# Libraries

LuaLink provides a way to load external Java libraries for use in your scripts, as well as to define and use embedded Lua libraries.

Lua libraries are almost identical to scripts, but there are a few differences.

• Each Lua library should be placed in a separate folder in the /plugins/LuaLink/libs directory. ^{For example /plugins/LuaLink/libs/example/main.lua will be available as example or example.main.}
• Entry point of a Lua library should be always be a main.lua file.
  ^{Different entry points are still possible however, and can be imported using a . denoted path, for example: require("my_lib.my_entry_point")}
• Lua Libraries are loaded on demand, using the require keyword.
  ^{For example, if we want to use the example library in our script, we can import it using the require("example").}

local Counter = {}

-- Creates a new Counter instance.
function Counter.new()
    return {
        count = 0,

        -- Increments this Counter by 1.
        increment = function(self)
            self.count = self.count + 1
        end,

        -- Decrements this Counter by 1.
        decrement = function(self)
            self.count = self.count - 1
        end,

        -- Returns the current Counter value.
        get = function(self)
            return self.count
        end
    }
end

return Counter

This is a simple Counter class that can be used to increment and decrement a counter.

Now, if we want to use the Counter class in our script, we can import it using the require keyword.

local Counter = require("counter")

-- Creating a new instance of the Counter class.
local counter = Counter:new()
-- Incrementing the counter three times.
counter:increment()
counter:increment()
counter:increment()
-- Decrementing the counter once.
counter:decrement()
-- Printing current value of the counter to the console.
print(counter:get() .. " is the current value.")

[00:00:00 INFO]: [LuaLink/example_script] 2 is the current value.

External Java/Kotlin libraries can be added by configuring the /plugins/LuaLink/libraries.json file. Dependencies will be downloaded and exposed to the scripting runtime after server restart.

{
    // Repositories to be used for dependency resolution.
    "repositories": {
        // Repository definition using simple format.
        "PaperMC": "https://repo.papermc.io/repository/maven-public/",
        // Repository definition with credentials authentication.
        "SomePrivateRepository": {
            "url": "https://repo.example.com/private",
            "username": "RepositoryUsername",
            "password": "SecretRepositoryPassword123"
        }
    },
    // Dependencies to be downloaded and exposed to the scripting runtime.
    // Entries must be specified using Maven coordinate format: groupId:artifactId:version
    "dependencies": [
        "io.papermc:paperlib:1.0.7"
    ]
}

In this example, we are adding PaperLib library of version 1.0.7 from PaperMC repository. You can also see how and authenticate with a private repository using credentials, which might be essential when working with closed-source projects or GitHub Packages.

After restarting the server, we should be able to import and access any class that belongs to specified library(-ies).

local PaperLib = import("io.papermc.lib.PaperLib")

script.logger:info("Is the server running Paper? " .. (PaperLib:isPaper() and "YES" or "NO") .. "!")

[00:00:00 INFO]: [LuaLink/example_script] Is the server running Paper? YES!

While this example may not be the best use of PaperLib - especially because LuaLink requires you to run the plugin on Paper - it is still a good example of how to use external libraries in your scripts.