Java Reference
In-Depth Information
In the preceding examples, you learned how to query a database by explicitly establishing
a
Connection
to the database, preparing a
Statement
for querying the database and exe-
cuting the query. In this section, we demonstrate the
RowSet
interface
, which configures
the database connection and prepares query statements automatically. The interface
Row-
Set
provides several
set
methods that allow you to specify the properties needed to establish
a connection (such as the database URL, username and password of the database) and cre-
ate a
Statement
(such as a query).
RowSet
also provides several
get
methods that return
these properties.
Connected and Disconnected
RowSet
s
There are two types of
RowSet
objects—connected and disconnected. A
connected
RowSet
object connects to the database once and remains connected while the object is in use. A
disconnected
RowSet
object connects to the database, executes a query to retrieve the data
from the database and then closes the connection. A program may change the data in a
disconnected
RowSet
while it's disconnected. Modified data can be updated in the data-
base after a disconnected
RowSet
reestablishes the connection with the database.
Package
javax.sql.rowset
contains two subinterfaces of
RowSet
—
JdbcRowSet
and
CachedRowSet
.
JdbcRowSet
, a connected
RowSet
, acts as a wrapper around a
ResultSet
object and allows you to scroll through and update the rows in the
ResultSet
. Recall that
by default, a
ResultSet
object is nonscrollable and read only—you must explicitly set the
result-set type constant to
TYPE_SCROLL_INSENSITIVE
and set the result-set concurrency
constant to
CONCUR_UPDATABLE
to make a
ResultSet
object scrollable and updatable. A
JdbcRowSet
object is scrollable and updatable by default.
CachedRowSet
, a disconnected
RowSet
, caches the data of a
ResultSet
in memory and disconnects from the database.
Like
JdbcRowSet
, a
CachedRowSet
object is scrollable and updatable by default. A
Cached-
RowSet
object is also
serializable
, so it can be passed between Java applications through a
network, such as the Internet. However,
CachedRowSet
has a limitation—the amount of
data that can be stored in memory is limited. Package
javax.sql.rowset
contains three
other subinterfaces of
RowSet
.
Portability Tip 24.5
A
RowSet
can provide scrolling capability for drivers that do not support scrollable
Re-
sultSet
s.
Using a
RowSet
Figure 24.29 reimplements the example of Fig. 24.23 using a
RowSet
. Rather than estab-
lish the connection and create a
Statement
explicitly, Fig. 24.29 uses a
JdbcRowSet
object
to create a
Connection
and a
Statement
automatically.
Class
RowSetProvider
(package
javax.sql.rowset
) provides
static
method
new-
Factory
which returns a an object that implements interface
RowSetFactory
(package
javax.sql.rowset
) that can be used to create various types of
RowSet
s. Lines 18-19 in
the
try
-with-resources statement use
RowSetFactory
method
createJdbcRowSet
to
obtain a
JdbcRowSet
object.
Lines 22-24 set the
RowSet
properties that the
DriverManager
uses to establish a data-
base connection. Line 22 invokes
JdbcRowSet
method
setUrl
to specify the database
