Extending iBATIS - iBATIS in Action - page 270

Therefore it is difficult for the iBATIS framework to support all databases using a
single type handler implementation. To deal with these situations, iBATIS supports
custom type handlers that allow you to customize the way that certain types are
handled. Using a custom type handler, you can tell iBATIS how to map relational
database types to Java types. You can even override the built-in type handlers. This
section will explain how.

12.2.1 Implementing a custom type handler

To implement a custom TypeHandler , you only need to implement part of the
functionality. That functionality is defined in a simple interface called TypeHan-
dlerCallback . It is defined in listing 12.1.

Listing 12.1 TypeHandlerCallback

public interface TypeHandlerCallback {

public void setParameter(
ParameterSetter setter, Object parameter)
throws SQLException;

public Object getResult(ResultGetter getter)
throws SQLException;

public Object valueOf(String s);

}

Let's step through the implementation of a TypeHandlerCallback . For the pur-
poses of this example, let's assume we have a database that uses the words “ YES ” and
“ NO ” to represent boolean values (i.e., true and false, respectively). Table 12.2
shows this example.

Table 12.2 Using YES and NO to represent boolean values

UserID Username PasswordHashcode Enabled

1 asmith 1190B32A35FACBEF YES

2 brobertson 35FACBEFAF35FAC2 YES

3 cjohnson AF35FAC21190B32A NO