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Class ncsa.horizon.util.MessageCenter

java.lang.Object
  |
  +--ncsa.horizon.util.MessageCenter

public class MessageCenter

extends java.lang.Object

implements MessageCenter.Slots

a manager of a set of message streams used for communicating with the user.

A MessageCenter provides a place for one or more objects to send text messages that are meant for view by the user. Typically when one wants to send a message to the user, one often calls System.out.println; however, in a GUI-type application, the visible destination of such message (e.g. a browser's Java console) may not be very noticable to the user. Instead, one might rather want to display them in a TextArea object. Or, the user might only want them to appear in certain applications or circumstances like during debugging. This class provides an application and its objects a place to send messages, whether or not they should appear or not. Where the messages appear can be set once at the application level or altered throughout the session.

A MessageCenter maintains a stack of MultiPrintWriters, that the user can choose from to send messages to. By default, these Writers do not print their messages anywhere--they just disappear into the bit-bucket; however, one can attach one or more output streams any of the MultiPrintWriters so that any message written to the MultiPrintWriters will be multicasted to all the streams attached to it. Each MultiPrintWriter--or slot--can take different kinds of messages. Four default writers--OUT, ERR, DEBUG, STATUS, and HELP--are provided automatically; however, any number of writer slots can be added as necessary. The different slots are referred to via an integer slot index with the default buffers occupying slots 0 thru 4.

Here's an example of its use:

     MessageCenter mc = new MessageCenter();
     mc.addToSlot(OUT, System.out);         // send OUT messages to stdout

     // send some messages
     mc.println(mc.OUT, "This is a message.");          // appear on stdout.
     mc.println(mc.OUT, "This is a another message.");  //   this, too.
     mc.println(mc.DEBUG, "About to give user help.")     // these do not 
     mc.println(mc.HELP, "Click any button to proceed.")  //    appear.

     // create a new buffer
     int test = nextIndex();
     mc.addToSlot(test, System.err)   // send two slot choice to stderr
     mc.println(test, "I now have " + (mc.maxIndex() + 1) + " buffer slots");
 

As the name implies, a MessageCenter is meant to service a number of client objects wishing to print to different or the same buffers. Horizon maintains a MessageCenter via a public final static member field of the Horizon class. Clients can either use that MessageCenter direcly from that reference or extract out the streams of interest, load them with real target streams, and save the streams of interest--or, save the reference away locally for future use.

If an application wants messages saved away in memory for access later, one can attach a MessageBuffer stream to a slot. The MessageBuffer can be accessed later by a GUI component such as a TextArea for display.

See Also:

MultiPrintWriter, MessageBuffer, Horizon

Inner Class Summary

static

MessageCenter.Slots predefined slots for MessageCenter output streams.

Field Summary

java.util.Vector

writers the collection of MessageBuffer objects

Constructor Summary

MessageCenter()
Create a new MessageCenter.

MessageCenter(boolean useSysStrms, boolean debug)
Create a new MessageCenter

Method Summary

void	addSysStreams() add System.out to the OUT and System.err to the ERR and STATUS slots.
void	addToSlot(int slot, java.io.PrintWriter wr) add a PrintWriter to a slot
void	addToSlot(int slot, java.io.Writer wr) add a Writer to a slot
void	addToSlot(int slot, java.io.OutputStream os) add an OutputStream to a slot
MultiPrintWriter	getPrintWriter(int slot) return the MultiPrintWriter in a given slot.
static void	main(java.lang.String[] argv)
int	maxIndex() return the maximum buffer index currently in use.
int	nextIndex() return the next available index for a message buffer
void	println(int slot, java.lang.String s) print a String and a newline to the streams at a given slot.
void	print(int slot, java.lang.String s) print a String to the streams at a given slot.
void	removeFromSlot(int slot, java.io.Writer wr) remove a PrintWriter from a slot
void	removeFromSlot(int slot, java.io.OutputStream os) remove a PrintWriter from a slot
void	removeSysStreams() remove System.out and System.err to the OUT and ERR slots, respectively

Methods inherited from class java.lang.Object

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

Field Detail

writers

protected java.util.Vector writers

the collection of MessageBuffer objects

Constructor Detail

MessageCenter

public MessageCenter()

Create a new MessageCenter.

MessageCenter

public MessageCenter(boolean useSysStrms,
                     boolean debug)

Create a new MessageCenter

Parameters:

useSysStrms - if true, attach System.out and System.err to the OUT and ERR streams, respectively

debug - if true, attach System.err to the DEBUG

Method Detail

getPrintWriter

public MultiPrintWriter getPrintWriter(int slot)
                                                 throws java.lang.ArrayIndexOutOfBoundsException

return the MultiPrintWriter in a given slot. If it does not already exist, it will be created.

Throws:

java.lang.ArrayIndexOutOfBoundsException - if slot < 0

addToSlot

public void addToSlot(int slot,
                      java.io.PrintWriter wr)
              throws java.lang.ArrayIndexOutOfBoundsException

add a PrintWriter to a slot

addToSlot

public void addToSlot(int slot,
                      java.io.Writer wr)
              throws java.lang.ArrayIndexOutOfBoundsException

add a Writer to a slot

addToSlot

public void addToSlot(int slot,
                      java.io.OutputStream os)
              throws java.lang.ArrayIndexOutOfBoundsException

add an OutputStream to a slot

removeFromSlot

public void removeFromSlot(int slot,
                           java.io.Writer wr)

remove a PrintWriter from a slot

removeFromSlot

public void removeFromSlot(int slot,
                           java.io.OutputStream os)

remove a PrintWriter from a slot

addSysStreams

public void addSysStreams()

add System.out to the OUT and System.err to the ERR and STATUS slots.

removeSysStreams

public void removeSysStreams()

remove System.out and System.err to the OUT and ERR slots, respectively

print

public void print(int slot,
                  java.lang.String s)

print a String to the streams at a given slot. If the slot does not exist, nothing happens.

println

public void println(int slot,
                    java.lang.String s)

print a String and a newline to the streams at a given slot. If the slot does not exist, nothing happens.

maxIndex

public final int maxIndex()

return the maximum buffer index currently in use.

nextIndex

public int nextIndex()

return the next available index for a message buffer

main

public static void main(java.lang.String[] argv)