JavaServer Pages, 3rd Edition

Using a PropertyEditor for Conversion

If the standard conversion rules are not enough for your needs, you can use a bean PropertyEditor to convert a literal string value to any Java data type you like. If an action attribute value is specified as a literal string for an attribute of a type other than String, the container looks for a property editor that can convert the string to the attribute’s data type. The property editor is also used for EL expressions that evaluate to a String, and for <jsp:attribute> element values.

Say you have an attribute of type java.util.Date. To let the page author specify it as a text value, you need a PropertyEditor that converts a String to a Date. Here’s how it’s done.

First you implement the PropertyEditor:

package com.foo;
  
import java.beans.*;
import java.text.*;
import java.util.*;
public class MyDatePE extends PropertyEditorSupport 
    implements PropertyEditor {
  
    private SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    private Date value;
  
    public Object getValue(  ) {
        return value;
    }
  
    public void setAsText(String text) 
        throws IllegalArgumentException {
  
        try {
            value = sdf.parse(text);
        }
        catch (ParseException e) {
            throw new IllegalArgumentException(e.getMessage(  ));
        }
    }
}

The container calls the setAsText( ) method with the attribute’s String value. This method creates a Date object from the string and saves it in the instance variable named value. The container then calls the getValue( ) method—which returns the new Date object—and uses the value ...