Java Reference
In-Depth Information
How It Works
If your application requires the storage of string values, you need to know how large
those strings might possibly become. Most databases have an upper boundary when it
comes to the storage size of
VARCHAR
fields. For instance, the Oracle database has an
upper boundary of 2,000 characters and anything exceeding that length will be cut off.
If you have large amounts of text that need to be stored, use a
CLOB
field in the data-
base.
A
CLOB
is handled a bit differently from a string within Java code. In fact, it is ac-
tually a bit odd to work with the first couple of times you use it because you have to
create a
CLOB
from a
Connection
.
Note
In reality,
CLOB
s and
BLOB
s (binary large objects) are not stored in the Oracle
table where they are defined. Instead, a large object (
LOB)
locator is stored in the table
column. Oracle might place the
CLOB
in a separate file on the database server. When
Java creates the
Clob
object, it can be used to hold data for update to a specific
LOB
location in the database or to retrieve the data from a specific
LOB
location within the
database.
Let's take a look at the
loadClob()
method contained in the solution to this re-
cipe. As you can see, a
Clob
object is created using the
Connection cre-
ateClob()
method. Once the
Clob
has been created, you set its contents using the
setString()
method by passing the position indicating where to place the string
and the string of text itself:
textClob = conn.createClob();
textClob.setString(1, "This will be the recipe text in
clob format");
Once you have created and populated the
Clob
, you simply pass it to the database
using the
PreparedStatement setClob()
method. In the case of this example,
the
PreparedStatement
performs a database insert into the
RECIPE_TEXT
table
by calling the
executeUpdate()
method as usual.
Querying a
Clob
is fairly straightforward as well. As you can see in the
readClob()
method that is contained within the solution to this recipe, a
Pre-
paredStatement
query is set up and the results are retrieved into a
ResultSet
.
