238

General Considerations

ground, by invoking the Web service in a different thread, and then updating the user

interface when the information is received. The client is able to continue its interac 

tion with the user until the service returns the information. With other types of cli 

ents, the user is often left with what appears to be a frozen screen or a nonfunctional

or locked application, since the client application blocks during the call to the Web

service. In short, the user does not know whether the application is still alive.

A J2SE client can use the 

SwingUtilities.invokeLater

 method to make the

call to the service in a separate thread, and thus to achieve a better user experi 

ence. (See Code Example 5.19.) This method takes a single argument of an object

implementing the 

Runnable

 interface. When the 

invokeLater

 method is invoked,

the J2SE platform creates another thread to run in background mode by invoking

the 

run

 method on the 

Runnable

 class. 

private void trackOrder() {

setStatus("Tracking Order " + getOrderId());

GetOrderDetails gd = new GetOrderDetails(this);

SwingUtilities.invokeLater(gd);

}

class GetOrderDetails implements Runnable {

private OTClientGUI gui;

private String orderId;

boolean done = false;

GetOrderDetails(OTClientGUI gui) {

this.gui = gui;

this.orderId = gui.getOrderId();

}

public void run() {

if (!done) {

try {

gui. setStatus("Looking for Order " + orderId);

OrderDetails od = WSProcessor.getOrderDetails(orderId); 

if (od != null) {

gui.setDetails(od);

}

} catch (OrderNotFoundException ex) {

gui.clearDetails();