广东惠讯公司面试题.doc

Assignment for Distributed Programming using Java IntroductionThe VideoQueasy store already has an extensive Web site, but is contemplating moving towards an online system to support ecommerce activities. In particular, they are looking at making online hire of videos that will be delivered to the home. At some later stage (when everyone is on broadband) they may deliver the videos through streaming media rather than home delivery. The VideoQueasy store is aware that customers often want snack food while they are watching movies, and so has come to an arrangement with local take-away stores such as Hungry Jills so that customers can order food at the same time as they order videos. VideoQueasy is aware that there are a variety of competing technologies such as Web pages, RPC systems such as Web services, remote object systems such as CORBA, and distributed object systems. In order to future proof itself against technology changes it wants a traditional client-server system as its initial implementation. However, the implementation must be structured in such a way that other middleware technologies can be plugged in with the minimum of changes. This assignment has graded levels. The simplest version will be given a Pass if done satisfactorily, but to gain higher grades more features will have to be added. DetailsYou will need to implement a client and one or more servers using a socket-based protocol. A customer (client) will need to be able to make the following requests to the VideoQueasy server: l What categories of video are in stock? The response should be a list such as Horror, Humour, Drama, etc l For a given category, what movies are available? l What is the availability of a particular movie? l What is the cost and rental period of a particular movie? l What take-away shops are there? l What is the menu for a particular shop? l Add to a shopping cart a video or some take-away items l Check out the shopping cart and give credit card information Presentation l You should not assume any particular way of presenting results l A user interface may be a GUI interface, a text-based interface or maybe another program with no interface at all. l Dont change the messages just to suit whatever presentation you want to use DeliverablesYou should hand in the following l A statement of which level of assessment you are aiming at, and the parts you have completed l A specification of all messages between client and server(s). This specification should include enough details about message formats that someone else could implement a client or server (in any language, not just Java) to handle the messages. Note that a clear and unambiguous specification is regarded as one of the most important parts of this assignment l Finite state transition diagrams where appropriate l UML diagrams showing the classes and their linkages l Hard-copy listings of all classes for each client and server l Electronic copies of all classes for each client and server l Instructions about how to install and run each client and server You will be asked to demonstrate your system during a tutorial. Assignment levelsGeneral comments: l Your clients can use a text-based interface, reading from System.in and writing to System.out, or can use a graphical interface with AWT or Swing objects. It does not matter which you choose, the mark will not depend on the user-interface style l The quality of classes and of code for methods will be assessed. Poor quality code will lose marks. In particular, sloppy indentation will be regarded as an indicator of erroneous code. l Consistency between specifications, diagrams and code will be checked Pass level A client talking to a single server. The server handles all of the VideoQueasy requests. The server keeps lists of the videos and their types. It also has a list of take-away stores and their menus. All of this can be done using local files and/or lists and tables kept in memory. All clients and servers will be written in Java. However, you should not assume that the other end of a communication channel will be in Java - it could be in some other language such as C# or Perl. So do not use any Java-specific techniques such as serialising Java objects. This level demonstrates that you can specify a protocol for communication between a client and a single server and implement this protocol in a simple way. Extra level The specification given above will gain a Pass grade if done satisfactorily. Higher grades will be given on completion of additional functionality. Each additional function will gain an extra grade (to a maximum of HD). The additional functions are Interoperability This assignment is to be done in groups of one or two. However, for the message specification a group can cooperate with another group. The groups can agree on a common specification and perform completely independant implementations. If the client from one group can use the server from another and vice versa then this will demonstrate interoperability JDBC All databases are managed by a database system such as Access, Oracle or MySQL. The server communicates with the database by JDBC calls. This level shows that you can manage a typical 3-tier system with presentation, logic and database handled separately. Multiple servers Each take-away shop runs its own server. VideoQueasy will forward certain requests (such as the menu) directly to the shops server rather than maintaining information on its own server. This level demonstrates that you can deal with a multi-tier system with many servers at the backend Security All sensitive accesses are performed using security mechanisms, such as encryption and validation. Each server should be able to validate its identity using certificates This level shows that you can handle the authorisation, security and privacy issues that can arise Web access Web access to the VideoQueasy service should be made available. This will mean a CGI script/Java servlet/etc that can act as a client to the VideoQueasy server. This will involve a set of Web pages and HTTP backends to handle form requests. This is in addition to an ordinary client, not as a replacement This level will add alternative access mechanisms to the service, which makes it Web-accessible to humans Version control The client should be downloadable from a Web page as a JNLP (Java Network Loader Protocol) application. This will allow the client code to be downloaded/upgraded and run. This level will help with version control issues. In order to use it, you will need to understand and use a formal specification document. XML Messages should be sent as XML messages, using JAXB to marshal and unmarshal them. This will give practice in using XML, including writing DTDs. Final level The final level will be the sum of all extensions. For example, adding separate take-away shop servers with JDBC backends and a Web frontend will be worth