ConvertFrom-Excel-To-Json.ps1

function Get-ExcelData([parameter(Mandatory=$true, ValueFromPipeline=$true)]$files, [switch]$withHeader) {

	function Get-ExcelData-Header([ref]$rowsRef) {
		if (($withHeader) -and ($rowsRef.Value.Count -gt 0)) {
			$row = $rowsRef.Value.item(1)
			try {
				$columns = $row.columns
				try {
					for ($c = 1; $c -le $columns.Count; ++$c) {
						$col = $columns.item($c)
						try {
							$col.Text
						}
						finally {
							[Runtime.Interopservices.Marshal]::ReleaseComObject($col) | out-null
						}
					}
				}
				finally {
					[Runtime.Interopservices.Marshal]::ReleaseComObject($columns) | out-null
				}
			}
			finally {
				[Runtime.Interopservices.Marshal]::ReleaseComObject($row) | out-null
			}
		}
		else {
			@()
		}
	}

	function Get-ExcelData-Values([ref]$rowsRef) {
		$fromIndex = if($withHeader) {2} else {1}

		if ($rowsRef.Value.count -gt $fromIndex) {
			for ($r = $fromIndex; $r -le $rowsRef.Value.count; ++$r) {
				$row = $rowsRef.Value.item($r)
				$columns = $row.Columns
				try {
					$values = for ($c = 1; $c -le $columns.Count; ++$c) {
						$col = $columns.item($c)
						try {
							$col.Value()
						}
						finally {
							[Runtime.Interopservices.Marshal]::ReleaseComObject($col) | out-null
						}
					}
				}
				finally {
					[Runtime.Interopservices.Marshal]::ReleaseComObject($columns) | out-null
					[Runtime.Interopservices.Marshal]::ReleaseComObject($row) | out-null
				}

				(,$values)
			}
		}
		else {
			@()
		}
	}


	$excel = New-Object -ComObject Excel.Application
	$excel.Visible = $false
	try {
		$workBooks = $excel.Workbooks
		try {
			([array]$results) += foreach ($path in $files) {
				$fileName = (new-object IO.FileInfo $path).baseName
				$workBook = $workBooks.Open($path)
				try {
					$sheets = $workBook.workSheets
					try {
						$sheetCount = $sheets.Count
						for ($i = 1; $i -le $sheetCount; ++$i) {
							$sheet = $sheets.item($i)
							$range = $sheet.usedRange
							$rows = $range.rows
							try {
								new-object PSObject -property @{ 
									file = $fileName;
									name = $sheet.name; 
									headers = (Get-ExcelData-Header ([ref]$rows)); 
									values = (Get-ExcelData-Values ([ref]$rows)); 
								}
							}
							finally {
								[Runtime.Interopservices.Marshal]::ReleaseComObject($rows) | out-null
								[Runtime.Interopservices.Marshal]::ReleaseComObject($range) | out-null
								[Runtime.Interopservices.Marshal]::ReleaseComObject($sheet) | out-null
							}
						}
					}
					finally {
						[Runtime.Interopservices.Marshal]::ReleaseComObject($sheets) | out-null
					}
				}
				finally {
					$workBook.Close()
					[Runtime.Interopservices.Marshal]::ReleaseComObject($workBook) | out-null
				}
			}

			$results
		}
		finally {
			[Runtime.Interopservices.Marshal]::ReleaseComObject($workBooks) | out-null
		}
	}
	finally {
		$excel.Quit()
		[Runtime.Interopservices.Marshal]::ReleaseComObject($excel) | out-null
	}
}

function Merge-KV([array]$keys, [array]$values) {
	$len = [Math]::min($keys.length, $values.length)

	$o = new-object psobject

	for ($i = 0; $i -lt $len; ++$i) {
		add-member -inputobject $o -membertype noteproperty -name $keys[$i] -value $values[$i]
	}

	$o
}

function ConvertTo-Json(
		[parameter(Mandatory=$true, ValueFromPipeline=$true)]$sources, 
		$indentSize = 4) 
{
	function processInternal($item, $indent) {
		$map = @{
			"Object[]" = { processArray $item $indent }; 
			"PSCustomObject" = { processObject $item $indent };
		}

		if ($item -ne $null) {
			$typeName = $item.getType().name
			if ($map.containsKey($typeName)) {
				return & ($map[$typeName])
			}
			else {
				$n = $null
				if ([decimal]::TryParse($item, [ref]$n)) {
					return (" " * $indent) + $n
				}
				elseif ($item -is [datetime]) {
					return (" " * $indent) + '"' + $item.ToString("yyyy-MM-ddThh:mm:ssZ") + '"'
				}
			}
		}
		
		(" " * $indent) + '"' + $item + '"'
	}

	function processArray([array]$items, $indent) {
		$indentStr = " " * $indent

		$results = foreach ($item in $items) {
			processInternal $item ($indent+$indentSize)
		}

		"${indentStr}[`r`n$([string]::join(",`r`n", $results))`r`n${indentStr}]"
	}

	function processObject($obj, $indent) {
		$indentStr = " " * $indent

		$fields = $($obj | member -membertype noteproperty)
		if ($fields.length -gt 0) {
			$results = foreach ($field in $fields) {
				$key = processInternal ($field.name) ($indent+$indentSize)
				$value = processInternal $obj.$($field.name) ($indent+$indentSize)

				"${key}: $($value.trim())"
			}

			"${indentStr}`{`r`n$([string]::join(",`r`n", $results))`r`n${indentStr}`}"
		}
		else {
			"{}"
		}
	}

	processInternal $sources 0
}

sample.ps1

function Convert-Excel-To-Json($path) {
	ls $path/*.xlsx | %{ $_.fullname } |
	Get-ExcelData -withHeader | %{ 
		$f = new-object IO.DirectoryInfo "${path}/$($_.file)"
		$f.create()
		$headers = $_.headers
		,($_.values | % { merge-kv $headers $_ }) |
		ConvertTo-Json |
		out-file -encoding utf8 "$($f.fullName)/$($_.name).json"
	}
}