
//A high grade of optimistic synchronization
break;
case: SyncProvider.GRADE_CHECK_MODIFIED_AT_COMMIT
//A low grade of optimistic synchronization
break;
case: SyncProvider.GRADE_LOCK_WHEN_LOADED
// A pessimistic synchronization grade
break;
case: SyncProvider.GRADE_LOCK_WHEN_MODIFIED
// A pessimistic synchronization grade
break;
case: SyncProvider.GRADE_NONE
// No synchronization with the originating data source provided
break;
}
switch (sync.getDataSourcLock() {
case: SyncProvider.DATASOURCE_DB_LOCK
// A lock is placed on the entire datasource that is used by the
//
It is also possible using the static utility method in the
RowSet
object
break;
case: SyncProvider.DATASOURCE_NO_LOCK
// No locks remain on the originating data source.
break;
case: SyncProvider.DATASOURCE_ROW_LOCK
// A lock is placed on the rows that are touched by the original
// SQL statement used to populate
// the RowSet object that is using the SyncProvider
break;
case: DATASOURCE_TABLE_LOCK
// A lock is placed on all tables that are touched by the original
// SQL statement used to populated
// the RowSet object that is using the SyncProvider
break;
SyncFactory
class to determine the list of SyncProvider
implementations currently registered with the SyncFactory
.
Enumeration e = SyncFactory.getRegisteredProviders();
4.0 Resolving Synchronization Conflicts
The interface SyncResolver
provides a way for an application to
decide manually what to do when a conflict occurs. When the CachedRowSet
method acceptChanges
finishes and has detected one or more conflicts,
it throws a SyncProviderException
object. An application can
catch the exception and
have it retrieve a SyncResolver
object by calling the method
SyncProviderException.getSyncResolver()
.
SyncResolver
object, which is a special kind of
CachedRowSet
object or
a JdbcRowSet
object that has implemented the SyncResolver
interface, examines the conflicts row by row. It is a duplicate of the
RowSet
object being synchronized except that it contains only the data
from the data source this is causing a conflict. All of the other column values are
set to null
. To navigate from one conflict value to another, a
SyncResolver
object provides the methods nextConflict
and
previousConflict
.
SyncResolver
interface also
provides methods for doing the following:
RowSet
object if it needs
to be changed
CachedRowSet
method acceptChanges
is called, it
delegates to the RowSet
object's SyncProvider
object.
How the writer provided by that SyncProvider
object is implemented
determines what level (grade) of checking for conflicts will be done. After all
checking for conflicts is completed and one or more conflicts has been found, the method
acceptChanges
throws a SyncProviderException
object. The
application can catch the exception and use it to obtain a SyncResolver
object.
SyncResolver
methods to get information
about each conflict and decide what to do. If the application logic or the user
decides that a value in the RowSet
object should be the one to
persist, the application or user can overwrite the data source value with it.
SyncResolver
interface has more detail.
5.0 Related Specifications
6.0 Related Documentation
Overview
Package
Class
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Java™ Platform
Standard Ed. 6
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