如何在 Java 应用程序中在 Android 上运行 Lua 脚本？

Question

我正在用 Java 开发一个使用 Lua 脚本的 Android 游戏。为了执行这些脚本，我将 LuaJ 与 Java 的 ScriptEngine 类一起使用。比如……

ScriptEngineManager sem = new ScriptEngineManager();
scriptEngine = sem.getEngineByExtension(".lua");
script = ((Compilable)scriptEngine).compile("some lua here");

但是，这显然在 Android 上不受支持（这与 android 没有完整的 JVM 有关，我在某处读到过）。有没有办法可以在 Android 上使用 Lua 脚本？也许有一个 LuaJ 替代品？也许有一种方法可以直接使用 LuaJ 编译和执行 Lua 脚本（虽然我不知道如何）。

仅供参考，当我尝试在 Android 上运行此代码时看到此错误：

05-06 16:12:32.870: E/dalvikvm(17509): Could not find class 'javax.script.ScriptEngineManager', referenced from method unearth.levels.LevelReader.<init>
05-06 16:12:32.870: W/dalvikvm(17509): VFY: unable to resolve new-instance 787 (Ljavax/script/ScriptEngineManager;) in Lunearth/levels/LevelReader;
05-06 16:12:32.870: D/dalvikvm(17509): VFY: replacing opcode 0x22 at 0x0018
05-06 16:12:32.875: E/dalvikvm(17509): Could not find class 'javax.script.Compilable', referenced from method unearth.levels.LevelReader.parseScript
05-06 16:12:32.875: W/dalvikvm(17509): VFY: unable to resolve check-cast 782 (Ljavax/script/Compilable;) in Lunearth/levels/LevelReader;
05-06 16:12:32.875: D/dalvikvm(17509): VFY: replacing opcode 0x1f at 0x0047
05-06 16:12:32.875: W/dalvikvm(17509): VFY: unable to resolve exception class 788 (Ljavax/script/ScriptException;)
05-06 16:12:32.875: W/dalvikvm(17509): VFY: unable to find exception handler at addr 0x51
05-06 16:12:32.875: W/dalvikvm(17509): VFY:  rejected Lunearth/levels/LevelReader;.parseScript (Lorg/w3c/dom/Element;Lunearth/levels/Level;)V
05-06 16:12:32.875: W/dalvikvm(17509): VFY:  rejecting opcode 0x0d at 0x0051
05-06 16:12:32.875: W/dalvikvm(17509): VFY:  rejected Lunearth/levels/LevelReader;.parseScript (Lorg/w3c/dom/Element;Lunearth/levels/Level;)V
05-06 16:12:32.875: W/dalvikvm(17509): Verifier rejected class Lunearth/levels/LevelReader;
05-06 16:12:32.890: W/dalvikvm(17509): threadid=11: thread exiting with uncaught exception (group=0x40c331f8)
05-06 16:12:32.895: E/AndroidRuntime(17509): FATAL EXCEPTION: GLThread 1062
05-06 16:12:32.895: E/AndroidRuntime(17509): java.lang.VerifyError: unearth/levels/LevelReader
05-06 16:12:32.895: E/AndroidRuntime(17509):    at unearth.Game.startGame(Game.java:201)
05-06 16:12:32.895: E/AndroidRuntime(17509):    at unearth.Game.update(Game.java:713)
05-06 16:12:32.895: E/AndroidRuntime(17509):    at unearth.screens.LoadScreen.update(LoadScreen.java:56)
05-06 16:12:32.895: E/AndroidRuntime(17509):    at unearth.UnearthListener.render(UnearthListener.java:71)
05-06 16:12:32.895: E/AndroidRuntime(17509):    at com.badlogic.gdx.backends.android.AndroidGraphics.onDrawFrame(AndroidGraphics.java:423)
05-06 16:12:32.895: E/AndroidRuntime(17509):    at android.opengl.GLSurfaceView$GLThread.guardedRun(GLSurfaceView.java:1462)
05-06 16:12:32.895: E/AndroidRuntime(17509):    at android.opengl.GLSurfaceView$GLThread.run(GLSurfaceView.java:1216)
05-06 16:12:58.600: D/dalvikvm(17509): GC_CONCURRENT freed 334K, 3% free 16196K/16647K, paused 2ms+6ms

更新：

也许这个项目有一些有用的代码？ http://code.google.com/p/android-scripting/

Answer 1

我找到了在 Android 上使用 LuaJ 的方法！ :-)

关键是直接使用 LuaJ API，而不是通过javax.script。由于没有教程，这有点棘手，所以这里有一个前后，这样其他人就不必通过 LuaJ 源代码和 JavaDoc 来挑选。我真的希望这对某人有所帮助，因为它让我发疯了！

注意：“secretgame”不是我游戏的实际名称；-)

之后：

package secretgame.scripting;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;

import org.luaj.vm2.LuaClosure;
import org.luaj.vm2.LuaTable;
import org.luaj.vm2.LuaValue;
import org.luaj.vm2.Prototype;
import org.luaj.vm2.compiler.LuaC;
import org.luaj.vm2.lib.jse.CoerceJavaToLua;
import org.luaj.vm2.lib.jse.JsePlatform;

import secretgame.SecretGameException;
import secretgame.events.EventArgs;
import secretgame.levels.Level;

public class DirectLuaj implements Lua
{
  private final Level level;
  private final ScriptTools scriptTools;
  private final ScriptEvents scriptEvents;
  private int nextId = 0;
  private ArrayList<LuaClosure> scripts = new ArrayList<LuaClosure>();

  public DirectLuaj(Level level, ScriptTools scriptTools,
      ScriptEvents scriptEvents)
  {
    this.level = level;
    this.scriptTools = scriptTools;
    this.scriptEvents = scriptEvents;
  }

  @Override
  public int add(String scriptText) throws SecretGameException
  {
    try {
      InputStream input = new ByteArrayInputStream(scriptText.getBytes());
      Prototype p = LuaC.compile(input, "script");
      LuaValue g = JsePlatform.standardGlobals();
      LuaClosure c = new LuaClosure(p, g);
      scripts.add(c);
    }
    catch (IOException e) {
      throw new SecretGameException("compile failed", e);
    }

    return nextId++;
  }

  @Override
  public void run(int id, EventArgs args) throws SecretGameException
  {
    LuaClosure script = scripts.get(id);

    LuaTable bindings = new LuaTable();

    bindings.set("java", toLua(scriptTools));
    bindings.set("level", toLua(level));
    bindings.set("args", toLua(args));
    bindings.set("events", toLua(scriptEvents));

    script.setfenv(bindings);

    script.call();
  }

  private LuaValue toLua(Object javaValue) {
    return javaValue == null? LuaValue.NIL:
            javaValue instanceof LuaValue? (LuaValue) javaValue:
            CoerceJavaToLua.coerce(javaValue);
  }
}

之前：

package secretgame.scripting;

import java.util.ArrayList;

import javax.script.Bindings;
import javax.script.Compilable;
import javax.script.CompiledScript;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

import secretgame.SecretGameException;
import secretgame.events.EventArgs;
import secretgame.levels.Level;

// sadly this won't work on Android because there's no such thing
// as javax.script in Dalvik ... dumb Android java :|
public class JavaxScriptingLua implements Lua
{
  private ScriptEngine scriptEngine;
  private final Level level;
  private final ScriptTools scriptTools;
  private final ScriptEvents scriptEvents;
  private int nextId = 0;
  private ArrayList<CompiledScript> scripts = new ArrayList<CompiledScript>();

  public JavaxScriptingLua(Level level, ScriptTools scriptTools, ScriptEvents scriptEvents)
  {
    this.level = level;
    this.scriptTools = scriptTools;
    this.scriptEvents = scriptEvents;

    ScriptEngineManager sem = new ScriptEngineManager();
    scriptEngine = sem.getEngineByExtension(".lua");
  }

  public int add(String scriptText) throws SecretGameException
  {
    try {
      CompiledScript script = ((Compilable)scriptEngine).compile(scriptText);
      scripts.add(script);
    }
    catch (ScriptException e) {
      throw new SecretGameException("could not compile lua.", e);
    }

    return nextId++;
  }

  public void run(int id, EventArgs args) throws SecretGameException
  {    
    Bindings bindings = scriptEngine.createBindings();

    bindings.put("java", scriptTools);
    bindings.put("level", level);
    bindings.put("args", args);
    bindings.put("events", scriptEvents);

    try {
      scripts.get(id).eval(bindings);
    }
    catch (ScriptException e) {
      throw new SecretGameException("could not run script.", e);
    }
  }
}

Answer 2

除了 LuaJ，您还可以（也）将 LuaJava 与使用 NDK 为 Android 编译的 Lua 一起使用。这允许 Lua 完全访问 Java 中可用的任何内容。查看this example 了解如何开始。

Lua 5.1.4 + LuaJava 编译后在libs 目录（单个libluajava.so 文件）中提供，如果您不想摆弄NDK，但无论如何设置相对容易。

Answer 3

要在 Android 上使用 Lua，您可以使用 JNLua + Lua 5.2（用 C 实现）。唯一支持 JSR 223 (javax.script) 的 Android 端口在这里：https://github.com/danke-sra/jnlua-android

使用这个端口，你可以做你想做的事：

ScriptEngine scriptEngine = new LuaScriptEngineFactory().getEngine(); scriptEngine.eval("lua statements");

Answer 4

但是，Android 显然不支持此功能

正确。

与 android 没有完整的 JVM 有关，我在某处读到

正确。如果您查看the JavaDocs，您会发现Android SDK 中不存在javax.script。

也许我会尝试一下：https://github.com/damonkohler/sl4a

这是一种选择。另一种方法是通过 NDK 将 Lua 解释器嵌入到您的应用中，如 this sample application。