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Massey University
159.251 - Software Design and Construction
Assignment 2 (22%)
You must submit your final work using the stream submission system no later than Wednesday
16th Nov. 2022.
You are expected to manage your source code, this includes making frequent backups. It is
strongly recommended (but not required) to use a private git repository for this assignment,
and commit as frequently as possible.
How to submit
1. Upload a zip file consisting of:
a. The Maven project folder (inc. pom.xml)
b. performance-analysis.pdf -measure time and memory consumption
c. coverage.pdf/html - the pdf or html version of the coverage report created by
2. upload this file to stream - note: the max upload size is set to 20 MB
3. verify the submission: download the zip file, unzip it into a new folder and inspect
content, run Maven from the command line, check the output including generated jar
Work individually to create the following program in Java.
Create a project assign251_2 using the Maven project layout, and within this project, create a
project that implements custom appender and layout objects for Log4j. For this, you will need to
create an appender and layout that work with the other Log4j objects (i.e. implementing
relevant Log4j abstract classes or interfaces), test them and run profiling tools on them to gauge
their correctness and efficiency.
Note there is no main class for this project, it will be run via your tests from sections 3 and 4.
You may want to consider a test driven development methodology where your first step is to
start with section 3 and work backwards. This will allow you to check that your classes are
working correctly as you go.
1. Implement a log4j appender assign251_2.MemAppender [7 marks]
In this task, you will need to implement a custom log4j appender, which can be used directly
with the log4j logger. This MemAppender, unlike normal appenders, stores logs in memory and
prints them on demand. There is a limit to how many log events will be kept in memory (this
should be configurable), and if the maximum is reached, the oldest logs should be deleted.
Implementation details:
- It enforces the singleton pattern.
- It stores the LoggingEvents in a list. This is supplied by dependency injection (note: if
you have already created a default, that is okay).
- It will need a layout. This will need to be able to be supplied when the MemAppender is
collected, and via the setLayout() method. If a layout is not supplied, and code calling it
is needed, appropriate precondition checks should be used (as some code may not use
the appender with the layout, so it is a valid option not to supply one, as long as you
don’t use any functionality that requires it).
- There are three ways to get information about the LoggingEvents that it stores:
a. Call the method getCurrentLogs() which will return an unmodifiable list of the
b. Call the method getEventStrings() which will return an unmodifiable list of
strings (generated using a layout stored in the MemAppender).
c. Call the method printLogs() which will print the logging events to the console
using the layout and then clear the logs from its memory.
- It has a property called maxSize, which needs to be configurable. When this size is
reached, the oldest logs should be removed to make space for the new ones.
- The number of discarded logs should be tracked, and can be accessed using
getDiscardedLogCount(). This should be stored as a long type, as there may be many
discarded logs.
Note: Be careful to observe the DRY principle - there are overlapping requirements above.
3.5 marks Correct implementation of the singleton pattern and dependency injection
options for the list and layout.
2 marks Correct implementation of the information printing / collection methods,
along with sensible precondition checks where appropriate.
1.5 mark Correct implementation of maxSize and associated features.
2. A layout assign251_2.VelocityLayout [3 marks]
a. VelocityLayout basically works like PatternLayout, but uses Velocity as the
template engine. This layout should work with log4j appenders as well as the
b. Variable to be supported:
i. c (category)
ii. d (date using the default toString() representation)
iii. m (message)
iv. p (priority)
v. t (thread)
vi. n (line separator)
c. This means that the variable syntax is different, e.g. use $m instead of %m
d. VelocityLayout should have options to set its pattern both in the constructor and
via a setter. An example string pattern could look like:
“[$p] $c $d: $m”
3. Write tests that test your appender and layout in combination with different loggers,
levels and appenders [4 marks]
a. Use JUnit for testing your appender and layout. Aim for good test coverage and
precise asserts.
b. Use the tests to show both the appender and layout working with different
combinations of built in log4j classes as well as with each other.
c. Tests should be stored in the appropriate locations according to the Maven folder
4. Write tests to stress-test your appender/layout by creating a large amount of log
statements [6 marks]
a. Create a separate test class for stress tests.
b. Use these tests to compare the performance between MemAppender using a
LinkedList, MemAppender using an ArrayList, ConsoleAppender and
FileAppender - measure time and memory consumption (using JConsole or
VisualVM or any profiler)
c. Consider how to output your logs in such a way that makes comparisons
between the MemAppender and other appenders sensible.
d. Use these scripts to compare the performance between PatternLayout and
e. Stress tests should test performance before and after maxSize has been
reached, and with different maxSize values.
i. parameterised tests may be helpful here.
f. Write a short report summarising your findings (embed screenshots of memory
usage charts in this reports taken from VisualVM). The report name should be
g. Measure your test coverage of the written tests by generating a branch and
statement coverage reports using Jacoco or Emma. Submit this report with your
project (should be placed under ~/target/ folder”
Note that the marks for this section will be based around your reporting, the effectiveness of
your stress tests in probing into the efficiency of the classes, and the overall integration testing,
checking that these classes work in combination with other relevant out-of-the-box classes.
5. Write a Maven build script [2 marks]
a. The Maven script should be used to build the project including compiling, testing,
measuring test coverage, dependency analysis. All dependencies should be
managed with your maven build.
b. Use the jacoco Maven plugin for measuring test coverage.
● You can use any development environment you prefer as it is a Maven project.
● Library whitelist: only the following libraries and libraries they depend on can be used:
Apache log4j, Apache Velocity, JUnit, Google Guava, Apache Commons Collections,
Jacoco and Emma (for code coverage).
1. Code that is not self-documenting, or long or complex methods.
2. Violating the Maven standard project layout or Java naming conventions.
3. Use of absolute paths (e.g., libraries should not be referenced using absolute paths like
“C:\\Users\\..”, instead use relative references w.r.t. the project root folder)
4. References to local libraries (libraries should be referenced via the Maven repository)
5. Use of libraries not on the whitelist
Bonus Question [2 marks]
You can get 100% for the assignment without this. This will give you additional marks up to the
maximum if you lose some elsewhere.
Create an MBean object for each instance of the MemAppender to add JMX monitoring to this
object, the properties to be monitored are:
1. the log messages as array
2. the estimated size of the cached logs (total characters)
3. the number of logs that have been discarded
We will check submissions for plagiarism. Additionally we will randomly choose
students and conduct a video interview with them to assess their understanding of the
submitted code. Please read the Massey guidelines on plagiarism and dishonesty for details:
Your assessment will be based on the following criteria:
Criteria Mark
Implementation of log4j appender assign251_2.MemAppender 7
Correct implementation of the singleton pattern and dependency injection
options for the list and layout.
Correct implementation of the information printing / collection methods,
along with sensible precondition checks where appropriate
Correct implementation of maxSize and associated features. 1.5
Implementation of layout assign251_2.VelocityLayout 3
Correct use of the Velocity template engine 1
Works with appenders and MemAppender 1
Supports listed variables 1
Testing the implemented appender and layout 4
Use of Junit with good coverage and precise asserts 2
Tests show that the appender and layout work with different combinations of
built-in log4j classes and each other
Tests stored in appropriate locations following Maven directory structure 0.5
Stress-testing your appender/layout 6
Separate class for stress tests 0.5
Comparison of performance between MemAppender using LinkedList,
ArrayList, ConsoleAppender and FileAppender - with measurements: time,
memory consumption for different maxSizes
Scripts to compare velocity and pattern layout 1
Report of stress test findings with an analysis of the stress test results and
Test coverage reports 0.5
Build management 2
Uses maven for dependency, coverage (using jacoco) 2
Implementation of an MBean object for instances of MemAppender for JMX
monitoring of properties: log messages, estimated size of cached logs,
number of logs discarded

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