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From Christofer Dutz <>
Subject [General] Working on code generator ... was: Re: [DISCUSS] Which template engine to use for the code-generator
Date Fri, 01 Mar 2019 15:20:34 GMT
Hi all,

so after having a first generic generator thingy working, I am now working on building helpers
and templates for code generation.

For now I would like to write it that it works with the schemas I already created and to fail
miserably if something is not as expected. 
It's not planned on being used as a general purpose tool, so I guess this is ok ... if we
encounter problems when implementing other protocols I would then opt for securing the parts
that cause errors.
Now building some bullet-proof solution is probably a waste of time.

What do you think?


Am 28.02.19, 15:37 schrieb "Christofer Dutz" <>:

    Hi all,
    so I just pushed a first very raw version of the plugin.
    The configuration currently looks like this:
    The above config references both templates and dfdl schema locally, but it is my intention
to support classpath paths in there too.
    The package name is needed as the templates are language dependent and not protocol dependent
and the protocols don't know about packages.
    In the end, a user would add a "runtime" dependency to the module for a "template" project
and a "protocol" module.
    For example we would have:
    - JavaTemplates 
    - CppTemplates
    - PythonTemplates
    - CsTemplates
    And protocol modules for every supported protocol:
    - S7Protocol
    - ADSProtocol
    - ModbusProtocol
    - EtherNetIPProtocol
    And with this we could generate:
    - plc4j-s7-driver (package: "", JavaTemplates, S7Protocol)
    - plc4j-modbus-driver (package: "", JavaTemplates, S7Protocol)
    - plc4cpp-s7-driver (package: "org.apache.plc4x.cpp.s7", CppTemplates, S7Protocol)
    I guess you get the point ...
    Right now the plugin can accept a number of templates and a dfdl schema file. The plugin
parses this and for every root complexType it executes each of the templates.
    If the template wants to output something, the first line of the generated output will
contain the file-name and directory structure for the output. 
    After that comes the real content of the file.
    Still have to work on the loading of resources from the classpath as this requires adding
more modules (the template modules) so I'm currently concentrating on how to generate code
    Here I'll probably work on some helpers for common things I come across during my template
    Just wanted to keep you guys updated ... 
    Am 28.02.19, 10:15 schrieb "Julian Feinauer" <>:
        Hi Chris,
        I used and like both.
        But I have the impression that Freemarker is a bit more widespread for code generation
(is e.g. used in Apache Drill) in contrast to velcotiy which is often used for websites (my
        So I agree and also prefer freemarker for us.
        Von: Christofer Dutz <>
        Gesendet: Donnerstag, 28. Februar 2019 09:11:26
        Betreff: [DISCUSS] Which template engine to use for the code-generator
        Hi all,
        so yesterday I did the first commit for a new maven plugin (And yes it’s intentionally
not part of the main build).
        So today I will start with the code generation part … the thing is that we will
be using a templating system to define the templates for a given output format.
        Right now we could coose:
          *   Apache Velocity (
          *   Apache Freemarker (
        Usually the choice for an Apache project would have been Velocity as this was the
Apache project, but as recently Freemarker also is an Apache project, I would prefer the later.
        In my day job I have had the need to use Tempating engines multiple times and whenever
I used Freemarker, things were a lot simpler.
        So if there are now objections, I would start using Freemarker.

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