ChartDirector 6.1 (Java Edition)

Realtime Chart with Track Line (Web)

NOTE: This section describes Realtime Chart with Track Line for web applications only. For Windows applications, please refer to Realtime Chart with Track Line (Windows).

This sample program demonstrates a realtime chart with configurable chart update rate, in which the chart image is being updated via AJAX means. It includes a track cursor that updates the legend dynamically to display the data values as the mouse cursor moves over the chart. When the mouse is not over the chart, the track cursor will display the latest data values.

When the script starts to run, the first thing it does is to use WebChartViewer.isPartialUpdateRequest to detect if it is handling an AJAX chart update or an initial page request. If it is an AJAX chart update, it just draws the chart and sends back an AJAX response using WebChartViewer.partialUpdateChart. If it is an initial page request, it processes the request as usual.

The chart is updated by calling JsChartViewer.partialUpdate on the browser side. This method sends an AJAX chart update request to the server to update the chart without refreshing the web page. The charting code in the server always draws the chart using the most up-to-date data. By using a timer to call JsChartViewer.partialUpdate periodically, we can get a real time chart.

The track cursor drawing code is essentially the same as that in Track Line with Legend (Web). Please refer to that example for the explanation of the code.

Files in this Demonstration

This sample script requires the following files. When developing your own script using this sample script as a template, please ensure you copy the necessary files to the proper directories (typically the same directory as the script) and reference them using proper paths.

realtimetrack.jspMain source code for this demo.
getchart.jspThe standard utility script used in the image url for retrieving the chart image from
The script file for JsChartViewer, and the supporting cursor and image files. They must be in the same directory.

Source Code Listing

[JSP Version] jspdemo/realtimetrack.jsp
<%@page import="ChartDirector.*, java.util.*"%>
// Draw the chart
private void drawChart(WebChartViewer viewer)
    // Data to draw the chart. In this demo, the data buffer will be filled by a random data
    // generator. In real life, the data is probably stored in a buffer (eg. a database table, a
    // text file, or some global memory) and updated by other means.

    // We use a data buffer to emulate the last 240 samples.
    int sampleSize = 240;
    double[] dataSeries1 = new double[sampleSize];
    double[] dataSeries2 = new double[sampleSize];
    double[] dataSeries3 = new double[sampleSize];
    Date[] timeStamps = new Date[sampleSize];

    // Our pseudo random number generator
    double firstDate = new Date().getTime() / 1000 - timeStamps.length;
    for (int i = 0; i < timeStamps.length; ++i) {
        double p = firstDate + i;
        timeStamps[i] = new Date((long)p * 1000);
        dataSeries1[i] = Math.cos(p * 2.1) * 10 + 1 / (Math.cos(p) * Math.cos(p) + 0.01) + 20;
        dataSeries2[i] = 100 * Math.sin(p / 27.7) * Math.sin(p / 10.1) + 150;
        dataSeries3[i] = 100 * Math.cos(p / 6.7) * Math.cos(p / 11.9) + 150;

    // Create an XYChart object 600 x 270 pixels in size, with light grey (f4f4f4) background, black
    // (000000) border, 1 pixel raised effect, and with a rounded frame.
    XYChart c = new XYChart(600, 270, 0xf4f4f4, 0x000000, 0);

    // Set the plotarea at (55, 57) and of size 520 x 185 pixels. Use white (ffffff) background.
    // Enable both horizontal and vertical grids by setting their colors to grey (cccccc). Set
    // clipping mode to clip the data lines to the plot area.
    c.setPlotArea(55, 57, 520, 185, 0xffffff, -1, -1, 0xcccccc, 0xcccccc);

    // Add a title to the chart using 15pt Times New Roman Bold Italic font, with a light grey
    // (dddddd) background, black (000000) border, and a glass like raised effect.
    c.addTitle("Field Intensity at Observation Satellite", "Times New Roman Bold Italic", 15
        ).setBackground(0xdddddd, 0x000000, Chart.glassEffect());

    // Configure the y-axis with a 10pt Arial Bold axis title
    c.yAxis().setTitle("Intensity (V/m)", "Arial Bold", 10);

    // Configure the x-axis to auto-scale with at least 75 pixels between major tick and 15 pixels
    // between minor ticks. This shows more minor grid lines on the chart.
    c.xAxis().setTickDensity(75, 15);

    // Set the axes width to 2 pixels

    // Set the x-axis label format

    // Create a line layer to plot the lines
    LineLayer layer = c.addLineLayer2();

    // The x-coordinates are the timeStamps.

    // The 3 data series are used to draw 3 lines. Here we put the latest data values as part of the
    // data set name, so you can see them updated in the legend box.
    layer.addDataSet(dataSeries1, 0xff0000, "Alpha");
    layer.addDataSet(dataSeries2, 0x00cc00, "Beta");
    layer.addDataSet(dataSeries3, 0x0000ff, "Gamma");

    // Output the chart
    String chartQuery = c.makeSession(viewer.getRequest(), viewer.getId());

    // Set the chart URL to the viewer
    viewer.setImageUrl("getchart.jsp?" + chartQuery);

    // Output Javascript chart model to the browser to support tracking cursor

// This script handles both the full page request, as well as the subsequent partial updates (AJAX
// chart updates). We need to determine the type of request first before we processing it.

// Create the WebChartViewer object
WebChartViewer viewer = new WebChartViewer(request, "chart1");

if (viewer.isPartialUpdateRequest()) {
    // Is a partial update request. Draw the chart and perform a partial response.

// If the code reaches here, it is a full page request.

<!DOCTYPE html>
    <title>Realtime Chart with Track Line</title>
    <script type="text/javascript" src="cdjcv.js"></script>
<body style="margin:0px">
<script type="text/javascript">

// Execute the following initialization code after the web page is loaded
JsChartViewer.addEventListener(window, 'load', function() {
    var viewer = JsChartViewer.get('<%=viewer.getId()%>');

    // Draw track cursor when mouse is moving over plotarea or if the chart is updated. In the latter case,
    // if the mouse is not on the plot area, we will update the legend to show the latest data values.
    viewer.attachHandler(["MouseMovePlotArea", "TouchStartPlotArea", "TouchMovePlotArea", "ChartMove",
        "PostUpdate", "Now"], function(e) {
        this.preventDefault(e);   // Prevent the browser from using touch events for other actions
        trackLineLegend(viewer, viewer.getPlotAreaMouseX());

    // When the chart is being updated, by default, an "Updating" box will pop up. In this example, we
    // will disable this box.
    viewer.updatingMsg = "";

// Draw track line with legend
function trackLineLegend(viewer, mouseX)
    // Remove all previously drawn tracking object

    // The chart and its plot area
    var c = viewer.getChart();
    var plotArea = c.getPlotArea();

    // Get the data x-value that is nearest to the mouse, and find its pixel coordinate.
    var xValue = c.getNearestXValue(mouseX);
    var xCoor = c.getXCoor(xValue);
    if (xCoor == null)

    // Draw a vertical track line at the x-position
    viewer.drawVLine("trackLine", xCoor, plotArea.getTopY(), plotArea.getBottomY(), "black 1px dotted");

    // Array to hold the legend entries
    var legendEntries = [];

    // Iterate through all layers to build the legend array
    for (var i = 0; i < c.getLayerCount(); ++i)
        var layer = c.getLayerByZ(i);

        // The data array index of the x-value
        var xIndex = layer.getXIndexOf(xValue);

        // Iterate through all the data sets in the layer
        for (var j = 0; j < layer.getDataSetCount(); ++j)
            var dataSet = layer.getDataSetByZ(j);

            // We are only interested in visible data sets with names, as they are required for legend entries.
            var dataName = dataSet.getDataName();
            var color = dataSet.getDataColor();
            if ((!dataName) || (color == null))

            // Build the legend entry, consist of a colored square box, the name and the data value.
            var dataValue = dataSet.getValue(xIndex);
            legendEntries.push("<nobr>" + viewer.htmlRect(7, 7, color) + " " + dataName + ": " +
                ((dataValue == null) ? "N/A" : dataValue.toPrecision(4)) + viewer.htmlRect(20, 0) + "</nobr> ");

            // Draw a track dot for data points within the plot area
            var yCoor = c.getYCoor(dataSet.getPosition(xIndex), dataSet.getUseYAxis());
            if ((yCoor != null) && (yCoor >= plotArea.getTopY()) && (yCoor <= plotArea.getBottomY()))
                viewer.showTextBox("dataPoint" + i + "_" + j, xCoor, yCoor, JsChartViewer.Center,
                    viewer.htmlRect(7, 7, color));

    // Create the legend by joining the legend entries.
    var legend = "<nobr>[" + c.xAxis().getFormattedLabel(xValue, "hh:nn:ss") + "]" + viewer.htmlRect(20, 0) +
        "</nobr> " + legendEntries.reverse().join("");

    // Display the legend on the top of the plot area
    viewer.showTextBox("legend", plotArea.getLeftX(), plotArea.getTopY(), JsChartViewer.BottomLeft, legend,
        "width:" + plotArea.getWidth() + "px;font:bold 11px Arial;padding:3px;-webkit-text-size-adjust:100%;");

// Executes once every second to update the countdown display. Updates the chart when the countdown reaches 0.
function timerTick()
    // Get the update period and the time left
    var updatePeriod = parseInt(document.getElementById("UpdatePeriod").value);
    var timeLeft = Math.min(parseInt(document.getElementById("TimeRemaining").innerHTML), updatePeriod) - 1;

    if (timeLeft == 0)
        // Can update the chart now
    else if (timeLeft < 0)
        // Reset the update period
        timeLeft += updatePeriod;

    // Update the countdown display
    document.getElementById("TimeRemaining").innerHTML = timeLeft;
window.setInterval("timerTick()", 1000);

<table cellspacing="0" cellpadding="0" border="0">
        <td align="right" colspan="2" style="background:#000088; color:#ffff00; padding:0px 4px 2px 0px;">
            <a style="color:#FFFF00; font:italic bold 10pt Arial; text-decoration:none" href="">
                Advanced Software Engineering
    <tr valign="top">
        <td style="width:150px; background:#c0c0ff; border-right:black 1px solid; border-bottom:black 1px solid;">
            <br />
            <br />
            <div style="font: 9pt Verdana; padding:10px;">
                <b>Update Period</b><br />
                <select id="UpdatePeriod" style="width:130px">
                    <option value="5">5</option>
                    <option value="10" selected="selected">10</option>
                    <option value="20">20</option>
                    <option value="30">30</option>
                    <option value="60">60</option>
            <div style="font:9pt Verdana; padding:10px;">
                <b>Time Remaining</b><br />
                <div style="width:128px; border:#888888 1px inset;">
                    <div style="margin:3px" id="TimeRemaining">0</div>
            <div style="font: bold 20pt Arial; margin:5px 0px 0px 5px;">
                Realtime Chart with Track Line
            <hr style="border:solid 1px #000080" />
            <div style="padding:0px 5px 5px 10px">
                <!-- ****** Here is the chart image ****** -->