ByteScout Cloud API Server – PDF To Image API – VB.NET – Convert PDF To JPEG From URL Asynchronously

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Module1.vb

      
Imports System.IO
Imports System.Net
Imports System.Threading
Imports Newtonsoft.Json.Linq

' Please NOTE: In this sample we're assuming Cloud Api Server is hosted at "https://localhost". 
' If it's not then please replace this with with your hosting url.

' Cloud API asynchronous "PDF To JPEG" job example.
' Allows to avoid timeout errors when processing huge or scanned PDF documents.
Module Module1
 	' Source PDF file
	Const SourceFileUrl As String = "https://bytescout-com.s3.amazonaws.com/files/demo-files/cloud-api/pdf-to-image/sample.pdf"
	' Comma-separated list of page indices (or ranges) to process. Leave empty for all pages. Example: '0,2-5,7-'.
	Const Pages As String = ""
	' PDF document password. Leave empty for unprotected documents.
	Const Password As String = ""
	' (!) Make asynchronous job
	Const Async As Boolean = True

	Sub Main()

		' Create standard .NET web client instance
		Dim webClient As WebClient = New WebClient()

		' Prepare URL for `PDF To JPEG` API call
		Dim query As String = Uri.EscapeUriString(String.Format(
			"https://localhost/pdf/convert/to/jpg?password={0}&pages={1}&url={2}&async={3}",
			Password,
			Pages,
			SourceFileUrl,
			Async))

		Try
			' Execute request
			Dim response As String = webClient.DownloadString(query)

			' Parse JSON response
			Dim json As JObject = JObject.Parse(response)

			If json("error").ToObject(Of Boolean) = False Then

				' Asynchronous job ID
				Dim jobId As String = json("jobId").ToString()
				' URL of generated JSON file available after the job completion; it will contain URLs of result JPEG files.
				Dim resultJsonFileUrl As String = json("url").ToString()

				' Check the job status in a loop. 
				' If you don't want to pause the main thread you can rework the code 
				' to use a separate thread for the status checking and completion.
				Do
					Dim status As String = CheckJobStatus(jobId) ' Possible statuses: "working", "failed", "aborted", "success".

					' Display timestamp and status (for demo purposes)
					Console.WriteLine(DateTime.Now.ToLongTimeString() + ": " + status)

					If status = "success" Then

						' Download JSON file as string
						Dim jsonFileString As String = webClient.DownloadString(resultJsonFileUrl)

						Dim resultFilesUrls As JArray = JArray.Parse(jsonFileString)

						' Download generated JPEG files
						Dim page As Integer = 1
						For Each token As JToken In resultFilesUrls

							Dim resultFileUrl As String = token.ToString()
							Dim localFileName As String = String.Format(".\page{0}.jpg", page)

							webClient.DownloadFile(resultFileUrl, localFileName)

							Console.WriteLine("Downloaded ""{0}"".", localFileName)
							page = page + 1

						Next

						Exit Do

					ElseIf status = "working" Then

						' Pause for a few seconds
						Thread.Sleep(3000)

					Else

						Console.WriteLine(status)
						Exit Do

					End If

				Loop

			Else
				Console.WriteLine(json("message").ToString())
			End If

		Catch ex As WebException
			Console.WriteLine(ex.ToString())
		End Try

		webClient.Dispose()


		Console.WriteLine()
		Console.WriteLine("Press any key...")
		Console.ReadKey()

	End Sub

	Function CheckJobStatus(jobId As String) As String

		Using webClient As WebClient = New WebClient()

			Dim url As String = "https://localhost/job/check?jobid=" + jobId

			Dim response As String = webClient.DownloadString(url)
			Dim json As JObject = JObject.Parse(response)

			Return Convert.ToString(json("status"))

		End Using

	End Function

End Module

    

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packages.config

      
<?xml version="1.0" encoding="utf-8"?>
<packages>
  <package id="Newtonsoft.Json" version="10.0.3" targetFramework="net40" />
</packages>
    

ON-PREMISE OFFLINE SDK

60 Day Free Trial or Visit ByteScout Cloud API Server Home Page

Explore ByteScout Cloud API Server Documentation

Explore Samples

Sign Up for ByteScout Cloud API Server Online Training

ON-DEMAND REST WEB API

Get Your API Key

Explore Web API Docs

Explore Web API Samples

ON-PREMISE OFFLINE SDK

60 Day Free Trial or Visit ByteScout Cloud API Server Home Page

Explore ByteScout Cloud API Server Documentation

Explore Samples

Sign Up for ByteScout Cloud API Server Online Training

ON-DEMAND REST WEB API

Get Your API Key

Explore Web API Docs

Explore Web API Samples