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Friday, July 8, 2011

JDBC: Using RowSet Objects

A JDBC RowSet object holds tabular data in a way that makes it more flexible and easier to use than a result set.

Oracle has defined five RowSet interfaces for some of the more popular uses of a RowSet, and standard reference are available for these RowSet interfaces. In this tutorial you will learn how to use these reference implementations.

These versions of the RowSet interface and their implementations have been provided as a convenience for programmers. Programmers are free write their own versions of the javax.sql.RowSet interface, to extend the implementations of the five RowSet interfaces, or to write their own implementations. However, many programmers will probably find that the standard reference implementations already fit their needs and will use them as is.

This section introduces you to the RowSet interface and the following interfaces that extend this interface:

  • JdbcRowSet
  • CachedRowSet
  • WebRowSet
  • JoinRowSet
  • FilteredRowSet

The following topics are covered:
  • What Can RowSet Objects Do?
  • Kinds of RowSet Objects

What Can RowSet Objects Do?

All RowSet objects are derived from the ResultSet interface and therefore share its capabilities. What makes JDBC RowSet objects special is that they add these new capabilities:
  • Function as JavaBeans Component
  • Add Scrollability or Updatability

Function as JavaBeans Component

All RowSet objects are JavaBeans components. This means that they have the following:
  • Properties
  • JavaBeans Notification Mechanism


All RowSet objects have properties. A property is a field that has corresponding getter and setter methods. Properties are exposed to builder tools (such as those that come with the IDEs JDveloper and Eclipse) that enable you to visually manipulate beans.

JavaBeans Notification Mechanism

RowSet objects use the JavaBeans event model, in which registered components are notified when certain events occur. For all RowSet objects, three events trigger notifications:
  • A cursor movement
  • The update, insertion, or deletion of a row
  • A change to the entire RowSet contents

The notification of an event goes to all listeners, components that have implemented the RowSetListener interface and have had themselves added to the RowSet object's list of components to be notified when any of the three events occurs.

A listener could be a GUI component such as a bar graph. If the bar graph is tracking data in a RowSet object, the listener would want to know the new data values whenever the data changed. The listener would therefore implement the RowSetListener methods to define what it will do when a particular event occurs. Then the listener also must be added to the RowSet object's list of listeners.

The following line of code registers the bar graph component bg with the RowSet object rs.

Now bg will be notified each time the cursor moves, a row is changed, or all of rs gets new data.

Add Scrollability or Updatability

Some DBMSs do not support result sets that can be scrolled (scrollable), and some do not support result sets that can be updated (updatable).

If a driver for that DBMS does not add the ability to scroll or update result sets, you can use a RowSet object to do it. A RowSet object is scrollable and updatable by default, so by populating a RowSet object with the contents of a result set, you can effectively make the result set scrollable and updatable.

Kinds of RowSet Objects

RowSet object is considered either connected or disconnected. A connected RowSet object uses a JDBC driver to make a connection to a relational database and maintains that connection throughout its life span.

disconnected RowSet object makes a connection to a data source only to read in data from a ResultSet object or to write data back to the data source. After reading data from or writing data to its data source, the RowSet object disconnects from it, thus becoming "disconnected." During much of its life span, a disconnected RowSet object has no connection to its data source and operates independently.

The next two sections tell you what being connected or disconnected means in terms of what a RowSet object can do.

Connected RowSet Objects

Only one of the standard RowSet implementations is a connected RowSet object: JdbcRowSet. Always being connected to a database, a JdbcRowSet object is most similar to a ResultSet object and is often used as a wrapper to make an otherwise non-scrollable and read-only ResultSet object scrollable and updatable.

As a JavaBeans component, a JdbcRowSet object can be used, for example, in a GUI tool to select a JDBC driver. A JdbcRowSet object can be used this way because it is effectively a wrapper for the driver that obtained its connection to the database.

Disconnected RowSet Objects

The other four implementations are disconnected RowSet implementations. Disconnected RowSet objects have all the capabilities of connected RowSet objects plus they have the additional capabilities available only to disconnected RowSet objects. For example, not having to maintain a connection to a data source makes disconnected RowSet objects far more lightweight than a JdbcRowSet object or a ResultSet object.

Disconnected RowSet objects are also serializable, and the combination of being both serializable and lightweight makes them ideal for sending data over a network. They can even be used for sending data to thin clients such as PDAs and mobile phones.

The CachedRowSet interface defines the basic capabilities available to all disconnected RowSet objects. The other three are extensions of the CachedRowSet interface, which provide more specialized capabilities. The following information shows how they are related:

CachedRowSet object has all the capabilities of a JdbcRowSet object plus it can also do the following:
  • Obtain a connection to a data source and execute a query
  • Read the data from the resulting ResultSet object and populate itself with that data
  • Manipulate data and make changes to data while it is disconnected
  • Reconnect to the data source to write changes back to it
  • Check for conflicts with the data source and resolve those conflicts

WebRowSet object has all the capabilities of a CachedRowSet object plus it can also do the following:
  • Write itself as an XML document
  • Read an XML document that describes a WebRowSet object

JoinRowSet object has all the capabilities of a WebRowSet object (and therefore also those of a CachedRowSet object) plus it can also do the following:
  • Form the equivalent of a SQL JOIN without having to connect to a data source

FilteredRowSet object likewise has all the capabilities of a WebRowSet object (and therefore also a CachedRowSet object) plus it can also do the following:
  • Apply filtering criteria so that only selected data is visible. This is equivalent to executing a query on a RowSet object without having to use a query language or connect to a data source.