Reviews : Java Books :
JSP Tag Libraries : Chapter 10: Iterating with Tags

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.

How to Add Java Applets to Your Site

New on the Java Boutique:

New Review:

Time Management Made Easy with the Quartz Enterprise Job Scheduler
Why not just use the Java timer API? This open source scheduling API boasts simplicity, ease-of-integration, a well-rounded feature set, and it's free!

New Applet:

Reverse Complement
Reverse Complement is a simple applet that converts DNA or RNA sequences into three useful formats.

Elsewhere on internet.com:

WebDeveloper Java
Lots of Java information on webdeveloper.com

WDVL Java
Thorough Java resource at the Web Developer's Virtual Library.

ScriptSearch Java
Hundreds of free Java code files to download.

jGuru: Your View of the Java Universe
Customizable portal with online training, FAQs, regular news updates, and tutorials.