如何将对象传递给暴露的 luaj 函数? [英] How can I pass objects to an exposed luaj function?

问题描述

我正在尝试使用 Luaj + java 构建控制器.我有以下java类

I am trying to build a controller using Luaj + java. I have the following java classes

public class Duck {
  public void talk() { System.out.println("Duck quacks!"); }
  public void walk() { System.out.println("Duck walks!"); }
}

public class Person {
  public void talk() { System.out.println("Person talks!"); }
  public void walk() { System.out.println("Person walks!"); }
}

以及控制器的以下 lua 脚本:

and the following lua script for the controller:

onTalk(obj) 
  obj:talk();
end

onWalk(obj)
   obj:walk();
end

理想情况下，我想定义一个控制器(用 lua 编写)，我将在其中保留程序的所有逻辑，并且我想将来自该控制器的 API 公开给我的 Java 代码.我试图使用以下方法:

I would ideally like to define one controller (written in lua) where I will keep all of the program's logic, and I would like to expose API from that controller to my java code. I was trying to use the following approach:

ScriptEngineManager sem     = new ScriptEngineManager();
ScriptEngine        engine  = sem.getEngineByExtension(".lua");
ScriptEngineFactory factory = engine.getFactory();

// Script defined above
CompiledScript cs = ((Compilable)engine).compile(MY_LUA_SCRIPT);
SimpleBindings b = new SimpleBindings();

b = newSimpletBindings();

LuaValue onWalkHandler = (LuaValue)b.get("onWalk");
//func.call(LuaValue.valueOf(duck)); // Passing duck object does not work ???

我无法将对象传递给 LuaValue.如何将 java 对象传递给 lua 脚本?

I am not able to pass the object to the LuaValue. How can I pass a java object to the lua script?

PS:一般来说，在使用 Java 和嵌入式脚本时，人们是将函数捆绑在一个脚本中，还是每个回调都有一个单独的脚本?

PS: In general, when using Java and embedded scripting, do people bundle functions in one script, or is there a separate script for every callback?

推荐答案

我正在搜索 luaj 条目，发现您没有得到答复.你的问题很有趣，让我搜索.然后我意识到这是 2 年前问过的……我希望我的回答对其他人有用！基于luaj-3.0-alpha1的代码.

I was searching luaj entries and found your unanswered. Your question was interesting and made me search. Then I realized that it was asked 2 years ago... I hope my answer can be useful to somebody else! Code based on luaj-3.0-alpha1.

我们需要一个有效的 Lua 脚本(你忘记了 function 关键字):

We need a valid Lua script (you forgot the function keyword):

function onTalk(javaObj)
  print(type(javaObj) .. " " .. tostring(javaObj))
  print(javaObj.name)
  javaObj:talk()
  return true
end

function onWalk(javaObj)
  javaObj:walk()
  return 1, "km"
end

我添加了一点痕迹...我还制作了类似于您的课程:

I added a bit of trace... I also made classes similar to your:

class Dog
{
  public String name;
  Dog(String n) { name = n; }
  public void talk() { System.out.println("Dog " + name + " barks!"); }
  public void walk() { System.out.println("Dog " + name + " walks..."); }
}
class Cat
{
  String name;
  Cat(String n) { name = n; }
  public void talk() { System.out.println("Cat " + name + " meows!"); }
  public void walk() { System.out.println("Cat " + name + " walks..."); }
}

也添加一个字段来测试这个.对于我的测试，我只是在创建它们的实例的方法中声明了类:

Adding a field to test this too. For my test, I just declared the classes inside the method creating their instances:

Dog dog = new Dog("Rex");
Cat cat = new Cat("Felix");

我首先尝试将这些 Java 对象转换为 Lua，使用 LuaValue luaDog = LuaValue.userdataOf(dog); 但它不起作用:我们确实有用户数据，如跟踪所示，但是没有元表，所以我们不能调用方法也不能访问字段.

I first tried to convert these Java objects to Lua, using LuaValue luaDog = LuaValue.userdataOf(dog); but it doesn't work: we indeed have userdata, as shown by the traces, but no metatable, so we cannot call the methods nor access the fields.

找了好久，终于找到了正确的咒语:

After searching a lot, I found out the right incantation:

CompiledScript script = ((Compilable) scriptEngine).compile(reader);
Bindings sb = new SimpleBindings();
script.eval(sb); // Put the Lua functions into the sb environment
LuaValue luaDog = CoerceJavaToLua.coerce(dog); // Java to Lua
LuaFunction onTalk = (LuaFunction) sb.get("onTalk"); // Get Lua function
LuaValue b = onTalk.call(luaDog); // Call the function
System.out.println("onTalk answered: " + b);
LuaFunction onWalk = (LuaFunction) sb.get("onWalk");
LuaValue[] dogs = { luaDog };
Varargs dist = onWalk.invoke(LuaValue.varargsOf(dogs)); // Alternative
System.out.println("onWalk returned: " + dist);

我很欣赏 Luaj API... :-) 可能更适合 Java 程序员，而其他库似乎更多地针对 Lua/C 程序员...

I appreciate the Luaj API... :-) Probably more made for Java programmers while other libraries seem to aim more at Lua / C programmers...

这篇关于如何将对象传递给暴露的 luaj 函数?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！