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The attributes section of a UIDescriptor can carry any other information about the user interface object that is deemed useful. Currently this includes the following: A UIFactoryTypes contains a set of Strings for the fully qualified class names of the factory this entry contains. The current factory hierarchy is very shallow, so this may be just a singleton set, such as {JFrameFactory.TYPE_NAME}. There is an unfortunate wrinkle with Java sets and Jini entries: the lookup matching mechanism for entries tests byte equality of serialized forms, and most implementations of the Set interface are not constant across all JVMs. So instead of common set types such as HashSet, you should use special types such as com.artima.lookup.util. ConsistentSet. This type has a constructor that takes a Set in its constructor, which makes already messy code a bit more messy: Set attribs = new HashSet(); Set typeNames = new HashSet(); typeNames.add(JFrameFactory.TYPE_NAME); typeNames = new ConsistentSet(typeNames); attribs.add(new UIFactoryTypes(typeNames)); attribs = new ConsistentSet(attribs);

Note that a client is not usually interested in the actual type of the factory, but rather of the interface it implements. This is just like Jini services themselves, where we only need to know the methods that can be called, and we are not concerned with the implementation details. Inclusion of an AccessibleUI object is a statement that the user interface implements javax.accessibility.Accessible and that the user interface works well with assistive technologies. A Locales object specifies the locales supported by the user interface. A RequiredPackages object contains information about all of the packages that the user interface needs to run. This is not a guarantee that the user interface will actually run, nor is it a guarantee that the interface will be usable! But it may help a client decide whether or not to use a particular user interface.

The file classifier has been used throughout this book as a simple example of a service, to illustrate various features of Jini. We can use the file classifier here, too, by supplying simple user interfaces into the service. Such a user interface consists of a text field to enter a file name and a display of the MIME type of the file name. There is only a main role for this service, as no administration needs to be performed. Figure 24-1 shows what a user interface for a file classifier could look like.

Figure 24-1. File classifier user interface After the service has been invoked, it could pop up a dialog box as shown in Figure 24-2.

A factory for the main role that will produce an AWT Frame is as follows: /** * FileClassifierFrameFactory.java */ package ui; import net.jini.lookup.ui.factory.FrameFactory; import net.jini.lookup.entry.UIDescriptor; import java.awt.Frame; import net.jini.core.entry.Entry; import net.jini.core.lookup.ServiceItem; public class FileClassifierFrameFactory implements FrameFactory { /** * Return a new FileClassifierFrame that implements the * MainUI role */ public Frame getFrame(Object roleObject) { // we should check to see what role we have to return if (! (roleObject instanceof ServiceItem)) { // unknown role type object // can we return null return null; } ServiceItem item = (ServiceItem) roleObject; // Do sanity checking that the UIDescriptor has a MainUI role Entry[] entries = item.attributeSets; for (int n = 0; n < entries.length; n++) { if (entries[n] instanceof UIDescriptor) { UIDescriptor desc = (UIDescriptor) entries[n]; if (desc.role.equals(net.jini.lookup.ui.MainUI.ROLE)) { // OK, we are in the MainUI role, so return a UI for that Frame frame = new FileClassifierFrame(item, "File Classifier"); return frame; } } } // couldn't find a role the factory can create return null; } } // FileClassifierFrameFactory The following is the user interface object that performs this role: /** * FileClassifierFrame.java */ package ui; import java.awt.*;