Java Reference
In-Depth Information
Let's look at an example of this. Assume a class relationship like the one described
earlier in figure 10.2. In this diagram, there is an
AccountDao
interface and an
AccountDaoImpl
class that implements that interface. To use the
DaoManager
to get
the
DAO
, use the following code:
AccountDao accountDao = (AccountDao)
daoManager.getDao(AccountDao.class);
In this line of code, we declare our
AccountDao
variable, request it from the
DaoManager
instance using the interface name, and then cast it to the
AccountDao
interface, because the
DAO
manager simply returns
Object
.
In the previous version of the
DAO
, it was also possible to pass in a String
instead of an interface class. In version 2.
x
, that functionality was dropped,
because it eliminated a potential point of failure. By forcing the use of a class
name for identifying
DAO
implementations, you ensure that misspellings can be
avoided in the Java environment, because if the interface name is misspelled, the
code will not compile. Early failure is a good thing.
So, now that you have a solid foundational understanding of what you can do
with the i
BATIS
DAO
framework, we can start looking at other more advanced uses
of it.
10.3 Configuration tips
Although the
DAO
configuration looks very simple on the surface, it still offers a
great deal of flexibility. By creatively configuring the
DAO
manager, you can
accomplish some pretty sophisticated approaches to common problems. Let's
look at a few of them.
10.3.1
Multiple servers
As mentioned earlier, it is not uncommon in most development shops to have
different servers for their development,
QC
testing,
UA
testing, and production
environments.
In these cases, it is very useful to be able to remove the environment-specific
information from the
dao.xml
file and put it into an external file. The
properties
element was created to accomplish just that sort of thing. Listing 10.3 is a sample
dao.xml
file that uses this technique to make the
JDBC
settings external to the
dao.xml
file.
