Class JavaService

Namespace

McServerLauncher.Services

Assembly

McServerLauncher.dll

Detects the machine's Java installations and, if needed, downloads the right version (Adoptium Temurin) for a specific Minecraft version. Works on Windows and Linux.

public class JavaService

Inheritance

object

JavaService

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Methods

AcceptsFlags(string, IReadOnlyList<string>)

Whether this Java starts with flags: java <flags> -version exits cleanly.

public bool AcceptsFlags(string javaExe, IReadOnlyList<string> flags)

Parameters

javaExe string

flags IReadOnlyList<string>

Returns

bool

Remarks

A JVM refuses to start at all over an option it does not know, or one that needs an unlock flag it was not given. The memory profile only uses options that are final in the versions it gives them to, but a vendor build can still differ, and the price of being wrong is a server that does not start. Asking costs one short JVM run per Java and set of flags; the answer is remembered against the file like the version is, and for a bare "java" for as long as the app runs.

DetectInstalled()

Searches for the java executable in common locations and returns their versions.

public List<JavaService.JavaInstall> DetectInstalled()

Returns

List<JavaService.JavaInstall>

EnsureJavaAsync(int, IProgress<string>?, CancellationToken)

Returns the path to a java executable compatible with the required version. If none is installed, downloads and installs the matching Temurin. Throws if it can't.

public Task<string> EnsureJavaAsync(int requiredMajor, IProgress<string>? log, CancellationToken ct = default)

Parameters

requiredMajor int

log IProgress<string>

ct CancellationToken

Returns

Task<string>

GetGameVersionFromJar(string)

Reads the Minecraft version a server.jar belongs to (modern vanilla jars include it in version.json as "id"). Returns null if it can't be determined.

public string? GetGameVersionFromJar(string jarPath)

Parameters

jarPath string

Returns

string

GetMajorVersion(string)

The major version (8, 17, 21, 25...) of a Java executable. 0 on failure.

public int GetMajorVersion(string javaExe)

Parameters

javaExe string

Returns

int

GetRequiredJavaFromForgeLibraries(string, string?)

Reads the required Java for a modern Forge server, which has no runnable server.jar of its own (it launches through an @args-file, so GetRequiredJavaFromJar(string) on the configured jar path always fails): the Forge installer keeps the vanilla server jar under "libraries/net/minecraft/server/<version>/", and that jar carries the usual version.json. Prefers the folder matching gameVersion (a leftover from a previous Minecraft version could linger after an upgrade), then tries any other. Returns null if no readable jar is found.

public int? GetRequiredJavaFromForgeLibraries(string serverFolder, string? gameVersion)

Parameters

serverFolder string

gameVersion string

Returns

int?

GetRequiredJavaFromJar(string)

Reads the Java a server.jar needs (modern versions include it in version.json). Returns null if it can't be determined (very old servers or non-standard jars).

public int? GetRequiredJavaFromJar(string jarPath)

Parameters

jarPath string

Returns

int?

GetRuntime(string)

The version, VM and word size of a Java executable. Unknown on failure.

public JavaService.JavaRuntime GetRuntime(string javaExe)

Parameters

javaExe string

Returns

JavaService.JavaRuntime

Remarks

Asking means starting a JVM, a fraction of a second to more than one on a slow disk, and it was asked twice on every start — once to check the Java and again to build the command line — on the UI thread, and once per JDK found when a server was created. The answer only changes when the file does, so it is remembered against the file's size and write time; a Java updated in place is asked again.

A bare "java" resolved through the PATH has no file to stamp and is not remembered.

IsCompatible(int, int)

An installed Java version is valid for the required one (exact, or newer if 17+).

public static bool IsCompatible(int installed, int required)

Parameters

installed int

required int

Returns

bool

Remarks

One exception, for Java 16 — what Mojang declares for Minecraft 1.17 and 1.17.1. Adoptium publishes no Java 16 at all, so if 17 did not count, a 1.17 server could neither use the Java 17 already on the machine nor download a 16, and would not start without a Java installed by hand. 17 runs those versions; anything later is not promised to.