Entry that enables a UI for a service to be associated
* with the service in the attribute sets of the service item.
* UIDescriptor holds a marshalled UI factory object, as
* well as a role string, a sub-role string, and set of attributes that describe the
* UI generated by the factory.
*
*
*/
public class UIDescriptor extends AbstractEntry {
private static final long serialVersionUID = -4862086482826820670L;
/**
* Gives the fully qualified name of the interface that represents
* the role of the UI generated by the marshalled UI factory.
* If the client program unmarshals the UI factory and invokes a factory method, the
* UI returned by the factory method must implement the role the interface specified by
* role.
*
*
* For a client program to be able to use a UI, the client has to have prior knowledge
* of the UI semantics, which is defined by the UI's role type. Thus, for a client
* to be able to use a UI, the client must understand the semantics
* of the type whose fully qualified name is given in the String
* referenced from the role field of that UI's UIDescriptor.
*
*
* For example, two role types that are defined in the net.jini.lookup.ui
* package by the Jini Service UI Specification are MainUI, for a main UI
* to a Jini service, and AdminUI, for an administration UI. Other role types
* may be defined by the Jini Service UI Specification and by individual Jini service API
* specifications.
*
*
* As the strings referenced from the role field are Java type names, they
* are intended to be manipulated by client programs only. They should not be shown to a user.
*/
public String role;
/**
* A String to facilitate searching whose value represents the main UI toolkit (for example
* Swing or AWT) which the produced UI makes use of. The value to which this field should
* be set is defined by the semantics of the factory type. (This field is intended
* to facilitate searches. For example, a client can search for all blender services that have Swing
* MainUI's.)
*/
public String toolkit;
/**
* A set of objects that describe the UI generated by the marshalled UI factory.
*/
public Set attributes;
/**
* The get() method of this MarshalledObject
* must return an object that implements one or more UI factory interfaces. The actual
* UI factory type or types implemented by the returned object
* must be described by a UIFactoryTypes attribute placed in
* the attributes set of this UIDescriptor.
*/
public MarshalledObject factory;
/**
* Constructs a UIDescriptor with all fields set to null.
*/
public UIDescriptor() {
}
/**
* Constructs a UIDescriptor with the fields set to passed values.
* This constructor copies the contents of the passed attributes Set into a
* serializable read-only Set that has a
* consistent serialized form across all VMs, and initializes the attributes
* field with the consistent Set.
*
* @param role the role
* @param toolkit the toolkit
* @param attributes the attributes
* @param factory the factory
*/
public UIDescriptor(String role, String toolkit, Set attributes,
MarshalledObject factory) {
this.role = role;
this.toolkit = toolkit;
if (attributes != null) {
this.attributes = new ConsistentSet(attributes);
}
else {
this.attributes = null;
}
this.factory = factory;
}
/**
* A convenience method for unmarshalling the UI factory stored
* in the MarshalledObject referenced from the
* factory field. This method saves a reference
* to the current context class loader, sets the context class loader
* to the class loader passed as parentLoader, invokes
* get() on the marshalled object, then resets the
* context class loader to the saved reference before returning
* the object produced by get().
*
*
The class loader
* passed in parentLoader should be able to load classes
* needed when the UI interacts with the roleObject passed as the first
* parameter to the factory method. For example, if the roleObject is
* the service item (as it is for the MainUI and AdminUI
* roles), the class loader passed in parentLoader could be
* the class loader with which the service proxy object referenced
* from the service item's service field was loaded.
* For example:
*
*
* Object uiFactory = uiDescriptor.getUIFactory(
* serviceItem.service.getClass().getClassLoader());
*
*
* @throws NullPointerException if parentLoader is null.
* @return the unmarshalled UI factory
*/
public final Object getUIFactory(final ClassLoader parentLoader)
throws IOException, ClassNotFoundException {
if (parentLoader == null) {
throw new NullPointerException();
}
Object uiFactory;
final Thread currentThread = Thread.currentThread();
// First, get a reference to the current context class loader,
// so it can be restored after the unmarshalling
ClassLoader original = currentThread.getContextClassLoader();
try {
currentThread.setContextClassLoader(parentLoader);
uiFactory = factory.get();
}
finally {
currentThread.setContextClassLoader(original);
}
return uiFactory;
}
}