Getting Started with LuaJ

Copyright © 2009-2010 Luaj.org. Freely available under the terms of the Luaj license.

introduction · examples · concepts · libraries · building · downloads · release notes

This is an alpha release for a luaj 2.0. The most recent stable release is 1.0.3

1 - Introduction

Goals of Luaj

• Java-centric implementation built to use Java features like garbage collection, and class dispatch.
• Lightweight to allow for small, fast interpretation of lua bytecode.
• Complete set of libraries and tools for integration into real-world projects.
• Multi-platform to be able to run on JME, JSE, or JEE environments.
• Dependable due to sufficient unit testing of vm and library features.

Differences with 1.0

• Support for compiling lua into Java off-line for JME, and at runtime for JSE.
• Fastest possible bytecode processing for interpreted code.
• More alignment with C API (see names.csv for details)
• Improved class and package naming conventions.
• Improved unit tests of core classes.

2 - Simple Examples

Run a script in Java SE

From the main distribution directory line type:

	java -cp lib/luaj-jse-2.0-alpha1.jar lua examples/lua/hello.lua

You should see the following output:

	hello, world

Compile a script to lua bytecode

From the main distribution directory line type:

	java -cp lib/luaj-jse-2.0-alpha1.jar luac examples/lua/hello.lua
	java -cp lib/luaj-jse-2.0-alpha1.jar lua luac.out

The compiled output "luac.out" is lua bytecode and should run and produce the same result.

Compile a script to java bytecode

Luaj can compile to lua bytecode if the bcel library is on the class path. From the main distribution directory line type:

	ant bcel-lib
	java -cp lib/luaj-jse-2.0-alpha1.jar;lib/bcel-5.2.jar luajc -s examples/lua -d . hello.lua
	java -cp lib/luaj-jse-2.0-alpha1.jar;. lua -l hello

The output hello.class is Java bytecode, should run and produce the same result. There is no runtime dependency on the bcel library, but the compiled classes must be in the class path.

Run a script in a Java Application

The following pattern is used within Java SE

	import org.luaj.vm2.*;
	import org.luaj.vm2.lib.*;

	String script = "examples/lua/hello.lua";
	LuaValue _G = JsePlatform.standardGlobals();
	_G.get("dofile").call( LuaValue.valueOf(script) );

A simple example may be found in

	examples/jse/SampleJseMain.java

You must include the library lib/luaj-jse-2.0-alpha1.jar in your class path.

Run a script in a MIDlet

The for MIDlets the JmePlatform is used instead:

	import org.luaj.vm2.*;
	import org.luaj.vm2.lib.*;

	String script = "examples/lua/hello.lua";
	LuaValue _G = JmePlatform.standardGlobals();
	_G.get("dofile").call( LuaValue.valueOf(script) );

The file must be a resource within within the midlet jar for dofile() to find it. Any files included via require() must also be part of the midlet resources.

A simple example may be found in

	examples/jme/SampleMIDlet.java

You must include the library lib/luaj-jme-2.0-alpha1.jar in your midlet jar.

An ant script to build and run the midlet is in

	build-midlet.xml

You must install the wireless toolkit and define WTK_HOME for this script to work.

Excluding the lua bytecode compiler

To exclude the lua-to-lua-bytecode compiler, do not call standardGlobals() or debugGlobals() but instead initialize globals with including only those libraries that are needed and omitting the line:

	org.luaj.vm2.compiler.LuaC.install();

Including the lua-to-Java-bytecode compiler

To compile from lua to Java bytecode for all lua loaded at runtime, install the LuaJC compiler after globals have been created using:

	org.luaj.vm2.jse.luajc.LuaJC.install();

This will compile all lua bytecode into Java bytecode, regardless of if they are loaded as lua source or lua binary files.

The bcel library must be on the class path for this to work.

Run a script using JSR-233 Dynamic Scripting

The standard use of JSR-233 scripting engines may be used:

	ScriptEngineManager mgr = new ScriptEngineManager();
	ScriptEngine e = mgr.getEngineByExtension(".lua");
	e.put("x", 25);
	e.eval("y = math.sqrt(x)");
	System.out.println( "y="+e.get("y") );

All standard aspects of script engines including compiled statements should be supported.

You must include the library lib/luaj-jse-2.0-alpha1.jar in your class path.

A working example may be found in

	examples/jse/ScriptEngineSample.java

3 - Concepts

Globals

JsePlatform

JmePlatform

4 - Libraries

Standard Libraries

The following libraries are loaded in py both JsePlatform.standardGlobals() and JmePlatform.standardGlobals():

	base
	coroutine
	io
	math
	os
	package
	string
	table

The JsePlatform.standardGlobals() globals also include:

           
	luajava 

The JsePlatform.debugGlobals() and JsePlatform.debugGlobals() functions produce globals that include:

           
	debug

I/O Library

The JmePlatform.standardGlobals() instantiated the io library io in

	src/jme/org/luaj/vm2/lib/jme/JmeIoLib.java

	src/jse/org/luaj/vm2/lib/jse/JseIoLib.java

OS Library

The basic os library implementation us used by JmePlatform and is in:

	src/core/org/luaj/lib/OsLib.java

	src/jse/org/luaj/vm2/lib/jse/JseOsLib.java

Debug Library

	require 'org.luaj.vm2.lib.DebugLib'

The Luajava Library

The following lua script will open a swiing frame on Java SE:

	jframe = luajava.bindClass( "javax.swing.JFrame" )
	frame = luajava.newInstance( "javax.swing.JFrame", "Texts" );
	frame:setDefaultCloseOperation(jframe.EXIT_ON_CLOSE)
	frame:setSize(300,400)
	frame:setVisible(true)

See a longer sample in src/test/res/swingapp.lua for details, or try running it using:

	java -cp lib/luaj-jse-2.0-alpha1.jar lua src/test/res/swingapp.lua

The Java ME platform does not include this library, and it cannot be made to work because of the lack of a reflection API in Java SE.

The lua connand line tool includes luajava.

5 - Building and Testing

Building the jars

Other targets exist for creating distribution file an measuring code coverage of unit tests.

Unit tests

The main luaj JUnit tests are organized into a JUnit 3 suite:

	test/junit/org/luaj/vm2/AllTests.lua

Unit test scripts can be found in these locations

	test/lua/*.lua
	test/junit/org/luaj/vm2/compiler/lua5.1-tests.zip
	test/junit/org/luaj/vm2/compiler/regressions.zip
	test/junit/org/luaj/vm2/vm1/luajvm1-tests.zip

Code coverage

A build script for running unit tests and producing code coverage statistics is in

	build-coverage.xml

6 - Downloads

Downloads and Project Pages

	SourceForge Luaj Project Page
	SourceForge Luaj Download Area

and LuaForge:

	LuaForge Luaj Project Page
	LuaForge Luaj Project Area

7 - Release Notes

Main Changes by Version