gnu.cajo.utils

Class BaseProxy

java.lang.Object

gnu.cajo.utils.BaseProxy

All Implemented Interfaces:

Serializable

public abstract class BaseProxy
extends Object
implements Serializable

A standard abstract base class for proxy objects. Proxies are remote object interfaces to server objects. They are intended to offload routine processing. They differ from server objects in that they are sent to remote VMs to operate, and are often not even instantiated in the runtime of the server's VM.

Version:

1.0, 01-Nov-99 Initial release

Author:

John Catherino

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	BaseProxy.MainThread The main processing thread of this object.
class	BaseProxy.Panel A standard base class for graphical proxy objects.

Field Summary

Fields

Modifier and Type	Field and Description
String	bundle The path/filename of the resource bundle in the proxy's codebase jar file.
Container	container A reference to the proxy's graphical user interface, if any.
protected RemoteInvoke	item The reference to the sending server, on which the proxy may asynchronously callback.
protected Remote	remoteThis A remote reference to the proxy itself, which it can send to its server, or other remote VMs on which they can asynchronously callback.
protected BaseProxy.MainThread	runnable A reference to the proxy's processing code.
String[]	strings The collection of strings to be displayed at the host VM.
Thread	thread The processing thread of the proxy object, it will be started automatically upon arrival at the client when the init method is invoked.

Constructor Summary

Constructors

Constructor and Description
BaseProxy() Nothing is performed in the constructor.

Method Summary

Methods

Modifier and Type	Method and Description
void	contact(String url) This method is canonically called when an proxy announces its reference via the Multicast class.
String	getDescription() This method is invoked by remote users of this object.
Remote	getItem(String url) A method will load either an object, or a zipped marshalled object (zedmob) of an object, from a URL, file, or from a remote rmiregistry.
Container	init(Remote remoteRef) This function is called by the hosting client on upon the proxy's arrival.
void	setItem(RemoteInvoke item) This function is called by the ItemServer during its bind operation.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

remoteThis

protected transient Remote remoteThis

A remote reference to the proxy itself, which it can send to its server, or other remote VMs on which they can asynchronously callback.

item

protected RemoteInvoke item

The reference to the sending server, on which the proxy may asynchronously callback. It is set by the ItemServer during the bind operation.

runnable

protected BaseProxy.MainThread runnable

A reference to the proxy's processing code. If non-null, it will be started automatically upon arrival at the host. Its thread can be accessed through the thread member.

thread

public transient Thread thread

The processing thread of the proxy object, it will be started automatically upon arrival at the client when the init method is invoked.

container

public Container container

A reference to the proxy's graphical user interface, if any. It will be returned to the client as a result of its initialization invocation.

bundle

public String bundle

The path/filename of the resource bundle in the proxy's codebase jar file. It will be used to localize any displayed strings, to the language of the proxy recipient, as close as possible, if supplied. It is declared public since its value is typically assigned by a builder application.

strings

public String[] strings

The collection of strings to be displayed at the host VM. On instantiation at the host, the array will be loaded with localized strings from the most appropriate resource bundle for the locale of the receiving VM, if provided. It is public since its value is typically assigned by a builder program.

Constructor Detail

BaseProxy

public BaseProxy()

Nothing is performed in the constructor. Construction and configuration of the proxy are generally performed by a builder application.

Method Detail

setItem

public void setItem(RemoteInvoke item)

This function is called by the ItemServer during its bind operation.

Parameters:

item - A remote reference to the server object, on which the proxy may asynchronously call back to it.

init

public Container init(Remote remoteRef)

This function is called by the hosting client on upon the proxy's arrival. The client will provide a reference to the proxy, remoted in the context of the client's VM. This value will be saved in the remoteThis member, and can be provided to other remote objects, on which they can contact the proxy. If the proxy has a string bundle, the localized strings most closely matching the locale of the receiving host will be loaded. If the proxy is graphical in nature, i.e. provides a graphical user interface, this method will return it to the host, so that it may display it, if it wishes.

Parameters:

remoteRef - A reference to the proxy, remoted in the context of the client's VM.

Returns:

The proxy's graphical user interface, if it has one, otherwise null.

getItem

public Remote getItem(String url)
               throws RemoteException,
                      NotBoundException,
                      IOException,
                      ClassNotFoundException,
                      InstantiationException,
                      IllegalAccessException,
                      MalformedURLException

A method will load either an object, or a zipped marshalled object (zedmob) of an object, from a URL, file, or from a remote rmiregistry. If the object is in a local file, it can be either inside the server's jar file, or on its local file system.

Loading an object from a file can be specified in one of three ways:

• As a URL; in the format file://path/name.
• As a class file; in the format path/name
• As a serialized object; in the format /path/name

Parameters:

url - The URL where to get the object: file://, http://, ftp://, /path/name, path/name, or //[host][:port]/[name]. The host, port, and name, are all optional. If missing the host is presumed local, the port 1099, and the name "main". The referenced resource can be returned as a MarshalledObject, it will be extracted automatically. If the URL is null, it will be assumed to be ///.

Returns:

A remote reference to the object contained in the URL. It may be either local, or remote to this VM.

Throws:

RemoteException - if the remote registry could not be reached, or the remote instance could not be be created.

NotBoundException - if the requested name is not in the registry.

IOException - if the zedmob format is invalid.

ClassNotFoundException - if a proxy was sent to the VM, and proxy hosting was not enabled.

InstantiationException - when the URL specifies a class name which cannot be instantiated at runtime.

IllegalAccessException - when the url specifies a class name and it does not support a no-arg constructor.

MalformedURLException - if the URL is not in the format explained

getDescription

public String getDescription()

This method is invoked by remote users of this object. It is expected that subclasses will override this method to provide detailed usage information. Use of HTML for particularly long descriptions is permitted. By default this method will return: not defined.

Returns:

A description of the callable methods, their arguments, returns, and functionality.

contact

public void contact(String url)

This method is canonically called when an proxy announces its reference via the Multicast class. It is expected to receive the URLs of objects that heard the announcement, and wish to be contacted.

Parameters:

url - A //host:port/name type URL on which the 'first-contact' object of a remote VM can be reached.