Calling Groovy classes from Java?

[Christophe Henry <ch...@c-henry.fr>]

Hello,

I was wondering how much Groovy classes could be called from Java.

I am aware that solutions to call Groovy scripts are available like 
GroovyScriptLoader but I was thinking about simpler solutions.

This afternoon, while working on a classic Maven project, I noticed 
something weird : some Groovy classes were in the auto-completion list 
that IntelliJ was displaying me. So I decided to do a test and try 
calling a Groovy class from Java.

So I tried the following code :

```
String[] strings = { "Hello world"} ;
System.out.println(new GStringImpl(new Object[0], strings) ;
```

And it worked. So I suppose this is possible, in a way, that, if I wrote 
a Groovy class, I could instantiate it and call it's methods from Java 
code, right?
-- 
/Cordialement,
Christophe Henry/

Re: Calling Groovy classes from Java?

[Keegan Witt <ke...@gmail.com>]

Hi Christophe,

Speaking first to your example of invoking GDK classes from Java: Yes, this
can be done.  Although sometimes it can be less usable (for example if you
want to call a method that takes a closure as an argument).  I hadn't heard
of GroovyScriptLoader, but I've seen the JSR223 and GroovyShell.evaluate()
techniques used.  But a fair amount of the time it isn't necessary.

To your second point on invoking your own Groovy classes from Java:  Yes!
Tons of folks have done this.  I do find it helpful though to make my
Groovy classes a it easier for Java to consume by explicitly typing the
entry points Java will access so that you can avoid casting.  The only
times I'd suggest going the script route (besides for actual scripts) is if
there were lots of cumbersome constructs (for example, the closure arg I
mentioned, or a DSL) that made it too painful to use Java directly.  In
general though, you can mix & match pretty painlessly.

Groovy's classes are Java bytecode (most of them are even written in Java),
and can be invoked from any other language that compiles to Java bytecode,
including Java.

Oh, and for the future, you may want to address questions like this on the
user list (users@groovy.incubator.apache.org).  This list is meant for
discussing the development of Groovy itself.

-Keegan

On Wed, Aug 12, 2015 at 11:55 AM, Christophe Henry <ch...@c-henry.fr>
wrote:

> Hello,
>
> I was wondering how much Groovy classes could be called from Java.
>
> I am aware that solutions to call Groovy scripts are available like
> GroovyScriptLoader but I was thinking about simpler solutions.
>
> This afternoon, while working on a classic Maven project, I noticed
> something weird : some Groovy classes were in the auto-completion list that
> IntelliJ was displaying me. So I decided to do a test and try calling a
> Groovy class from Java.
>
> So I tried the following code :
>
> ```
> String[] strings = { "Hello world"} ;
> System.out.println(new GStringImpl(new Object[0], strings) ;
> ```
>
> And it worked. So I suppose this is possible, in a way, that, if I wrote a
> Groovy class, I could instantiate it and call it's methods from Java code,
> right?
> --
>
> *Cordialement, Christophe Henry*
>