10. 5. 3 FieldGetter and ReflectionFieldGetter
Let's start by looking at the FieldGetter interface, which provides one method to
set the object whose fields we'll want to retrieve and a second method to get those
fields from the object. We present this interface in listing 10.15, along with an
implementation of it called ReflectionFieldGetter whose job is to implement a FieldGetter
that gets JavaBeans properties (through reflection).
Listing 10.15 Source code of FieldGetter and ReflectionFieldGetter
package book.util;
import java.beans.IntrospectionException;
import java.lang.reflect.InvocationTargetException;
public interface FieldGetter {
public void setObject( Object o) 
throws IllegalArgumentException;
public Object getField( String fieldName) 
throws IllegalAccessException;
}
public class ReflectionFieldGetter implements FieldGetter {
static LocalStrings ls =
LocalStrings.getLocalStrings(ReflectionFieldGetter.class);
protected Object o;
public void setObject(Object o) 
throws IllegalArgumentException
{
this. o = o;
}
public Object getField(String fieldName) 
throws IllegalAccessException
{
try {
return BeanUtil.getObjectPropertyValue( o,
fieldName,
null);
} catch(InvocationTargetException ex) {
} catch(IllegalAccessException ex) {
} catch(IntrospectionException ex) {
} catch(NoSuchMethodException ex) {
}
// Throw an exception
}
}
Generic method to set the object whose fields we'll later retrieve.
Generic method to get an object's field by name.
For ReflectionFieldGetter, setObject will be set with a JavaBean.
For ReflectionFieldGetter, getField uses reflection (seen in chapter 8) to get a field from the JavaBean.
FieldGetter has two methods: setObject() that tells the getter which object we
are going to query for a field and getField() to procure the field's value. When
using a FieldGetter, instantiate it, then set an object into the FieldGetter using setObject(),
and then call getField() to get the values of the wanted fields. For
error notification, FieldGetter's methods can throw exceptions (e. g., if the object
set into the FieldGetter implementation is not of the right type, say a ResultSet
for a database-aware FieldGetter). To further clarify FieldGetter, listing 10.15
also shows the implementation of ReflectionFieldGetter which implements the FieldGetter
functionality for JavaBeans by using the reflection API. Remembering
the types of objects IterateTag enumerates, it is reasonable to assume that it is
going to step over beans in its iterations.
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