Java Reference
In-Depth Information
<phones id="${db:id('Telephone')}" user_id="${db:id('User')}" type="0"
number="481 516-2342"/>
</dataset>
Instead of using hardcoded
ID
s for each class (like
${id}
and
${phoneId}
), this new
version uses a generic
${db:id('ClassName')}
function, which is much more flexi-
ble. The
db:id()
function then returns the respective
ID
for a given class, which is
either the value defined by the Hibernate listener or 1 by default (which means no
entity has been generated by
JPA
for that class. In this case the value doesn't matter,
but using 1 makes it easier to debug in case of errors). To add support for this func-
tion, first we need to change
ELContextImpl
to support function mapping, as shown
in listing 18.12.
Listing 18.12
Changes to
ELContextImpl
to support the
id
function
[...]
public final class
ELContextImpl
extends
ELContext {
[...]
private
FunctionMapper functionMapper =
new
ELFunctionMapperImpl();
[...]
@Override
public
FunctionMapper getFunctionMapper() {
return
functionMapper;
}
[...]
}
The
ID
function itself is defined at
ELFunctionMapperImpl
, shown in listing 18.13.
Listing 18.13
Custom EL functions (
ELFunctionMapperImpl
)
[...]
public class
ELFunctionMapperImpl
extends
FunctionMapper {
private static final
Map<String, Method> METHODS =
new
HashMap<String, Method>();
private static final
Map<String,Long> IDS =
new
HashMap<String, Long>();
private static final int
INITIAL_ID = 1;
B
C
static
{
for
( Method method : ELFunctionMapperImpl.
class
.getDeclaredMethods() ) {
int
modifiers = method.getModifiers();
String name = method.getName();
if
( Modifier.isStatic(modifiers) && name.startsWith("db_")) {
METHODS.put(name.replace('_', ':'), method);
}
}
}
@Override
public
Method resolveFunction(String prefix, String localName) {
return
METHODS.get(prefix+":"+localName);
}
D
