GR8Conf 2009: Groovy Usage Patterns by Dierk König

Seven Groovy usage patterns for Java developers Dierk König dierk.koenig@canoo.com søndag den 17. maj 2009

Welcome! Dierk König Canoo fellow, www.canoo.com Rich Internet Applications Committer to Groovy and Grails Author: Groovy in Action søndag den 17. maj 2009

The 7 usage patterns • Super Glue • Liquid Heart • Keyhole Surgery • Smart Configuration • Unlimited Openness • House-Elf Scripts • Prototype Examples in Groovy søndag den 17. maj 2009

#1 Super Glue • Build application from existing building blocks • Java makes perfect infrastructure: middleware, frameworks, widget sets, services • Scripting makes a flexible (agile) applikation layer: views und controller • Grails, GSP, JBoss Seam, WebWork, Struts 2 Actions,... • Example: combination of XML parser, Java networking and Swing widget set in order to build a standard RSS feed reader søndag den 17. maj 2009

Super Glue example: RSS Reader def url ='http://www.groovyblogs.org/feed/rss' def items = new XmlParser().parse(url).channel.item def cols = 'pubDate title description'.tokenize() groovy.swing.SwingBuilder.build { frame(id:'f', title: 'Groovy Blogs', visible:true) { scrollPane { table { tableModel(list: items) { cols.each { col -> closureColumn header: col, read: { it[col].text() } }}}}} f.pack() } søndag den 17. maj 2009

#2 Liquid Heart • Externalize business models • Given application structure in Java • Allow to learn about the business: keep entities, relations, and behaviour flexible through scripting • Usages: Spring beans, JBoss components,rule engines (groovyrules.dev.java.net, JSR-94), Grails, enterprise risk management for world-leading insurances • Example: calculation rules for bonus allocation søndag den 17. maj 2009

Liquid Heart example: bonus allocation revenue = employee.revenue switch(revenue / 1000) { case 0..100 : return revenue * 0.04 case 100..200 : return revenue * 0.05 case {it > 200} : bonusClub.add(employee) return revenue * 0.06 } Binding binding = new Binding(); binding.setVariable("employee", employee); binding.setVariable("bonusClub", bonusClub); GroovyShell shell = new GroovyShell(binding); File script = new File(filename); float bonus = (float) shell.evaluate(script); søndag den 17. maj 2009

#3 Keyhole Surgery • Minimal-invasive surgery "in vivo" • Lots of need for runtime inspection and modifications • Ad-hoc queries are not foreseeable • "Backdoor" for the live execution of scripts • Particularly useful for product support, failure analysis, hot fixes, emergencies • Usages: Oracle JMX Beans, XWiki, SnipSnap, Ant, Canoo WebTest, Grails Console, GAE, ULC Admin Console • Example: a live Groovy Servlet søndag den 17. maj 2009

Surgery through a Servlet keyhole Problems with the database connection? def ds = Config.dataSource ds.connection = new DebugConnection(ds.connection) Remove malicious users from the servlet context users = servletContext.getAttribute('users') bad = users.findAll { user -> user.cart.items.any { it.price < 0 } } servletContext.setAttribute('users', users - bad) søndag den 17. maj 2009

#4 Smart Configuration • Enhance configuration with logic • Replace dumb XML configs • Use references, loops, conditionals, inheritance, execution logic, runtime environment adaption, ... • Typical scenario for domain specific languages (DSLs), Groovy Builder, Grails plugins, product customization, Groovy for OpenOffice: Community Innovation Program Silver Award Winner • Example: Navis SPARCS N4 søndag den 17. maj 2009

Smart Config example: container routing def ensureEvent = { change -> if (! event.getMostRecentEvent(change) { event.postNewEvent(change) } } switch (event.REROUTE_CTR) { case 'OutboundCarrierId' : ensureEvent('CHANGE_VSL') break case 'POD' : if (! event.CHANGE_VSL) ensureEvent('CHANGE_POD') break } søndag den 17. maj 2009

#5 Unlimited Openness • Every line of code may be changed • It's impossible (and not desirable!) to design for every possible future requirement • Allow for easily changing the code without tedious setup for compilation and deployment • Follow the lessons of Perl, PHP, Python,... • Example: groovyblogs.org, PillarOne søndag den 17. maj 2009

#6 House Elf • Delegate the housework • Build automation, continuous integration, deployment, installer, service monitoring, reports, statistics, automated documentation, functional tests, HTML scraping, Web remote control, XML-RPC, WebServices • Usages with Ant, Maven, AntBuilder, Gant, Gradle, Canoo WebTest, Grails scaffolding, ... • Examples: hooking scripts into Ant søndag den 17. maj 2009

House Elf: musical Ant <groovy> import org.apache.tools.ant.* import org.jfugue.* project.addBuildListener(new PlayListener()) class PlayListener implements BuildListener { def play = { new Player().play(new Pattern(it)) } void buildStarted(event) {} void buildFinished(event) { } void messageLogged(event) { } void targetStarted(event) { play("D E") } void targetFinished(event) { play("C5maj") } void taskStarted(event) {} void taskFinished(event) {} } </groovy> søndag den 17. maj 2009

House Elf: musical Ant <groovy> import org.apache.tools.ant.* import org.jfugue.* project.addBuildListener(new PlayListener()) class PlayListener implements BuildListener { def play = { new Player().play(new Pattern(it)) } void targetStarted(event) { play("D E") } void targetFinished(event) { play("C5maj") } } </groovy> søndag den 17. maj 2009

House Elf: musical Ant <groovy> import org.apache.tools.ant.* import org.jfugue.* def play = { new Player().play(new Pattern(it)) } void targetStarted(event) { play("D E") } void targetFinished(event) { play("C5maj") } project.addBuildListener(player as BuildListener) } </groovy> søndag den 17. maj 2009

House Elf: musical Ant <groovy> import org.apache.tools.ant.* import org.jfugue.* def play = { new Player().play(new Pattern(it)) } def player = [ targetStarted: { play("D E") }, targetFinished: { play("C5maj") } ] project.addBuildListener(player as BuildListener) } </groovy> søndag den 17. maj 2009

House Elf: musical Ant <groovy> import org.apache.tools.ant.* import org.jfugue.* def play = { new Player().play(new Pattern(it)) } def player = [ targetStarted : { play "D E" }, targetFinished : { play "C5maj" } ] project.addBuildListener(player as BuildListener) } </groovy> søndag den 17. maj 2009

#7 Prototype • Feasibility study on the target platform • "Spikes" for technological or algorithmic ideas with more expressiveness, quicker feedback, and enhanced analysis capabilities • Later port to Java is optional • Usages: early user feedback about the domain model through a functional Grails prototype, algorithms for image manipulation • Example: prime number disassembly søndag den 17. maj 2009

Prototype example: prime numbers boolean isPrime(x) { return ! (2..<x).any { y -> x % y == 0 } } int primeBelow(x) { (x..1).find { isPrime(it) } } List primeFactors(x) { if (isPrime(x)) return [x] int p = primeBelow(x) while (p > 1) { if (x % p == 0) return [p, *primeFactors(x.intdiv(p))] p = primeBelow(p-1) } } for (n in 100..110) { println "$n : "+primeFactors(n)} søndag den 17. maj 2009

Prime numbers: counting modulo ops class ModCountCategory { static int count = 0 static int mod(Integer self, Integer argument) { count++ return self - argument * self.intdiv(argument) } } use (ModCountCategory) { for (n in 1000..1010) { ModCountCategory.count = 0 factors = primeFactors(n) println "$n : $factors".padRight(30) + "(in " + "${ModCountCategory.count}".padLeft(5) + " steps)" assert n == factors.inject(1){result, item -> result *= item } } } søndag den 17. maj 2009

Pattern Summary • Super Glue • Liquid Heart • Keyhole Surgery • Smart Configuration • Unlimited Openness • House-Elf Scripts • Prototype Keep groovin' ! søndag den 17. maj 2009

More Information • Groovy in Action groovy.canoo.com/gina Manning, 2007, Foreword by James Gosling König mit Glover, Laforge, King, Skeet • groovy.codehaus.org, grails.org groovyblogs.org, searchgroovy.org søndag den 17. maj 2009

Questions? More patterns in the pipeline: Lipstick - API enhancements Ghost - generating invisible code <your suggestion here> søndag den 17. maj 2009

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GR8Conf 2009: Groovy Usage Patterns by Dierk König

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