问题

我正在尝试在 Packer 实例上使用 PowerShell 的 Invoke-WebRequest 命令安装 Java，然而，我遇到了以下错误；

```powershell
无法索引空数组。
在第1行第94个字符处：+ ... content | %{[regex]::matches($_, ''(?:<a title="Download Java software ...
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : NullArray

命令：

[Net.ServicePointManager]::SecurityProtocol = 'tls12'

$URL = (Invoke-WebRequest -UseBasicParsing https://www.java.com/en/download/manual.jsp).Content | %{[regex]::matches($_, ''(?:<a title="Download Java software for Windows .64-bit." href=")(.*)(?:">)').Groups[1].Value}

Invoke-WebRequest -UseBasicParsing -OutFile jre8.exe $URL

Start-Process .\jre8.exe '/s REBOOT=0 SPONSORS=0 AUTO_UPDATE=0' -wait

几周前我能够成功运行它，但是从昨天开始出现了上述错误。
有什么建议吗？

谢谢。

<details>
<summary>英文:</summary>

I am trying to install java using powershell Invoke-WebRequest command on packer instance however, I am getting below error;

Cannot index into a null array.
At line:1 char:94

• ... content | %{[regex]::matches($_, '(?:<a title="Download Java software ...

•             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  

  • CategoryInfo : InvalidOperation: (:) [], RuntimeException
  • FullyQualifiedErrorId : NullArray

Command;

`[Net.ServicePointManager]::SecurityProtocol = "tls12"`

`$URL = (Invoke-WebRequest -UseBasicParsing https://www.java.com/en/download/manual.jsp).Content | %{[regex]::matches($_, '(?:<a title="Download Java software for Windows .64-bit." href=")(.*)(?:">)').Groups[1].Value}`

`Invoke-WebRequest -UseBasicParsing -OutFile jre8.exe $URL`

`Start-Process .\jre8.exe '/s REBOOT=0 SPONSORS=0 AUTO_UPDATE=0' -wait`

Few weeks ago I was able to run it successfully but since yesterday getting the above error.
Any advise?

Thanks.

</details>


# 答案1
**得分**: 2

这是因为在网页上并不存在类似于“Download Java software for Windows”的字符串。由于正则表达式没有匹配到任何内容，“Groups”成员也不存在，所以当尝试索引一个不存在的成员时会出现错误。

你可以使用浏览器的“查看源代码”命令，或者将内容保存到文本文件中，然后像这样使用记事本查看：

    $cc = (Invoke-WebRequest -UseBasicParsing https://www.java.com/en/download/manual.jsp).Content
    Set-Content -Path c:\temp\javapage.txt -Value $cc
    notepad c:\temp\javapage.txt

该页面加载了大量的Javascript代码，用于生成在浏览器中看到的实际页面。

<details>
<summary>英文:</summary>

This happens, as there is no such as string as `Download Java software for Windows` on the web page. Since the regex doesn&#39;t match anything, `Groups` member doesn&#39;t exist and you&#39;ll get an error about trying to index into a non-existing member.

Either use a web browser&#39;s View Source command, or save the content on a text file and view it with Notepad like so,

    $cc = (Invoke-WebRequest -UseBasicParsing https://www.java.com/en/download/manual.jsp).Content
    Set-Content -Path c:\temp\javapage.txt -Value $cc
    notepad c:\temp\javapage.txt

The page loads a bunch of Javascript that generates the actual page seen on a browser.

</details>