问题
This question asks how to setup your path variable in Windows to include the Java bin directory allowing you to use the javac command from the prompt. The solution posted to this question states you should hard code the absolute path of the latest Java installation.
In this case it happens to be c:\program files\java\jdk1.6.0_16\bin
I believe once Java update 17, 18 and beyond are installed your javac cmd will still be using this older version, correct?
Am I missing something?? Is there a way to set this to automatically use the most recent installed java update??
回答1:
I believe once Java update 17, 18 and beyond are installed your javac cmd will still be using this older version, correct?
Correct. When java is update, what get's updated is the JRE ( java runtime environment )
That automatically set your java plugin ( used in the browser ) and your java command set to the latest version. ( Open a terminal and type java -version )
The SDK ( Java SDK ) which contains the javac is not changed. You have to do it manually.
One option is do what mhaller says.
I go further using the environment variables in Windows.
MyPC/RigthClick/Properties/Advaced/EnvironmentVariables/
From there I add JAVA_HOME poiting to the desired JDK path ( c:\jsdk_x_x_x ) and set the PATH variable to:
whatever;_it_had;_before;%JAVA_HOME%\bin
Is there a way to set this to automatically use the most recent installed java update??
For the JRE it would be automatically set, for the SDK you'll only need to modify the system variables and change the value of JAVA_HOME
回答2:
Use the variable set by the Java Installer instead:
set path="%path%;%JAVA_HOME%\bin"
回答3:
The following Powershell script works very well for this:
Remove-PathFolders -Folders "*\Java\jdk*" -EnvironmentVariableTarget $([System.EnvironmentVariableTarget]::Machine)
$jdkDp = (Get-ChildItem -Path "C:\Program Files (x86)\Java\jdk*" | Sort-Object name | Select-Object -Last 1).FullName
Add-PathFolders -Folders $($jdkDp + "\bin\") -EnvironmentVariableTarget $([System.EnvironmentVariableTarget]::Machine)
Get-PathFolders -EnvironmentVariableTarget $([System.EnvironmentVariableTarget]::Machine)
Which use the following custom functions inspired from here (you can include everything in the same UpdateJavaPath.ps1 script):
<#
.SYNOPSIS
Gets the list of folders specified in the Path environment variable.
.PARAMETER EnvironmentVariableTarget
Specifies the "scope" to use when querying the Path environment variable
("Process", "Machine", or "User"). Defaults to "Process" if the parameter is
not specified.
.EXAMPLE
.\Get-PathFolders.ps1
C:\Windows\system32\WindowsPowerShell\v1.0\
C:\Windows\system32
C:\Windows
C:\Windows\System32\Wbem
...
Description
-----------
The output from this example lists each folder in the Path environment variable
for the current process.
.EXAMPLE
.\Get-PathFolders.ps1 User
C:\NotBackedUp\Public\Toolbox
Description
-----------
The output from this example assumes one folder
("C:\NotBackedUp\Public\Toolbox") has previously been added to the user's Path
environment variable.
#>
Function Get-PathFolders() {
param(
[string] $EnvironmentVariableTarget = "Process")
Set-StrictMode -Version Latest
$ErrorActionPreference = "Stop"
[string[]] $pathFolders = [Environment]::GetEnvironmentVariable(
"Path",
$EnvironmentVariableTarget) -Split ";"
If ($pathFolders -ne $null)
{
Write-Output $pathFolders
}
}
<#
.SYNOPSIS
Adds one or more folders to the Path environment variable.
.PARAMETER Folders
Specifies the folders to add to the Path environment variable..
.PARAMETER EnvironmentVariableTarget
Specifies the "scope" to use for the Path environment variable ("Process",
"Machine", or "User"). Defaults to "Process" if the parameter is not specified.
.EXAMPLE
.\Add-PathFolders.ps1 C:\NotBackedUp\Public\Toolbox
#>
Function Add-PathFolders() {
param(
[parameter(Mandatory = $true, ValueFromPipeline = $true)]
[string[]] $Folders,
[string] $EnvironmentVariableTarget = "Process")
begin
{
Set-StrictMode -Version Latest
$ErrorActionPreference = "Stop"
Write-Verbose "Path environment variable target: $EnvironmentVariableTarget"
[bool] $isInputFromPipeline =
($PSBoundParameters.ContainsKey("Folders") -eq $false)
[int] $foldersAdded = 0
[string[]] $pathFolders = [Environment]::GetEnvironmentVariable(
"Path",
$EnvironmentVariableTarget) -Split ";"
[Collections.ArrayList] $folderList = New-Object Collections.ArrayList
$pathFolders | foreach {
$folderList.Add($_) | Out-Null
}
}
process
{
If ($isInputFromPipeline -eq $true)
{
$items = $_
}
Else
{
$items = $Folders
}
$items | foreach {
[string] $folder = $_
[bool] $isFolderInList = $false
$folderList | foreach {
If ([string]::Compare($_, $folder, $true) -eq 0)
{
Write-Verbose ("The folder ($folder) is already included" `
+ " in the Path environment variable.")
$isFolderInList = $true
return
}
}
If ($isFolderInList -eq $false)
{
Write-Verbose ("Adding folder ($folder) to Path environment" `
+ " variable...")
$folderList.Add($folder) | Out-Null
$foldersAdded++
}
}
}
end
{
If ($foldersAdded -eq 0)
{
Write-Verbose ("No changes to the Path environment variable are" `
+ " necessary.")
return
}
[string] $delimitedFolders = $folderList -Join ";"
[Environment]::SetEnvironmentVariable(
"Path",
$delimitedFolders,
$EnvironmentVariableTarget)
Write-Verbose ("Successfully added $foldersAdded folder(s) to Path" `
+ " environment variable.")
}
}
<#
.SYNOPSIS
Removes one or more folders from the Path environment variable.
.PARAMETER Folders
Specifies the folders to remove from the Path environment variable..
.PARAMETER EnvironmentVariableTarget
Specifies the "scope" to use for the Path environment variable ("Process",
"Machine", or "User"). Defaults to "Process" if the parameter is not specified.
.EXAMPLE
.\Remove-PathFolders.ps1 C:\NotBackedUp\Public\Toolbox
#>
Function Remove-PathFolders(){
param(
[parameter(Mandatory = $true, ValueFromPipeline = $true)]
[string[]] $Folders,
[string] $EnvironmentVariableTarget = "Process")
begin
{
Set-StrictMode -Version Latest
$ErrorActionPreference = "Stop"
Write-Verbose "Path environment variable target: $EnvironmentVariableTarget"
[bool] $isInputFromPipeline =
($PSBoundParameters.ContainsKey("Folders") -eq $false)
[int] $foldersRemoved = 0
[string[]] $pathFolders = [Environment]::GetEnvironmentVariable(
"Path",
$EnvironmentVariableTarget) -Split ";"
[Collections.ArrayList] $folderList = New-Object Collections.ArrayList
$pathFolders | foreach {
$folderList.Add($_) | Out-Null
}
}
process
{
If ($isInputFromPipeline -eq $true)
{
$items = $_
}
Else
{
$items = $Folders
}
$items | foreach {
[string] $folder = $_
[bool] $isFolderInList = $false
for ([int] $i = 0; $i -lt $folderList.Count; $i++)
{
#If ([string]::Compare($folderList[$i], $folder, $true) -eq 0)
if (($folderList[$i] -like $folder) -or ($folderList[$i] -eq ""))
{
$isFolderInList = $true
Write-Verbose ("Removing folder ($folderList[$i]) from Path" `
+ " environment variable...")
$folderList.RemoveAt($i)
$i--
$foldersRemoved++
}
}
If ($isFolderInList -eq $false)
{
Write-Verbose ("The folder ($folder) is not specified in the Path" `
+ " list.")
}
}
}
end
{
If ($foldersRemoved -eq 0)
{
Write-Verbose ("No changes to the Path environment variable are" `
+ " necessary.")
return
}
[string] $delimitedFolders = $folderList -Join ";"
[Environment]::SetEnvironmentVariable(
"Path",
$delimitedFolders,
$EnvironmentVariableTarget)
Write-Verbose ("Successfully removed $foldersRemoved folder(s) from Path" `
+ " environment variable.")
}
}
来源：https://stackoverflow.com/questions/1690815/update-windows-path-variable-when-java-is-updated-automatically