Folks,
Here is the proposal. The audience for this tool is those that dislike
RMI in that it needs special interfaces (must extend Remote, must
specify RemoteException). Those people that dislike RMI may have come
across Glue ( http://www.themindelectric.com/products/glue/glue.html )
and its unhindered interface publication scheme. People that dabble
with .NET claim that it has a similar unencumbered method publication
scheme.
AltRMI is the same idea as Glue but not over SOAP. Again, this is not
for people that think there is nothing wrong with RMI as is. The first
alpha version has been used by Avalon-Cornerstone as a XML configurable
'block' that other blocks can depend on. That block has already been
used by AvalonDB - a full RDBMS being built by a few of us in
Avalon-Cornerstone's CVS. Incidentally, AltRMI was code ripped out of
AvalonDB and generalized.
There are a few differences with Glue :
1) Not over SOAP. In this respect Glue is a very accomplished bit of work.
2) AltRMI can be instrcted as to what is pass by value and what is pass
by reference (Glue can't).
3) Glue does not generate client side proxy code, AltRMI does. The Glue
solution is compatible with JDK1.1, 1.2, 1.3, 1.4 (according to Graham
Glass) and therefore very flexible. The secret solution Glue uses does
not support introspection on the client side. AltRMI does generate
proxy classes for client side use. As such it is introspectable. This
is of most use to scripting languages/envs (Rhino, Beanshell etc). At
the bottom of this email is a example generated proxy class.
We (I) need to build a community around AltRMI. There are quite a few
things to do. Please take a few minutes to read the following proposal.
If you are interested in running AltRMI, its CVS dir contains a README
file for instructions. Alt positive ideas/patches very welcome.
Regards,
- Paul H
--------------------------------------------------------------------------
JAKARTA COMMONS - ALTERNATIVE (TO) REMOTE METHOD INVOCATION - "AltRMI"
--------------------------------------------------------------------------
Abstract:
The AltRMI package provides an alternative to Java's RMI. Apart from
simply
being an alternative it provides the following features:
1) Any interface publishing
- no forcing of extension of java.rmi.Remote
- no forced declarations of "throws RemoteException"
* These two features are part of the reason why Graham Glass's 'Glue'
product is so successful. His API goes several stages futher in that
it pubishes APIs via SOAP so that any language in any location can
use Glue published Java services.
2) Multiple transports
- Plain Sockets / ObjectStream
- via RMI
- Piped with same VM / ObjectStream
- Direct within same VM
- SOAP (planned)
- Might require additional undynamic "toWSDL()" step.
- CORBA (planned)
- Might require additional undynamic "toIDL()" step.
- Plain sockets / custom messaging (planned)
- JMS (planned)
3) Speed
- Using the AltRMI over RMI transport as a baseline. Measuring 100,000
method invocations after discarding the first for the purposes of
timing, ObjStream over sockets is three times faster, ObjStream over
Pipe is eleven times faster, Direct is a thousand times faster. Granted
there could be less of an advantage if compared to a proper RMI solution
(not layered), or one that is in the same VM with different threads.
4) Interface/Impl separated design.
- AltRMI can be build easily into any application or application
framework.
Individual aspects can be reimplemented (or overridden) as the need
arises.
5) Choice of location of generated Proxy class.
- Classes providing client side implementation of the transported
interface(s) can be either on the client side or the server side (and
duly transported) at time of lookup.
6) Choice of castability of generated proxy class.
- To suit remote facilities that are happy with refection and do
not need to cast to an interface to use a bean (I am thinking of
beanshell) the proxy class can be generated without specifying
that it implements the interface(s).
7) Suspendable/Resumable service.
- The Server supports suspend() and resume(). With the current impl this
replies in a timely fashion to the client that the client should try
later. The client waits for the notified amount of time and seamlessly
trys the requets again. A server could cycle through suspended and back
to resumed will not affect the client except for the a delay.
8) Recovering transport
- AltRMI tries to recover its transports should they fail. The recovery
is pluggable in that the developer can choose when/how/if the connection
handler tries to recover the connection. Any inprogress, but
disconnected method invocation will attempt to be recoved and just
return
as normal, albeit after a longer than normal delay.
9) Event API
- For suspensions, abnormal ends of connection etc, there is a listener
that can be set that will allow actions to be taken. Abnormally
terminated connections will by default try to be reconnected, the
listener can decide if, how many, and how often the retries occur.
10) Unpublishable and republishable API
- The server is able to unpublish a service. In conjuction with
suspend()/resume() a service can be republished, upgraded etc
whilst in use, or just offlined.
11) Startable API for Server
- The server implements and acts upon start() and stop() methods.
12) No just pass by value.
- AltRMI started life as 'pass by value' only. In now supports return
types and parameters wrapped in another AltRMI Facade.
13) No duplicate instances.
- If you call Person p = getPerson("Fred") twice you will get the same
instance on the client side is it is the same instance on the server
side.
Limitations:
1) Use in EJB
- This is not of any use for EJB Home/Remote interfaces. The container
maker chooses the transport for use that container, not the bean coder.
This is intended for other client server solutions. Beside RMI over
IIOP
is Sun specified.
Todo:
1) Other transports
- SOAP, CORBA (with WDSL & IDL generation steps)
- Other RMI (over IIOP, over HTTP)
- Custom, socket protocol
- JMS
2) BCEL for generated proxy class.
- The current impl writes java source then compiles it. We could do this
inline with BCEL. This as an heavier, but more design perfect
alternative to the current server side impl.
- BCEL is really difficult to use if you are not skilled in it!!
3) Client and Server code for secure conversations.
4) Authentication and Authorisation on lookup(..).
Initial committers:
Paul Hammant (hammant)
--------------------------------------------------------------------------
Example Generated Proxy class. Not for editing, not normally
for user viewing. A step similar to rmic.
--------------------------------------------------------------------------
public final class AltrmiGeneratedHello_Main implements
org.apache.commons.altrmi.test.TestInterface {
private transient
org.apache.commons.altrmi.client.impl.BaseServedObject mBaseServedObject;
public AltrmiGeneratedHello_Main
(org.apache.commons.altrmi.client.impl.BaseServedObject baseServedObject) {
mBaseServedObject = baseServedObject;
}
public void hello (java.lang.String v0) {
Object[] args = new Object[1];
args[0] = v0;
try {
mBaseServedObject.altrmiProcessVoidRequest("hello(java.lang.String)",args);
} catch (Throwable t) {
if (t instanceof RuntimeException) {
throw (RuntimeException) t;
} else if (t instanceof Error) {
throw (Error) t;
} else {
throw new
org.apache.commons.altrmi.common.AltrmiInvocationException("Should never
get here" + t.getMessage());
}
}
}
public boolean hello3 (short v0) throws
java.beans.PropertyVetoException, java.io.IOException{
Object[] args = new Object[1];
args[0] = new Short(v0);
try {
Object retVal =
mBaseServedObject.altrmiProcessObjectRequest("hello3(short)",args);
return ((Boolean) retVal).booleanValue();
} catch (Throwable t) {
if (t instanceof java.beans.PropertyVetoException) {
throw (java.beans.PropertyVetoException) t;
} else if (t instanceof java.io.IOException) {
throw (java.io.IOException) t;
} else if (t instanceof RuntimeException) {
throw (RuntimeException) t;
} else if (t instanceof Error) {
throw (Error) t;
} else {
throw new
org.apache.commons.altrmi.common.AltrmiInvocationException("Should never
get here" + t.getMessage());
}
}
}
}
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