java代写

ds­18­s2­assignment2 is an optional argument that specifies the destination path for your repository on your local machine.

Note that you can have more than one copy of your code checked out, you will need to update it to avoid conflicts.
See the svn documentation (http://www.cs.adelaide.edu.au/docs/svn­instr.pdf) for details on how this can be done. However, for now, we will assume you have just the one working copy.

Working in your repository

As you work on your code you will be adding and committing files to your repository. The Subversion documentation explains and has examples on performing these actions.

It is strongly advised that you:

Commit regularly
Use meaningful commit messages Develop your tests incrementally

Assignment Submission

Use the Computer Science Web Submission System (https://cs.adelaide.edu.au/services/websubmission/) system to submit assignments.

You are allowed to commit as many times as you like.

The Web Submission System will only perform basic checks for any required files.
On submission there will be not assigned marks.
The assignment will be marked by a teacher who will upload the marks into the Web Submission System. Keep an eye on the forums for announcements regarding marks.

Assignment Descripon Objecve

To gain an understanding of what is required to build a client/server system, by building a simple system that aggregates and distributes ATOM feeds.

Introducon

Information management and tracking becomes more difficult as the number of things to track increases. For most users, the number of web pages that they wish to keep track of is quite large and, if they had to remember to check everything manually, it’s easy to forget a webpage or two when you’re tired or busy. Enter syndication, a mechanism by which a website can publish summaries as a feed that you can sign up to, so that you can be notified when something new has happened and then, if it interests you, go and look at it. Initial efforts in the world of syndication included the development of the RSS family of protocols but

content servers and the read clients. The content server will PUT content on the server, while the read client will GET content from the server.

Elements

The main elements of this assignment are:

An ATOM server (or aggregation server) that responds to requests for feeds and also accepts feed updates from clients. The aggregation server will store feed information persistently, only removing it when the content server who provided it is no longer in contact, or when the feed item is not one of the most recent 25.

A client that makes an HTTP GET request to the server and then displays the feed data, stripped of its XML information.
A CONTENT SERVER that makes an HTTP PUT request to the server and then uploads a new version of the feed to the server, replacing the old one. This feed information is assembled into ATOM XML after being read from a file on the content server’s local filesystem.

All code elements will be written in the Java programming language. Your clients are expected to have a thorough failure handling mechanism where they behave predictably in the face of failure, maintain consistency, are not prone to race conditions and recover reliably and predictably.

Summary of this prac

In this assignment, you will build the aggregation system described below, including a failure management system to deal with as many of the possible failure modes that you can think of for this problem. This obviously includes client, server and network failure, but now you must deal with the following additional constraints (come back to these constraints after you read the description below):

1. Multiple clients may attempt to GET simultaneously and are required to GET the aggregated feed that is correct for the Lamport clock adjusted time if interleaved with any PUTs. Hence, if A PUT, a GET, and another PUT arrive in that sequence then the first PUT must be applied and the content server advised, then the GET returns the updated feed to the client then the next PUT is applied. In each case, the participants will be guaranteed that this order is maintained if they are using Lamport clocks.
2. Multiple content servers may attempt to simultaneously PUT. This must be serialised and the order maintained by Lamport clock timestamp.
3. Your aggregation server will expire and remove any content from a content server that it has not communicated within the last 15 seconds. You may choose the mechanism for this but you must consider efficiency and scale.
4. All elements in your assignment must be capable of implementing Lamport clocks, for synchronization and coordination purposes.

Your Aggregaon Server

To keep things simple, we will assume that there is one file in your filesystem which contains a list of entries and where are they come from. It does not need to be an ATOM format, but it must be able to convert to a standard ATOM file when the client sends a GET request. However, this file must survive the server crashing and re­starting, including recovering if the file was being updated when the server crashed! Your server should restore it as was before re­starting or a crash. You should, therefore, be thinking about the PUT as a request to handle the information passed in, possibly to an intermediate storage format, rather than just as overwriting a file. This reflects the subtle nature of PUT ­ it is not just a file write request! You should check the feed file provided from a PUT request to ensure that it is valid. The file details that you can expect are detailed in the Content Server specification.

All the entities in your system must be capable of maintaining a Lamport clock.

The first time your ATOM feed is created, you should return status 201 ­ HTTP_CREATED. If later uploads are ok, you should return status 200. (This means, if a Content Server first connects to the Aggregtion Server, then return 201 as succeed code, then before the content server lost connection, all other succeed response should use 200). Any request other than GET or PUT should return status 400 (note: this is not standard but to simplify your task). Sending no content to the server should cause a 204 status code to be returned. Finally, if the ATOM XML does not make sense you may return status code 500 ­ Internal server error.

Your server will, by default, start on port 4567 but will accept a single command line argument that gives the starting port number. Your server’s main method will reside in a file called AggregationServer.java .

Your server is designed to stay current and will remove any items in the feed that have come from content servers which it has not communicated with for 15 seconds. How you do this is up to you but please be efficient!

Your GET client

Your GET client will start up, read the command line to find the server name and port number (in URL format) and will send a GET request for the ATOM feed. This feed will then be stripped of XML and displayed, one line at a time, with the attribute and its value. Your GET client’s main method will reside in a file called GETClient.java . Possible formats for the server name and port number include “http://servername.domain.domain:portnumber”, “http://servername:portnumber” (with implicit domain information) and “servername:portnumber” (with implicit domain and protocol information).

You should display the output so that it is easy to read but you do not need to provide active hyperlinks. You should also make this client failure­tolerant and, obviously, you will have to make your client capable of maintaining a Lamport clock.

Your Content Server

Your content server will start up, reading two parameters from the command line, where the first is the server name and port number (as for GET) and the second is the location of a file in the file system local to the Content Server (It is expected that this file located in your project folder). The file will contain a number of fields from the ATOM format that are to be assembled into an ATOM XML feed and then uploaded to the server. You may assume that all fields are text and that there will be no embedded HTML or XHMTL. The list of ATOM elements that you need to support are:

2018/10/6 Assignment 2 (Cruz & David)

https://myuni.adelaide.edu.au/courses/36234/assignments/84332

7/12

… </feed>

Your content server will need to confirm that it has received the correct acknowledgment from the server and then check to make sure that the information is in the feed as it was expecting. It must also support Lamport clocks.

Some basic suggesons

The following would be a good approach to solving this problem:

Think about how you will test this and how you are going to build each piece. What are the individual steps?
Write a simple version of your servers and client to make sure that you can communicate between them. Use known working ATOM feeds for testing parts of your system and read all of the relevant spec sections carefully!

There are many default Java XML parsers out there, learn how to use them rather than write your own. Both options are acceptable, but we have found that it does save time to use existing ones (if not for anything, you have a ton of tutorials out there!)
We strongly recommend that you implement this assignment using Sockets rather than HttpServer

Try modularising your code; for example, ATOM Feed parse function is required in all places, so it is better to have all those functions in one class, then reused in other places.

Notes on Lamport Clocks

Please note that you will have to implement Lamport clocks and the update mechanisms in your entire system. This implies that each entity will keep a local Lamport clock and that this clock will get updated as the entity communicates with other entities or processes events. It is up to you to determine which events (such as send, receive or processing) the entity will consider in the Lamport clock update (for example, a System.out.println might not be interesting). This granularity will influence the performance of your implementation. The local Lamport clocks will need to be sent through to other entities with every message/request (like in the request header) ­ you are responsible for ensuring that this tagging occurs and for the local update of Lamport clocks once messages/requests are received. Towards this, follow the algorithm discussed in class and/or in the Lamport clocks paper accessible from the forum. As part of this requirement, we are aware that your method for embedding Lamport clock information in your communications may mean that you lose interoperability with other clients and servers. This is an acceptable outcome for this assignment but, usually, we would take a standards­based approach to ensure that we maintain interoperability.

And lastly,

START EARLY!

Don’t get caught out at the last minute trying to do the entire assignment at once ­ it is easy to misjudge the complexity and hours required for this assignment.

Contact the course coordinator, lectures or tutors if you need help getting started.

You are encouraged to post questions on the forums.

Submissions Design Sketch

The design sketch is a rough architecture of your system for us to be able to provide feedback on early. You may want to consider use cases of your system and the flow of information through it in the sketch, or simply the components you have thought of and where they sit in the system.

Hints:

Functional analysis is good
A component view (even if it’s extremely coarse: clients, Atom server, content servers) is required Multi­threaded interactions are a good place to focus some design effort. Show how you ensure that your thread interactions are safe (no races or unsafe mutations) and live (no deadlocks).
Explain how many server replicas you need and why
UML is a good way of expressing software designs, but it is not mandated.
It would be useful to know how you will test each part
Diagrams are awesome

Commit a Design.pdf into your svn assignment directory and submit it via websubmission (https://cs.adelaide.edu.au/services/websubmission/?sub_assign=assignment3) .

Note: Assignments with no design file will receive a mark of zero.

For COMP SCI 7076 students, this design file will form the basis of your final submission; see below.

Preview

We strongly advise that you submit a draft revision/preview of your completed assignment 2 so that we can provide you with feedback.

You will receive feedback within 1 week. The feedback will be detailed but carries no marks. You are given the opportunity to revise and change your work based on the feedback for the final submission so you use it while you can.

Final revision

If you received feedback in the last submission, please add a PDF (Changes.pdf) that includes a discussion of the feedback received and what changes you decided to make and why.

Reflecon / Report ‐ COMP SCI 3012 Students only

Reflect on your work on assignment 2. As a minimum, you must answer the following questions with no more than 2 pages in total. Submit the reflection as a PDF via Canvas.

1. Design and Implementation

1. Do you assess the difficulty of assignments before starting? If so, how do you do this?
2. Do you generally (not just for this assignment) develop a design before starting software

   development? If so, describe what process you follow in the design stage, and what kinds of things would be included in your design (i.e. flowcharts, UML, text description, pseudocode, etc) and how far do you go before you stop.

3. What would you have done differently in your design and implementation of this assignment?

2. Time Management

1. Do you generally hand in your work on time?
2. How do you organise your time in working on an assignment? Do you break up the assignment into

   parts, and if so, how do you do this?

3. Software Process

1. Overall, describe your software development process and include a diagram of your process in your description.
2. Are there any changes you would make to your process to improve it?

If you would like to give feedback on the assignment itself so that it can be improved, we would also like to hear what you have to say. You may also email the feedback to the lecturers or post on the forums as well.

Design and Report ‐ COMP SCI 7076 Students only

Students in the masters’ version of this course are required to submit a design of the system and a report describing their testing, due at the final due date for this assignment. Both are required to be submitted in PDF format. The report may be up to 3 pages in length.

Design

The design document must be submitted via SVN in this assignments directory as Design.pdf. The design should address:

the requirements of the system
the architecture
how the architecture meets all of the stated requirements
explain the purpose of any non­trivial comments
a Verification Matrix showing how every requirement will be tested

You should include diagrams as necessary.

Note: You should attempt to finalise your design document before coding and definitely before writing the report. If you find yourself working on the design with the report, then you will have gained no benefit of going through the design process and it will be more difficult for you to complete this assignment correctly and on time.

Report

The report document must be submitted via Canvas (to this assignment listing). It should contain:

A brief introduction outlining the content of your report
Observations on your design, and how much modification you had to make once you started development.
The results of your testing, in accordance with your verification matrix: how your testing was done, a description of each test case you have gone through, what are they testing, what is expected when designing the test case, and what is the result from your code (logs generated from code or a screenshot) and your conclusion (code has fulfilled the test case or not).

Assessment
COMP SCI 3012 students only

The allocation of marks for this assignment is as follows:

60% ­ Software solution 35% ­ Automated testing 5% ­ Reflection

The assessment of your software solution will be allocated as follows:

10% ­ Code quality, following the checklist in Appendix A (below)
20% ­ Architecture design decisions
30% ­ Support for basic functionality, following the checklist in Appendix B (below)
40% ­ Support for full functionality and quality of design, following the checklist in Appendix B (below)

The assessment of your testing will be allocated as follows:

The range of test cases considered
rather than focus on the number of tests, are you identifying the most important test cases with a good spread across possible cases?
The clarity of your test cases
your test harness should be verbose enough to ensure that we understand both what you have tested and the outcome of the tests

Your testing architecture, ideally captured in a testing document should become an important part of your development process!

COMP SCI 7076 students only

The allocation of marks for this assignment is as follows:

50% ­ Software solution 30% ­ Automated testing 20% ­ Design + Test Report

You are not required to complete the reflection component as per COMP SCI 3012 students (see above), however you are more than welcome to include a Reflection section within your report.

The assessment of your software solution and automated testing will be assessed the same way as the COMP SCI 3012 students (see above).