How to create a page that loads an image from a servlet that invokes the services of a JavaBean.
You can run this technique code from:
NOTE First make sure that database is running on your localhost SilverStream Server | |
See the chapter on using utility classes, JAR files, and JavaBeans in the Programmer's Guide |
This technique uses a servlet called srvletGifEncoder to load a graph into a SilverStream page. The servlet delegates responsibility for creating the chart image to a JavaBean called JCChart, which is provided by KLG. The servlet gets the data for the chart from the database by using two AgaData objects (dataOrderDetails and dataCategories). Once the image has been created, the servlet invokes the services of a class called GifEncoder, which is provided by Acme, to generate the GIF from the image.
NOTE In this example, the JavaBean is instantiated on the server, not the client. In addition, the JavaBean is multithreaded to allow the resource to be shared. Since the server owns the reference to the object, the Java window that pops up on the server will not be closed until the server shuts down.
The pageLoaded event and the pageActionPerformed event for the Generate Graph button both set the source of the image to the URL for the servlet (GifEncoder).
The pageLoaded event sets the graph type to Variety (total by product category) and the chart type to Bar:
Related reading
rbBar.setState(true);
rbVariety.setState(true);
imgGraphs.setSrc("../../GIFEncoder?GT=V&CT=B");
The pageActionPerformed event for the Generate Graph button gets the graph type and chart type from the user and passes the user's settings to the servlet:
if (rbVariety.getState())
graphType="GT=V";
else {
graphType="GT=R";
rbBar.setState(true);
}
if (rbBar.getState())
chartType="CT=B";
if (rbPie.getState())
chartType="CT=P";
if (rbStacked.getState())
chartType="CT=S";
imgGraphs.setSrc("../../GIFEncoder?" +
graphType + "&" + chartType);
The srvletGifEncoder servlet imports classes in the Acme.JPM.Encoders package, which was uploaded to the server in the Acme.jar file. This package contains the GifEncoder class. The servlet also imports classes in the jclass package, which was uploaded to the server in the jcchart361J.jar file. This package contains the JCChart JavaBean provided by KLG:
... ... import Acme.JPM.Encoders.*; ... //import KLG Stuff import jclass.chart.*; import jclass.util.JCEnvironment;
The srvletGifEncoder servlet defines a member variable called m_JCChart that contains a reference to the JCChart JavaBean:
... ... JCChart m_JCChart = new JCChart (); ...
The service method in the srvletGifEncoder servlet checks the parameters passed into the servlet to see what graph type and chart type were requested by the page. Depending on the graph type requested, it calls one of several methods (totalByCategory(), revenueTotals(), or revenueEmployees()) to create the graph image. Then it passes the image returned to the constructor for the GifEncoder class and calls the encode() method on the GifEncoder class:
if (TRACE_ON)
System.out.println(M_THIS + ".service()");
synchronized(this)
{
AgoHttpRequestEvent request = (AgoHttpRequestEvent) req;
AgoHttpReplyEvent response = (AgoHttpReplyEvent) res;
m_sDBName =
((AgoHttpRequestEvent)req).getDatabase().getName();
// Find out what to graph
// GT ==> GraphType CT ==> ChartType
// V ==> Variety B ==> Bar
// R ==> Revenue P ==> Pie
// S ==> Stacked
m_graphType = (String) request.getParameter("GT");
m_chartType = (String) request.getParameter("CT");
Image img = null;
if (m_graphType.equals("V"))
img = totalByCategory((AgoHttpRequestEvent)request);
if (m_graphType.equals("R"))
img = revenueTotals((AgoHttpRequestEvent) request);
if (m_graphType.equals("E"))
img = revenueEmployees();
OutputStream out = response.getOutputStream();
GifEncoder gif = new GifEncoder (img, out);
gif.encode();
String mimetype = "image/gif";
response.setContentType(mimetype);
response.setStatus(response.SC_OK);
}
The totalByCategory() and revenueTotals() methods construct the graph image. Both of these methods make method calls to the JCChart object. For example, the totalByCategory() method calls methods on the JCChart object to set the size and the chart type, as well as other attributes of the chart image. Finally, the totalByCategory() method calls the snapshot() method to get back the Image object:
...
...
m_JCChart.show();
m_JCChart.setSize(new Dimension(400,300));
m_panel.add (m_JCChart);
m_frame.add (m_panel);
try {
StringBufferInputStream sbisEmpData = new
StringBufferInputStream (sbGraphData.toString());
m_JCChart.getDataView(0).setDataSource ( new
InputStreamDataSource (sbisEmpData));
// Figure out how to chart the data
if (m_chartType.equals("B"))
m_JCChart.getDataView(0).setChartType (JCChart.BAR);
if (m_chartType.equals("P"))
m_JCChart.getDataView(0).setChartType (JCChart.PIE);
if (m_chartType.equals("S"))
m_JCChart.getDataView(0).setChartType (JCChart.STACKING_BAR);
m_JCChart.getDataView(0).getYAxis().setGridIsShowing(true);
m_JCChart.getChartArea().setDepth(10);
m_JCChart.getChartArea().setRotation(10);
m_JCChart.getChartArea().setElevation(10);
m_JCChart.getHeader().getLabel().setText
("[FONT=timesroman-bold-20] TOP FIVE (5) [COLOR=BLUE]
by Variety [DEFAULT_COLOR] [DEFAULT_FONT]", true);
m_JCChart.getFooter().setIsShowing(true);
m_JCChart.getFooter().getLabel().setText
("KL Group JClass Chart JavBean", true);
m_JCChart.getLegend().setIsShowing(true);
}
catch (IOException _e){
System.out.println (_e.toString());
}
Image img = m_JCChart.snapshot();
return img;