One bound RMI name can be used by Multiple client? [closed] - java

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I am trying to run 3 RMI servers on single (96 Ram) machine. From three different machine clients are calling, but for three clients I have given 3 different port numbers and binded object name are also different for all three client.
For 1st 2 client I got the output and for thirst one I am not getting any output. Only "Null Pointer exception" I am getting on client side. On Server side I have given -Xms250m to -Xmx 20g on all 3 server. On client all have 8 GB ram I have given -Xmx6g.

You need to use a customized RMIRegistry port to have two or more registry instances run in a same machine. See this fully working RMI Server and Client example, you can run multiple clients connecting to the same remote object instance. Remember to synchronize internal behaviour of the service implementation.
Here is a remote service interface and implementation run on server machine.
import java.rmi.*;
public interface CounterService extends Remote {
public void setValue(String value) throws RemoteException;
public String getValue() throws RemoteException;
}
- - - - - -
import java.rmi.*;
public class CounterServiceImpl implements CounterService {
private int callCount=0;
private String name;
private String value;
public CounterServiceImpl(String name) {
this.name=name;
this.value="";
}
public synchronized void setValue(String value) throws RemoteException {
callCount++;
this.value=value;
}
public synchronized String getValue() throws RemoteException {
callCount++;
return String.format("%s (name=%s, callcount=%d)", value, name, callCount);
}
}
Here is a RMI client and server implementation.
import java.util.*;
import java.rmi.*;
import java.rmi.registry.Registry;
import java.rmi.registry.LocateRegistry;
import java.rmi.server.UnicastRemoteObject;
import java.rmi.server.ExportException;
public class RMITest1Client {
private static Random randomInt = new Random();
public static int getRandomInt(int min, int max) {
int range = (max - min) + 1;
return randomInt.nextInt(range) + min;
}
public static void main(String[] args) throws Exception {
String rmiEndPoint = args[0];
String serviceName = args[1];
CounterService counter = (CounterService)Naming.lookup(rmiEndPoint+"/"+serviceName);
System.out.println("Connected to " + rmiEndPoint+"/"+serviceName);
for(int idx=0; idx<10; idx++) {
System.out.println("getValue="+counter.getValue());
Thread.sleep(getRandomInt(1, 5)*1000);
counter.setValue( "val"+getRandomInt(100, 999) );
Thread.sleep(getRandomInt(1, 5)*1000);
}
}
}
- - - - - -
import java.rmi.*;
import java.rmi.registry.Registry;
import java.rmi.registry.LocateRegistry;
import java.rmi.server.UnicastRemoteObject;
import java.rmi.server.ExportException;
public class RMITest1Server {
public static void main(String[] args) throws Exception {
// create the RMIregistry service
int port = Integer.parseInt(args[0]);
Registry registry;
try {
System.out.println("RMIRegistry on port " + port);
registry = LocateRegistry.createRegistry(port);
} catch (ExportException ex) {
// registry may already be created by another process,
// get reference to an existing registry instance.
System.out.println("Creating registry failed, try to connect an existing registry, ex="+ex.getMessage());
registry = LocateRegistry.getRegistry(port);
}
CounterService counter = new CounterServiceImpl("counter1");
UnicastRemoteObject.exportObject(counter, port);
registry.rebind("counter1", counter);
counter = new CounterServiceImpl("counter2");
UnicastRemoteObject.exportObject(counter, port);
registry.rebind("counter2", counter);
System.out.println("Running...");
Thread.sleep(30000);
// close registry objects
for(String serviceName : registry.list()) {
try {
System.out.println("RMIRegistry unbind " + serviceName);
Remote obj = (Remote)registry.lookup(serviceName);
UnicastRemoteObject.unexportObject(obj, true);
} catch (Exception ex) { }
try { registry.unbind(serviceName); } catch (Exception ex) { }
}
System.out.println("RMIRegistry closed");
System.exit(0); // mandatory if RMIRegistry was started in this JVM instance
}
}
Here are test scripts to run server and client.
**goServer.bat**
#SET /p port=Server port (2222, 3333, 0=exit):
#IF "0"=="%port%" GOTO :EOF
java -cp "./lib/*;" RMITest1Server %port%
pause
- - - - - -
**goClient.bat**
#SET /p port=Server port (2222, 3333, 0=exit):
#IF "0"=="%port%" GOTO :EOF
#SET /p service=Service index (1,2):
java -cp "./lib/*;" RMITest1Client rmi://127.0.0.1:%port% counter%service%
pause

Related

Java create/overwrite http server

I'm creating a plugin on a certain platform (the details are irrelevant) and need to create a HTTP endpoint. In normal circumstances you'd create a http server and stop it whenever you're done using it or when the application stops, however, in my case I can't detect when the plugin is being uninstalled/reinstalled.
The problem
When someone installs my plugin twice, the second time it will throw an error because I'm trying to create a http server on a port which is already in use. Since it's being reinstalled, I can't save the http server on some static variable either. In other words, I need to be able to stop a previously created http server without having any reference to it.
My attempt
I figured the only way to interact with the original reference to the http server would be to create a thread whenever the http server starts, and then overwrite the interrupt() method to stop the server, but somehow I'm still receiving the 'port is already in use' error. I'm using Undertow as my http server library, but this problem applies to any http server implementation.
import io.undertow.Undertow;
import io.undertow.util.Headers;
public class SomeServlet extends Thread {
private static final String THREAD_NAME = "some-servlet-container-5391301";
private static final int PORT = 5839;
private Undertow server;
public static void listen() { // this method is called whenever my plugin is installed
deleteExistingServer();
new SomeServlet().start();
}
private static void deleteExistingServer() {
for (Thread t : Thread.getAllStackTraces().keySet()) {
if (t.getName().equals(THREAD_NAME)) {
t.interrupt();
}
}
}
#Override
public void run() {
createServer();
}
#Override
public void interrupt() {
try {
System.out.println("INTERRUPT");
this.server.stop();
} finally {
super.interrupt();
}
}
private void createServer() {
this.server = Undertow.builder()
.addHttpListener(PORT, "localhost")
.setHandler(exchange -> {
exchange.getResponseHeaders().put(Headers.CONTENT_TYPE, "text/plain");
exchange.getResponseSender().send("Hello World!");
})
.build();
this.server.start();
}
}
Desired behaviour
Whenever listen() is called, it will remove any previously existing http server and create a new one, without relying on storing the server on a static variable.
You could try com.sun.net.httpserver.HttpServer. Use http://localhost:8765/stop to stop and 'http://localhost:8765/test' for test request:
import com.sun.net.httpserver.HttpServer;
import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;
public class TestHttpServer {
public static void main(String[] args) throws IOException {
final HttpServer server = HttpServer.create();
server.bind(new InetSocketAddress(8765), 0);
server.createContext("/test", httpExchange -> {
String response = "<html>TEST!!!</html>";
httpExchange.sendResponseHeaders(200, response.length());
OutputStream os = httpExchange.getResponseBody();
os.write(response.getBytes());
os.close();
});
server.createContext("/stop", httpExchange -> server.stop(1));
server.start();
}
}

Matlab Java Interoperability

Our web app acts as an integration layer which allows the users to run Matlab code (Matlab is a scientific programming language) which was compiled to Java, packaged up as jar files via browser (selected ones as in above image, except for remote_proxy-1.0.0.jar which is not, it is used for RMI).
The problem is that, Matlab Java runtime, contained inside the javabuilder-1.0.0.jar file, has a process-wide blocking mechanism which means if the first user sends an HTTP request to execute the cdf_read-1.0.0.jar or any Matlab-compiled-to-Java jars at all, then subsequent requests will block until the first one finishes and it will take no less than 5 seconds since JNI is used to invoke the native Matlab code and because the app server just spawns new threads to serve each request, but once again, due to the process-wide locking mechanism of Matlab Java runtime, these newly spawned threads will just block waiting for the first request to be fulfilled, thus our app can technically serve one user at a time.
So to work around this problem, for each such request, we start a new JVM process, send the request to this new process to run the job using RMI, then return the result back to the app server's process, then destroy the spawned process. So we've solved the blocking issue, but this is not very good at all in terms of memory used, this is a niche app, so number of users is in the range of thoudsands. Below is the code used to start a new process to run the BootStrap class which starts a new RMI registry, and binds a remote object to run the job.
package rmi;
import java.io.*;
import java.nio.file.*;
import static java.util.stream.Collectors.joining;
import java.util.stream.Stream;
import javax.enterprise.concurrent.ManagedExecutorService;
import org.slf4j.LoggerFactory;
//TODO: Remove sout
public class ProcessInit {
public static Process startRMIServer(ManagedExecutorService pool, String WEBINF, int port, String jar) {
ProcessBuilder pb = new ProcessBuilder();
Path wd = Paths.get(WEBINF);
pb.directory(wd.resolve("classes").toFile());
Path lib = wd.resolve("lib");
String cp = Stream.of("javabuilder-1.0.0.jar", "remote_proxy-1.0.0.jar", jar)
.map(e -> lib.resolve(e).toString())
.collect(joining(File.pathSeparator));
pb.command("java", "-cp", "." + File.pathSeparator + cp, "rmi.BootStrap", String.valueOf(port));
while (true) {
try {
Process p = pb.start();
pool.execute(() -> flushIStream(p.getInputStream()));
pool.execute(() -> flushIStream(p.getErrorStream()));
return p;
} catch (Exception ex) {
ex.printStackTrace();
System.out.println("Retrying....");
}
}
}
private static void flushIStream(InputStream is) {
try (BufferedReader br = new BufferedReader(new InputStreamReader(is))) {
br.lines().forEach(System.out::println);
} catch (IOException ex) {
LoggerFactory.getLogger(ProcessInit.class.getName()).error(ex.getMessage());
}
}
}
This class is used to start a new RMI registry so each HTTP request to execute Matlab code can be run in a separate process, the reason we do this is because each RMI registry is bound to a process, so we need a separate registry for each JVM process.
package rmi;
import java.rmi.RemoteException;
import java.rmi.registry.*;
import java.rmi.server.UnicastRemoteObject;
import java.util.logging.*;
import remote_proxy.*;
//TODO: Remove sout
public class BootStrap {
public static void main(String[] args) {
int port = Integer.parseInt(args[0]);
System.out.println("Instantiating a task runner implementation on port: " + port );
try {
System.setProperty("java.rmi.server.hostname", "localhost");
TaskRunner runner = new TaskRunnerRemoteObject();
TaskRunner stub = (TaskRunner)UnicastRemoteObject.exportObject(runner, 0);
Registry reg = LocateRegistry.createRegistry(port);
reg.rebind("runner" + port, stub);
} catch (RemoteException ex) {
Logger.getLogger(BootStrap.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
This class allows to submit the request to execute the Matlab code, returns the result, and kill the newly spawned process.
package rmi.tasks;
import java.rmi.*;
import java.rmi.registry.*;
import java.util.Random;
import java.util.concurrent.*;
import java.util.logging.*;
import javax.enterprise.concurrent.ManagedExecutorService;
import remote_proxy.*;
import rmi.ProcessInit;
public final class Tasks {
/**
* #param pool This instance should be injected using #Resource(name = "java:comp/DefaultManagedExecutorService")
* #param task This is an implementation of the Task interface, this
* implementation should extend from MATLAB class and accept any necessary
* arguments, e.g Class1 and it must implement Serializable interface
* #param WEBINF WEB-INF directory
* #param jar Name of the jar that contains this MATLAB function
* #throws RemoteException
* #throws NotBoundException
*/
public static final <T> T runTask(ManagedExecutorService pool, Task<T> task, String WEBINF, String jar) throws RemoteException, NotBoundException {
int port = new Random().nextInt(1000) + 2000;
Future<Process> process = pool.submit(() -> ProcessInit.startRMIServer(pool, WEBINF, port, jar));
Registry reg = LocateRegistry.getRegistry(port);
TaskRunner generator = (TaskRunner) reg.lookup("runner" + port);
T result = generator.runTask(task);
destroyProcess(process);
return result;
}
private static void destroyProcess(Future<Process> process) {
try {
System.out.println("KILLING THIS PROCESS");
process.get().destroy();
System.out.println("DONE KILLING THIS PROCESS");
} catch (InterruptedException | ExecutionException ex) {
Logger.getLogger(Tasks.class.getName()).log(Level.SEVERE, null, ex);
System.out.println("DONE KILLING THIS PROCESS");
}
}
}
The questions:
Do I have to start a new separate RMI registry and bind a remote to it for each new process?
Is there a better way to achieve the same result?
You don't want JVM startup time to be part of the perceived transaction time. I would start a large number of RMI JVMs ahead of time, dependending on the expected number of concurrent requests, which could be in the hundreds or even thousands.
You only need one Registry: rmiregistry.exe. Start it on its default port and with an appropriate CLASSPATH so it can find all your stubs and application classes they depend on.
Bind each remote object into that Registry with sequentially-increasing names of the general form runner%d.
Have your RMI client pick a 'runner' at random from the known range 1-N where N is the number of runners. You may need a more sophisticated mechanism than mere randomness to ensure that the runner is free at the time.
You don't need multiple Registry ports or even multiple Registries.

Java denying access to property permissions

new to parallel/distributed computing and having issues with a client-server program I'm trying to write. What's supposed to happen is the server receives an integer from the client and sends back the sum all the numbers leading up to it (ex, user enters 5, server calculates 1+2+3+4+5, server sends back 15). I'm still trying to figure it out, so I've hard coded the input on the client side.
This is what I have on the server side:
import java.rmi.*;
import java.rmi.server.*;
import java.rmi.registry.*;
import java.net.*;
import java.util.*;
public class Server {
public static void main(String[]args) {
try{
int port = 16790;
String host = "localhost";
CalculateSumServerImpl export = new CalculateSumServerImpl();
LocateRegistry.createRegistry(port);
String registryURL = "rmi://" + host + ":" + port + "/sum";
Naming.rebind(registryURL, export);
System.out.println("Server ready");
} catch (Exception e) {
e.printStackTrace();
}
} }
//to calculate the sum
import java.rmi.*;
import java.rmi.server.*;
public class CalculateSumServerImpl extends UnicastRemoteObject implements CalServerInterface {
public int n; //value entered
public int sum; //sum
protected CalculateSumServerImpl() throws RemoteException {
super();
}
#Override
public int calculateSum(int n) throws RemoteException {
n = (n*(n+1))/2; //sum of 1 + 2 + 3 + .. + n
sum = n;
return sum;
} }
//interface
import java.rmi.Remote;
public interface CalServerInterface extends Remote {
public int calculateSum(int n ) throws java.rmi.RemoteException;
}
And on the client side:
import java.rmi.*;
import java.util.PropertyPermission;
public class Client {
public static void main(String[]args) {
System.setSecurityManager(new java.rmi.RMISecurityManager());
System.setProperty("java.net.preferIPv4Stack" , "true");
try {
int port = 16790;
String host = "localhost";
String registryURL = "rmi://" + host + ":" + port + "/sum";
Project4ServerInterface obj = (Project4ServerInterface)Naming.lookup(registryURL);
System.out.println("Lookup completed.");
int output = obj.calculateSum(3);
System.out.println("Sum is: " + output);
} catch (Exception e) {
e.printStackTrace();
}
System.setProperty("java.net.preferIPv4Stack","true");
} }
And I've implemented the Interface on the client side as well.
The error that I've been getting on the client side is:
Exception in thread "main" java.security.AccessControlException: access denied ("java.util.PropertyPermission" "java.net.preferIPv4Stack" "write")
at java.security.AccessControlContext.checkPermission(AccessControlContext.java:472)
at java.security.AccessController.checkPermission(AccessController.java:884)
at java.lang.SecurityManager.checkPermission(SecurityManager.java:549)
at java.lang.System.setProperty(System.java:792)
at project04client.Client.main(Client.java:10)
with the error pointing to the line with this code:
System.setProperty("java.net.preferIPv4Stack" , "true");
Anyone have any experience trouble shooting this error?
Thanks!
The problem is that you have set a security manager for the entire (client) application that won't let you modify system properties.
The simple fix is to set the system properties you need to set before you set the RMI security manager.
Alternatively, you may be able to get rid of the System.setSecurityManager(...) call entirely. You (probably) only need it if you want the client to be able to download classes from your RMI service.
I tried setting the system property before the security manager and got an AccessControlException, denying socket permissions.
That doesn't make much sense. You would only get an AccessControlException if there was a security manager in place at that point. There shouldn't be ... unless this is applet code or similar launched in a web browser. Also, I don't know why a call to set a property would be denied saying that you don't have socket permissions.
When I took the security manager out completely, I got an UnmarshalException pointing to the interface.
You also need to add the classes / interfaces for the objects that tou will be unmarshalling to the client-side classpath.
Actually, I just noticed that the javadoc for RMISecurityManager says:
"RMISecurityManager implements a policy identical to the policy implemented by SecurityManager. RMI applications should use the SecurityManager class or another appropriate SecurityManager implementation instead of this class."

RMI dynamic class loading in java, how to separate and launch code on localhost?

I have a bit confusion about how dynamic class loading mechanism works. I implemented below classes and when they are all in the same src directory and i launch them from my ide, server and client works. But when i separate them i can't make it work. There are many guides that explaining how RMI works etc but they don't explain how should i separate files and launch them one everything is ok.
So what i have done:
Compiled all classes and obtained corrisponding .class files. Then i created a folder and subfolders to separate client, server and common classes:
home/
|-myuser/
|--rmitest/
|--server/
| Server.class
|-- client/
| Client.class, client.policy
|-- common/
NotifyEventImpl.class, NotifyEventInterface.class, ServerImpl.class, ServerInterface.class
This is a homework question server and client will both work on localhost. Anyway, then whe i launch server with
$ java -Djava.rmi.server.codebase=/home/myuser/rmitest/common/ Server .
it can't find classes
Exception in thread "main" java.lang.NoClassDefFoundError: ServerImpl
at Server.main(Server.java:15)
Caused by: java.lang.ClassNotFoundException: ServerImpl
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
... 1 more
So how should i do it to get it work? My seperation of classes is correct? How should i launch server and client? Thanks.
Below you find my classes:
public interface ServerInterface extends Remote{
void registerForCallback(NotifyEventInterface clientInterface)
throws RemoteException;
}
public class ServerImpl extends UnicastRemoteObject implements ServerInterface {
private List<NotifyEventInterface> clients;
public ServerImpl() throws RemoteException{
super();
clients = new ArrayList<NotifyEventInterface>();
}
public synchronized void registerForCallback(NotifyEventInterface ClientInterface) throws RemoteException{
if(!clients.contains(ClientInterface)){
clients.add(ClientInterface);
System.out.println("New client registered");
}
}
public void update(int value) throws RemoteException {
doCallbacks(value);
}
private synchronized void doCallbacks(int value) throws RemoteException {
System.out.println("Starting callbacks");
Iterator i = clients.iterator();
while(i.hasNext()){
NotifyEventInterface client = (NotifyEventInterface) i.next();
client.notifyEvent(value);
}
System.out.println("Callbacks complete");
}
}
public class Server {
public static void main(String[] args) {
ServerImpl serverObj = new ServerImpl();
int portNum = 39000;
startRegistry(portNum);
String registryUrl = "//:" + portNum + "/common";
Naming.rebind(registryUrl, serverObj);
System.out.println("Server is ready");
while(true){
int val = (int) (Math.random() * 1000);
System.out.println("New update " + val);
serverObj.update(val);
Thread.sleep(1500);
}
}
private static void startRegistry(int rmiPortNum) throws RemoteException{
try {
Registry registry = LocateRegistry.getRegistry(rmiPortNum);
registry.list( );
} catch (RemoteException ex) {
System.out.println("RMI registry is not located at port " + rmiPortNum);
Registry registry = LocateRegistry.createRegistry(rmiPortNum);
System.out.println("RMI registry created at port " + rmiPortNum);
}
}
}
public interface NotifyEventInterface extends Remote {
void notifyEvent(int value) throws RemoteException;
}
public class NotifyEventImpl implements NotifyEventInterface{
public NotifyEventImpl() throws RemoteException{
super();
}
#Override
public void notifyEvent(int value) throws RemoteException {
String returnMessage = "Update event received " + value;
System.out.println(returnMessage);
}
}
Compiled all classes and obtained corrisponding .class files. Then i created a folder and subfolders to separate client, server and common classes
Wrong. You should separate them first, at source code level, with corresponding package statements in the source code. Then compile. The compiler will then put the .class files into a directory structure corresponding to the package hierarchy.
NB ServerImpl is not a common class. It is only used by the server.

Jini/JavaSpaces discovery error

On this article: http://java.sun.com/developer/technicalArticles/tools/JavaSpaces/ is a tutorial how to run JavaSpaces client. I wrote these classes in Eclipse, started Launch-All script and Run example. It works.
After that I exported these classes into executable jar (JavaSpaceClient.jar) and tried that jar with following command:
java -jar JavaSpaceClient.jar
It works fine, gives me result:
Searching for a JavaSpace...
A JavaSpace has been discovered.
Writing a message into the space...
Reading a message from the space...
The message read is: Здраво JavaSpace свете!
My problem is when I move this jar file on my other LAN computer, it shows me error when I type same command. Here is error:
cica#cica-System-Name:~/Desktop$ java -jar JavaSpaceClient.jar
Searching for a JavaSpace...
Jul 27, 2011 11:20:54 PM net.jini.discovery.LookupDiscovery$UnicastDiscoveryTask run
INFO: exception occurred during unicast discovery to biske-Inspiron-1525:4160 with constraints InvocationConstraints[reqs: {}, prefs: {}]
java.net.UnknownHostException: biske-Inspiron-1525
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:175)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:384)
at java.net.Socket.connect(Socket.java:546)
at java.net.Socket.connect(Socket.java:495)
at com.sun.jini.discovery.internal.MultiIPDiscovery.getSingleResponse(MultiIPDiscovery.java:134)
at com.sun.jini.discovery.internal.MultiIPDiscovery.getResponse(MultiIPDiscovery.java:75)
at net.jini.discovery.LookupDiscovery$UnicastDiscoveryTask.run(LookupDiscovery.java:1756)
at net.jini.discovery.LookupDiscovery$DecodeAnnouncementTask.run(LookupDiscovery.java:1599)
at com.sun.jini.thread.TaskManager$TaskThread.run(TaskManager.java:331)
I just writes "Searching for JavaSpace..." and after a while prints these error messages.
Can someone help me with this error?
EDIT:
For discovery I am using LookupDiscovery class I've found on Internet:
import java.io.IOException;
import java.rmi.RemoteException;
import net.jini.core.lookup.ServiceRegistrar;
import net.jini.core.lookup.ServiceTemplate;
import net.jini.discovery.LookupDiscovery;
import net.jini.discovery.DiscoveryListener;
import net.jini.discovery.DiscoveryEvent;
/**
A class which supports a simple JINI multicast lookup. It doesn't register
with any ServiceRegistrars it simply interrogates each one that's
discovered for a ServiceItem associated with the passed interface class.
i.e. The service needs to already have registered because we won't notice
new arrivals. [ServiceRegistrar is the interface implemented by JINI
lookup services].
#todo Be more dynamic in our lookups - see above
#author Dan Creswell (dan#dancres.org)
#version 1.00, 7/9/2003
*/
public class Lookup implements DiscoveryListener {
private ServiceTemplate theTemplate;
private LookupDiscovery theDiscoverer;
private Object theProxy;
/**
#param aServiceInterface the class of the type of service you are
looking for. Class is usually an interface class.
*/
public Lookup(Class aServiceInterface) {
Class[] myServiceTypes = new Class[] {aServiceInterface};
theTemplate = new ServiceTemplate(null, myServiceTypes, null);
}
/**
Having created a Lookup (which means it now knows what type of service
you require), invoke this method to attempt to locate a service
of that type. The result should be cast to the interface of the
service you originally specified to the constructor.
#return proxy for the service type you requested - could be an rmi
stub or an intelligent proxy.
*/
Object getService() {
synchronized(this) {
if (theDiscoverer == null) {
try {
theDiscoverer =
new LookupDiscovery(LookupDiscovery.ALL_GROUPS);
theDiscoverer.addDiscoveryListener(this);
} catch (IOException anIOE) {
System.err.println("Failed to init lookup");
anIOE.printStackTrace(System.err);
}
}
}
return waitForProxy();
}
/**
Location of a service causes the creation of some threads. Call this
method to shut those threads down either before exiting or after a
proxy has been returned from getService().
*/
void terminate() {
synchronized(this) {
if (theDiscoverer != null)
theDiscoverer.terminate();
}
}
/**
Caller of getService ends up here, blocked until we find a proxy.
#return the newly downloaded proxy
*/
private Object waitForProxy() {
synchronized(this) {
while (theProxy == null) {
try {
wait();
} catch (InterruptedException anIE) {
}
}
return theProxy;
}
}
/**
Invoked to inform a blocked client waiting in waitForProxy that
one is now available.
#param aProxy the newly downloaded proxy
*/
private void signalGotProxy(Object aProxy) {
synchronized(this) {
if (theProxy == null) {
theProxy = aProxy;
notify();
}
}
}
/**
Everytime a new ServiceRegistrar is found, we will be called back on
this interface with a reference to it. We then ask it for a service
instance of the type specified in our constructor.
*/
public void discovered(DiscoveryEvent anEvent) {
synchronized(this) {
if (theProxy != null)
return;
}
ServiceRegistrar[] myRegs = anEvent.getRegistrars();
for (int i = 0; i < myRegs.length; i++) {
ServiceRegistrar myReg = myRegs[i];
Object myProxy = null;
try {
myProxy = myReg.lookup(theTemplate);
if (myProxy != null) {
signalGotProxy(myProxy);
break;
}
} catch (RemoteException anRE) {
System.err.println("ServiceRegistrar barfed");
anRE.printStackTrace(System.err);
}
}
}
/**
When a ServiceRegistrar "disappears" due to network partition etc.
we will be advised via a call to this method - as we only care about
new ServiceRegistrars, we do nothing here.
*/
public void discarded(DiscoveryEvent anEvent) {
}
}
My client program tries simply to search for JavaSpaces service write MessageEntry into and then retrieves message and prints it out. Here is client program:
import net.jini.space.JavaSpace;
public class SpaceClient {
public static void main(String argv[]) {
try {
MessageEntry msg = new MessageEntry();
msg.content = "Hello JavaSpaces wordls!";
System.out.println("Searching for JavaSpaces...");
Lookup finder = new Lookup(JavaSpace.class);
JavaSpace space = (JavaSpace) finder.getService();
System.out.println("JavaSpaces discovered.");
System.out.println("Writing into JavaSpaces...");
space.write(msg, null, 60*60*1000);
MessageEntry template = new MessageEntry();
System.out.println("Reading message from JavaSpaces...");
MessageEntry result = (MessageEntry) space.read(template, null, Long.MAX_VALUE);
System.out.println("Message: "+result.content);
} catch(Exception e) {
e.printStackTrace();
}
}
}
And of course this is MessageEntry class:
import net.jini.core.entry.*;
public class MessageEntry implements Entry {
public String content;
public MessageEntry() {
}
public MessageEntry(String content) {
this.content = content;
}
public String toString() {
return "MessageContent: " + content;
}
}
EDIT2:
I did discovery on two Windows computers.
After that I tried Windows - Ubuntu combiantion and it doesn't work. Maybe there are some network problems? When I ping each another everything is ok. Maybe there are some DNS issues on Ubuntu..
EDIT3:
Windows - Ubuntu combination works if JavaSpaces service is started up on Windows and client program is on Ubuntu. When I try to do reverse, to run JavaSpaces service on Ubuntu and run client on Windows error occurs.
Obviously there is some problem with Ubuntu. Ubuntu has installed OpenJDK installed by default. I installed Oracle JDK, and set JAVA_HOME and put JAVA_HOME/bin into PATH variable. I wonder maybe there is some problem with different versions of Java, maybe I am not using right one.
It is possible that the service registrar that you are running (on host biske-Inspiron-1525 at port 4160), is discovering it's hostname incorrectly (without domain name) and is therefore sending out the announcements with a short hostname. Therefore, after discovering the service registrar, it is possible that subsequently the client is trying to make a connection to the service registrar it cannot resolve the hostname if it is on a different domain.
To ensure that the service registrar is running with the correct hostname, try starting it with the following command line attribute:
-Dcom.sun.jini.reggie.unicastDiscoveryHost="biske-Inspiron-1525.and.its.domain"
It appears that you are doing unicast discovery to a specific host and port and that you can't look up that host.
Assuming you can resolve the name biske-Inspiron-1525 with DNS try removing the ":4160" part and see if the unicast lookup succeeds then.
Here is an example of the code I use to look up a service. It's a bit more complicated because I implement ServiceDiscoveryListener and handle service discovery that way. I actually keep a list of services and dynamically switch between then when one fails but I stripped that part out of the example. I am also using the Configuration part of Jini which I'll explain afterwards. The service interface I am using here is called "TheService":
public class JiniClient implements ServiceDiscoveryListener {
private TheService service = null;
private Class[] serviceClasses;
private ServiceTemplate serviceTemplate;
public JiniClient(String[] configFiles) throws ConfigurationException {
Configuration config = ConfigurationProvider.getInstance(configFiles,
getClass().getClassLoader());
// Set the security manager
System.setSecurityManager(new RMISecurityManager());
// Define the service we are interested in.
serviceClasses = new Class[] {TheService.class};
serviceTemplate = new ServiceTemplate(null, serviceClasses, null);
// Build a cache of all discovered services and monitor changes
ServiceDiscoveryManager serviceMgr = null;
DiscoveryManagement mgr = null;
try {
mgr = (DiscoveryManagement)config.getEntry(
getClass().getName(), // component
"discoveryManager", // name
DiscoveryManagement.class); // type
if (null == mgr) {
throw new ConfigurationException("entry for component " +
getClass().getName() + " name " +
"discoveryManager must be non-null");
}
} catch (Exception e) {
/* This will catch both NoSuchEntryException and
* ConfigurationException. Putting them both
* below just to make that clear.
*/
if( (e instanceof NoSuchEntryException) ||
(e instanceof ConfigurationException)) {
// default value
try {
System.err.println("Warning, using default multicast discover.");
mgr = new LookupDiscoveryManager(LookupDiscovery.ALL_GROUPS,
null, // unicast locators
null); // DiscoveryListener
} catch(IOException ioe) {
e.printStackTrace();
throw new RuntimeException("Unable to create lookup discovery manager: " + e.toString());
}
}
}
try {
serviceMgr = new ServiceDiscoveryManager(mgr, new LeaseRenewalManager());
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException("Unable to create service discovery manager: " + e.toString());
}
try {
serviceMgr.createLookupCache(serviceTemplate,
null, // no filter
this); // listener
} catch(Exception e) {
e.printStackTrace();
throw new RuntimeException("Unable to create serviceCache: " + e.getMessage());
}
}
public void serviceAdded(ServiceDiscoveryEvent evt) {
/* Called when a service is discovered */
ServiceItem postItem = evt.getPostEventServiceItem();
//System.out.println("Service appeared: " +
// postItem.service.getClass().toString());
if(postItem.service instanceof TheService) {
/* You may be looking for multiple services.
* The serviceAdded method will be called for each
* so you can use instanceof to figure out if
* this is the one you want.
*/
service = (TheService)postItem.service;
}
}
public void serviceRemoved(ServiceDiscoveryEvent evt) {
/* This notifies you of when a service goes away.
* You could keep a list of services and then remove this
* service from the list.
*/
}
public void serviceChanged(ServiceDiscoveryEvent evt) {
/* Likewise, this is called when a service changes in some way. */
}
The Configuration system allows you to dynamically configure the discovery method so you can switch to discover specific unicast systems or multicast without changing the app. Here is an example of a unicast discovery configuration file that you could pass to the above objects constructor:
import net.jini.core.discovery.LookupLocator;
import net.jini.discovery.LookupDiscoveryManager;
import net.jini.discovery.LookupDiscovery;
com.company.JiniClient {
discoveryManager = new LookupDiscoveryManager(
LookupDiscovery.ALL_GROUPS,
new LookupLocator[] { new LookupLocator("jini://biske-Inspiron-1525.mycompany.com")},
null,
this); // the current config
}
I found solution! That was dns issue. On Ubuntu my /etc/hosts file was:
192.168.1.3 biske-Inspiron-1525 # Added by NetworkManager
127.0.0.1 localhost.localdomain localhost
::1 biske-Inspiron-1525 localhost6.localdomain6 localhost6
127.0.1.1 biske-Inspiron-1525
# The following lines are desirable for IPv6 capable hosts
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts
I've just removed line 127.0.1.1 biske-Inspiron-1525 and now it works fine.
Little thing was destroyed million of my nerves :)

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