rmi.html

java 基础的 一点东西,,可以看看

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

<A NAME="compile"></A>
<H4>Compile the Example</H4> 

These instructions assume development is in the <CODE>zelda</CODE> 
home directory.  The server program is compiled in the home directory 
for user <CODE>zelda</CODE>, but copied to the <CODE>public_html</CODE>
directory for user <CODE>zelda</CODE> where it runs.

<P>
Here is the command sequence for
the Unix and Win32 platforms; an explanation follows.

</FONT>

<PRE>
<STRONG>Unix:</STRONG>
cd /home/zelda/classes
javac Send.java
javac RemoteServer.java
javac RMIClient2.java
javac RMIClient1.java
rmic -d . RemoteServer
cp RemoteServer*.class /home/zelda/public_html/classes
cp Send.class /home/zelda/public_html/classes
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

</FONT>

<PRE>
<STRONG>Win32:</STRONG>
cd \home\zelda\classes
javac Send.java
javac RemoteServer.java
javac RMIClient2.java
javac RMIClient1.java
rmic -d . RemoteServer
copy RemoteServer*.class \home\zelda\public_html\classes
copy Send.class \home\zelda\public_html\classes
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

The first two <CODE>javac</CODE> commands compile the
<CODE>RemoteServer</CODE> and <CODE>Send</CODE> class and
interface.  The third <CODE>javac</CODE> command compiles the
<CODE>RMIClient2</CODE> class. The last <CODE>javac</CODE> command 
compiles the <CODE>RMIClient1</CODE> class.

<P>
The next line runs the <CODE>rmic</CODE> command on the 
<CODE>RemoteServer</CODE> server class. This command produces output 
class files of the form <CODE>ClassName_Stub.class</CODE>
and <CODE>ClassName_Skel.class</CODE>. These output classes
let clients invoke methods on the <CODE>RemoteServer</CODE>
server object. 

<P>
The first copy command moves the <CODE>RemoteServer</CODE>
class file with its associated <CODE>skel</CODE> and 
<CODE>stub</CODE> class files to a publicly accessible 
location in the <CODE>/home/zelda/public_html/classes</CODE>
directory, which is on the server machine,
so they can be publicly accessed and downloaded. 
They are placed in the <CODE>public_html</CODE> directory to be 
under the web server running on the server machine because
these files are accessed by client programs using URLs.

<P>
The second copy command moves the <CODE>Send</CODE> class file 
to the same location for the same reason. The
<CODE>RMIClient1</CODE> and <CODE>RMIClient2</CODE> class files
are not made publicly accessible; they communicate from their
client machines using URLs
to access and download the remote object files in the
<CODE>public_html</CODE> directory.

<UL>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<CODE>RMIClient1</CODE> is invoked from a client-side directory
and uses the 
server-side web server and client-side Java VM to download the 
publicly accessible files. </FONT>

<P>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif"><CODE>RMIClient2</CODE> is invoked from a client-side directory
and uses the server-side web server and client-side Java VM to
download the publicly accessible files. </FONT>
</UL>

<P>
<IMG SRC="./Art/web.gif" WIDTH="372" HEIGHT="327" ALT="">

<A NAME="regis"></A>
<H4>Start the RMI Registry</H4>

Before you start the client programs, you must start the
RMI Registry, which is a server-side naming repository 
that allows remote clients to get a reference to the remote 
server object. 

<P>
Before you start the RMI Registry, make sure the
shell or window in which you run the <CODE>rmiregistry</CODE>
command does not have a <CODE>CLASSPATH</CODE> environment variable
that points to the remote object classes, including
the <CODE>stub</CODE> and <CODE>skel</CODE> classes, anywhere
on your system. If the RMI Registry finds these classes
when it starts, it will not load them from the server-side Java 
VM, which will create problems when clients try to download the 
remote server classes.

<P>
<A NAME="registry"></A>
The following commands unset the <CODE>CLASSPATH</CODE> and
 start the RMI Registry on the default
1099 port. You can specify a different port by
adding the port number as follows:
<CODE>rmiregistry 4444 &amp;</CODE>. If you specify a different
port number, you must specify the same port number in
your <A HREF="#port">server-side</A> code as well.

</FONT>

<PRE>
<STRONG>Unix:</STRONG>
cd /home/zelda/public_html/classes
unsetenv CLASSPATH
rmiregistry &amp;
</PRE>

<PRE>
<STRONG>Win32:</STRONG>
cd \home\zelda\public_html\classes
set CLASSPATH=
start rmiregistry 
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

<BLOCKQUOTE>
<HR>
<STRONG>Note:</STRONG> You might want to set the
<CODE>CLASSPATH</CODE> back to its original
setting at this point.
<HR>
</BLOCKQUOTE>

<A NAME="remote"></A>
<H4>Run the RemoteServer Server Object</H4>

To run the example programs, start <CODE>RemoteServer</CODE>
first. If you start either  <CODE>RMIClient1</CODE>
or <CODE>RMIClient2</CODE> first, they will not be able
to establish a connection because the remote
server object is not running.

<P>
In this example, <CODE>RemoteServer</CODE> is started from the
<CODE>/home/zelda/public_html/classes</CODE> directory.

<P>
The lines beginning at <CODE>java</CODE> should be all on
one line with spaces where the lines break. The properties
specified with the <CODE>-D</CODE>
option to the <CODE>java</CODE> interpreter command
are program attributes that manage the behavior of the program
for this invocation.

</FONT>

<PRE>
<STRONG>Unix:</STRONG>
cd /home/zelda/public_html/classes
java 
-Djava.rmi.server.codebase=http://kq6py/~zelda/classes
-Djava.rmi.server.hostname=kq6py.eng.sun.com
-Djava.security.policy=java.policy RemoteServer
</PRE>

<PRE>
<STRONG>Win32:</STRONG>
cd \home\zelda\public_html\classes
java -Djava.rmi.server.codebase=file:
       c:\home\zelda\public_html\classes
-Djava.rmi.server.hostname=kq6py.eng.sun.com
-Djava.security.policy=java.policy RemoteServer
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

<UL>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">The 
<CODE>java.rmi.server.codebase</CODE> property specifies
where the publicly accessible classes are located.</FONT>
<P>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">The 
<CODE>java.rmi.server.hostname</CODE> property is the
complete host name of the server where the publicly accessible
classes reside.</FONT>
<P>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">The 
<CODE>java.rmi.security.policy</CODE> property specifies
the <A HREF="./Code/java.policy">policy file</A>
with the permissions needed to run the remote server object and
access the remote server classes for download.</FONT>

<P>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">The class to execute 
(<CODE>RemoteServer</CODE>).</FONT>
</UL>

<A NAME="1"></A>
<H4>Run the RMIClient1 Program</H4>

Here is the command sequence for the Unix and Win32 platforms;
an explanation follows.

<P>
In this example, <CODE>RMIClient1</CODE> is started from the
<CODE>/home/zelda/classes</CODE> directory.

<P>
The lines beginning at <CODE>java</CODE> should be all on
one line with spaces where the lines break.
Properties specified with the
<CODE>-D</CODE> option to the <CODE>java</CODE> interpreter
command are program attributes that manage the behavior of the program
for this invocation.

</FONT>

<PRE>
<STRONG>Unix:</STRONG>
cd /home/zelda/classes

java -Djava.rmi.server.codebase=
                         http://kq6py/~zelda/classes/
-Djava.security.policy=java.policy 
                  RMIClient1 kq6py.eng.sun.com
</PRE>

<PRE>
<STRONG>Win32:</STRONG>
cd \home\zelda\classes

java -Djava.rmi.server.codebase=
                         file:c:\home\zelda\classes\
-Djava.security.policy=java.policy 
                         RMIClient1 kq6py.eng.sun.com
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

<UL>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">The 
<CODE>java.rmi.server.codebase</CODE> property specifies
where the publicly accessible classes for downloading are located.</FONT>
<P>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">The 
<CODE>java.security.policy</CODE> property specifies
the <A HREF="./Code/java.policy">policy file</A>
with the permissions needed to run the client program and access
the remote server classes.</FONT>
<P>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">The client program 
class to execute (<CODE>RMIClient1</CODE>),
and the host name of the server (<CODE>Kq6py</CODE>) where
the remote server classes are.</FONT>
</UL>

<A NAME="2"></A>
<H4>Run RMIClient2</H4>

Here is the command sequence for the Unix and Win32
platforms; an explanation follows.

<P>
In this example, <CODE>RMIClient2</CODE> is started from the
<CODE>/home/zelda/classes</CODE> directory.

<P>
The lines beginning at <CODE>java</CODE> should be all on
one line with spaces where the lines break. The properties
specified with the <CODE>-D</CODE>
option to the <CODE>java</CODE> interpreter command
are program attributes that manage the behavior of the program
for this invocation.

</FONT>

<PRE>
<STRONG>Unix:</STRONG>
cd /home/zelda/classes
java -Djava.rmi.server.codebase=
                         http://kq6py/~zelda/classes
-Djava.security.policy=java.policy 
                         RMIClient2 kq6py.eng.sun.com
</PRE>

<PRE>
<STRONG>Win32:</STRONG>
cd \home\zelda\classes
java -Djava.rmi.server.codebase=
                file:c:\home\zelda\public_html\classes
-Djava.security.policy=java.policy 
                         RMIClient2 kq6py.eng.sun.com
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

<UL>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">The 
<CODE>java.rmi.server.codebase</CODE> property specifies
where the publicly accessible classes are located.</FONT>
<P>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">The 
<CODE>java.rmi.server.hostname</CODE> property is the
complete host name of the server where the publicly accessible
classes reside.</FONT>
<P>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">The 
<CODE>java.rmi.security.policy</CODE> property specifies
the <A HREF="./Code/java.policy">policy file</A>
with the permissions needed to run the remote server object and
access the remote server classes for download.</FONT>
<P>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">The class to 
execute (<CODE>RMIClient2</CODE>).</FONT>
</UL>

<A NAME="send"></A>
<H3>RemoteServer Class</H3>

The <A HREF="./Code/RemoteServer.java">RemoteServer</A> class 
extends <CODE>UnicastRemoteObject</CODE> and implements the
<CODE>sendData</CODE> and <CODE>getData</CODE> methods
declared in the <CODE>Send</CODE> interface. These
are the remotely accessible methods.

<P>
<CODE>UnicastRemoteObject</CODE> implements a number of
<CODE>java.lang.Object</CODE> methods for remote objects
and includes constructors and static methods to make
a remote object available to receive method calls from
client programs.

</FONT>

<PRE>
class RemoteServer extends UnicastRemoteObject
                 implements Send {

  String text;

  public RemoteServer() throws RemoteException {
    super();
  }

  public void sendData(String gotText){
    text = gotText;
  }

  public String getData(){
    return text;
  }
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

The <CODE>main</CODE> method installs the
<CODE>RMISecurityManager</CODE> and opens
a connection with a port on the machine
where the server program runs.
The security manager determines whether there is a policy file
that lets downloaded code perform tasks that require permissions.

<A NAME="port"></A>
The <CODE>main</CODE> method creates a name for the