Based on the example of the XWiki Open Source project (http://xwiki.org) this session will describe a number of practices to improve the quality of a Java project. Also, it will show how to implement these practices so that they are automatically checked and enforced. Some examples include: *How to make sure your project does not break binary compatibility unintentionally and, more generally, how to successfully evolve an API without breaking your users; *How to manage the JAR hell and avoid duplication of classes in your application at runtime; *How to automatically control the test coverage and the associated policies; *How to automate functional testing of web applications and how to avoid false-positives that plague any project..
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Implementing quality in Java projects
1. Implementing Quality
on Java projects
Vincent Massol
Committer XWiki
CTO XWiki SAS
@vmassol
Saturday, April 20, 13
2. Vincent Massol
• Speaker Bio
•CTO XWiki SAS
• Your Projects
•XWiki (community-driven open source project)
•Past: Maven, Apache Cargo, Apache Cactus, Pattern
Testing
• Other Credentials:
•LesCastCodeurs podcast
•Creator of OSSGTP open source group in Paris
Saturday, April 20, 13
4. The XWiki project in summary
• 9 years old
• 28 active
committers
• 7 committers
do 80% of
work
• 700K
NCLOC
• 11 commits/
day
Saturday, April 20, 13
5. Examples of Quality actions
• Coding rules (Checkstyle, ...)
• Test coverage
• Track bugs
• Don’t use Commons Lang 2.x
• Use SLF4J and don’t draw
Log4J/JCL in dependencies
• Automated build
• Automated unit tests
• Stable automated functional
tests
• Ensure API stability
• Code reviews
• License header checks
• Release with Java 6
• Ensure javadoc exist
• Prevent JAR hell
• Release often (every 2 weeks)
• Collaborative design
• Test on supported
environments (DB & Browsers)
Saturday, April 20, 13
13. API Stability - Young APIs
/**
* ...
* @since 5.0M1
*/
@Unstable(<optional explanation>)
public EntityReference createEntityReference(String name,...)
{
...
}
+ max duration for keeping the annotation!
Saturday, April 20, 13
14. API Stability - Next steps
• Annotation or package for SPI?
• Better define when to use the @Unstable
annotation
• Not possible to add a new method to an existing
Interface without breaking compatibility
•Java 8 and Virtual Extension/Defender methods
interface TestInterface {
public void testMe();
public void newMethod() default {
System.out.println("Default from interface"); }
Saturday, April 20, 13
18. Surprising results...
• Commons Beanutils bundles some classes from Commons
Collections, apparently to avoid drawing a dependency to it...
• Xalan bundles a lot of other projects (org/apache/xml/**, org/
apache/bcel/**, JLex/**, java_cup/**, org/apache/regexp/**). In
addition, it even has these jars in its source tree without any
indication about their versions...
• stax-api, geronimo-stax-api_1.0_spec and xml-apis all draw
javax.xml.stream.* classes
• xmlbeans and xml-apis draw incompatible versions of
org.w3c.dom.* classes
14 exceptions in total!
Saturday, April 20, 13
19. Maven: dependency version issue
<dependencies>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.4.0</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>0.9.9</version>
<!-- Depends on org.slf4j:slf4j-api:1.5.0 -->
</dependency>
</dependencies>
Will run logback 0.9.9
with slf4J-api 1.4.0
instead of 1.5.0!
Saturday, April 20, 13
22. The Problem
More bugs reported, overall
quality goes down and harder to
debug software
Saturday, April 20, 13
23. Use Jacoco to fail the build
<plugin>
<groupId>org.jacoco</groupId>
<artifactId>jacoco-maven-plugin</artifactId>
<executions>
<execution><id>jacoco-prepare</id>
<goals><goal>prepare-agent</goal></goals>
</execution>
<execution><id>jacoco-check</id>
<goals><goal>check</goal></goals>
</execution>
</executions>
<configuration>
<check>
<instructionRatio>${xwiki.jacoco.instructionRatio}</...>
</check>}
Saturday, April 20, 13
24. Strategy
• When devs add code (and thus
tests), increase the TPC percentage
• Put the Jacoco check in “Quality”
Maven Profile
• Have a CI job to execute that
profile regularly
•About 15% overhead compared to build
without checks
• “Cheat mode”: Add easier-to-write
test
Saturday, April 20, 13
25. Quizz Time!
[INFO] --- jacoco-maven-plugin:0.6.2.201302030002:check (jacoco-check)
[INFO] All coverage checks have been met.
[INFO] --- jacoco-maven-plugin:0.6.2.201302030002:check (jacoco-check)
[WARNING] Insufficient code coverage for INSTRUCTION: 75.52% < 75.53%
Step 1: Building on my local machine gives the following:
Step 2: Building on the CI machine gave:
Non determinism! Why?
Saturday, April 20, 13
26. Quizz Answer
private Map componentEntries = new ConcurrentHashMap();
...
for (Map.Entry entry : componentEntries.entrySet())
{
if (entry.getValue().instance == component) {
key = entry.getKey();
oldDescriptor = entry.getValue().descriptor;
break;
}
}
... because the JVM is non deterministic!
Saturday, April 20, 13
28. The Problem
Too many false positives
leading to developers not
paying attention to CI emails
anymore... leading to failing
software
Saturday, April 20, 13
29. False positives examples
• The JVM has crashed
• VNC is down (we run Selenium tests)
• Browser crash (we run Selenium tests)
• Git connection issue
• Machine slowness (if XWiki cannot start under 2 minutes
then it means the machine has some problems)
• Nexus is down (we deploy our artifacts to a Nexus
repository)
• Connection issue (Read time out)
Saturday, April 20, 13
30. Step 1: Groovy PostBuild Plugin (1/2)
def messages = [
[".*A fatal error has been detected by the Java Runtime Environment.*",
"JVM Crash", "A JVM crash happened!"],
[".*Error: cannot open display: :1.0.*",
"VNC not running", "VNC connection issue!"],
...
]
def shouldSendEmail = true
messages.each { message ->
if (manager.logContains(message.get(0))) {
manager.addWarningBadge(message.get(1))
manager.createSummary("warning.gif").appendText(...)
manager.buildUnstable()
shouldSendEmail = false
}
}
Saturday, April 20, 13
31. Step 1: Groovy PostBuild Plugin (2/2)
... continued from previous slide...
if (!shouldSendEmail) {
def pa = new ParametersAction([
new BooleanParameterValue("noEmail", true)
])
manager.build.addAction(pa)
}
Saturday, April 20, 13
32. Step 2: Mail Ext Plugin
import hudson.model.*
build.actions.each { action ->
if (action instanceof ParametersAction) {
if (action.getParameter("noEmail")) {
cancel = true
}
}
}
Pre-send Script
Saturday, April 20, 13
33. Results
+ use the Scriptler plugin to automate configuration for all jobs
Saturday, April 20, 13
35. The Problem
Bugs increasing, even
simple to fix
ones, devs focusing too much on
new features (i.e. scope creep)
vs fixing what exists
Bugs created vs closed
Saturday, April 20, 13
36. Bug Fixing Day
• Every Thursday
• Goal is to close the max number of bugs
• Triaging: Can be closed with Won’t fix,
Duplicate, Cannot Reproduce, etc
• Close low hanging fruits in priority
• Started with last 365 days then with last 547
days and currently with last 730 days (we
need to catch up with 6 bugs!)
Saturday, April 20, 13
39. Parting words
• Slowly add new quality check over time
• Everyone must be on board
• Favor Active Quality (i.e. make the build fail) over
Passive checks
• Be ready to adapt/remove checks if found not useful
enough
• Quality brings some risks:
•Potentially less committers for your project (especially open
source)
Saturday, April 20, 13
40. Be proud of your Quality!
“I have offended God and
mankind because my work
didn't reach the quality it should
have.”
Leonardo da Vinci, on his death bed
Saturday, April 20, 13