Display Streamed Data in Figure Window - MATLAB & Simulink (original) (raw)

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This example shows how to customize an HTTP StringConsumer class—PricesStreamer—to display streamed data from a hypothetical website in a MATLAB® figure window. To create a working example:

Identify a URL, similar to:
url = matlab.net.URI('','accountId',,'','');
Modify PricesStreamer.putData to read data specific to your web service

The following tasks are described in this topic. For information about displaying table data in a figure window, see uitable.

PricesStreamer Class
Map Data to MATLAB uitable Object
Display Data in JSON Format
Terminate Data Stream
Call PricesStreamer

`PricesStreamer` Class

PricesStreamer.m is a subclass of theStringConsumer class, which is a subclass ofContentConsumer. PricesStreamer receives streamed data customized to the data provided by a specific web service. In this example, the structure of the data is:

% Data contains one or more CRLF-separated JSON structures.
% Each structure is one of the format: % {"heartbeat"="timestamp"} % {"tick"="timestamp", "bid"=bid, "ask"=ask} % where timestamp is a GMT time and bid and ask are numbers.

MATLAB calls the PricesStreamer.putData function for each chunk of data received from the server. The function first converts the rawuint8 bytes to a JSON string usingStringConsumer. Next, it gets a MATLAB structure from the JSON string using jsondecode and then displays the data in a table in a figure, adding one line to the top of the table for each increment of data. You can modify the putData function to do something else with the data, for example, plot a real-time graph or display delta prices. PricesStreamer sets thestop return value to stop the operation when the user closes the figure. For more information, see putData.

classdef PricesStreamer < matlab.net.http.io.StringConsumer % PricesStreamer accepts streamed JSON % and displays the result in a uitable in a figure window.

% Copyright 2016-2017 The MathWorks, Inc.
properties
    Figure
    Table
    Endit logical
    HaveTick logical
end

methods (Access=protected)
    function length = start(obj)
        if obj.Response.StatusCode ~= matlab.net.http.StatusCode.OK
            length = 0;
        else
            length = obj.start@matlab.net.http.io.StringConsumer;
            obj.Figure = figure('CloseRequestFcn',@obj.endit);
            obj.Figure.Position(4) = 550;
            obj.Figure.Position(2) = 50;
            obj.Table = uitable(obj.Figure,...
                'ColumnName',{'Time','Bid','Ask'},...
                'ColumnWidth',{130,'auto','auto'});
            obj.Table.Position(4) = 500;
            obj.Table.Data = cell(0,3);
            obj.Endit = false;
            obj.HaveTick = false;
        end
    end
end

methods
    function [len,stop] = putData(obj, data)
        % Data contains one or more CRLF-separated JSON structures.  
        % Each structure is one of the format:
        %   {"heartbeat"="timestamp"}
        %   {"tick"="timestamp", "bid"=bid, "ask"=ask}
        % where timestamp is a GMT time and bid and ask are numbers.
        if obj.Endit
            data = [];
            delete(obj.Figure);
        end
        first = obj.CurrentLength + 1;
        [len,stop] = obj.putData@matlab.net.http.io.StringConsumer(data);
        if isempty(data) || stop
            if ischar(data)       % data == '' means user ctrl/c'ed, so set to
                obj.Endit = true; % delete figure on next close
            end
            stop = true;
        else
            stop = false;
            last = obj.CurrentLength;
            newData = obj.Response.Body.Data.extractBetween(first,last);
            % split at CRLFs
            strings = strsplit(newData, '\r\n');
            try
                cellfun(@obj.displayJSON, strings);
            catch e
                fprintf('Error on JSON:\n%s<EOF>\n',data);
                obj.Endit = true;
                rethrow(e);
            end
        end
    end
    
    function displayJSON(obj, str)
        if ~isempty(str)
            try
                val = jsondecode(str);
            catch e
                fprintf('Error "%s" on JSON:\n%s<EOF>\n',e.message,str);
                rethrow(e);
            end
            if isfield(val,'tick')
                tick = val.tick;
                newdata = {cvtime(val.tick.time),tick.bid,tick.ask};
                setExtent = ~obj.HaveTick;
                obj.HaveTick = true;
            elseif isfield(val, 'heartbeat')
                newdata = {cvtime(val.heartbeat.time),'',''};
                setExtent = false;
            end
            obj.Table.Data = [newdata;obj.Table.Data];
            if setExtent || ~mod(log10(length(obj.Table.Data)),1)
                % set extent on first tick and every power of 10
                % add 15 for width of scroll bar
                obj.Table.Position(3) = obj.Table.Extent(3) + 15;
            end
            drawnow
        end
    end
    
    function endit(obj,~,~)
        % endit callback from close(obj.Figure)
        if exist('obj','var') && isvalid(obj)
            if obj.Endit
                if isvalid(obj.Figure)
                    delete(obj.Figure);
                end
            else
                obj.Endit = true;
            end
        end
    end
    
    function delete(obj)
        if ~isempty(obj.Figure) && isvalid(obj.Figure)
            delete(obj.Figure);
        end
    end
end

end

function time = cvtime(time) % Format time data for display time = datetime(time,'InputFormat','yyyy-MM-dd''T''HH:mm:ss.S''Z''','TimeZone','GMT'); time.TimeZone = 'local'; time = char(time, 'dd-MMM-yyyy HH:mm:ss.S'); end

Map Data to MATLAB `uitable` Object

Identify the data structures for your use case by reading API information from the web service. The data for this example contains one or more CRLF-separated JSON structures. The format for the structures is one of the following, wheretimestamp is a GMT time and bid andask are numbers.

{"heartbeat"="timestamp"}
{"tick"="timestamp", "bid"=bid, "ask"=ask}

To read this specific format, override the putData method. The following statements from thePricesStreamer class useStringConsumer.putData to read the next buffer, then select the JSON strings.

first = obj.CurrentLength + 1; [len,stop] = obj.putData@matlab.net.http.io.StringConsumer(data); last = obj.CurrentLength; newData = obj.Response.Body.Data.extractBetween(first,last); % split at CRLFs strings = strsplit(newData, '\r\n');

Display Data in JSON Format

The following statements from the displayJSON function individually handle the JSON tick andheartbeat structures. A helper functioncvtime formats the time data for display in the table.

function displayJSON(obj, str) ... val = jsondecode(str); if isfield(val,'tick') tick = val.tick; newdata = {cvtime(val.tick.time),tick.bid,tick.ask}; ... elseif isfield(val, 'heartbeat') newdata = {cvtime(val.heartbeat.time),'',''}; ... end obj.Table.Data = [newdata;obj.Table.Data]; ... end

Terminate Data Stream

In this example, MATLAB receives data as long as the web service is active. The user can terminate the stream by closing the figure window or by pressingCtrl+C. To inform MATLAB of a user interruption, set the stop argument inputData to false. Clean-up tasks include closing the figure using the CloseRequestFcn property and deleting the object using the PricesStreamer.delete function.

Call `PricesStreamer`

The following code provides a framework for retrieving data from a web service. To run the code, you must provide values for content within <> characters. The URL for your web service might include additional parameters, such as login information and other information specified as name, value pair arguments. To utilize the PricesStreamer, add it to your call to send. For information about creating request messages, see Call Web Services from MATLAB Using HTTP.

url = matlab.net.URI('','accountId',,'',''); authInfo = matlab.net.http.AuthInfo(matlab.net.http.AuthenticationScheme.Bearer,... 'Encoded',''); af = matlab.net.http.field.AuthorizationField('Authorization',authInfo); r = matlab.net.http.RequestMessage('get',af); consumer = PricesStreamer; % SavePayload set to retain all results - useful for debugging [resp,req,hist] = r.send(url,matlab.net.http.HTTPOptions('SavePayload',true),consumer); % Show the results for debugging show(resp)

The following is an example of data from a web service sending data described inMap Data to MATLAB uitable Object.

HTTP/1.1 200 Ok Server: openresty/1.9.15.1 Date: Wed, 06 Sep 2017 19:26:56 GMT Content-Type: application/json Transfer-Encoding: chunked Connection: close Access-Control-Allow-Origin: *

{"tick":{"instrument":"AUD_CAD","time":"2017-09-06T19:26:54.304054Z","bid":0.97679,"ask":0.97703}} {"heartbeat":{"time":"2017-09-06T19:26:56.253091Z"}} {"tick":{"instrument":"AUD_CAD","time":"2017-09-06T19:26:57.226918Z","bid":0.97678,"ask":0.97703}} {"tick":{"instrument":"AUD_CAD","time":"2017-09-06T19:26:58.226909Z","bid":0.97678,"ask":0.97705}} {"heartbeat":{"time":"2017-09-06T19:26:58.720409Z"}} {"tick":{"instrument":"AUD_CAD","time":"2017-09-06T19:27:00.733194Z","bid":0.97679,"ask":0.97704}} {"heartbeat":{"time":"2017-09-06T19:27:01.251202Z"}} {"tick":{"instrument":"AUD_CAD","time":"2017-09-06T19:27:01.757501Z","bid":0.9768,"ask":0.97706}} {"heartbeat":{"time":"2017-09-06T19:27:03.720469Z"}}

Display Streamed Data in Figure Window - MATLAB & Simulink (original) (raw)

PricesStreamer Class

Map Data to MATLAB uitable Object

Display Data in JSON Format

Terminate Data Stream

Call PricesStreamer

See Also

`PricesStreamer` Class

Map Data to MATLAB `uitable` Object

Call `PricesStreamer`