如何在 powershell 中将哈希表转换为 json 字符串？

我正在尝试将哈希表转换为 json 对象，以便在带有 powershell 2.0 的 Web 服务中使用。

$testhash = @{
    Name = 'John Doe'
    Age = 10
    Amount = 10.1
    MixedItems = (1,2,3,"a")
    NestedHash = @{
        nestedkey = "nextedvalue"
    }
}

function toJson($obj){

    $ms = New-Object IO.MemoryStream
    $type = $obj.getType()
    [Type[]]$types = ($obj | select -expand PsTypeNames |  Select -unique) + [type]'System.Management.Automation.PSObject'
    $js = New-Object System.Runtime.Serialization.Json.DataContractJsonSerializer $type, $types, ([int]::MaxValue), $false, $null, $false
    $js.writeObject($ms, $obj) | out-null
    $utf8.GetString( $ms.ToArray(), 0, $ms.Length )
    $ms.Dispose() | out-null
}

toJson $testhash
'[{"Key":"Name","Value":"John Doe"},{"Key":"Age","Value":10},{"Key":"Amount","Value":10.1},{"Key":"NestedHash","Value":[{"__type":"KeyValuePairOfanyTypeanyType:#System.Collections.Generic","key":"nestedkey","value":"nextedvalue"}]},{"Key":"MixedItems","Value":[1,2,3,"a"]}]'

我在用着DataContractJsonSerializer 构造函数 http://msdn.microsoft.com/en-us/library/bb919563.aspx以某种方式应该抑制类型信息，但显然不是。我也对它提取键和值对感到有趣，但我也不希望它这样做。我究竟做错了什么？

好的，manojlds 回答了 v2，所以我将在这里列出 v3 的等效内容：

PS> @{name="oisin"; age=37} | convertto-json
{
    "age":  37,
    "name":  "oisin"
}

相当干净一点，对吧？

PowerShell 3.0 CTP2：http://www.microsoft.com/download/en/details.aspx?id=27548 http://www.microsoft.com/download/en/details.aspx?id=27548