Report Viewer supports push technology by means of interacting with a parameter server. A programmer can write a parameter server using the class quadbase.reportdesigner.ReportViewer.ParamServer to supply updated data continuously for Report Viewer to plot the report.

On the client side, the HTML syntax is:

<applet code = "quadbase.reportdesigner.ReportViewer.Viewer.class" width=640 height=480>
<PARAM name="filename" value="example.rpt">
<PARAM name="ParameterServer" value="machine:portno">
</applet>
            

Once the browser has loaded Report Viewer class and the report data from the web server, Report Viewer attempts to connect to the specific machine and port number identified in the parameter. For security reasons untrusted applets are not allowed to open a connection to other machines. The parameter server can interact with Report Viewer in order to update and manipulate the records held by Report Viewer.

On the server side, a server program should be written to listen to the port number. This server can be written using the class quadbase.reportdesigner.ReportViewer.ParamServer.

Upon opening a connection, the server will supply data to Report Viewer.

The constructor for the server is:

public ParamServer(DataInputStream in, DataOutputStream out)
            

Where in and out are the socket input and output used to communicate with the server.

ParamServer has three basic methods to manipulate the records in Report Viewer:

int addRecord(Object record[]);
int deleteRecord(int recordNo);
int updateRecord(Object record[], int recordNo);
            

After a sequence of record updates a final call

void repaint();
            

will send a request to Report Viewer to repaint the report using the new data.

The following Java program provides an example of using the parameter server class to generate new reports. Report API for ParamServer is provided in the online API documentation. In this example, one field in the twelfth record is simply updated with an integer chosen at random. In a real application, a programmer would have to write the code which enables the parameter server to interact with the data source.

import java.io.*;
import java.net.*;
import java.util.*;
import quadbase.reportdesigner.ReportViewer.ParamServer;

// Sample Program to update the data in EspressReport Viewer
// using Parameter Server
public class pserver extends Thread {
protected int port = 1997; // port no for report viewer to connect

protected ServerSocket listen_socket;

public static void fail(Exception e, String msg) {
System.err.println(msg + ":" + e);
System.exit(1);
}

public pserver() {
try {
listen_socket = new ServerSocket(port);
}
catch (IOException e) {
fail(e, "Exception creating server socket");
}
this.start();
}
public void run() {
try {
while(true) {
// create a thread for each connection to handle the
// request
Socket client_socket = listen_socket.accept();
Connection c = new Connection(client_socket);
}
}
catch (IOException e) {
fail(e, "Exception while listening for connections");
}
}
public static void main(String[] args) {
new pserver();
}
}

class Connection extends Thread {
protected Socket client;
protected DataInputStream in;
protected DataOutputStream out;

public Connection(Socket client_socket) {
client = client_socket;
try { // get the input and output stream
in = new DataInputStream(client.getInputStream());
out = new
DataOutputStream(client.getOutputStream());
}
catch (IOException e) {
try {
client.close();
}
catch (IOException e2) {}
return;
}
this.start();
}

public void run() {
ParamServer paramserver;
Random random = new Random(System.currentTimeMillis());
try {
paramserver = new ParamServer(in, out);
System.out.println("Total no of record = " + paramserver.getRecordNo());

// get record 12 from the report viewer
Object rec[] = paramserver.getRecord(12);
for (int i=0; i < 100; i++) {
// update the third field of record 12
rec[3] = new Integer(random.nextInt() % 30);
paramserver.updateRecord(rec, 12);
// tell the report viewer to repaint //after every tenth record is updated
if (i % 10 == 0)
paramserver.repaint();
}
}
catch (IOException e) {}
finally {
try {
client.close();
}
catch (IOException e2) {}
}
}
}
            

Report Viewer would have read an HTML file of the form:

<html>
<title>Sample Report</title>
<applet code = "quadbase.reportdesigner.ReportViewer.Viewer.class" width=600 height=450>
<PARAM name="filename" value="PServer.cht">
<PARAM name="ParameterServer" value=":1997">
</applet>
</html>
            

Here the Java class that Report Viewer reads is the name of a report file Pserver.rpt and the next line specifies the machine and port to which Report Viewer should open a connection. EspressManager will then provide information to Report Viewer at regular intervals such as updated records so that Report Viewer can refresh the report it displays.