分布式计算原理与应用(Distributed-Computing)第八章课件.ppt

1、12/20/2022Distributed Computing,M.L.Liu1Advanced Remote Method InvocationsM.L.Liu12/20/2022Distributed Computing,M.L.Liu2RMI Advanced topicsnThe Java RMI API has a rich collection of features.nWe will look at some of RMIs more interesting advanced features,namely:n stub downloadingnsecurity managern

2、client callback.nAlthough these features are not inherent to the distributed object paradigm,they are helpful mechanisms and can be useful to application developers.12/20/2022Distributed Computing,M.L.Liu3The Java RMI ArchitectureC lientServerstubrem ote reference layertransport layerskeletonrem ote

3、 reference layertransport layerl;ogical data pathphysical data pathsupports the interface withthe application programm aps the platform-independent stub/skeletonlayer to the platform-dependent transportlayer;carries out rem ote reference protocolssets up,m aintains,and shuts downconnections;and carr

4、ies out thetransport protocol12/20/2022Distributed Computing,M.L.Liu4Java RMI Client Server InteractionClient hostServer hostRMI registrySomeServer.classSomeInterface_stub.classSomeInterface_skel.classClient.classSomeInterface_stub.class12341.Client looks up the interface object in the RMIregistry o

5、n the server host.2.The RMIRegistry returns a remote reference to the interface object.3.If the interface objects stub is not on the client host and if it is so arranged by the server,the stub is downloaded from an HTTP server.4.Via the server stub,the client process interacts with the skeleton of t

6、he interface object to access the methods in the server object.HTTP hostX12/20/2022Distributed Computing,M.L.Liu5RMI Stub DownloadingnRMI is designed to allow stubs to be made available to the client dynamically.Doing so allows changes to be made in the remote methods without affecting the client pr

7、ogram.nThe stub can be filed with an web server and be downloaded using HTTP.nSecurity measures are needed to prevent both the client side and the server side:nA java security policy file needs to be set on the server host and also on the client host.nA Java Security Manager should be instantiated i

8、n both the client and server programs.12/20/2022Distributed Computing,M.L.Liu6Stub downloadingnIf the stub is to be downloaded from a remote server,transfer the stub class to the appropriate directory on that server,e.g.,www.csc.calpoly.edu/mliu/www,and make sure that the access permission to the fi

9、le is set.nWhen activating the server,specify command options:java -Djava.rmi.serve.codebase=/-Djava.rmi.server.hostname=-Djava.security.policy=where is the URL for the stub class,e.g.,http:/www.csc.calpoly.edu/mliu/class is the name of the host on which the server runs,and specifies where the secur

10、ity policy file for this application is to be found,e.g.,java.security if you have a file by that name in the directory where the server class is.12/20/2022Distributed Computing,M.L.Liu7The java.policy filenThe RMI security manager does not permit network access.The RMI security manager does not per

11、mit network access.Exceptions can be made via the specification in a java.policy file.Exceptions can be made via the specification in a java.policy file.grant grant /permits socket access to all common TCP ports,including the /permits socket access to all common TCP ports,including the defaultdefaul

12、t /RMI registry port(1099)need for both the client and the /RMI registry port(1099)need for both the client and the server.server.permission .SocketPermission permission .SocketPermission *:1024-65535,:1024-65535,connect,accept,resolve;connect,accept,resolve;/permits socket access to port 80,the def

13、ault HTTP port /permits socket access to port 80,the default HTTP port neededneeded /by client to contact an HTTP server for stub downloading /by client to contact an HTTP server for stub downloading permission .SocketPermission permission .SocketPermission *:80,connect;:80,connect;nThis file can be

14、 filed in the same directory as the server class file.This file can be filed in the same directory as the server class file.nWhen activiating When activiating the client,a java.policy file also should be the client,a java.policy file also should be specified:specified:java-Djava.security.policy=java

15、.policy SomeClient java-Djava.security.policy=java.policy SomeClientnSee See http:/ and and http:/ Computing,M.L.Liu8File Placementsjava.policySomeClient.classjava.polcySomeServer.classSomeInterface_stub.classSomeInterface.Skeleton.classSomeInterface_stub.classClient hostclient directoryServer hosts

16、erver directoryHTTP Server12/20/2022Distributed Computing,M.L.Liu9RMI Security ManagernSince RMI involves access to/from a foreign host,and possibly object downloading,it is important for both the server and the client to protect its system from malicious access.nThe RMISecurityManager is a class pr

17、ovided Java,and can be instantiated in both the client and the server for limiting access priviledges.nYou can write your own security manager,if so desired.try System.setSecurityManager(new RMISecurityManager();catch 12/20/2022Distributed Computing,M.L.Liu10Algorithm for building an RMI Application

18、Server side:1.Open a directory for all the files to be generated for this application.2.Specify the remote-server interface,and compile it to generate the interface class file.3.Build the remote server class by implementing the interface,and compile it using javac.4.Use rmic to process the server cl

19、ass to generate a stub.class file and a skelton.class file:rmic SomeServer5.If stub downloading is desired,copy the stub file to an appropriate directory on the HTTP host.6.Activate the RMIRegistry,if it has not already been activated.7.Set up a java.policy file.8.Activate the server,specifying(i)th

20、e codebase if stub downloading is desired,(ii)the server host name,and(iii)the security policy file.12/20/2022Distributed Computing,M.L.Liu11Alogorithm for building an RMI ApplicationClient side:1.Open a directory for all the files to be generated for this application.2.Implement the client program

21、or applet,and compile it to generate the client class.3.If stub downloading is not in effect,copy the server interface stub class file by hand.4.Set up a java.policy file.5.Activate the client,specifying(i)the server host name,and(ii)the security policy file.12/20/2022Distributed Computing,M.L.Liu12

22、RMI Callbacks12/20/2022Distributed Computing,M.L.Liu13IntroductionnIn the client server model,the server is passive:the IPC is initiated by the client;the server waits for the arrival of requests and provides responses.nSome applications require the server to initiate communication upon certain even

23、ts.Examples applications are:n monitoringn gamesn auctioningn voting/pollingn chat-toomn message/bulletin boardn groupware12/20/2022Distributed Computing,M.L.Liu14Polling vs.CallbackIn the absence of callback,a client will have to poll a passive server repeatedly if it needs to be notified that an e

24、vent has occurred at the server end.ServerClient.PollingServerClientCallbackA client issues a request to theserver repeatedly until thedesired response is obtained.A client registers itself with theserver,and wait until the servercalls back.a remote method call12/20/2022Distributed Computing,M.L.Liu

25、15Two-way communicationsnSome applications require that both sides may initiate IPC.nUsing sockets,duplex communication can be achieved by using two sockets on either side.nWith connection-oriented sockets,each side acts as both a client and a server.requestresponserequestresponseProcess 1Process 11

26、2/20/2022Distributed Computing,M.L.Liu16RMI CallbacksnA callback client registers itself with an RMI server.nThe server makes a callback to each registered client upon the occurrence of a certain event.The callback listC1C2C3C4C5callbackServerClientsRMI calls12/20/2022Distributed Computing,M.L.Liu17

27、Callback Client-Server InteractionsClient hostServer hostRMI registrySomeServer.classSomeInterface_stub.classSomeInterface_skel.classClient.class121.Client looks up the interface object in the RMIregistry on the server host.2.The RMIRegistry returns a remote reference to the interface object.3.Via t

28、he server stub,the client process invokes a remote method to register itself for callback,passing a remote reference to itself to the server.The server saves the reference in its callback list.4.Via the server stub,the client process interacts with the skeleton of the interface object to access the

29、methods in the interface object.5.When the anticipated event takes place,the server makes a callback to each registered client via the callback interface stub on the server side and the callback interface skeleton on the client side.XCallbackInterface_skel.classCallbackInterface_stub.class53,412/20/

30、2022Distributed Computing,M.L.Liu18Callback application filesClient.classClientInterface.classServerInterface.classClientImpl.classServerImpl_Stub.classClientImpl_skel.classObject client hostobject client directoryServer.classServerInterface.classClientInterface.classServerImpl.classClientImpl_Stub.

31、classServerImpl_skel.classObject server hostobject server directory12/20/2022Distributed Computing,M.L.Liu19RMI Callback file placementsjava.policySomeClient.classjava.polcySomeServer.classSomeInterface_stub.classSomeInterface.Skeleton.classSomeInterface_stub.classClient hostclient directoryServer h

32、ostserver directoryHTTP ServerCallbackInterface_stub.classCallbackInterface_skel.class12/20/2022Distributed Computing,M.L.Liu20The Hello Application with CallbacksayHello()HelloInterfaceUnicastRemoteObjectHelloImplHelloServerlistRegistry()startRegistry()serverregistryclientrebind()lookup()sayHello()

33、sequence diagramUML diagramnotifyMe()CallbackClientInterfaceUnicastRemoteObjectC allbackC lientm plC allbackC lientaddCallback()notifyMe()12/20/2022Distributed Computing,M.L.Liu21RMI Callback InterfacenThe server provides a remote method which allows a client to register itself for callbacks.nA Remo

34、te interface for the callback is needed,in addition to the server-side interface.nThe interface specifies a method for accepting a callback from the server.nThe client program is a subclass of RemoteObject and implements the callback interface,including the callback method.nThe client registers itse

35、lf for callback in its main method.nThe server invokes the clients remote method upon the occurrence of the anticipated event.12/20/2022Distributed Computing,M.L.Liu22Remote Interface for Serverpublic interface HelloInterface extends Remote /remote method public String sayHello()throws java.rmi.Remo

36、teException;/method to be invoked by a client to add itself to the callback list public void addCallback(HelloCallbackInterface CallbackObject)throws java.rmi.RemoteException;12/20/2022Distributed Computing,M.L.Liu23Remote Interface for Callback Client/an interface specifying a callback methodpublic

37、 interface HelloCallbackInterface extends java.rmi.Remote /method to be called by the server on callback public void callMe(String message )throws java.rmi.RemoteException;12/20/2022Distributed Computing,M.L.Liu24HelloServer,with callbackpublic class HelloServer extends UnicastRemoteObject implement

38、s HelloInterface static int RMIPort;/vector for store list of callback objects private static Vector callbackObjects;public HelloServer()throws RemoteException super();/instantiate a Vector object for storing callback objects callbackObjects=new Vector();/method for client to call to add itself to i

39、ts callback public void addCallback(HelloCallbackInterface CallbackObject)/store the callback object into the vector System.out.println(Server got an addCallback call.);callbackObjects.addElement(CallbackObject);12/20/2022Distributed Computing,M.L.Liu25 HelloServer,with callback-2public static void

40、main(String args)registry=LocateRegistry.createRegistry(RMIPort);callback();/end main private static void callback()for(int i=0;i callbackObjects.size();i+)System.out.println(Now performing the+i+th callbackn);/convert the vector object to a callback object HelloCallbackInterface client=(HelloCallba

41、ckInterface)callbackObjects.elementAt(i);client.callMe(Server calling back to client +i);12/20/2022Distributed Computing,M.L.Liu26Alogorithm for building an RMI Callback ApplicationServer side:1.Open a directory for all the files to be generated for this application.2.Specify the remote-server inter

42、face,and compile it to generate the interface class file.3.Build the remote server class by implementing the interface,and compile it using javac.4.Use rmic to process the server class to generate a stub.class file and a skelton.class file:rmic SomeServer5.If stub downloading is desired,copy the stu

43、b file to an appropriate directory on the HTTP host.6.Activate the RMIRegistry,if it has not already been activated.7.Set up a java.policy file.8.Activate the server,specifying(i)the codebase if stub downloading is desired,(ii)the server host name,and(iii)the security policy file.9.Obtain the Callba

44、ckInterface.Compile it with javac,then use rmic to generate the stub file for the callback.12/20/2022Distributed Computing,M.L.Liu27Alogorithm for building an RMI Callback ApplicationClient side:1.Open a directory for all the files to be generated for this application.2.Implement the client program

45、or applet,and compile it to generate the client class.3.If stub downloading is not in effect,copy the server interface stub class file by hand.4.Implement the callback interface.Compile it using javac,then using rmic to generate a stub class and a skeleton class for it.5.Set up a java.policy file.6.

46、Activate the client,specifying(i)the server host name,and(ii)the security policy file.12/20/2022Distributed Computing,M.L.Liu28HelloClient,with callback HelloClient()/constructor System.setSecurityManager(new RMISecurityManager();/export this object as a remote object UnicastRemoteObject.exportObjec

47、t(this);/Registry registry=LocateRegistry.getRegistry(localhost,RMIPort);h=(HelloInterface)registry.lookup(helloLiu);h.addCallback(this);/end constructor /call back method-this displays the message sent by the server public void callMe(String message)System.out.println(Call back received:+message);p

48、ublic static void main(String args)/HelloClient client =new HelloClient();/while(true);/end while /end main/end HelloClient class12/20/2022Distributed Computing,M.L.Liu29HelloServer,HelloClientUnicastRemoteObjectHelloInterfacesayHelloHelloServerRMIPortsayHelloClass Diagram for HelloServerHelloClient

49、RMIregistryHelloServergetRegistrysayHelloEvent diagram for the Hello applicationaddCallbackUnicastRemoteObjectCallbackInterfacesayHelloRMIPortsayHelloClass Diagram for HelloClientHelloClientcallMeaddCallbackcallMe12/20/2022Distributed Computing,M.L.Liu30Summary-1nClient callback:Client callback:nCli

50、ent callback is useful for an application where the clients desire to be notified by the server of the occurrence of some event.nClient callback allows an object server to make remote method call to a client via a reference to a client remote interface.12/20/2022Distributed Computing,M.L.Liu31Summar