RMI 面试题与答案
问题 6. Does RMI-IIOP support dynamic downloading of classes?
No, RMI-IIOP doesn't support dynamic downloading of the classes as it is done with CORBA in DII (Dynamic Interface Invocation).Actually RMI-IIOP combines the usability of Java Remote Method Invocation (RMI) with the interoperability of the Internet Inter-ORB Protocol (IIOP).So in order to attain this interoperability between RMI and CORBA,some of the features that are supported by RMI but not CORBA and vice versa are eliminated from the RMI-IIOP specification.
问题 7. Can RMI and Corba based applications interact ?
Yes they can. RMI is available with IIOP as the transport protocol instead of JRMP.
问题 8. What is Remote Procedure Calls, RPC?
A request from one program that is located in one computer can be used by another computer in a network environment without understanding the underlying network details. This is done by a protocol called Remote Procedure Calls. In this client / server environment (network environment), the request is from a client to the server that provides the service from a server.
RPC is also called as inter-process communication. RPC extends the normal procedure calls across the network which is necessary in distributed computing models and for harnessing the power of the multiple processors.
In distributed systems, a client calls a procedure stored on a server. This is called calling a remote procedure stored on a server. Though, the call is made as if the procedure was stored on the local machine.
The steps in which a RPC is made are:
* The client calls the procedure
* The client stub builds the message.
* The message is sent over the network.
* The Server OS gives the message to the server stub.
* The server stub unpacks the message.
* The stub makes a local call to the procedure.
* The server does the work and returns the result to the server stub.
* The stub packs the message and traps to the kernel.
* The remote kernel sends the message the client kernel.
* The client kernel gives the message to the client stub.
* The client stub unpacks the result and gives to the client.
问题 9. Explain the advantages and disadvantages of RPC.
Advantages of RPC:
* Server independent
* Process-oriented and thread oriented models supported by RPC
* The development of distributed systems is simple because it uses straightforward semantics and easier.
* Like the common communications between the portions of an application, the development of the procedures for the remote calls is quite general.
* The procedure calls preserves the business logics which is apt for the application.
* The code re-writing / re-developing effort is minimized.
* Enables the usage of the applications used in the distributed environment, not only in the local environment.
* RPC provides interoperability between CORBA ORB implementations.
* A lightweight RPC protocol permits efficient implementations.
Disadvantages of RPC:
* Context switching increases scheduling costs
* RPC is not a standard it is an idea that can be implemented in many ways
* RPC does not solve the most of the distribution creation problems
* RPC is only interaction based. This does not offer any flexibility in terms of hardware architecture.
* RPC implementations are not yet mature.
* It requires the TCP/IP protocol. Other transport protocols are not supported yet.
* Not yet proven over wide-area networks.
问题 10. Explain the difference between RPC and RMI.
RMI:
* The remote objects are accessed by the references
* Implements object to object implementation among different java objects to implement distributed communication model.
- RMI passes the objects as parameters to remote methods.
- RMI invokes the remote methods from the objects
RPC:
* The process is through methods / functions
* Proxy server is involved in processing the procedure calls
* Calls a procedure remotely like invoking the methods
* The remoteness is not exactly transparent to the client
用户评价最有帮助的内容：
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- Does RMI-IIOP support dynamic downloading of classes?