ZK Spreadsheet Essentials/Working with ZK Spreadsheet/Implement Your Own Formula Functions/Register as a TLD

ZK Spreadsheet allows developers to write their own custom formula functions. One way of implementing them is as a Java static method and another one to implement it as EL function and register it in a TLD.

Purpose

Implement a custom formula function as an EL function and register it in a TLD.

Define EL function

Define your custom formula function as an EL function. For example here is an EL function to convert USD to TWD.

public class CurrencyFns {

	public static double toTWD(double usdNum, double twdRate) {
		return usdNum * twdRate;
	}
}

Register and config as a TLD

Register above defined toTWD EL function in a TLD as shown below.

<?xml version="1.0" encoding="UTF-8" ?>
<taglib>
	<uri>http://www.zkoss.org/zss/example/custom</uri>
	<description>
		User defined functions.
	</description>
	<import>
		<import-name>CurrencyFns</import-name>
		<import-class>org.zkoss.zss.example.CurrencyFns</import-class>
	</import>

	<function>
		<name>toTWD</name>
		<function-class>org.zkoss.zss.example.CurrencyFns
		</function-class>
		<function-signature>double toTWD(double,double);</function-signature>
		<description>
			Returns equivalent amount in TWD for the given amount in USD.
		</description>
	</function>
</taglib>

Configure this TLD in /metainfo/tld/config.xml which can be find in the classpath. For example, you could put it under WEB-INF/classes/metainfo/tld/config.xml, or as part of a JAR file.

<config>
	<taglib>
		<taglib-uri>http://www.zkoss.org/zss/example/custom</taglib-uri>
		<taglib-location>/web/WEB-INF/tld/custom.tld</taglib-location>
	</taglib>
</config>

taglib directive

To be able to use above defined toTWD EL Function as a custom ZK Spreadsheet formula fuction declare its registed TLD in your ZUL page using taglib directive [1].

<?page title="ZSS" contentType="text/html;charset=UTF-8"?>
<?taglib uri="http://www.zkoss.org/zss/example/custom" prefix="zss" ?>
<zk>
	<window title="ZSS User Defined Functions" border="normal" width="100%" height="100%">
		<spreadsheet width="800px" height="800px"
			src="/test2/xls/elfn.xlsx" maxrows="20" maxcolumns="10">
		</spreadsheet>
	</window>
</zk>

Note that taglib prefix attribute value must be set to "zss" for ZK Spreadsheet to invoke implementation for such custom formula function.

Usage

Once defined and declared above custom formula function can be used just like any other built-in functions of Excel.

=toTWD(A1,B1)

All source code listed in this book is at Github.