Android Tutorial HttpUtils - Android web services are now simple!

Status
Not open for further replies.
OkHttpUtils2 is now available. OkHttpUtils2 is an improved version and is recommended for new projects. You shouldn't use HttpUtils (v1)!

HttpUtils is made of a code module and a service module. These two modules make it very simple to download online resources and upload data.

The advantages of using HttpUtils are:
  • Much simpler than working with HttpClient directly.
  • Handles parallel calls efficiently and correctly (protects from RejectedExecutionException exceptions).
  • Downloads are not affected by the activity life cycle.
Using HttpUtils

A simple example of downloading a page and returning the page as string:
B4X:
Sub Globals
 Dim b4a As String
 b4a = "http://www.basic4ppc.com"
End Sub

Sub Activity_Create (FirstTime As Boolean)
 HttpUtils.CallbackActivity = "Main" 'Current activity name.
 HttpUtils.CallbackJobDoneSub = "JobDone"
 HttpUtils.Download("Job1", b4a)
End Sub

Sub JobDone (Job As String)
 Dim s As String
 If HttpUtils.IsSuccess(b4a) Then
  s = HttpUtils.GetString(b4a)
 End If
End Sub
First we configure the callback subs. Then we call HttpUtils.Download or HttpUtils.DownloadList. These calls submit a job request to HttpUtils.
A job is made of one or more links.
HttpUtils raises two types of events while processing a job. The UrlDone event is raised for each successful download with the downloaded url and the JobDone event is raised when the whole job finishes.
You cannot submit a new job while a current job is running (though a job can contain many links).

We have three ways to access a downloaded resource:
  • HttpUtils.GetString(Url As String) - Returns the resource as string
  • HttpUtils.GetBitmap(Url As String) - Returns the resource as bitmap
  • HttpUtils.GetInputStream(Url As String) - Returns an InputStream which allows you to manually read the downloaded resource.
These three methods should only be called after the job is done or inside the UrlDone event sub (for that specific Url).
After downloading a resource the Url serves as the key for that resource.

Inside JobDone event sub you should call HttpUtils.IsSuccess before accessing any Url as it is possible that some or all of the downloads have failed. This is not necessary in UrlDone event as UrlDone is called for each successful download.

Second example:
In this example we first download an image and set it as the activity background. Then we download another 6 Urls and print the last one as string. The code for this example is attached.
B4X:
Sub Process_Globals
    Dim ImageUrl As String
    ImageUrl = "http://www.basic4ppc.com/android/images/logo2.png"
    Dim Job2Links As List
End Sub

Sub Globals

End Sub

Sub Activity_Create(FirstTime As Boolean)
    HttpUtils.CallbackActivity = "Main"
    HttpUtils.CallbackJobDoneSub = "JobDone"
    HttpUtils.CallbackUrlDoneSub = "UrlDone"
    Job2Links.Initialize
    Job2Links.AddAll(Array As String( _
        "http://www.google.com", "http://www.yahoo.com", _
        "http://www.bing.com", "http://www.cnn.com", _
        "http://www.twitter.com", "http://www.facebook.com"))
  
    HttpUtils.Download("Job1", ImageUrl)
End Sub

Sub Activity_Resume
    'Check whether a job has finished while the activity was paused.
    If HttpUtils.Complete = True Then JobDone(HttpUtils.Job)
End Sub
Sub UrlDone(Url As String)
    Log(Url & " done")
End Sub
Sub JobDone (Job As String)
    Select Job
        Case "Job1"
            If HttpUtils.IsSuccess(ImageUrl) Then
                Dim b As Bitmap
                b = HttpUtils.GetBitmap(ImageUrl)
                Activity.SetBackgroundImage(b)
            End If
            'Start the second job
            HttpUtils.DownloadList("Job2", Job2Links)
        Case "Job2"
            For i = 0 To HttpUtils.Tasks.Size - 1
                link = HttpUtils.Tasks.Get(i)
                Log(link & ": success=" & HttpUtils.IsSuccess(link))
            Next
            If HttpUtils.IsSuccess("http://www.google.com") Then
                Log(HttpUtils.GetString("http://www.google.com"))
            End If
    End Select
    HttpUtils.Complete = False 'Turn off the complete flag so we won't handle it again if the activity is resumed.
End Sub
What happens when the user presses on the Home key during a download?
The download will complete successfully (we are using a service for this).
However your activity will be paused and the UrlDone and JobDone events will not fire.

When our activity is resumed we should check if we missed anything. This is done with this code:
B4X:
Sub Activity_Resume
    'Check whether a job has finished while the activity was paused.
    If HttpUtils.Complete = True Then JobDone(HttpUtils.Job)
End Sub
We are calling JobDone ourselves if needed.
In Sub JobDone we reset the Complete flag so we know that this job was handled.
UrlDone event should be considered a "nice to have" feature. Your code should be prepared to handle the case where some UrlDone events were missed due to the activity being paused.

The FlickrViewer example was rewritten and the attached code uses this module.
In this example we first go to the "main" page. In this page we find 9 links to 9 images. We submit a second job with all these links.

We show each image as soon as it is ready by using the UrlDone event.
In JobDone we check if all Urls were handled. We can miss some of these events if the activity was paused during download.

flickr_viewer1.png



HttpUtils, similar to DBUtils, aims to simplify common tasks that many developers face. The code is available for you. So changes can be made as needed.

Updates:

V1.04 - The service is now destroyed when it is no longer needed and recreated when needed again. This version also fixes a bug that caused the application to crash if the service was started after the process was killed.

V1.02 - PostString, PostBytes and PostFile methods added to HttpUtils.
These methods make it easy to post data to a web service (using http POST method).
The behavior of these methods is similar to Download and DownloadList. JobDone event is raised after the response from the server is read.

The latest version (v1.04) is included in HttpUtilsExample.
 

Attachments

  • FlickrViewer.zip
    9.8 KB · Views: 2,928
  • HttpUtilsExample.zip
    7.8 KB · Views: 5,311
Last edited:

netchicken

Active Member
Licensed User
Thanks guys :)

I solved it with NJDudes Words example. There was an easier way afterall!

Basically get the string, cut off the beginning starting with the IndexOf and then cut off the end with the SubString2. (I skipped replacing " with ' as slowing down the program too much)

B4X:
Dim allcode As String
Dim ratingcode As String
   
allcode = Response.GetString("UTF8") 'Get the whole page
            
                     'strip the string back 
ratingcode = allcode.SubString(allcode.IndexOf("class=" & QUOTE & "meter certified numeric " & QUOTE & ">")) ' get the start of the string
            
ratingcode = ratingcode.SubString2(33, ratingcode.IndexOf("</span>")) 'get the end of the string (33 counts forward to get rid of the code from above

lblrating.Text = "Rating = " & ratingcode
Hope this helps others
 

NeoTechni

Well-Known Member
Licensed User
Tried to compile it in 1.80 and now it says

Error description: Unknown type: httpclient
Are you missing a library reference?
Occurred on line: 3
Dim hc As HttpClient

Ah, it unchecked some of the libraries. Weird
 
Last edited:

robh

Member
Licensed User
Error in sub:httputils_internalcheckifcanstart

I'm receiving the attached error when calling a webservice, this is on an existing application that has been in place for approx 2 months, the problem only seems to have surfaced after ugrading to 1.80. Any advice greatly appreciated.

Many thanks in advance.
 

Attachments

  • internalcheckifcanstart.jpg
    internalcheckifcanstart.jpg
    20.6 KB · Views: 265

serkanpolat

Member
Licensed User
Erel,
is it possible to get the progress of download?
i mean i want to download a file but i want to show the progress in a progressbar..
how can i do it?
 

robh

Member
Licensed User
I'm receiving the attached error when calling a webservice, this is on an existing application that has been in place for approx 2 months, the problem only seems to have surfaced after ugrading to 1.80. Any advice greatly appreciated.

Many thanks in advance.

Hi Erel, I have downloaded the latest httputils files and I'm now receiving a different error, still related to the internalcheckifcanstart sub, see log below.

Any help greatly appreciated.



Starting Job: Job1


httputils_internalcheckifcanstart (B4A line: 74)
SuccessfulUrls.Initialize



java.lang.NullPointerException
at gary.MeyerPortal.httputils._internalcheckifcanstart(httputils.java:227)
at gary.MeyerPortal.httputils._postbytes(httputils.java:274)
at gary.MeyerPortal.httputils._poststring(httputils.java:398)
at gary.MeyerPortal.activitycheckstock._beginsearch(activitycheckstock.java:351)
at gary.MeyerPortal.activitycheckstock._btnsearch_click(activitycheckstock.java:370)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:491)
at anywheresoftware.b4a.BA.raiseEvent2(BA.java:113)
at anywheresoftware.b4a.BA.raiseEvent2(BA.java:101)
at anywheresoftware.b4a.BA.raiseEvent(BA.java:97)
at anywheresoftware.b4a.objects.ViewWrapper$1.onClick(ViewWrapper.java:49)
at android.view.View.performClick(View.java:3110)
at android.view.View$PerformClick.run(View.java:11934)
at android.os.Handler.handleCallback(Handler.java:587)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:132)
at android.app.ActivityThread.main(ActivityThread.java:4157)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:491)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
at dalvik.system.NativeStart.main(Native Method)
java.lang.NullPointerException
 

Inman

Well-Known Member
Licensed User
Is it possible to abort a job (containing a number of urls to download) and start a new one?
 
Status
Not open for further replies.
Top