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Home » Modeling » M2T (model-to-text transformation) » Running the result of a JET transform
Running the result of a JET transform [message #52826] Sat, 01 November 2008 13:27 Go to next message
Paul Hammond is currently offline Paul HammondFriend
Messages: 17
Registered: July 2009
Junior Member

I am trying to use JET2, on Eclipse 3.4 and am a total JET beginner. I
have looked quite a lot at the available documentation for my problem,
read quite a few tutorials and stuff on IBMs and Eclipses website, but I
haven't yet come across what I'm looking for.

I have no problem creating the JET project, and creating a simple
template, and running the JET transformation to produce the JET output
Java files, the "JSP" like compilation stage.

Now I want to execute these Java files which will actually produce my
actual output text from the template, but I can't seem to do it as I'm
getting NullPointerExceptions in the JET2InternalPlatform class.

From the stack traces that I'm getting, I'm coming to the conclusion that
classes that are used in the JET plugin itself are required and really the
generated code also has to run in the context of the JET2 plugin.

I'm willing to take whatever steps are required to get it to run, but
ideally what I'd like to be able to do, is run the template
transformation, then run the produced code assuming it succeeds, if not in
one fell swoop, then at least just a button click or an Ant task for each
one assuming everything is configured correctly.

In addition I'd like to be able to have another project share my JET
project and be able to run the generated Java classes through simply
configuring their project correctly.

Finally I'd like to be able to deploy it as a standalone app (to run the
generated code as one app, and to generate the code as another), and
ideally package it as a plugin that I can then just include as a plugin in
another app (again both to generate the code, and to run the generated
code), and everything required to run, including classpaths for building
and runtime would just get set correctly.

I realise this is asking quite a lot and it's moving into plugin territory
etc, but even if I could just get to running the generated code, that
would get me going and be a great start.

My template is simplicity itself...

<%@taglib prefix="ws" id="org.eclipse.jet.workspaceTags" %>
<%@jet imports="org.eclipse.emf.ecore.*"%>

<c:load url="myModel/model/model.ecore" urlContext="workspace"
loader="org.eclipse.jet.emf" var="myEcore"/>
Object object=context.getVariable("myEcore");
<%= object %>

Here is the method in another class I create in the same project I create
to try and run the generated _jet_transformation class.

static public void methodOne() throws Exception
String[] jetTransformsToSearch = { "a.b.c"};
// final InternalJET2Platform internalJET2Platform=new
final String templatePath = "templates/main.jet";
final JET2Context context = new JET2Context(null);
final BufferedJET2Writer out = new BodyContentWriter(); jetTransformsToSearch, new
JET2TemplateManager.ITemplateOperation() {
public void run(JET2TemplateManager.ITemplateRunner templateRunner) {
templateRunner.generate( templatePath, context, out );
// do something with the result
String output = out.getContent();

Compiles no problem. But I had to include as external JARs 4 to 5 Eclipse
core, OSG, and other plugin JARs in the debug configuration Classpath tab
to get it to run. Then I get...

Exception in thread "main" java.lang.ExceptionInInitializerError
at java:133)
at autoSysDirector.JetTest.methodOne(
at autoSysDirector.JetTest.main(
Caused by: java.lang.NullPointerException
at org.eclipse.jet.JET2Platform.<clinit>(
... 3 more

Now this null is because the plugin member variable of
InternalJET2Platform is null, I suspect because it's only set when the JET
code is run as a plugin itself. This of course is required during the
transformation, but also seems to be required during the execution of the
generated code.

Below is the line I've commented out above.

final InternalJET2Platform internalJET2Platform=new InternalJET2Platform();

This constructor sets the plugin static attribute to the
InternalJET2Platform object itself, however, so when I uncomment that and
include it, I get....

org.eclipse.jet.internal.runtime.InstalledJETBundleProvider. startup(
org.eclipse.jet.internal.InternalJET2Platform.checkBundleMan ager(
org.eclipse.jet.internal.InternalJET2Platform.getBundleManag er(
at org.eclipse.jet.JET2Platform.getJETBundleManager(JET2Platfor
at java:133)
at autoSysDirector.JetTest.methodOne(
at autoSysDirector.JetTest.main(

This will probably go on and on. I think I have to run the transformed
code itself in the context of the JET plugin.

Any pointers greatly appreciated.


Re: Running the result of a JET transform [message #52883 is a reply to message #52826] Mon, 03 November 2008 16:57 Go to previous messageGo to next message
Paul Elder is currently offline Paul ElderFriend
Messages: 849
Registered: July 2009
Senior Member

JET2 projects/transformations must run within Eclipse. They depend on not
only the jet plugin, but also on the Eclipse/OSGi environment being active.
That means that the simple:

class Main {
public static void main(String[] args) {
// do some magic to invoke JET transform

will NOT work, even if you manage to get absolutely every plug-in loaded
into the classpath.

To run a JET transformation you have a number of possibilities:

1) run it from the Eclipse Run UI.
a) Click the menu Run > Run Configurations
b) Select JET Transformation in the left-hand tree, then click the New
c) Browse for the file that will serve as input to your transformation.
d) Select the JET transformation from the ID combo box.
e) Click Run

2) run it from an ANT script (which is executed by the Eclipse Ant runner)
via the <jet.transform> ant task.

Details on the JET ant task are here: e.jet.doc/references/ant/antTasks.xhtml

From within Eclipse, you can run an ANT build 'hosted in Eclipse' by
clicking Run > External Tools > External Tools Configurations. Choose your
Ant build script, and on the JRE tab, choose 'Run in the same JRE as the

To run an ANT build headlessly, you need at a minimum an command line like:

eclipse -application org.eclipse.ant.core.antRunner -data
....your-ws-location... ...normal Ant command line options go here...

3) run it from a plug-in (which is itself configured into an Eclipse
environment) using JET2Platform.runTransformXXX.
The easiest way to do this would be to:
a) use the new plug-in wizard, and then use the 'Templates' page of the
wizard to create a Hello, world plug-in.
b) In manifest editor for the plug-in, add org.elcipse.jet as a dependency.
c) Find the action class created by the project wizard, and your call to

As for packaging your solution, JET transformations are Eclipse plug-ins.
They can be packaged as part of a larger solution. For example, the new JET
project wizard invokes a JET transformation.

As for running outside of Eclipse, I hope to get JET
transformations/templates to do this in the upcoming Galileo release. But,
in that case, I expect some loss of functionality, as some JET tags depend
on Eclipse functionality (the java:* tags, for example).

Re: Running the result of a JET transform [message #52963 is a reply to message #52883] Thu, 06 November 2008 22:51 Go to previous messageGo to next message
Paul Hammond is currently offline Paul HammondFriend
Messages: 17
Registered: July 2009
Junior Member
Thanks for your detailed post Paul.

Yes I kind of thought that might be the case about the plugin thing, I
think plain JET1 examples made me unsure as they seem to be able to work
outside the confines of a plugin. I have had no problem running the
template, even before I posted, but I can't get it to produce any output,
I thought it might be producing the .class files, but it's supposed to
execute them on ones input. I run the simple sample.xml file with just
<root></root> by right clicking on it and selecting 'Run as JET input' and
send it through a simple template that simply has some plain text, even
executes some System.outs, but all it says in the console window is
'Successful Execution'. Shouldn't everything in my top level template end
up on the console as it's not being directed to a file?

Where does the output of the top level template main.jet go to?

Re: Running the result of a JET transform [message #52988 is a reply to message #52963] Fri, 07 November 2008 16:43 Go to previous messageGo to next message
Paul Elder is currently offline Paul ElderFriend
Messages: 849
Registered: July 2009
Senior Member

I'll answer your specific question. But, fundamentally, I don't understand
what you're trying to achieve. I think if I did, I (and JET) could be of
much greater use to you.

Answers to your specifc question
> Where does the output of the top level template main.jet go to?

When running a JET transformation, the main template is run for its side
effects (i.e. the tags it executes) - the expanded template is currently

If you want to save text to a file, look at the ws:file tag.

If you want to write text to the execution log, take a look at the c:log

What are you trying to acheive?
This is from a re-reading of your original post. Let's leave JET entirely
out of the picture, and talk about your goals. From what I see, you want to:

1) Create a tool (I'll call it ToolX) that produces some Java code given
some parameter(s) From your template, the parameter might an ECore model.
2) The Java source code created by ToolX (lets call in SourceCodeA) should
be deployable in stand alone appl.
3) You want the production of SourceCodeA and is compilation into is
compiled from (call it CompileCodeB) to be as automatic as possible.
4) You want ToolX to be reusable, so that with different inputs, you can get
SourceCodeB, SourceCodeC, etc....
5) It is unclear (to me) whether you want ToolX and the compilation of
SourceCodeA into CompiledCodeB to be deployable as a stand alone

Now, lets integrate JET and Eclipse back into that picture:

* JET is a tool accomplishing #1, #2 and #4, so long as you are content with
running ToolX within the Eclipse environment. Regardless of JET being bound
to Eclipse, it can still produce SourceCodeA that has nothing to do with
* Eclipse is an ideal enviornment for achieving #3. Eclipse Java projects
automatically (and incrementally) compiled. The invocation of ToolX
(assuming a JET implementation) can also be automated by introducing a Ant
* As for #5, there would be issues/roadblocks with a JET-based ToolX. But
then you'd also be faced with all the issues of compiling Java code, and
successfully loading and executing it. Basing such a stand-alone application
on OSGi and perhaps the Eclipse JDT (Java development tools) might greatly
simplify things. And, in that situation, using JET would no longer be an

If this is the way you want to go, this is how I would approach creating
ToolX with JET:

1) Create an example of SourceCodeA. Include all the variations you can
think ToolX should produce. If you need ant scripts to compile and jar this,
create those too. While you're doing this, make sure you're using Eclipse
effectively, too. Name and configure the Eclipse projects the way you'd want
it: Is the JVM version specified the way you want? What about copyright
notices, warning levels, etc...? And, how about JUnits to confirm that the
code works?

2) Start looking at all the files (not just the Java classes) created in #1,
and look for things would be driven by input to ToolX. This represent
'points of variability'. You need to relate each point-of-variabililty and
each file/artifact in #1 to some part of the input you will give to ToolX.
If you don't already have a 'model' of the input to ToolX, then these points
of variability and artifacts can serve to drive its development.

3) Once you have a model in place, you can start creating JET templates. An
easy way is to copy files for #1, and replace the points of variability
already identified with references to the ToolX's input. You don't
necessarily want to create a JET template for each file in #1, but you do
want to account for file is some way. E.g. these .class files are produced
by the Java compiler; this .java files would all be produced by this one JET
template; ...

4) Finally, orchestrate the template execution by writing main.jet, which
would traverse the ToolX input, and fire off the various JET templates using
ws:file tags.

Does this help?

Re: Running the result of a JET transform [message #53405 is a reply to message #52988] Sun, 23 November 2008 19:36 Go to previous message
Paul Hammond is currently offline Paul HammondFriend
Messages: 17
Registered: July 2009
Junior Member
Thanks Paul for your help.

I've made some headway since, and am up and running. Rather than replying
straight away, I thought I'd play around a bit more and get more au fait
with what I can and can't do and then come back to you.

So I'll post again at a future date with a description of how I have it
working, the ideal scenario, and perhaps some more questions/suggestions.

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