Java

Java downloads and manages the Java Runtime Environment required to run Minecraft. In most cases, you do not need to use this class directly — when java.install is set to 'auto' (the default), Launcher handles Java automatically as part of the launch pipeline.

Use Java directly if you want to pre-download Java before the player hits the Play button, or if you need to verify an existing Java installation.

import { Java } from 'eml-lib'

downloadJava()

async function downloadJava() {
  const java = new Java({
    url: 'https://at.myserver.com',
    root: 'myserver',
    minecraft: { version: '1.21.1' }
  })

  java.on('download_progress', (p) => console.log(`Downloading Java: ${p.downloaded.amount}/${p.total.amount}`))

  await java.download()
}

Constructor

Parameter	Type	Description	Required?
config.root	string	Name of the root game directory, without a leading dot.	Yes
config.url	string	URL of your EML AdminTool instance or manifest. Used to resolve the Minecraft version if config.minecraft.version is not set.	No
config.minecraft.version	string	The Minecraft version to install Java for. Supports 'latest_release' and 'latest_snapshot'. If omitted, the version is fetched from the url.	No

getFiles() method

Returns the list of Java files that need to be downloaded for the target Minecraft version, without downloading them.

Parameter	Type	Description	Required?
manifest	MinecraftManifest	A pre-fetched Minecraft version manifest. If omitted, the manifest is fetched automatically.	No

Returns: Promise<File[]>

Throws: FETCH_ERROR — If the manifest cannot be fetched.

download() method

Downloads the Java runtime for the target Minecraft version.

Returns: Promise<void>

Throws: DOWNLOAD_ERROR — If a file download fails.

Emits: download_progress — A Java file is downloading. • download_error — A download failed. • download_end — All Java files have been downloaded.

check() method

Verifies that a Java executable is correctly installed and matches the required major version.

Parameter	Type	Description	Required?
absolutePath	string	Absolute path to the Java executable. Use ${X} as a placeholder for the major version number.	No (defaults to the path managed by EML Lib)
majorVersion	number	The required Java major version.	No (defaults to 8)

Returns: Promise<{ version: string, arch: '64-bit' | '32-bit' }>

Throws: JAVA_ERROR — If the executable is not found, cannot be run, or does not match the required major version.