B4J Tutorial [BANano+jSERVER=BANanoServer] Going full circle


B4J has an excellent jetty based server: the jServer library. BANanoServer uses this lib and provides you with a lot of goodies to make building WebApps with B4J very simple.

NOTE: This library is in the full BANano library zip file.

NOTE: You can still use BANano without the BANanoServer Library as it did before in case you want to use another backend like PHP, but only having to program in one language has huge advantages and is what RAD is al about. :)

When you will look at the code of BANanoServer, ABM users will recognize the powerful Caching system, Root and http2 filters. In BANano, all that code is removed from your own projects view (but still accessible as it is an open source .b4xlib).

Some 'easy-to-use' methods to communicate between the browser and the server are added. (to call methods from each other and to exchange files).

EDIT: in te zip with the library is a Template.bjl file to use in a BANanoServer object. Note that a B4J jServer project (where BANanoServer is based on) must be a Non-UI project! So you can normally not use the abstract Designer. But with a 'hack', if you cpy a bjl file in an Non-UI project, you can use the Abstract Desgner by clicking on the 'open designer' link in the files panel.

Unfortunately, in the abstract designer, you can not use the Tools - Generate Members (it gives an error). You can however still use the individual Generate you get by right-clicking on a control:


EDIT 2: It looks like one can get around that second remark (Tools - Generate Members b y adding the jFX library to the project. Just don't use it and(you should see the remark "Library 'jFX' is not used. (warning #32)". I've looked into the jars and the generated code appears to be the same (correct @Erel?), just some extra (not used) classes are added to the fat jar.

A BANano+BANanoServer WebApp basically exists of the following components:

SERVERpage: the server side of a web page that can run ALL of the B4J code and B4J libraries
BROWSERPage: the browser side of a the web page that can run 99% of all the B4J code and BANano Libraries (no B4J libraries).
SHAREDCode: code that can contain both B4J and BANano code. Useful e.g. to write just one class that both sides need to use. It will be compiled to Java AND to JavaScript (by BANano).

And here is how the communication works. You will see the similarity I tried to archive between the SERVERPage and BROWSERPage classes to make it very easy for even a novice programmer.

Main (Setting up de server and BANano):
'Non-UI application (console / server application)
#Region Project Attributes
   #MergeLibraries: True
   #IgnoreWarnings: 16, 10, 14, 15
#End Region

Sub Process_Globals
   ' must be public in Main because everyone has to use this one.
   Public Server As BANanoServer
End Sub

Sub AppStart (Args() As String)
   ' initialize the BANano Server
   ' for our caching
   Server.SessionMaxInactiveIntervalSeconds = 60
   Server.CacheScavengePeriodSeconds = 30
   ' for our upload
   Server.UploadAllowedFileTypes = "ZIP;JPG"
   Server.UploadMaxSize = 1024*1024*5 ' 5 MB
   ' Other important ones
   ' the prefix of our BROWSER (BANano only code) classes that miror their SERVER counterpart (default is "BROWSER")
   Server.BROWSERPrefix = "BROWSER" ' IMPORTANT to set this one if you do not use this default Prefix!
   ' initialize BANano
   Server.BANano.Initialize("BANano", "BANanoServer" ,1)
   ' some B4J typical libs we want to be ignored by the Transpiler

   ' transpile all the BANano b4J code to javascript

   ' add your SERVER classes, not the BROWSER parts:
   Server.AddWebSocket("/ws/" & Server.BANano.StaticFolder & "/about" , "SERVERAbout")

   ' set the start page one will go to if they enter the site by the root
   Server.StartPage = "about"

   ' lets start the B4J server
   If Server.PortSSL <> 0 Then
       Server.StartServerHTTP2("keystore.jks", "SSLKeyStorePassword", "SSLKeyManagerPassword")
   End If
End Sub

'Return true to allow the default exceptions handler to handle the uncaught exception.
Sub Application_Error (Error As Exception, StackTrace As String) As Boolean
   Return True
End Sub

SERVERAbout (a SERVERPage that talks with its BROWSERPage counterpart):
' B4J compatible ONLY code, no BANano allowed.
'WebSocket class
Sub Class_Globals
   Private ws As WebSocket
   Private CacheReport As BANanoCacheReport
   ' a class used by both the SERVER and the BROWSER
   Private Human As SHAREDHuman
End Sub

Public Sub Initialize
End Sub

Private Sub WebSocket_Connected (WebSocket1 As WebSocket)

   ws = WebSocket1

   ' Lets update the cache with this class
   CacheReport = Main.Server.UpdateFromCache(Me, ws)
   Log("PageID: " & CacheReport.BANPageID)
   Log("Comes From Cache:" & CacheReport.ComesFromCache)
   Log("Is a reconnecting socket: " & CacheReport.IsReconnected)

   ' We can already send stuff to the browser, using normal B4J jServer code with Future
   Dim fut As Future = ws.RunFunctionWithResult("AddInTheBrowser", Array(20, 30))
   Log("BROWSER says sum of 20+30=" & fut.Value)

   ' or if no result is expected back
   ws.RunFunction("BROWSERTest", Array("Hello from the SERVER!"))

   ' IMPORTANT lets tell the browser we are ready to receive call from the browser
   ' Uses the classic WebSocket_Connected and WebSocket_DisConnected events on the browser size
   ' Use Main.Server.SendReady(ws, "ws") if you use the advanced events OnOpen, OnMessage, OnServerReady, ...
End Sub

Private Sub WebSocket_Disconnected
End Sub
' event raised to distribute incoming events coming from the BROWSER
public Sub BANano_ParseEvent(params As Map)
   Main.Server.ParseEvent(Me, ws, CacheReport.BANPageID, params)
End Sub
' event raised when a file has been uploaded
public Sub BANano_Uploaded(status As Int, fileName As String)
   Log(fileName & " = " & status)
   Select Case status
       Case 200 ' OK
       Case 500 ' was not a POST call
       Case 501 ' file to big
       Case 502 ' file type not allowed
   End Select
End Sub

' called from the BROWSER
public Sub AddOnTheServer(first As Int, second As Int) As Int
   Return first + second
End Sub

' called from the BROWSER
public Sub SERVERTest(msg As String)
   Log("BROWSER says '" & msg & "'")
End Sub

' called from the BROWSER
public Sub GetHuman() As String
   ' make a human that the browser can retrieve
   Human.Name = "Alain"
   Human.Gender = "Male"
   Return Human.ToJSON
End Sub

' called from the BROWSER
public Sub SetHuman(HumanStr As String)
   Log("Human.Name (changed in the browser) is " & Human.Name)
End Sub

BROWSERAbout (a BROWSERPage that talks with its SERVERPage counterpart):
'BANano compatible ONLY code. You can not use typical B4J libraries here.  Use their BANano version (if it exists)
'Making changes in a this module/class in B4J debug mode will NOT have any effect until recompiled!
#Region BANano
   ' <-------------- IMPORTANT! This is because we want this module to be transpiled by BANano
#End Region

Sub Class_Globals
   Private BANano As BANano 'ignore
   Private ws As BANanoWebSocket
   ' a class used by both the SERVER and the BROWSER
   Private Human As SHAREDHuman
   ' BANano Custom View objects that are on the UploadForm layout
   Private SKButton1 As SKButton 'ignore
   Private SKTextBox1 As SKTextBox 'ignore
   Private SKLabel1 As SKLabel 'ignore
End Sub

'Initializes the object. You can NOT add extra parameters!
Public Sub Initialize
   ' does the browser support websockets?
   If ws.IsSupported Then
       ' here we connect to our SERVERAbout websocket class using the 'classic' B4J Websocket events WebSocket_Connected and WebSocket_Disconnected
       ws.Initialize("ws://" & BANano.Location.GetHost & "/ws/" & BANano.StaticFolder & "/about")
   End If
End Sub

' Server says socket is ready
Sub WebSocket_Connected()
   Log("My B4J PageId: " & BANano.GetPageID)
   ' load de layoout for the upload
   BANano.LoadLayout("#body", "UploadForm")

   ' running a method on the server and wait for the result
   Dim value As Int = 0
   Dim prom As BANanoPromise = ws.RunFunctionWithResult("AddOnTheServer", Array(3 , 6))
       Log("SERVER says sum of 3+6=" & value)

   ' getting the human class from the server
   Dim humanJson As String
   Dim promHuman As BANanoPromise = ws.RunFunctionWithResult("GetHuman", Null)
       ' making a change to the object
       Human.Name = "Alain Bailleul"
       ' and sending it back
       ws.RunFunction("SetHuman", Array(Human.ToJSON))
       Log("Hello Human " & Human.Name & " (" & Human.Gender & ")")

   ' note that this will be logged BEFORE the sum and the Human retrieval.  If you want it AFTER then it has to be put inside the Promise
   ws.RunFunction("SERVERTest", Array("Hello from the BROWSER!"))

   ' get some assets from the server/internet
   Dim Files As List = Array("./assets/B4X.jpg", "https://jsonplaceholder.typicode.com/posts", "./assets/UTF8.txt")
   Dim responses() As String
   Dim dataUrlProm As BANanoPromise = BANano.GetFileAsDataURL(Files.Get(0), Null)
   Dim jsonObjProm As BANanoPromise = BANano.GetFileAsJSON(Files.Get(1), Null)
   Dim textProm As BANanoPromise = BANano.GetFileAsText(Files.Get(2), Null, "UTF-8")
   ' return when all 3 promises are done
   Dim prom As BANanoPromise = BANano.PromiseAll(Array(dataUrlProm, jsonObjProm, textProm))
       For i = 0 To responses.Length - 1
           Log(Files.Get(i) & ":")
End Sub

Sub WebSocket_Disconnected(event As BANanoEvent)
   Log("Websocket closed")
End Sub

' called from the SERVER
public Sub AddInTheBrowser(first As Int, second As Int) As Int
   Return first + second
End Sub

' called from the SERVER
public Sub BROWSERTest(msg As String)
   Log("SERVER says '" & msg & "'")
End Sub

' uploading a file to our server
Sub SKButton1_Click (event As BANanoEvent)
   Dim Response As BANanoObject
   ' get the file object
   Dim theFile As BANanoObject = SKTextBox1.File
   If theFile = Null Then
       BANano.Alert("Please select a file first!")
   End If
   ' prevent big uploads
   If theFile.GetField("size") > 1024 * 1024 * 5 Then
       BANano.Alert("File is to big!")
   End If
   ' returns a promise
   Dim prom As BANanoPromise = BANano.UploadFile(theFile)
       SKLabel1.Text = "Upload status: " & Response.GetField("status").Result
End Sub

SHAREDHuman (a SHAREDCode class that can be used both in a BROWSERPage and SERVERPage class):
'This class is shared between the BANanoServer and BANAno
'Use to specify which code is specific for the BANanoServer (B4J) and the BANano Browser part
'  #If #B4J
'  #Else
'  #End If
'Making changes in a this module/class in B4J debug mode will NOT have any effect on the BANano side until recompiled!
#Region BANano
   ' <-------------- IMPORTANT! This is because we want the non specific B4J code in this module to be transpiled by BANano
#End Region

Sub Class_Globals
   Public Name As String
   Public Gender As String
End Sub

'Initializes the object. You can add parameters to this method if needed.
Public Sub Initialize

End Sub

public Sub ToJSON() As String
   Dim m As Map = CreateMap("name": Name, "gender": Gender)

   #If B4J
       Dim json As JSONGenerator
   #Else 'if BANANO
       Dim json As BANanoJSONGenerator
   #End If
   Return json.ToString
End Sub

public Sub FromJson(jsonStr As String)
   Dim m As Map
   #if B4J
       Dim json As JSONParser
   #Else 'if BANAno
       Dim json As BANanoJSONParser
   #End If
   m = json.NextObject

   Name = m.Get("name")
   Gender = m.Get("gender")
End Sub

NOTE: a server.ini file can be put next ot the .jar (in the Objects folder when debugging). This is an example:

Last edited:


Licensed User
Longtime User
If I could do a +100 on the likes I would. This is awesome!!!!

Roberto P.

Well-Known Member
Licensed User
Longtime User
fantastic. great Alain

Now it will be difficult to understand the differences of ABMaterial and Banano Server and to understand when and why to use one or another?

expect your updates.

Happy holidays


Active Member
Licensed User
Longtime User
1. When I start New System 4.50 \ demo I get the following error

2. I do n’t know how to open it ,because there is an error


Licensed User
Longtime User
What is SKTextBox1 and does it have a File method? It’s the ”Dim theFile...” line that’s causing the error. Anything after that is just a result of the first error


Looking forward to the BANanoServer extended tutorial. I started a BANanoServer test project using your demo and all seems to be working well. I would love to see a backend SQL server connection example using this setup. Thank you!