In this article, I will walk you through the process of extending CTL (CloverDX Transformation Language) with your own custom functions implemented in Java. Think of this as adding your own Java functions to the standard CTL function library so that you can transparently use them wherever there’s a piece of CTL code—in Reformat transformations, Filter expressions, etc.
Imagine you have some custom complex logic already implemented in Java packages, maybe some 3rd party library with potentially dozens of outside dependencies. Let’s say you want to share that functionality across applications, CloverDX included. There might be thousands of lines of code that you don’t want to be re-implementing in CTL.
Other reasons for using Java over pure CTL are performance and the expressive power of Java. While performance begins to matter only with large volumes of data, CTL has never been designed to fully replace general purpose languages. CTL makes working with data records easy, however for very complex algorithms it lacks the expressiveness and eco-system of libraries that Java can give you.
In this article, we’re talking about native Java code working as CTL functions. That’s quite different from simply writing a shared function library in plain CTL. To do that, save a piece CTL code as a .ctl file somewhere in your project and then import it into other transformations using import construct like this:
//#CTL2
import "trans/filterFunctions.ctl";
function integer transform() {
$out.0.field1 = filterChars($in.0.field1); // filterChars() is declared in filterFunctions.ctl
return ALL;
}
From then, the code and functions declared in the .ctl file will be available in the scope the library was imported in.
As an example, we’ll be implementing two functions:
string getWords()string getWords(integer count)These functions will produce “Lorem Ipsum”—Latin-like bogus text for testing. For this purpose, we’ll use an external loremipsum Java library by Sven Jacobs (see, we already have external dependencies!).
CloverDX is an open platform that can be extended by users in many ways. The core of CloverDX lies in its modular “engine”. This is the execution layer that takes care of running your data transformations and that sits at the center of CloverDX Designer (Runtime) and Server. CTL and all user extensions are treated as “engine plugins”. For our purpose, we’ll need to extend the engine with our own plugin (Java package) containing our Lorem Ipsum functions.
CloverDX Designer presents another layer, working rather independently of the engine/Runtime. Designer is built on Eclipse, and it comes with its own set of plugins that form the GUI. For Designer to recognize our new functions we’ll need to make it aware of our engine plugin by wrapping it with a separate “Designer plugin”. This will make the new functions available for context assist, correct syntax highlighting in editors, etc.
Here’s what we’ll do:
org.jetel.ctl.extensions.TLFunctionLibrary.plugin.xml descriptor with ctlfunction extension definition.org.jetel.ctl.extensions.TLFunctionAnnotation annotation to mark “entry point” methods that will serve as the implementation of our CTL functions (as you may have some additional supporting private methods that you don’t want to turn into CTL functions).plugin.xml descriptor—this time with engineplugin extension definition.Once finished, the new functions will be available in Designer dialogs (e.g. Source tab in Transform Editor, Reformat code, etc.).
So, let’s get to it!
com.cloveretl.custom.loremipsum. Hit Next when done.
lib in the project root directory (right-click the project in Package Explorer or in Navigator to create that folder)lib/loremipsum-1.0.jar)
lib directory → Choose loremipsum-1.0.jar) and click OK.
LoremIpsumCTLLibrary and it will extend org.jetel.ctl.extensions.TLFunctionLibrary.
Let’s put the class into a package called com.cloveretl.customctl.loremipsum.
TLFunctionLibrary comes from the CloverDX Library we added to the project earlier. However, you don’t need to worry about this for now, it is already a part of the code below).
You don't need to set anything else here—you will paste the full source code of this class in the next step anyway (will work only if you kept the same name and package, otherwise you’ll have to do a bit of editing).
package com.cloveretl.custom.loremipsum;
import org.jetel.ctl.Stack;
import org.jetel.ctl.extensions.TLFunctionAnnotation;
import org.jetel.ctl.extensions.TLFunctionCallContext;
import org.jetel.ctl.extensions.TLFunctionLibrary;
import org.jetel.ctl.extensions.TLFunctionPrototype;
import de.svenjacobs.loremipsum.LoremIpsum;
public class LoremIpsumCTLLibrary extends TLFunctionLibrary {
LoremIpsum loremIpsum = new LoremIpsum();
@Override
public TLFunctionPrototype getExecutable(String functionName)
throws IllegalArgumentException {
TLFunctionPrototype ret =
"getWords".equals(functionName) ? new GetWordsFunction() : null;
return ret;
}
@Override
public String getName() {
return "LoremIpsumCTLLibrary";
}
@TLFunctionInitAnnotation
public static void getWordsInit(TLFunctionCallContext context) {
//for now, no initialization needed
//this is called only once
//can be used to set-up/initialize included 3rd party Java libraries
}
@TLFunctionAnnotation("Generates Lorem Ipsum text")
public String getWords(TLFunctionCallContext context) {
return this.loremIpsum.getWords();
}
@TLFunctionAnnotation("Generates Lorem Ipsum text")
public String getWords(TLFunctionCallContext context, Integer count) {
if(count==null) {
return this.getWords(context);
}
return this.loremIpsum.getWords(count);
}
class GetWordsFunction implements TLFunctionPrototype {
@Override
public void execute(Stack stack, TLFunctionCallContext context) {
if (context.getParams().length > 0) {
stack.push(getWords(context, stack.popInt()));
}else{
stack.push(getWords(context));
}
}
@Override
public void init(TLFunctionCallContext context) { }
}
}
plugin.xml in the root of the engine plugin project:
<plugin
id="com.cloveretl.custom.loremipsum"
version="0.0.0.devel"
provider-name="CloverDX">
<runtime>
<library path="bin/"/>
<library path="lib/loremipsum-1.0.jar"/>
</runtime>
<extension point-id="ctlfunction">
<parameter id="libraryName" value="LoremIpsumCTLLibrary"/>
<parameter id="className"
value="com.cloveretl.customctl.loremipsum.LoremIpsumCTLLibrary"/>
</extension>
</plugin>Alright, you’re half way through! Now let’s get on to setting up the CloverDX Designer plugin, so this library can be installed and used inside Designer.
com.cloveretl.designer.loremipsum.CLProvidercom.cloveretl.gui.plugin.engine.AbstractClassLoaderProvidercom.cloveretl.gui plugin to the list of Required Plug-ins
com.cloveretl.gui.enginePlugin to Plugin extensionpluginscom.cloveretl.designer.loremipsum.CLProvider<exportedPlugin
pluginId="com.cloveretl.custom.loremipsum">
</exportedPlugin>plugins under the com.cloveretl.designer.loremipsum project folder. As best practice, put your engine plugins into folders named after the plugin IDs.com.cloveretl.custom.loremipsum (see image below):
plugins/com.cloveretl.custom.loremipsum folder and select Import... → General → File system.
com.cloveretl.custom.loremipsum project location (the engine plugin project).plugin.xml (in the right panel).bin.lib.com.cloveretl.designer.loremipsum project—the one in the main directory, not the one that we have just imported to plugins folder!.
META-INFplugin.xmlplugins. (the Designer plugin folder)plugins/com.cloveretl.custom.loremipsum/bin/plugins/com.cloveretl.custom.loremipsum/lib/loremipsum-1.0.jarcom.cloveretl.designer.loremipsum (the Designer plugin) project and select “Export…” from the context menu.
Install into host. Repository: (no need to change anything else)Now you can try your new functions anywhere in CloverDX, let's see it in DataGenerator's Source tab:
If you foolowed this how-to, you should end-up with the new functions present/available in your CloverDX Designer. However, if you experience issue during building or installing, you may look at the attached projects source code .zip archive. It should be enough to import into your Designer workspace and deploy/export as mentioned in step 27 above.
The archive also contains ready to use Eclipse/Designer Update Site: com.cloveretl.designer.loremipsum.updatesite - this may be used to install the plugin via Help → Install New Software and then adding local repository (note: copy the content of the updatesite to some local directory). For more details, consult Eclipse's manual).
Well, you sucessfully deployed and tested your new plugin with CTL functions implementation in CloverDX Designer. Now is time to add this plugin to CloverDX Server, so transformations using your new functions also work in server environment.
clover.properties. It should reside in cloverconf subdirectory of the main directory where your CloverDX Server is installed into.engine.plugins.additional.src into the file (unless it is already there). This property should be set to a value which denotes a full path to the directory where CloverDX should look for your additional plugins. So make sure this is accessible (at least for reading) to whatever user CloverDX Server process runs under.customloremipsum.zipengine.plugins.additional.src points to. In our case, it is /opt/cloverserver/myplugins.