Loading java library functions to Luaj

Question

I am stuck with loading java functions so that it can be called from lua file using luaj.

What i currently do is create something like this :

in some_package/aif.java :

package some_package;

public class aif extends TwoArgFunction {

    public aif() {
    }

    @Override
        public LuaValue call(LuaValue modname, LuaValue env) {
        LuaValue library = tableOf();
        library.set("foo", new foo());
        env.set("aif", library);
        return library;
    }

    //the rest contains the implementations of java functions
}

and then in lua file :

require "some_package/aif"
--etc ...

and then in Main.java file :

public static void Main(String[] args) {
    String script = "lib/some_lua_file.lua";
    globals = JsePlatform.standardGlobals();
    LuaValue chunk = globals.loadFile(script);
    chunk.call( LuaValue.valueOf(script) );         
}

this code works , but what i want is that in lua file we dont have to use "require". I have achieved this similarly but in c++ using this line :

luaL_requiref(L, "aif", luaopen_aiflib, 1);

can we do like that in luaj? i tried :

globals.load(new aif());

but gets Exception in thread "main" org.luaj.vm2.LuaError: index expected, got nil (variable env in call function of aif class is nil)

anybody knows how to setup aif as lua libary to use with luaj?

score 7 · Answer 1 · answered Oct 28 '13 at 08:18

You can write your MyXArgImpl like the following:

package mypackage;

import org.luaj.vm2.LuaValue;
import org.luaj.vm2.lib.ZeroArgFunction;

public class MyZeroArgImpl extends ZeroArgFunction {
    public LuaValue call() {
        return valueOf("My Zero Arg Implementation");
    }
}

and then add it to your LUA as the following:

LuaValue globals = JsePlatform.standardGlobals();
globals.get("dofile").call( LuaValue.valueOf(yourScriptfile));
globals.set("callMyFunction", new MyZeroArgImpl());

Now you can call your function inside your LUA script even without require('...'):

print(callMyFunction())

score 4 · Accepted Answer · answered Apr 26 '13 at 12:10

I have found the answer after looking at the luaj implementation of Lua library.

i modified my code :

package some_package;

public class aif extends OneArgFunction{

    public aif() {
    }

    @Override
    public LuaValue call(LuaValue env) {
        Globals globals = env.checkglobals();
        LuaTable aif = new LuaTable();
        aif.set("foo", new foo());
        env.set("aif", aif);
        globals.package_.loaded.set("aif", aif);
        return aif;
    }

    //the rest contains the implementations of java functions
}

I code the aif class to TwoArgFunction is because the tutorial said to do so. Now with the above code, no need to require the class in lua file

score 3 · Answer 3 · answered Apr 19 '13 at 21:57

3

Lets say your script that you are loading has a function "receive_aif"

function receive_aif( aifObj )

    --This is how you can invoke public function associated with aifObj     
    aifObj:someAifFunction()

end

From java, you can pass aif instance as: (This should work with any java object )

aif aifObj = new aif()
LuaValue receive_aif_handle = globals.get("receive_aif");
LuaValue retvals = receive_aif_handle.call( CoerceJavaToLua.coerce( aifObj ) );

I am using similar constructs in my application using "3.0 aplha-2" release

answered Apr 19 '13 at 21:57

Icarus3

2,310
14
22

i havent tried this one. It just that i have java and c++ app that use the lua functions, and i am trying to make the lua code doesnt need to be different when it's used for c++. I already have both working, the difference is the lua file for java has "require some_package/aif", while the lua file for c++ dont. So I'm trying to find solution that will work for them both(your solution require different code for c++ and java) – bysreg Apr 22 '13 at 03:40

Loading java library functions to Luaj

3 Answers3