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<P><FONT size=5><I>Programming in Java Advanced Imaging</I></FONT> </CENTER><BR>
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<TD align=right><FONT size=3>C H A P T E R</FONT><FONT size=7><IMG
src="Client-Server Imaging.files/sm-space.gif">12</FONT></TD></TR></TBODY></TABLE></A></CENTER>
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<FONT size=6>Client-Server Imaging</FONT></TD></TR></TBODY></TABLE></A></CENTER>
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<P><BR><BR><BR>
<P><FONT size=7><B>T</B></FONT>HIS chapter describes JAI's client-server
imaging system.
<P><A name=51145>
<H2>12.1 <IMG
src="Client-Server Imaging.files/space.gif">Introduction</H2></A>Client-server
imaging provides the ability to distribute computation between a set of
processing nodes. For example, it is possible to set up a large, powerful
server that provides image processing services to several thin clients. With
JAI, it is possible for a client to set up a complex imaging chain on a
server, including references to source images on other network hosts, and to
request rendered output from the server.
<P>JAI uses Java Remote Method Invocation (RMI) to implement client-server
imaging. To communicate using Remote Method Invocation, both the client and
server must be running Java. A <EM>stub</EM> object is instantiated on the
client. The stub object forwards its method calls to a corresponding server
object. Method call arguments and return values are transmitted between the
client and server by means of the Java Development Environment's
<EM>serialization</EM> capability.
<P>The hostname and port depend on the local setup. The host must be running
an RMI registry process and have a <CODE>RemoteImageServer</CODE> listening at
the desired port.
<P>This call will result in the creation of a server-side
<CODE>RMIImageImpl</CODE> object and a client-side stub object. The client
stub serializes its method arguments and transfers them to the server over a
socket; the server serializes its return values and returns them in the same
manner.
<P><A name=51212>
<H2>12.2 <IMG src="Client-Server Imaging.files/space.gif">Server Name and Port
Number</H2></A>The <CODE>RemoteImage</CODE> constructor requires a
<CODE>serverName</CODE> parameter that consists of a host name and port
number, in the following format:
<P><PRE> host:port
</PRE>For example:
<P><PRE> camus.eng.sun.com:1099
</PRE>The port number is optional and need be supplied only if the host name
is supplied. If the <CODE>serverName</CODE> parameter is null, the default is
to search for the RMIImage service on the local host at the default
<EM>rmiregistry</EM> port (1099.
<P>
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<HR>
<B>API:</B> <CODE>javax.media.jai.RemoteImage </CODE>
<HR>
</TD></TR></TBODY></TABLE><PRE><UL>
<LI>RemoteImage(String serverName, RenderedImage source)
<P></P></LI></UL></PRE>
<DL><A name=55131>
<DT>
<DD>constructs a <CODE>RemoteImage</CODE> from a <CODE>RenderedImage</CODE>.
<P>
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<TD rowSpan=2><EM>Parameters</EM>:
<P></P>
<TD><CODE>serverName</CODE>
<P></P>
<TD>The name of the server in the appropriate format.
<P></P>
<TR vAlign=top>
<TD><CODE>source</CODE>
<P></P>
<TD>A <CODE>RenderedImage</CODE> source.
<P></P></TR></TBODY></TABLE></A>
<P></P></DD></DL><PRE><UL>
<LI>RemoteImage(String serverName, RenderedOp source)
<P></P></LI></UL></PRE>
<DL><A name=54667>
<DT>
<DD>constructs a <CODE>RemoteImage</CODE> from a <CODE>RenderedOp</CODE>,
i.e., an imaging DAG (directed acyclic graph). Note that the properties of
the <CODE>RemoteImage</CODE> will be those of the <CODE>RenderedOp</CODE>
node and not of its rendering. </A>
<P></P></DD></DL><PRE><UL>
<LI>RemoteImage(String serverName, RenderableOp source,
RenderContext renderContext)
<P></P></LI></UL></PRE>
<DL><A name=55160>
<DT>
<DD>constructs a <CODE>RemoteImage</CODE> from a <CODE>RenderableOp</CODE>
and <CODE>RenderContext</CODE>. The entire <CODE>RenderableOp</CODE> DAG
will be copied over to the server. Note that the properties of the
<CODE>RemoteImage</CODE> will be those of the <CODE>RenderableOp</CODE> node
and not of its rendering. </A>
<P></P></DD></DL><A name=51218>
<H2>12.3 <IMG src="Client-Server Imaging.files/space.gif">Setting the Timeout
Period and Number of Retries</H2></A>A network error or a delay caused by the
server failing to respond to the request for an image is dealt with through
retries. If, on the first attempt, the server fails to respond, the program
will wait a specified amount of time and then make another request for the
image. When the limit of retries is exceeded, a null Raster may be returned.
<P>The amount of time to wait between retries defaults to 1 second (1000
milliseconds). The <CODE>getTimeout</CODE> method is used to get the amount of
time between retries, in milliseconds. The <CODE>setTimeout</CODE> method is
used to set the amount of time between retries.
<P>The number of times the program will attempt to read the remote image may
be read with the <CODE>getNumRetries</CODE> method. The
<CODE>setNumRetries</CODE> method is used to set the maximum number of
retries.
<P>
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<TD>
<HR>
<B>API:</B> <CODE>javax.media.jai.RemoteImage </CODE>
<HR>
</TD></TR></TBODY></TABLE><PRE><UL>
<LI>void setTimeout(int timeout)
<P></P></LI></UL></PRE>
<DL><A name=54566>
<DT>
<DD>sets the amount of time between retries.
<P>
<TABLE cellPadding=3 border=3>
<CAPTION><FONT size=-1><B></B></FONT></CAPTION>
<TBODY>
<TR vAlign=top>
<TD><EM>Parameter</EM>:
<P></P>
<TD><CODE>timeout</CODE>
<P></P>
<TD>The time interval between retries in milliseconds.
<P></P></TR></TBODY></TABLE></A>
<P></P></DD></DL><PRE><UL>
<LI>int getTimeout()
<P></P></LI></UL></PRE>
<DL><A name=54587>
<DT>
<DD>returns the amount of time between retries. </A>
<P></P></DD></DL><PRE><UL>
<LI>void setNumRetries(int numRetries)
<P></P></LI></UL></PRE>
<DL><A name=54597>
<DT>
<DD>sets the number of retries.
<P>
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<CAPTION><FONT size=-1><B></B></FONT></CAPTION>
<TBODY>
<TR vAlign=top>
<TD><EM>Parameter</EM>:
<P></P>
<TD><CODE>numRetries</CODE>
<P></P>
<TD>The maximum number of retries. If this is a negative value, the
number of retries is unchanged.
<P></P></TR></TBODY></TABLE></A>
<P></P></DD></DL><A name=51951>
<H2>12.4 <IMG src="Client-Server Imaging.files/space.gif">Remote Imaging Test
Example</H2></A>This section contains two examples of remote imaging programs.
<P><A name=51974>
<H3>12.4.1 <IMG src="Client-Server Imaging.files/space.gif">Simple Remote
Imaging Example</H3></A><A
href="http://java.sun.com/products/java-media/jai/forDevelopers/jai1_0_1guide-unc/Client-server.doc.html#54012">Listing
12-1</A> shows a complete code example of a <CODE>RemoteImaging</CODE> test.
This example displays a 2 x 2 grid of <CODE>ScrollingImagePanel</CODE>s, with
each window displaying the sum of two byte images that were rescaled to the
range [0,127] prior to addition. The panels display the following specific
results:
<P>
<UL>
<LI>upper left: local rendering
<P></P></LI></UL>
<UL>
<LI>upper right: result of remote rendering of a RenderedOp graph
<P></P></LI></UL>
<UL>
<LI>lower left: result of remote loading of a RenderedImage
<P></P></LI></UL>
<UL>
<LI>lower right: result of remote rendering of a RenderableOp graph
<P></P></LI></UL>The lower right image is a dithered version of the sum image
passed through a color cube lookup table and may appear slightly different
from the other three images, which should be identical.
<P><CAPTION><FONT size=-1><B><A name=54012>
<CENTER><FONT size=-1><B><I>Listing 12-1 </I><IMG
src="Client-Server Imaging.files/sm-blank.gif" border=0> Remote Imaging
Example Program (Sheet 1 of 4)</B></FONT></CENTER></A>
<P></B></FONT></CAPTION>
<HR>
<TR valign="top"><TD rowspan="10" colspan="1"><PRE> import java.awt.*;
import java.awt.event.WindowEvent;
import java.awt.geom.*;
import java.awt.image.*;
import java.awt.image.renderable.*;
import java.util.*;
import javax.media.jai.*;
import javax.media.jai.operator.*;
import javax.media.jai.widget.*;
public class RemoteImagingTest extends WindowContainer {
</PRE><TR valign="top"><TR valign="top"><TR valign="top"><TR valign="top"><TR
valign="top"><TR valign="top"><TR valign="top"><TR valign="top"><TR
valign="top"><TR valign="top"><TD rowspan="2" colspan="1"><PRE> /** Default remote server. */
private static final String DEFAULT_SERVER =
"camus.eng.sun.com:1099";
</PRE><TR valign="top"><TR valign="top"><TD rowspan="3" colspan="1"><PRE> /** Tile dimensions. */
private static final int TILE_WIDTH = 256;
private static final int TILE_HEIGHT = 256;
</PRE><TR valign="top"><TR valign="top"><TR valign="top"><TD rowspan="3"
colspan="1"><PRE> public static void main(String args[]) {
String fileName1 = null;
String fileName2 = null;
</PRE><TR valign="top"><TR valign="top"><TR valign="top"><TD rowspan="7"
colspan="1"><PRE> // Check args.
if(!(args.length >= 0 && args.length <= 3)) {
System.out.println("\nUsage: java RemoteImagingTest "+
"[[[serverName] | [fileName1 fileName2]] | "+
"[serverName fileName1 fileName2]]"+"\n");
System.exit(1);
}
</PRE><TR valign="top"><TR valign="top"><TR valign="top"><TR valign="top"><TR
valign="top"><TR valign="top"><TR valign="top"><TD rowspan="9" colspan="1"><PRE> // Set the server name.
String serverName = null;
if(args.length == 0 || args.length == 2) {
serverName = DEFAULT_SERVER;
System.out.println("\nUsing default server '"+
DEFAULT_SERVER+"'\n");
} else {
serverName = args[0];
}
</PRE><TR valign="top"><TR valign="top"><TR valign="top"><TR valign="top"><TR
valign="top"><TR valign="top"><TR valign="top"><TR valign="top"><TR
valign="top"><TD rowspan="13" colspan="1"><PRE> // Set the file names.
if(args.length == 2) {
fileName1 = args[0];
fileName2 = args[1];
} else if(args.length == 3) {
fileName1 = args[1];
fileName2 = args[2];
} else {
fileName1 = "/import/jai/JAI_RP/test/images/Boat_At_Dock.tif";
fileName2 = "/import/jai/JAI_RP/test/images/FarmHouse.tif";
System.out.println("\nUsing default images '"+
fileName1 + "' and '" + fileName2 + "'\n");
}
</PRE><TR valign="top"><TR valign="top"><TR valign="top"><TR valign="top"><TR
valign="top"><TR valign="top"><TR valign="top"><TR valign="top"><TR
valign="top"><TR valign="top"><TR valign="top"><TR valign="top"><TR
valign="top"><TD rowspan="3" colspan="1"><PRE> RemoteImagingTest riTest =
new RemoteImagingTest(serverName, fileName1, fileName2);
}
</PRE><TR valign="top"><TR valign="top"><TR valign="top"><TD rowspan="11"
colspan="1"><PRE> /**
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