Re: Basic Jini problem and cast exceptions

Need to understand more about how your server is setup.

What command line are you using to start the server, specifically
are you setting the codebase property on the server?

What object is the server registering with the lookup service?

Also, what does jsk-all.policy look like? Is granting any permissions to 
  hello-client.jar ?

Jose Hernan Valdes Murguia wrote:
> Hello everybody. I have started working with jini always with a single 
> machine, after some time I decided to distributed my tools using virtual 
> machines; then, I saw details I have missed before. To warm up, a single 
> hello program was needed to focus on my future necessities, but I faced 
> two existential problems(exceptions) that I do not why they appear. 
> Because I do not know why they appear, I do not also know how to solve 
> them. Then, I would ask you to help me to understand the roots of my 
> problems, and show my mistakes. Let's start.
> 
> As usual my hello application has three components: the server, the 
> client and the service(dl package)
> 
> hello-server.jar:
>       net.jini.server.Server.class
> 
> hello-dl:
>       net.jini.core.Hello.class
>       net.jini.core.HelloServer.class  //Hello implementation
> 
> hello-client,jar:
>         net.jini.client.Client.class
>         net.jini.core.Hello.class
> 
> The server works as I expected to do, so I do not have much trouble at 
> all. However, the client is the problem.
> 
> This is the classpath I am using ( I attach this information because I 
> guess some of them may be the reason of my problem).
> 
> JINI_HOME=/opt/java/jini2_1
> APP_DIR=./
> CLASSPATH=$JINI_HOME/lib/jsk- lib.jar:$JINI_HOME/lib/jsk-platform.jar
> CLASSPATH=$CLASSPATH:$APP_DIR/hello-client.jar:$APP_DIR/hello-dl.jar
> export CLASSPATH
> 
> So, When I execute the following sh script everything works well.
> #This works well
> java -Djava.rmi.server.codebase=http://sakura:8080/hello-dl.jar \
>      -Djava.security.policy=$JINI_HOME/common/jsk-all.policy \
>      net.jini.client.Client 172.16.248.2 <http://172.16.248.2>
> 
> Although it works well, I have the hello-dl.jar in my classpath and in 
> my codebase parameter. as you can see.
> However, the implementation will change, so hello-dl.jar will also 
> vary.  I can imagine change the means of communication from sockets to 
> webservices, it does not matter. According to the Jini promise, the 
> client only needs to know about the interface( Hello.class) to work, and 
> because I do not want that my client has the HelloServer implementation 
> I package the jar client thus:
> 
> hello-client.jar:
>                 net.jini.client.Client.class
>                 net.jini.core.Hello.class
> Obviously, if I need a Hello reference to compile and run. (fool of my 
> ). The I run the following script to set out client working.
> 
> #sh begin
> JINI_HOME=/opt/java/jini2_1
> APP_DIR=./
> CLASSPATH=$JINI_HOME/lib/jsk-lib.jar:$JINI_HOME/lib/jsk-platform.jar:$APP_DIR/hello-client.jar
> export CLASSPATH
> java -Djava.rmi.server.codebase=http://sakura:8080/hello-dl.jar \
>      -Djava.security.policy=$JINI_HOME/common/jsk-all.policy \
>      net.jini.client.Client 172.16.248.2 <http://172.16.248.2>
> #sh end
> 
> Then I have this exception:
> 
> java.rmi.UnmarshalException: error unmarshalling return; nested 
> exception is:
>         java.lang.ClassNotFoundException: net.jini.core.HelloServer
>         at 
> com.sun.jini.reggie.RegistrarProxy.lookup(RegistrarProxy.java:120)
>         at net.jini.client.Client.init(Client.java:25)
>         at net.jini.client.Client.main(Client.java:72)
> Caused by: java.lang.ClassNotFoundException: net.jini.core.HelloServer
>         at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
>         at java.security.AccessController.doPrivileged (Native Method)
>         at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
>         at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
> 
> Now, my question is WHY, Why this happened. I search and read some 
> manual and jini tutorial but I can not answer my question. Maybe I have 
> not sought well at all. However, I knew that the client does not need to 
> set a codebase parameter because the lookup server will download all 
> needed files to execute the service on client machine. Then, using the 
> same path. I tried this:
> 
> java -Djava.security.policy=$JINI_HOME/common/jsk-all.policy 
> net.jini.client.Client 172.16.248.2 <http://172.16.248.2>
> 
> This seems to be the right way, but I have a casting exception.
> 
>     public void init(){
>        ...   
>              LookupLocator locator = new 
> LookupLocator("jini://"+ip+":4160");
>              ServiceRegistrar registrar = locator.getRegistrar();
>              ServiceTemplate serviceTemplate = new 
> ServiceTemplate(null,new Class[]{ Hello.class}, null);
>              Object obj = registrar.lookup(serviceTemplate);
>              System.out.println(" Is instance ["+ 
> Hello.class.isInstance(obj)+"] "); // prints "Is instance [false] "
>              Hello hello  = (Hello)obj; // There is the exception
>     ...
>    }
> 
> Exception in thread "main" java.lang.ClassCastException: 
> net.jini.core.HelloServer
>         at net.jini.client.Client.init (Client.java:42)
>         at net.jini.client.Client.main(Client.java:72)
> 
> Another detail I could add is that my HelloServer service has two 
> interfaces[ "java.io.Serializable", "net.jini.core.Hello"], but the 
> "Hello" interface of HelloService seems  not to be the same as "Hello" 
> I'm using in my HelloClient.java. ( Hello is also java.rmi.Remote )
> 
>   
>     Class []clazz = obj.getClass().getInterfaces();
>     System.out.println(  "["+clazz[0].equals(Hello.class )+"]" );
>     //that prints "[false]" although there have the same name, " 
> net.jini.core.Hello"
> 
> I can guess some answers. Both  hello in server side and client side are 
> not the same. But is this really the problem? Is how jini works? If I am 
> doing something wirdo and not correct please let me know about it. But I 
> think my requirement is simple. I do only need that my client know the 
> interfaces, but only the interfaces.
> 
> I hope this extend explanation can be enough to show you my doubts. Any 
> reference to a good jini document or article will be welcome.
> Regards,
> Jose Hernan Valdes Murguia
> 
>  
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