10.5.5 Updating IterateTag to perform field substitution
Now that the modifications to IterationTagSupport are complete, the road to
field substitution is open. All we need is to modify IterateTag and make it set the ReflectionFieldGetter
into IterationTagSupport in order to turn on field substitution.
The modifications to IterateTag are presented in listing 10.17 (unmodified
code was omitted and new code is in bold).
Listing 10. 17 An updated IterateTag handler class with field substitution support
package book.iteration;
// Some unmodified code was removed
import book.util.LibraryConfig;
// Some unmodified code was removed
public class IterateTag extends IterationTagSupport {
// Some unmodified code was removed
protected void fetchIterationSupport()
throws JspException
{
Object o = getPointed();
if( o instanceof Iterator) {
elementsList =
new IteratorIterationSupport((Iterator) o);
} else if( o instanceof Enumeration) {
elementsList =
new EnumerationIterationSupport((Enumeration) o);
} else if( o.getClass().isArray()) {
elementsList = new ArrayIterationSupport(o);
} else {
// Throw an exception to inform that we cannot
// iterate this object
}
if( LibraryConfig.isFieldPlacementInUse()) {
fGetter = new ReflectionFieldGetter();
}
}
// Some unmodified code was removed
}
Only fetchIterationSupport() was modified to add the ReflectionFieldGetter
into IterationTagSupport according to a property in the library configuration.
10.5.6 Field substitution in action
Once the tweaking of the iteration code is behind us, we can modify our original JSP
(which printed the shopping cart) and adapt it to use field substitution. The end
result of this adaptation is shown in listing 10.18 and, as you shall see, the loop that
populates the HTML table with cart items has been simplified.
Listing 10. 18 A JSP file that uses field substitution
<%@ page errorPage="error.jsp" %>
<%@ taglib
uri=" http://www.manning.com/jsptagsbook/iteration-taglib"
prefix=" iter" %>
<%@ taglib
uri=" http://www.manning.com/jsptagsbook/conditions-taglib"
prefix=" cond" %>
<%@ taglib
uri=" http://www.manning.com/jsptagsbook/beans-taglib"
prefix=" bean" %>
<html>
<body>
<cond:with name="cart" property="empty">
<cond:test condition="eq true">
Your cart is empty.
</cond:test>
<cond:test condition="eq false">
Your cart contains the following products:
<table>
<tr>< th> Product</th> <th> Quantity</th> <th> Price</th> </tr>
<iter:iterate name="cart" property="products" id="product">
<tr>
<td> <$ name $> </td>
<td> <$ quantity $> </td>
<td> <$ dollars $>.<$ cents$>$ </td>
</tr>
</iter:iterate>
<tr>
<td> Totals <td>
<td> <bean:show name="cart" property="dollars"/>.
<bean:show name="cart" property="cents"/>$ </td>
</tr>
</table>
</cond:test>
</cond:with>
</body>
</html>
This section showed more than a mere ease-of-use enhancement to the iteration
task. It showed how to add your own proprietary additions to the JSP syntax. Some
developers may reject the idea of working with proprietary JSP additions, since this
syntax will not be useful in other settings. However, the additions presented in this
chapter are based on custom tags, and since custom tags are a standard JSP feature,
the field replacement features developed here will run on all JSP engines. Although
our creation's nature is indeed proprietary, our tags and their additions can run any-where.
The simplicity of our field substitution syntax and the time it will save JSP
authors who use it are well worth the expense of a bit of proprietary syntax.
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