Programming in Java RMI tsaiwncsie nctu edu tw

Programming in Java RMI 蔡文能 交通大學資訊 程學系 tsaiwn@csie. nctu. edu. tw http: //www. csie. nctu. edu. tw/~tsaiwn/java/ 交通大學資訊 程學系

Java RMI Agenda RMI Introduction RPC vs. RMI Deployment RMI Example 交通大學資訊 程學系 蔡文能 10 -第 2頁

Java RMI Introduction Ø Ø Ø RMI enables the programmer to create distributed Java applications, in which the methods of remote Java objects can be invoked from other Java virtual machines, possibly on different hosts. A Java program can make a call on a remote object once it obtains a reference to the remote object, either by looking up the remote object in the naming service provided by RMI or by receiving the reference as an argument or a return value. A client can call a remote object in a server, and that server can also be a client of other remote objects. RMI uses object serialization to marshal and unmarshal parameters. 交通大學資訊 程學系 蔡文能 10 -第 5頁

Java RMI Serialization Action of encoding of an object into a stream of bytes RMI performs marshalling/unmarshalling via Java Serialization - Marshalling is the process of encoding arguments and results for transmission Thus, objects to be marshalled or unmarshalled must be serializable 交通大學資訊 程學系 蔡文能 10 -第 6頁

Java RMI Overview Remote Method Invocation - Java version of RPC Object Client ha. nctu. edu. tw 交通大學資訊 程學系 蔡文能 network method invocation Remote Object Server hehe. nctu. edu. tw 10 -第 7頁

Java RMI Remote Procedure Call (RPC) Client C P R blah, blah bar = foo(a, b); blah, blah 交通大學資訊 程學系 蔡文能 pro l o c to Server int foo(int x, int y ) { if (x>100) return(y-2); else if (x>10) return(y-x); else return(x+y); } 10 -第 8頁

Java RMI Middleware Layers Applications RPC, RMI, and events Request reply protocol Middleware layers e. Xternal Data Representation(XDR) Operating System 分層負責, 分 合作 交通大學資訊 程學系 蔡文能 10 -第 9頁

Java RMI RPC – Remote Procedure Call There a number of popular RPC specifications. Sun RPC is widely used. NFS (Network File System) is RPC based. RPC clients are processes that call remote procedures. RPC servers are processes that include procedure(s) that can be called by clients. Rich set of support tools. The RPC library is a collection of tools for automating the creation of RPC clients and servers. 交通大學資訊 程學系 蔡文能 10 -第 10頁

Java RMI Sun RPCGEN - There is a tool for automating the creation of RPC clients and servers. - The program rpcgen does most of the work for you. - The input to rpcgen is a protocol definition in the form of a list of remote procedures and parameter types. 交通大學資訊 程學系 蔡文能 10 -第 11頁

Java RMI RPCGEN Protocol Description Input File rpcgen Client Stubs foo_clnt. c foo. xx % rpcgen –C foo. xx XDR filters header file foo_xdr. c foo. h Server skeleton foo_svc. c C Source Code 交通大學資訊 程學系 蔡文能 10 -第 12頁

Java RMI RPC Programming RPC library - XDR routines - RPC run time library call rpc service register with portmapper dispatch incoming request to correct procedure - Program Generator rpcgen 交通大學資訊 程學系 蔡文能 10 -第 13頁

Java RMI RPC Run-time Library High- and Low-level functions that can be used by clients and servers. High-level functions provide simple access to RPC services. - For client: int callrpc(. . . ) - For server: int registerrpc(. . . ) - svc_run() is a dispatcher on server A dispatcher waits for incoming connections and invokes the appropriate function to handle each incoming request. 交通大學資訊 程學系 蔡文能 10 -第 14頁

Java RMI Procedure Arguments To reduce the complexity of the interface specification, Sun RPC includes support for a single argument to a remote procedure. * Typically the single argument is a structure that contains a number of values. * Newer versions can handle multiple args. 交通大學資訊 程學系 蔡文能 10 -第 15頁

Java RMI Procedure Identification Each procedure is identified by: - Hostname (IP Address) - Program Identifier (32 bit integer) - Procedure Identifier (32 bit integer) - Program Version identifier for testing and migration. 交通大學資訊 程學系 蔡文能 10 -第 16頁

Java RMI Program Identifiers Each remote program has a unique ID. Sun divided up the IDs: 0 x 0000 - 0 x 1 fffffff Sun 0 x 20000000 - 0 x 3 fffffff Sys. Admin 0 x 40000000 - 0 x 5 fffffff Transient 0 x 60000000 - 0 xffff Reserved 交通大學資訊 程學系 蔡文能 10 -第 17頁

Java RMI Procedure Identifiers & Program Version Numbers Procedure Identifiers usually start at 1 and are numbered sequentially Version Numbers typically start at 1 and are numbered sequentially. 交通大學資訊 程學系 蔡文能 10 -第 18頁

Java RMI Iterative Server Sun RPC specifies that at most one remote procedure within a program can be invoked at any given time. If a 2 nd procedure is called, the call blocks until the 1 st procedure has completed. Having an iterative server is useful for applications that may share data among procedures. Example: database - to avoid insert/delete/modify collisions. We can provide concurrency when necessary. . . 交通大學資訊 程學系 蔡文能 10 -第 19頁

Java RMI RPC example (1/7) This program shows you how to use a server program, a client program and an interface definition file to let the client program call the functions in the server program and get the results. Files: - ① test_proc. c --- the server file - ② test_client. c --- the client file - ③ test. xx --- the Interface Definition file of RPC - Files generated by rpcgen: rpcgen –C test. xx test_clnt. c test_svc. c test. h 交通大學資訊 程學系 蔡文能 10 -第 20頁

Java RMI RPC example (2/7) File test_proc. c (1/1) for server side #include "test. h" int *addd_1_svc(int *argp, struct svc_req *rqstp) { static int result; result = *argp + 1; return (&result); } int *decc_1_svc(int *argp, struct svc_req *rqstp) { static int result; result = *argp - 1; return (&result); } 交通大學資訊 程學系 蔡文能 10 -第 21頁

Java RMI RPC example (3/7) File test_client. c (1/3) for client side #include "test. h" /* test_client. c , page 1 */ void test_prog_1(char *host) { CLIENT *clnt; int *result_1; int addd_1_arg; int *result_2; int decc_1_arg; #ifndef DEBUG clnt = clnt_create(host, TEST_PROG, TEST_VERS, "netpath"); if (clnt == (CLIENT *) NULL) /* NULL is 0 */ { clnt_pcreateerror(host); exit(1); } /* to be continued */ 交通大學資訊 程學系 蔡文能 10 -第 22頁

Java RMI RPC example (4/7) File test_client. c (2/3) for client side #endif /* DEBUG */ /* test_client. c , page 2 */ scanf ("%d", &addd_1_arg); scanf ("%d", &decc_1_arg); result_1 = addd_1(&addd_1_arg, clnt); if (result_1 == (int *) NULL) { clnt_perror(clnt, "call failed"); } result_2 = decc_1(&decc_1_arg, clnt); if (result_2 == (int *) NULL) { clnt_perror(clnt, "call failed"); } printf ("addd_1_result = %dn", *result_1); printf ("decc_1_result = %dn", *result_2); #ifndef DEBUG clnt_destroy(clnt); #endif/* DEBUG */ } /* test_prog_1 *//* to be continued */ 交通大學資訊 程學系 蔡文能 10 -第 23頁

Java RMI RPC example (5/7) File test_client. c (3/3) for client side /* test_client. c , page 3 */ main(int argc, char *argv[]) { char *host; if (argc < 2) /* no host name given */ { printf("usage: %s server_hostn", argv[0]); exit(1); } host = argv[1]; test_prog_1(host); } 交通大學資訊 程學系 蔡文能 10 -第 24頁

Java RMI RPC example (6/7) File : test. xx rpcgen –C test. xx program TEST_PROG { version TEST_VERS { int ADDD(int)=1; int DECC(int)=2; }=1; }=0 x 31234567; 交通大學資訊 程學系 蔡文能 10 -第 25頁

Java RMI RPC example (7/7) Use rpcgen , C compiler, and Linking/loader - By rpcgen test. xx , you can get test_clnt. c, test_svc. c and test. h. - Compile/link on the client gcc -o test_client. c test_clnt. c -lnsl - Compile/link/run on the server (ccsun 2. csie. nctu. edu. tw) gcc -o test_svc. c test_proc. c -lrpcsvc -lnsl. /test_svc& - Run clien program on the client. /test ccsun 2. csie. nctu. edu. tw Demo on Sun machines 交通大學資訊 程學系 蔡文能 10 -第 26頁

Java RMI Test RPC -- Server Side 交通大學資訊 程學系 蔡文能 10 -第 28頁

Java RMI Another example of rpcgen file const MAX = 1000; typedef int File. Identifier; typedef int File. Pointer; typedef int Length; struct Data { int length; char buffer[MAX]; }; struct writeargs { File. Identifier f; File. Pointer position; Data data; }; 交通大學資訊 程學系 蔡文能 struct readargs { File. Identifier f; File. Pointer position; Length length; }; program FILEREADWRITE { version VERSION { void WRITE(writeargs)=1; Data READ(readargs)=2; 2 }=2; } = 9999; 10 -第 30頁

Java RMI High-Level Library Limitation The High-Level RPC library calls support UDP only (no TCP). You must use lower-level RPC library functions to use TCP. The High-Level library calls do not support any kind of authentication. 交通大學資訊 程學系 蔡文能 10 -第 31頁

Java RMI Low-level RPC Library Full control over all IPC options - TCP & UDP - Timeout values - Asynchronous procedure calls Multi-tasking Servers Broadcasting IPC : Inter-Process Communication 交通大學資訊 程學系 蔡文能 10 -第 32頁

Java The General RMI Architecture RMI The server must first bind its name to the registry The client lookup the server name in the registry to establish remote references. The Stub serializing the parameters to skeleton, the skeleton invoking the remote method and serializing the result back to the stub. 交通大學資訊 程學系 蔡文能 10 -第 33頁

Java The Stub and Skeleton RMI A client invokes a remote method, the call is first forwarded to stub. The stub is responsible for sending the remote call over to the serverside skeleton The stub opening a socket to the remote server, marshaling the object parameters and forwarding the data stream to the skeleton. A skeleton contains a method that receives the remote calls, unmarshals the parameters, and invokes the actual remote object implementation. 交通大學資訊 程學系 蔡文能 10 -第 34頁

Java Stubs RMI Stub - Client side Acts as an implementation of a remote interface Communicates with the real object over the network The stub class is generated from corresponding remote class by the RMI compiler rmic Note: As of the J 2 SE 5. 0 release, stub classes for remote objects no longer need to be pregenerated using the rmic stub compiler, unless the remote object needs to support clients running in pre-5. 0 VMs. 交通大學資訊 程學系 蔡文能 10 -第 35頁

Java skeletons RMI Skeleton - Server side Carries on a conversation with the stub; Reads the parameters for the method call from the link Call the real remote service Writes the return value from the service back to the stub 交通大學資訊 程學系 蔡文能 10 -第 36頁

Java RMI (in Java) “Flat” directory structure which attempts to provide some notion of location transparency-- client code uses a single name to find a server Client Code Client Stub Naming Service Activation Daemon Implement “Factories” using declarative descriptions of activatable objects network One JVM per Activation. Group. Automatically launched by Activation daemon and contains (potentially) many small scale, semi-independent servers which can share resources (like connection pools) and which live under the same security restrictions 交通大學資訊 程學系 蔡文能 Server Skeleton Server JVM Object Asociated to Activation Group 10 -第 37頁

Java RMI Layers Java Virtual Machine Client Object Remote Object Stub Skeleton Remote Reference Layer Transport Layer 交通大學資訊 程學系 蔡文能 TCP Copyright ? 1997 Alex Chaffee Transport Layer 10 -第 38頁

Java RMI Remote reference layer Defines and supports the invocation semantics of the RMI connection Provides a Remote. Ref object that represents the link to the remote service implementation object The stub objects use the invoke() method in Remote. Ref to forward the method call 交通大學資訊 程學系 蔡文能 10 -第 39頁

Java RMI Transport layer Provides basic connectivity - makes the connection between JVMs Based on TCP/IP connections between machines in a network 交通大學資訊 程學系 蔡文能 10 -第 40頁

Java RMI Finding Remote Objects It would be awkward if we needed to include a hostname, port and protocol with every remote method invocation. RMI provides a Naming Service through the RMI Registry that simplifies how programs specify the location of remote objects. - This naming service is a JDK utility called rmiregistry that runs at a well known address (by default). 交通大學資訊 程學系 蔡文能 10 -第 41頁

Java RMI Find Servers using Naming Service Simple interface to registry Implemented via 5 static methods on an object: public static String[] list(String name) public static Remote lookup(String name) public static void bind(String name, Remote obj) public static void rebind(String name, Remote obj) public static void unbind(String name) 交通大學資訊 程學系 蔡文能 10 -第 42頁

Java java. rmi. registry. Locate. Registry 交通大學資訊 程學系 蔡文能 RMI 10 -第 44頁

Java java. rmi. registry. Registry 交通大學資訊 程學系 蔡文能 RMI 10 -第 45頁

Java RMI Deployment(佈署): - Where does the server program finds it’s classes? - Where does the client program find it’s classes? - How are classes loaded from client to server and vice-versa? Remember that Object Serialization does not send the classes, only the data 交通大學資訊 程學系 蔡文能 10 -第 46頁

Java RMI Steps for Developing an RMI System 1. Define the Remote interface 2. Develop the remote object by implementing the remote interface. 3. Develop the client program. 4. Compile the Java source files. 5. Generate the client stubs and server skeletons. 6. Start the RMI registry. 7. Start the remote server objects. 8. Run the client 交通大學資訊 程學系 蔡文能 10 -第 47頁

Java RMI Class Loading - It’s all in the codebase Source from which to load classes into JVM - Usual CLASSPATH variable “local codebase” Set this while running both the server and the client but not rmiregistry - RMI client needs stubs from server Stubs downloaded from the server to the client using the java. rmi. server. codebase property - RMI server may need classes from the client Classes downloaded from the client to the server using the java. rmi. server. codebase property setup by the client - RMI registry needs to find stub classes If it finds them from CLASSPATH it will not convey the “true” code base associated with the stub class even if the server sets it. - Searches “local” code base initially, then searches the “java. rmi. server. codebase” 交通大學資訊 程學系 蔡文能 10 -第 48頁

Java RMI Downloading Stubs 交通大學資訊 程學系 蔡文能 10 -第 49頁

Java RMI Downloading Classes 交通大學資訊 程學系 蔡文能 10 -第 50頁

Java RMI Java Interfaces Similar to Class No implementation! All methods are abstract (virtual for C++ ). Everything is public. No constructor an Interface is an API that can be implemented by a Class. 交通大學資訊 程學系 蔡文能 10 -第 51頁

Java RMI Interfaces and Inheritence In Java a class can only extend a single superclass (single inheritence). A class can implement any number of interfaces. - end result is very similar to multiple inheritence. 交通大學資訊 程學系 蔡文能 10 -第 52頁

Java RMI Creating Remote object 1. 2. 3. 4. Define an interface which extends Remote interface Create the server program which implements that interface Compile the Java program Create the Stub Note: As of the J 2 SE 5. 0 release, stub classes for remote objects no longer need to be pregenerated using the rmic stub compiler, unless the remote object needs to support clients running in pre-5. 0 VMs. 交通大學資訊 程學系 蔡文能 10 -第 53頁

Java RMI Create the Stub A. In JBuilder use “JNI/RMI” tab in class properties to generate it automatically B. By hand: use rmic tool: rmic Compute. Engine Note: As of the J 2 SE 5. 0 release, stub classes for remote objects no longer need to be pregenerated using the rmic stub compiler, unless the remote object needs to support clients running in pre-5. 0 VMs. 交通大學資訊 程學系 蔡文能 10 -第 54頁

Java RMI Server Details – extending Remote Create an interface the extends the java. rmi. Remote interface. - This new interface includes all the public methods that will be available as remote methods. import java. rmi. *; public interface My. Remote extends Remote { public int foo(int x) throws Remote. Exception; public String blah(int y) throws Remote. Exception; . . . } 交通大學資訊 程學系 蔡文能 10 -第 55頁

Java RMI How the interface will be used Remote Interface extends Your Interface Class Remote. Server provides methods needed by extends Unicast. Remote. Object implements extends Class for your Remote Object 交通大學資訊 程學系 蔡文能 10 -第 56頁

Java RMI Server Details – Implementation Class Create a class that implements the interface. - The class should also extend Unicast. Remote. Object* This class needs a constructor that throws Remote. Exception ! This class is now used by rmic to create the stub and skeleton code. Note: As of the J 2 SE 5. 0 release, stub classes for remote objects no longer need to be pregenerated using the rmic stub compiler, unless the remote object needs to support clients running in pre-5. 0 VMs. *It doesn’t have to extend Unicast. Remote. Object, there is another way… 交通大學資訊 程學系 蔡文能 10 -第 57頁

Java RMI Generating stubs and skeleton Compile the remote interface and implementation: > javac My. Remote. java My. Remote. Impl. java Use rmic to generate My. Remote. Impl_stub. class, My. Remote. Impl_skel. class > rmic My. Remote. Impl Note: As of the J 2 SE 5. 0 release, stub classes for remote objects no longer need to be pregenerated using the rmic stub compiler, unless the remote object needs to support clients running in pre-5. 0 VMs. 交通大學資訊 程學系 蔡文能 10 -第 58頁

Java RMI Server Detail – main() The server main() needs to: - create a remote object. - register the object with the Naming service. public static void main(String args[]) { try { My. Remote. Impl r = new My. Remote. Impl(); java. Naming. bind(“joe”, r); } catch (Remote. Exception e) {. . . 交通大學資訊 程學系 蔡文能 10 -第 59頁

Java RMI Client Details The client needs to ask the Naming service for a reference to a remote object. - The client needs to know the hostname or IP address of the machine running the server. - The client needs to know the name of the remote object. The Naming service uses URLs to identify remote objects. rmi: //hostname/objectname 交通大學資訊 程學系 蔡文能 10 -第 60頁

Java RMI Using The Naming service Naming. lookup() method takes a string parameter that holds a URL indicating the remote object to lookup. rmi: //hostname/objectname Naming. lookup() returns an Object! Naming. lookup() can throw - Remote. Exception - Malformed. URLException 交通大學資訊 程學系 蔡文能 10 -第 61頁

Java RMI registry (1/2) A naming service - Maps names to remote objects - Provides clients with a mechanism to find remote services running on RMI servers Essential operations: bind/rebind, unbind, lookup - Bind adds a service entry to the registry - Unbind removes a service entry from the registry - Lookup allows clients to find the service’s address using service name 交通大學資訊 程學系 蔡文能 10 -第 67頁

Java RMI registry (2/2) Names in the registry use unique names - Recommend the name of the remote class that implements the remote interface For accessing a remote registry, use the following URL form - rmi: //host: port/service. Name - host is the machine on which the registry is running - The registry is listening on the port (default 1099) 交通大學資訊 程學系 蔡文能 10 -第 68頁

Java RMI Start the Java RMI registry By default, the registry runs on TCP port 1099. To start a registry on a different port, specify the port number from the command line. For example, to start the registry on port 2001 on a Windows platform: start rmiregistry 2001 If the registry will be running on a port other than 1099, you'll need to specify the port number in the calls to Locate. Registry. get. Registry in the Server and Client classes. For example, if the registry is running on port 2001 in this example, the call to get. Registry in the server would be: - Registry registry = Locate. Registry. get. Registry(2001); 交通大學資訊 程學系 蔡文能 10 -第 72頁

Java RMI classes Java. rmi. Remote - Interface supporting remote objects java. rmi. server. Unicast. Remote. Object - Continuously running server java. rmi. activation. Activatable - Server started by rmid daemon java. rmi. Naming - Lookup: Returns stub given a name Java. rmi. registry. Registry , Locate. Registry java. rmi. RMISecurity. Manager - Validates rights to access downloaded object 交通大學資訊 程學系 蔡文能 10 -第 74頁

Java RMI Other Technologies - CORBA - XML based SOAP / Web Service - J 2 EE/EJB - Micro. Soft’s. NET Has Common Language Runtime Tight Integration of Web Services and XML Multiple language integration - However only one platform Windows 交通大學資訊 程學系 蔡文能 10 -第 75頁

Java RMI Reference - RMI docs java. sun. com/products/jdk/rmi/ - Java Tutorial on RMI: http: //java. sun. com/j 2 se/1. 5. 0/docs/guide/rmi - Java. IDL java. sun. com/docs/books/tutorial/idl java. sun. com/products/jdk/idl/ www. omg. org/news/begin. htm - Jini www. artima. com/jini/resources 交通大學資訊 程學系 蔡文能 10 -第 76頁

Java RMI Programming Paradigms Imperative Programming (FORTRAN, C, Pascal, …) - The most common programming paradigm Functional Programming (LISP, …) Logic Programming (Prolog) (Declarative programming language; 宣告式語言) Object-Oriented Programming (Smalltalk, C++, Java, …) Simply using C++/Java constructs does not automatically lead to well-organized Object-Oriented Programs. 交通大學資訊 程學系 蔡文能 10 -第 78頁

Java RMI Why OO Programming? Better concepts and tools to model and represent the real world as closely as possible (including concurrency, e. g. , in Windows GUI) => model of reality => behavior modeling Better reusability & extensibility (inheritance) => reduce the time/cost of development Enhanced maintainability & improved reliability – “Encapsulation” and “Information Hiding” - Object only accessible through the external interface Internal implementation details are not visible outside Localized changes to implementation of classes Completeness: all required operations are defined Independent testing and maintenance Help writing good program more easily 交通大學資訊 程學系 蔡文能 10 -第 79頁

Java RMI RPC / RMI 謝謝捧場 http: //www. csie. nctu. edu. tw/~tsaiwn/java/ 蔡文能 交通大學資訊 程學系 蔡文能 10 -第 80頁