Java-Side Modules

To understand the following, you are expected to know how Lua's require works.

Classpath Lua Modules

With Java, in many cases you put your resources on the classpath, which may be a path accessible to Lua, or one lying in a JAR.

Of course, it is possible to load any Lua files manually by Class::getResourceAsStream and then reading it into a (direct) buffer and then Lua::load(buffer, name).

Alternatively, we provide a ClassPathLoader. One just initializes the Lua state by setting a external loader, and then they can forget about the Java side classpath and just require any classpath Lua modules from Lua.

For more flexibility, just extend ClassPathLoader or write your own ExternalLoader.

Java Side

try (Lua L = new Lua51()) {
    L.openLibrary("package");
    L.setExternalLoader(new ClassPathLoader());
}

Lua Side

-- Loads classpath:/luajava/luajava-compat.lua
local luajava = require('suite.luajava-compat')

Java Method Modules

This provides an approach to loading libraries written in Java, similar to Lua's package.loadlib. It does the following:

1. Split the module name by the last dot (.) into FullyQualifiedClassName.staticMethodName.
   • The method is expected to be of the form public static int method(Lua L);. See the Javadoc of JFunction for more info.
2. Call java.loadlib to encapsulate the Java static method into a C function to be used in Lua.
3. We leave the rest to Lua's require:
   • require calls the loader with two arguments: modname and an extra value.
   • The extra value is nil for LuaJava.

Java Library

package party.iroiro.luajava.docs;

import party.iroiro.luajava.Lua;

@SuppressWarnings("unused")
public class JavaSideExampleModule {
    public static int open(Lua L) {
L.createTable(0, 1);
L.push(l -> {
    l.push(1024);
    return 1;
});
L.setField(-2, "getNumber");
return 1;
    }
}

Java Side

try (Lua L = new Lua51()) {
    L.openLibrary("package");
    L.run("local LuaLib = require('party.iroiro.luajava.docs.JavaSideExampleModule.open');" +
    "assert(1024 == LuaLib.getNumber())");
}

Lua Side

local LuaLibOpen = java.loadlib('party.iroiro.luajava.docs.JavaSideExampleModule', 'open')
assert(1024 == LuaLibOpen().getNumber())

Binary Modules

Lua supports dynamically loading binary libraries, which utilizes Lua C API to interact with Lua runtime. A binary library, by its nature, is hardly portable and might not even work across Lua versions. To load binary modules, you will need to invoke LuaNative#loadAsGlobal manually. See Using Binary Lua Libraries for more info.