# Use case:

#

# The purpose of this script is to enable easier switching of the JDK being used as the JAVA_HOME in a CLI process.

#

# There are two ways of running this script:

#

# - Provide the path of the JDK to use.

# - Allow the script to find Azul and Eclipse JDKs using the registry keys on the machine.

#

# This script won't modify the User or Machine environment variables, only the Process environment variables.

# Additionally, because this uses registry keys and modifies Process environment variables this script is only usable

# on Windows. Linux and macOs users should use the tooling available on those OSes to switch the JAVA_HOME for the

# running process.

param(

[Parameter(Mandatory=$false)][string]$JdkPath

)

if (!$IsWindows) {

Write-Error "This script is only usable on Windows."

exit 1

}

if ("" -eq $JdkPath) {

# Use the HKEY_LOCAL_MACHINE registry keys to find JDK installs from Azul and Eclipse.

$registryBase = "HKLM:\SOFTWARE"

$azulJdks = "$registryBase\Azul Systems\Zulu"

$eclipseJdks = "$registryBase\Eclipse Adoptium\JDK"

$eclipseFoundationJdks = "$registryBase\Eclipse Foundation\JDK"

$microsoftJdks = "$registryBase\Microsoft\JDK"

# Collect all available JDK installations in the following format

#

# Option # | <Distributor> | <Major Version> | <Full Version> | <Install Location>

#

# For example

#

# 1 | Zulu | 17 | 17.28.13 | C:\Program Files\Zulu\zulu-17

#

# Then let the caller of the script select which version they want to make the new JAVA_HOME,

# if any version. Choosing not to select a new version will leave the current JAVA_HOME

# unmodified.

[System.Data.DataTable]$jdkOptions = New-Object System.Data.Datatable

[void]$jdkOptions.Columns.Add("Choice")

[void]$jdkOptions.Columns.Add("Distributor")

[void]$jdkOptions.Columns.Add("Major Version")

[void]$jdkOptions.Columns.Add("Full Version")

[void]$jdkOptions.Columns.Add("Install Location")

Write-Host "Searching for JDK installs from Azul and Eclipse"

$choiceNumber = 1

# Azul uses a registry key pattern of

#

# <Install Name> (ex zulu-17)

# - \ <CurrentVersion> (ex 17.28.13)

# <MajorVersion> (ex 17)

# <InstallationPath> (ex C:\Progam Files\Zulu\zulu-17\)

#

# There are additional properties that aren't needed and aren't included above.

#

# Select the installs in the following format

#

# Zulu | <MajorVersion> | <CurrentVersion> | <InstallationPath>

if (Test-Path -Path $azulJdks) {

foreach ($jdk in Get-ChildItem -Path $azulJdks) {

$jdkHKeyPath = $jdk.Name

$values = Get-ItemProperty -Path "Registry::$jdkHKeyPath"

[void]$jdkOptions.Rows.Add($choiceNumber, "Zulu", $values.MajorVersion, $values.CurrentVersion, $values.InstallationPath)

$choiceNumber++

}

}

# Eclipse uses a registry key pattern of

#

# <Current Version> (ex 17.0.4.8)

# - \ <Implementation> (ex hotspot)

# - \ <MSI>

# - \ <Path> (ex C:\Program Files\Eclipse Adoptium\jdk-17.0.4.8-hotspot\)

#

# There are additional properties that aren't needed and aren't included above.

#

# Select the installs in the following format

#

# Eclipse | <First number segment in Current Version> | <Current Version> | <Path>

if (Test-Path -Path $eclipseJdks) {

foreach ($jdk in Get-ChildItem -Path $eclipseJdks) {

$jdkHKeyPath = $jdk.Name

$jdkFullVersion = $jdk.PSChildName

$jdkChoicePath = (Get-ItemProperty -Path "Registry::$jdkHKeyPath\hotspot\MSI").Path

[void]$jdkOptions.Rows.Add($choiceNumber, "Eclipse", $jdkFullVersion.split(".")[0], $jdkFullVersion, $jdkChoicePath)

$choiceNumber++

}

}

if (Test-Path -Path $eclipseFoundationJdks) {

foreach ($jdk in Get-ChildItem -Path $eclipseFoundationJdks) {

$jdkHKeyPath = $jdk.Name

$jdkFullVersion = $jdk.PSChildName

$jdkChoicePath = (Get-ItemProperty -Path "Registry::$jdkHKeyPath\hotspot\MSI").Path

[void]$jdkOptions.Rows.Add($choiceNumber, "Eclipse", $jdkFullVersion.split(".")[0], $jdkFullVersion, $jdkChoicePath)

$choiceNumber++

}

}

# Microsoft uses a registry key pattern of

#

# <Current Version> (ex 17.0.7.7)

# - \ <Implementation> (ex hotspot)

# - \ <MSI>

# - \ <Path> (ex C:\Program Files\Microsoft\jdk-17.0.7.7-hotspot\)

#

# There are additional properties that aren't needed and aren't included above.

#

# Select the installs in the following format

#

# Microsoft | <First number segment in Current Version> | <Current Version> | <Path>

if (Test-Path -Path $microsoftJdks) {

foreach ($jdk in Get-ChildItem -Path $microsoftJdks) {

$jdkHKeyPath = $jdk.Name

$jdkFullVersion = $jdk.PSChildName

$jdkChoicePath = (Get-ItemProperty -Path "Registry::$jdkHKeyPath\hotspot\MSI").Path

[void]$jdkOptions.Rows.Add($choiceNumber, "Microsoft", $jdkFullVersion.split(".")[0], $jdkFullVersion, $jdkChoicePath)

$choiceNumber++

}

}

$choiceNumber--

$selection = $null

while ($null -eq $selection) {

$jdkOptions | Format-Table -AutoSize

$selection = Read-Host "Select the JDK to set (or keep current JDK by entering no option)"

if ($null -ne $selection) {

if ($selection.Trim() -eq "") {

break

}

$selectionNumber = $selection -as [int]

if ($null -eq $selectionNumber -or $selectionNumber -lt 1 -or $selectionNumber -gt $choiceNumber) {

Write-Host "Invalid selection '$selectionNumber', choose a choice from 1 to $choiceNumber"

$selection = $null

} else {

$JdkPath = $jdkOptions.Rows[$selection - 1]["Install Location"]

if ($JdkPath.EndsWith("\")) {

$JdkPath = $JdkPath.Substring(0, $JdkPath.Length - 1)

}

}

}

}

}

if ("" -ne $JdkPath) {

Write-Host "Beginning replacement of process environment variables"

Write-Host "Replacing current JAVA_HOME '$env:JAVA_HOME' with new JAVA_HOME '$JdkPath'"

$env:JAVA_HOME = $JdkPath

Write-Host "Setting '$JdkPath\bin' to the first value in Path"

$env:Path = "$JdkPath\bin;$env:Path"

}