An Introduction to Groovy for Java Developers

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An introduction to Groovy for Java developers with real-life examples that present how Groovy helped us win the 2nd prize in the Open Public Data Hackathon 2014 (http://www.ydmed.gov.gr/hackathon/)

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An Introduction to Groovy for Java Developers

  1. 1. An Introduction to Groovy for Java Developers Kostas Saidis www.niovity.com Java Hellenic User Group Meetup May 17, 2014
  2. 2. Outline Introduction to Groovy 1. Meet Groovy What is Groovy? Groovy History Why Groovy 2. Groovy Basics Using Groovy Language Overview Closures Lists and Ranges Maps 3. Real-life Groovy Open Public Data Hackathon Our Web App JSON and REST Groovlets
  3. 3. About Me Kostas Saidis saiko@niovity.com Software & Data Architect Twitter: @saikos Linkedin: http://gr.linkedin.com/in/saiko Short bio: Academia BSc @ cs.unipi.gr (2001) MSc @ di.uoa.gr (2004) PhD @ di.uoa.gr (2011) Industry Freelance consultant, developer & instructor since 1999 Founder & Managing Director Java Early Java enthusiast (1997) Diving into Groovy since 2011
  4. 4. Target audience Java developers with little or no experience in Groovy or dynamic languages.
  5. 5. So, what brings us here? The Java Platform 1. The language 2. The development kit 3. The virtual machine The JVM is the key component! The language and the JDK are aging, striving to catch up with new developments. Yet, Java 8 (with Streams and Lambdas) is a huge step forward!
  6. 6. What really brings us here! The fun of programming And Groovy programming is a whole lotta fun!
  7. 7. 1. Meet Groovy What is Groovy? Groovy History Why Groovy
  8. 8. What is Groovy? Groovy is a feature-rich Java-friendly dynamic language for the Java platform
  9. 9. Dynamic language? What is a dynamic language? A language that allows the types of variables to be changed at runtime... ...among other things! In Groovy We can also change the behavior of objects and classes at runtime (with Metaprogramming).
  10. 10. Example Introduce a new method in Strings 1 String.metaClass.isUpperCase = {−> 2 delegate.toCharArray().every{ Character.isUpperCase(it) } 3 } 4 assert "GROOVY".isUpperCase() == true 5 assert "java".isUpperCase() == false
  11. 11. Keep an open mind A language that doesn't affect the way you think about programming, is not worth knowing. Alan Perlis (1922 - 1990) ACM Turing Award, 1966
  12. 12. Languages and Typing Static vs. Dynamic Statically typed: resolves the types of variables during compilation. (e.g. Java) Dynamically typed: resolves the types of variables at runtime. (Groovy) Weak vs. Strong Strongly typed: you can't coerce to a wrong type --the language guarantees type conformance. (Java & Groovy) Weakly typed: you can screw everything up in all possible ways. (e.g. C)
  13. 13. Java-friendly? Groovy is: A super version of Java Augments Java with additional features → the GDK extends JDK in so many helpful ways! Designed as a companion language for Java seamless integration with Java → an additional jar at runtime! syntactically aligned with Java → syntactically correct Java will work in Groovy (with some gotchas)! compiles into JVM bytecode and preserves Java semantics → call Groovy from Java == call Java from Java! the 2nd language targeting the Java platform (JSR-241) → Java was the first!
  14. 14. Feature-rich? Groovy features Fully object-oriented -- e.g. Traits in new version (2.3). Optional typing --static or dynamic. Duck typing. List, map, range, regular expression literals. Operator overloading. Closures. GroovyBeans. GString and GPath. Multimethods and metaprogramming. Easily build custom DSLs (e.g. Gradle, Spock).
  15. 15. Example Optional Typing 1 def s1 = "saiko" 2 assert s1.class == String.class 3 s1 = 3 4 assert s1.class == Integer.class 5 Integer s2 = 3 6 try { 7 s2 = "saiko" 8 } 9 catch(ex) { 10 assert ex.message == "Cannot cast object 'saiko' with class ' java.lang.String' to class 'java.lang.Integer'" 11 }
  16. 16. Groovy History 2003: Started by James Strachan and Bob McWhirter. 2004: Commissioned into JSR 241 but was almost abandoned. 2005: Brought back to life by Guillaume Laforge and Jeremy Rayner. 2007: Groovy version 1.0. 2012: Groovy version 2.0. 2014: Groovy version 2.3 (official support for JDK 8).
  17. 17. Going Mainstream Awesome Groovy-based tools & frameworks Grails: Web development framework. Gradle: Build automation tool. (my next one, if you like!) Spock: Testing and specification framework. CodeNarc: Static analysis tool. easyb: Behavior-driven development framework. Geb: Browser automation tool. Griffon: Desktop app framework. GPars: Multi-paradigm concurrency framework. Groovy is supported by Pivotal.
  18. 18. Why Groovy? Open Source. → Apache v2.0 License. Near-zero learning curve. → You' ll become a Groovyist before you realize it! Leverage Java investment. → Rock-solid Java foundations. Focus on your problem/app. → No more boilerplate! More expressive, powerful and concise code. → Productivity boost!
  19. 19. A picture is worth some thousand words
  20. 20. 2. Groovy Basics Using Groovy Language Overview Closures Lists and Ranges Maps
  21. 21. Groovy Tools 1. groovyc: Compliles groovy sources to JVM class files. 2. groovysh: Executes code interactively. 3. groovyConsole: GUI for interactive code execution the best place to start . 4. groovy: Executes groovy scripts. Use it like bash, perl, python, etc. (#!/usr/bin/groovy). 5. groovydoc: Generates documentation (like javadoc).
  22. 22. Using the Groovy Console Use Groovy console to experiment, test and evaluate code.
  23. 23. Using the Groovy Interpreter What date/time is it? groovy −e "print new Date()" List files recursively groovy −e "new File('.'). eachFileRecurse { println it }"
  24. 24. Groovy scripts No mandatory class definitions, no main methods, no boilerplate. Groovy creates them for you automagically! Writing a Groovy script Fibonacci.groovy 1 def fib(n) { // a method: the return type is not mandatory 2 n<2 ? 1 : fib(n−1)+fib(n−2) 3 } 4 if (args) { // command−line args 5 println fib(args[0] as Integer) 6 }
  25. 25. Groovy scripts continued Running the script > groovy Fibonacci 8 34 > groovyc Fibonacci.groovy > java −cp $GROOVY_HOME/embeddable/ groovy−all.2.0.0.jar:. Fibonacci 8 34
  26. 26. The Groovy Syntax The majority of Java syntax is part of the Groovy syntax: packages imports control structures exception handling classes and methods object instantiation and method calls Gotchas: Arrays, additional Groovy keywords, equals checks, etc.
  27. 27. Default imports The following imports are included by default java.lang.* java.util.* java.net.* groovy.lang.* groovy.util.* java.math.BigInteger and java.math.BigDecimal
  28. 28. Groovy truth and equals Null value is false. Empty collection or map is false. Empty string is false. Zero value is false. Gotcha The == operator performs value equality (like Java equals() ). Use the method is for identity (available in every Groovy object).
  29. 29. Groovy truth Examples 1 def f = null 2 def t = "string" 3 assert f == false 4 assert t == true 5 list = [] 6 map = [a:1] 7 assert list == false 8 assert map == false 9 String s = "" 10 assert s == false 11 i = 1 12 z = 0.0 13 assert i == true 14 assert z == false
  30. 30. Optionals The following are optional: semicolons: required only when you write multiple statements in one line. variable types: you decide what should be static or dynamic. return statements: the last evaluated expression is the default return value Gotcha . parentheses: in method/function invocations Gotcha .
  31. 31. Optionals Examples 1 //a method 2 def fac(n) { n<=1? 1 : n*fac(n−1)} 3 assert fac(3) == 6 4 //a method with default arg value 5 Integer factorial(Integer n=3) { return (n<=1? 1 : n*factorial(n −1)) } 6 assert factorial(3) == 6 7 //invoke them without parentheses 8 def x = fac 3 9 def y = factorial 3 10 assert x == y 11 x = fac 3 + 1 //will calculate the factorial of 4. 12 assert x == fac(4) //Not always what you want! 13 x = fac(3 + 1) //use parentheses to disambiguate 14 //where parentheses are required 15 x = factorial() //Groovy will look for a property otherwise 16 assert x == fac(3)
  32. 32. Everything is an object In Groovy: all objects are derived from groovy.lang.GroovyObject, which extends java.lang.Object. all integral numbers are java.lang.Integers (or java.lang.Longs using the proper Java notation). all real numbers are java.math.BigDecimals. all booleans are java.lang.Booleans.
  33. 33. Example Everything's an object 1 def x = 1 2 int y = 1 3 assert x.class == Integer.class 4 assert y.class == Integer.class 5 def l = 1L 6 assert l.class == Long.class 7 def z = 0.3 8 assert z.class == BigDecimal.class 9 def flag = false 10 assert flag.class == Boolean.class
  34. 34. Strings Groovy strings support: Single quotes: ordinary strings. Double quotes: ordinary strings with variable expansion (GStrings). Triple quotes: multi-line strings with variable expansion (GStrings). Slashy strings: strings enclosed in slashes; no need to escape backslashes (useful for regular expressions and file paths). operator overloading.
  35. 35. Examples Strings 1 def mlStr = """ I am a multi−line 2 string!""" 3 def name = 'Angus';def surname = "Young" 4 //GStrings 5 def fullname = "$name $surname" 6 assert fullname == "Angus Young" 7 //operator overloading 8 def s = name * 3 9 assert s == "AngusAngusAngus" 10 s = fullname − name 11 assert s.trim() == surname 12 //slashy strings: preserve backslashes; no escaping is required 13 s = /nr/ 14 assert s.size() == 4
  36. 36. Numbers In Groovy all numbers are objects and BigDecimal arithmetic is used by default. Examples 1 def x = 3 2 assert x.plus(4) == x + 4 3 assert x.multiply(4) = x * 4 4 assert x.mod(4) == x % 4 5 //BigDecimal arithmetic 6 assert x/4 == x.div(4) 7 assert x/4 != x.intdiv(4) 8 assert 1/2 == 0.5 9 assert 1/3 == 0.3333333333
  37. 37. Java beans for human beings In Groovy classes/beans: Methods and classes are public by default. Members are private by default. The @PackageScope annotation is used for package scoped class members. Enhanced bean property support. Dynamic constructor arguments. Accessors (getters and setters) are generated automatically. You can use the this keyword inside static methods (which refers to this class).
  38. 38. Defining a Groovy class A Person class 1 class Person { 2 String name 3 String surname 4 @Override 5 String toString() { "$surname, $name" } 6 } Compile the Person.groovy groovyc Person.groovy Result: A ready to use Person.class
  39. 39. Use the Person class Examples From Groovy 1 p = new Person(name:"Theodoros", surname:"Kolokotronis") 2 assert p.toString() == "Theodoros Kolokotronis" From Java 1 public class UsingPerson { 2 public static void main(String[] args) { 3 Person p = new Person(); 4 p.setSurname("Young"); 5 p.setName("Angus"); 6 HashMap map = new HashMap(); 7 map.put("name", "James"); 8 map.put("surname", "Bond"); 9 Person p1 = new Person(map); 10 } 11 }
  40. 40. Additional Operators Safe navigation: x?.method() Elvis: x = y ?: "no y" Spread: ["java","groovy"]*.size() → [4,6] and more... <=> , =~ , ==~ , .@ , .&
  41. 41. Groovy powerful switch statement 1 switch(val) { 2 case "String": 3 //a string 4 break 5 case 10..100: 6 //a range 7 break 8 case Date: 9 //a date instance 10 break 11 case ~/gw+/: 12 //a reg−ex 13 break 14 case ['A', 'B']: 15 //a list 16 break 17 case { it instanceOf Number && it > Integer.MAX_VALUE } 18 //a closure 19 break 20 default: 21 //the default, treated as an "else" in Groovy (if 22 //all else fails, run the default). It should always 23 //be at the end of the switch statement. 24 }
  42. 42. Dynamic method dispatch Java dispatches methods according to the type of the arguments at compile time. Groovy dispatches methods according to the type of the arguments at runtime (multimethods). Example 1 public void foo(String arg) { System.out.println("String"); } 2 public void foo(Object o) { System.out.println("Object"); } 3 Object o = "The type of o at runtime is String"; 4 foo(o); Java output: Object Groovy output: String
  43. 43. Other differences from Java There is no distinction between checked and unchecked (runtime) exceptions. All exceptions are runtime exceptions! Assertions are enabled by default. Support for default values in method arguments. use , is and as are keywords. Don't use them as variable names. You cannot declare more than one variables in for loops. Arrays should be initialized with list-like syntax: int[] a = [1, 2, 3] . Avoid int a[] notation. Gotcha .
  44. 44. What is a closure? Definition A closure is a function together with a referencing environment. Closures are anonymous functions that: may accept parameters or return a value, can be assigned to variables, can be passed as arguments, capture the variables of their surrounding lexical scope.
  45. 45. Groovy closures Example 1 //a block of code assigned to a variable 2 def num = { int n −> n <=> 0 } 3 //what type is that? 4 assert num instanceof Closure 5 //it: the default closure argument 6 def num2 = { it <=> 0 } 7 assert num(−3) == num2(−3) 8 def x = 3 9 def times = { it * x } 10 assert times(3) == 9 11 x = 4 12 assert times(3) == 12
  46. 46. Functional Programming with Groovy Currying & Higher-order functions 1 def func = { Closure c, int i, int j −> 2 c.call(i, j) 3 } 4 def add = func.curry { int i, int j −> i + j } 5 assert add(1,2) == 3 Composition 1 def add1 = { it + 1} 2 def sq = { it*it } 3 assert sq(add1(2)) == 9 //composition 4 def trans1 = add1 >> sq //left to right 5 assert trans1(2) == sq(add1(2)) 6 def trans2 = add1 << sq //right to left 7 assert trans2(2) == add1(sq(2))
  47. 47. Closure owner and delegate Example 1 //All closures have 3 implicit variables: 2 //this: as in Java 3 //owner: the enclosing object (either a closure or this) 4 //delegate: defaults to owner but can be changed 5 def test = { 6 ((this == owner) && (owner == delegate)) 7 return { (this != owner) && (owner == delegate) } 8 } 9 assert test()() 10 //changing the delegate 11 def collectWithIndex = { Closure c−> 12 int i = 0 13 delegate.collect { c(it, i++) } 14 } 15 def map = ["name":"Angus", "surname":"Young"] 16 collectWithIndex.delegate = map 17 def list = collectWithIndex { entry, i −> [i, entry.key, entry. value] } 18 assert list.flatten() == [0, "name", "Angus", 1, "surname", " Young"]
  48. 48. Java 8 Lambda Expressions Groovy closures ̸= Java lambda expressions. Lambda expressions Language facility for implementing functional interfaces Interfaces with a single abstract method. Function, Predicate, Supplier, Consumer. Type inference at compile time. Free variables must be final or effective final. Do make your Java life easier.
  49. 49. Lists Groovy offers: Special syntax for list literals. Additional common list methods. Combine with closures for extremely expressive and powerful code! Examples 1 //a list 2 def list = [1, "2", 3.0] 3 //what type is that? 4 assert list.class == ArrayList.class 5 //list elements 6 assert list.get(1) == "2" 7 assert list[1] == "2" 8 assert list.getAt(1) == "2" 9 //list.getAt(i) equivalent to list[i] 10 //negative indexes − not for the standard list.get(i) 11 assert list[−1] == 3.0 12 assert list.getAt(−2) == "2"
  50. 50. More list examples 1 //another list 2 def list3 = [5, 3, 1, ] //trailing comma OK 3 list3[0] = 3 4 list3.putAt(0, 3) //list.putAt(i,val) equivalent to list[i]=val 5 list3.set(0, 3) 6 assert list3 == [3, 3, 1] 7 //the in operator 8 assert '2' in list 9 assert list.contains('2') 10 //operator overloading 11 assert list + [1] == [1, "2", 3.0, 1] 12 assert list − [1] == ["2", 3.0] 13 assert list * 2 == [1, "2", 3.0, 1, "2", 3.0] 14 assert list + list == list * 2 15 //append to list 16 assert list << 1 == [1, "2", 3.0, 1] 17 def otherList = [4, 5.0, "6"] 18 assert list << otherList == [1, "2", 3.0, 1, [4, 5.0, "6"]] 19 //methods 20 assert list.flatten() == [1, "2", 3.0, 1, 4, 5.0, "6"] 21 assert list.flatten().unique() == [1, "2", 3.0, 4, 5.0, "6"]
  51. 51. Even more list examples 1 //methods that accept closure arguments 2 otherList = list.flatten().collect { it as Integer } 3 assert otherList == [1, 2, 3, 1, 4, 5, 6] 4 def toInt = { Object o −> 5 try { return o as Integer } 6 catch(e) { return 0 } 7 } 8 assert list.flatten().collect(toInt) == otherList 9 assert [5, "6", "seven"].collect(toInt) == [5, 6, 0] 10 //convert a list to a set 11 def set = otherList as Set 12 assert otherList instanceof List 13 assert set instanceof Set 14 //collect is available to all groovy objects 15 set.collect { it + 1 } == [2, 3, 4, 5, 6, 7] 16 //list to string 17 assert otherList.unique().join(', ') == '1, 2, 3, 4, 5, 6'
  52. 52. Enough with these list examples 1 //some more list methods 2 assert otherList.count(1) == 2 3 assert otherList.sum() == 22 4 assert otherList.intersect([1, 3, 4]) == [1, 3, 4] 5 assert otherList.disjoint([0, 10, 20]) 6 assert otherList.min() == 1 7 assert otherList.max() == 6 8 assert otherList.reverse().unique().sort() == [1, 2, 3, 4, 5, 6] 9 //some more closures 10 assert otherList.findAll { it%2 == 0} == [2, 4, 6] 11 assert otherList.every { it > 0 } //checks whether the closure holds for every list element 12 assert !otherList.every { it < 1 } 13 def listWithNulls = [1, null, 2] 14 assert !listWithNulls.every() //checks whether groovy truth holds for every element 15 //the spread (*.) operator 16 def strings = ['one', 'the other', 'and another'] 17 assert strings*.size() == strings.collect { it.size() } 18 //list*.action() calls list.collect { it.action() } 19 assert strings*.toUpperCase() == ['ONE', 'THE OTHER', 'AND ANOTHER']
  53. 53. Ranges Groovy: treats ranges as first-class objects. offers special syntax for ranges. Examples 1 def letters = 'a'..'z' 2 def digits = 0..9 3 //what type is that? 4 assert letters.class == ObjectRange 5 assert digits.class == IntRange 6 //okay, but wait... 7 assert letters instanceof java.util.List 8 assert digits instanceof java.util.List 9 //ranges are lists of sequential values. 10 assert digits == [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] 11 assert letters[0] == 'a' 12 assert letters.size() == 26
  54. 54. More ranges examples 1 //methods 2 def otherDigits = digits.collect { it*2 } //or, equivalently 3 otherDigits = digits*.multiply(2) 4 assert otherDigits == [0, 2, 4, 6, 8, 10, 12, 14, 16, 18] 5 //half−open ranges 6 def digits2 = 0..<9 //0 up to 9 exclusive 7 assert digits2.size() == 9 8 //get the from,to values of ranges 9 assert digits.from == digits2.from 10 assert digits.to == digits2.to + 1 11 //another way to express a range 12 assert 1..4 == (1..4) 13 //looping 14 (1..4).each { print it } 15 //stepping 16 (1..4).step(2) { print it } 17 //slicing 18 def list = ['one', 'two', 'three', 'four', 'five', 'six'] 19 assert list[1..3] == ['two', 'three', 'four'] 20 assert list[0..<2] == ['one', 'two'] 21 assert list[−1] == 'six' 22 assert list[3..−1] == ['four', 'five', 'six'] 23 assert list[−1..−3] == ['six', 'five', 'four']
  55. 55. Maps Groovy: offers pecial syntax for map literals. provides dditional common map methods. uses maps + closures for duck typing: if it walks and swims like a duck, it is a duck! → rapid implementation of interfaces Examples 1 //a map 2 def map = ['id' : 12, 'name' : "John", 'surname' : "Doe"] 3 assert map.size() == 3 4 //keys which are valid Java identifiers need no quotes 5 def now = new Date() 6 def map2 = [ 7 id : 1, 8 value : 2.0, 9 "peter's birthday": now 10 ]
  56. 56. More maps examples 1 //we can use map.key when key is valid Java identifier 2 assert map2.id == 1 3 //we can quote the key if needed 4 assert map2."peter's birthday" == now 5 //we can also use subscription notation map[key] 6 assert map2["peter's birthday"] == now 7 //and the standard get method 8 assert map2.get('value') == 2 9 assert map.get('foo') == null 10 //default value when key not found 11 assert map.get('foo', 'No such key') == 'No such key' 12 //adds the default value in the map 13 assert map.containsKey('foo') 14 //what type is the map? 15 try { 16 assert map.class == LinkedHashMap.class 17 } 18 catch(Error e) { 19 assert map.class == null //the map is looking for the 'class ' key 20 map.getClass() == LinkedHashMap.class 21 }
  57. 57. Even more maps examples 1 //put/update values 2 map.newKey = "new key's value" 3 map2['newKey'] = map.newKey 4 //use parentheses to add the value of a var in a map (and not its name) 5 def anotherKey = "address" 6 map[(anotherKey)] = "Petraki 28" 7 assert map.address == "Petraki 28" 8 //iterate with each 9 map.each { println "In each: ${it.class}" } 10 //the closure argument is a Map.Entry instance 11 map.each { println "In each again: ${it.key} = ${it.value}" } 12 //all Java Map methods are here 13 assert !map.isEmpty() 14 assert map.containsKey('id') 15 assert map.containsValue(12) 16 //use a HashMap instead of a LinkedHashMap 17 def map3 = new HashMap() 18 assert map3.getClass() == HashMap.class 19 //empty map 20 def map4 = [:] 21 assert !map4//empty map is false
  58. 58. Some more maps examples 1 //find in map 2 assert ['id':12, 'foo':'No such key'] == map.findAll{ it.key. size() <= 3} 3 //group by 4 def list = [1, '2', 3, '4', '5', 6] 5 def map5 = list.groupBy { it.getClass().getSimpleName() } 6 assert ['String': ['2', '4', '5'], 'Integer': [1, 3, 6]] == map5 7 //store closures in a map 8 def actions = [ 9 login : { println "login" }, 10 logout : { println "logout" } 11 ] 12 //execute the closures 13 actions.login.call() //or 14 actions['logout'].call() //or 15 actions.logout()
  59. 59. Duck typing 1 //Duck typing − a comparator 2 def cmp = [ 3 compare : { a, b −> a.size() <=> b.size() } 4 ] as Comparator 5 assert cmp instanceof Comparator 6 //a list 7 def list2 = ['a' , 'quick', 'brown', 'fox', 'jumps', 'over', 'a' , 'lazy', 'dog'] 8 assert list2.sort(cmp) == ['a', 'a', 'fox', 'dog', 'over', 'lazy ', 'quick', 'brown', 'jumps'] 9 //a runnable 10 def r = [ 11 run : { 12 def t = Thread.currentThread() 13 println "Thread ${t.getId()} starting" 14 t.sleep(1000) 15 println "Thread ${t.getId()} finished" 16 } 17 ] as Runnable 18 assert r instanceof Runnable 19 new Thread(r).start()
  60. 60. Duck typing continued Another Example 1 interface Doer { 2 void doThis(); 3 void doThat(); 4 } 5 class DoerImpl implements Doer { 6 void doThis(){"Did this"} 7 void doThat(){"Did that"} 8 } 9 def doer1 = new DoerImpl() 10 assert doer1 instanceof Doer 11 def doer2 = [ 12 doThis:{"This done"}, 13 doThat:{"That done"} 14 ] as Doer 15 assert doer2 instanceof Doer
  61. 61. 3. Real-life Groovy Open Public Data Hackathon Our Web App JSON and REST Groovlets
  62. 62. Open Public Data Hackathon Held between 15 - 30 April 2014. Organized by the Ministry of Administration Reform and E-Governance (ydmed.gr), in association with: 1. aspete.gr 2. hua.gr 3. ellak.gr Requirement: deliver an app that utilizes open public data (from data.gov.gr or elsewhere).
  63. 63. We won the 2nd prize! And Groovy helped us do it! We shall discuss: 1. How to build a RESTful API with Groovy and Restlet. 2. How to build dynamic web pages with Groovlets.
  64. 64. Our Web App A prototype of a cloud service for Accessing/retrieving data Searching/querying data Visualizing/embedding data through a powerful RESTful API.
  65. 65. Quick demo here opendatacloud.gr
  66. 66. Technologies used Backend Java 7.x Apache Tomcat 7.0.x Groovy 2.2.x Restlet 2.2.0 Apache POI 3.10 Elastic Search 1.1.1 Frontend Bootstrap 3 jQuery 1.10 D3.js
  67. 67. The data model We have Kept thins as simple as possible. Data source groups: Sets of Data sources: Tabular data in excel files arranged in columns and rows. After all, it is a prototype!
  68. 68. The web.xml Two servlets 1 <servlet> 2 <servlet−name>RestletServlet</servlet−name> 3 <servlet−class>org.restlet.ext.servlet.ServerServlet</servlet− class> 4 <init−param> 5 <param−name>org.restlet.application</param−name> 6 <param−value>com.niovity.opd.restlet.App</param−value> 7 </init−param> 8 </servlet> 9 <servlet−mapping> 10 <servlet−name>RestletServlet</servlet−name> 11 <url−pattern>/api/v0/*</url−pattern> 12 </servlet−mapping> 13 <servlet> 14 <servlet−name>groovy</servlet−name> 15 <servlet−class>groovy.servlet.GroovyServlet</servlet−class> 16 </servlet> 17 <servlet−mapping> 18 <servlet−name>groovy</servlet−name> 19 <url−pattern>*.groovy</url−pattern> 20 </servlet−mapping>
  69. 69. The web.xml continued And a listener 1 <listener> 2 <listener−class>com.niovity.opd.Listener</listener−class> 3 </listener> 1 package com.niovity.opd 2 class Listener implements ServletContextListener { 3 @Override 4 void contextInitialized(ServletContextEvent e) { 5 try { 6 //Initialize log4j & elastic 7 ... 8 //Initialize the config 9 String basePath = ctx.getRealPath("/data") 10 Config.instance.init(basePath) 11 } catch(Exception e) { 12 System.err.println("Fatal error: ${e.getMessage()}") 13 e.printStackTrace(System.err) 14 throw new ServletException(e.getMessage(), e) 15 } 16 } 17 }
  70. 70. Groovy @Singleton Annotation Config 1 package com.niovity.opd 2 @Singleton class Config { 3 String basePath 4 Map<String, DataSourceGroup> sourceGroups = [:] 5 void init(String basePath) throws Exception { 6 this.basePath = basePath 7 def groups = [:] 8 DataSourceGroup nte = new DataSourceGroup( 9 id: "nte", 10 title:"...", ... 11 ) 12 nte.addDataSource(new DataSource(title: "...",...)) 13 groups.nte = nte 14 ... 15 sourceGroups = Collections.unmodifiableMap(groups) 16 } 17 }
  71. 71. The Restlet App The REST router 1 package com.niovity.opd.restlet 2 import org.restlet.Application 3 import org.restlet.Restlet 4 import org.restlet.routing.Router 5 class App extends Application { 6 @Override 7 synchronized Restlet createInboundRoot() { 8 Router router = new Router(getContext()) 9 router.attach "/groups", SourceGroups 10 router.attach "/{grp}/{src}", Source 11 router.attach "/search", Search 12 return router 13 } 14 }
  72. 72. An example of a Restlet GET the source groups 1 package com.niovity.opd.restlet 2 import ... 3 class SourceGroups extends ServerResource{ 4 @Override 5 protected Representation get() throws ResourceException { 6 def groups = Config.instance.sourceGroups 7 def result = [:] 8 result.total = groups.size() 9 result.groups = [] 10 groups.each { 11 def group = [id : it.key, title : it.value.title, ...] 12 group.sources = [] 13 it.value.dataSources().eachWithIndex { source, index −> 14 def src = [id:"/${it.key}/$index",...] 15 group.sources.push(src) 16 } 17 result.groups.push(group) 18 } 19 return new JsonRespresentation(result) 20 } 21 }
  73. 73. JSON JsonRepresentation 1 package com.niovity.opd.restlet 2 import groovy.json.JsonBuilder 3 import org.restlet.data.MediaType 4 import org.restlet.representation.WriterRepresentation 5 class JsonRespresentation extends WriterRepresentation { 6 private Map result 7 JsonRespresentation(Map result) { 8 super(MediaType.APPLICATION_JSON) 9 this.result = result ?: [:] 10 } 11 @Override 12 void write(Writer writer) throws IOException { 13 new JsonBuilder(result).writeTo(writer) 14 } 15 }
  74. 74. Groovlets Groovy scripts on the server side Compiled on the fly No boilerplate With some handy implicit variables provided by default request,response : Http servler request and response params : request parameters context, application : the ServletContext object session : the HttpSession object out : the writer of the response sout : the output stream of the response html: a groovy.xml.MarkupBuilder which writes to out
  75. 75. Display a data source in HTML table source.grovy 1 String groupId = request.getParameter("grp") 2 String srcId = request.getParameter("src") 3 def group = Config.instance.sourceGroups.get(groupId) 4 def sources = group.dataSources() 5 int index = srcId as Integer 6 def source = group.dataSources().get(index) 7 println """ 8 ... 9 <table class="table table−bordered table−striped" > 10 <thead> 11 <tr> 12 <th>#</th> 13 ${source.columnNames.collect {"<th>$it</th>"}.join("")} 14 </tr> 15 </thead> 16 <tbody > 17 """
  76. 76. HTML table continued source.grovy 1 source.rows.eachWithIndex {Map row, int i −> 2 println """ 3 <tr> 4 <td>${i+1}</td> 5 ${source.columnNames.collect{ "<td>${row.get(it)}</td>"}.join ("")} 6 </tr> 7 """ 8 } 9 println """ 10 </tbody> 11 </table> 12 ... 13 """
  77. 77. 4. Epilogue
  78. 78. Groovy is Java on steroids! Easy to use: Its integration with the Java platform is insanely brilliant! Expressive: Do more with less code! Effective: Focus on your app and stop wasting your time with the irrelevant! Agile: Groovy is agile and rapid prototyping is a few Groovy lines away! Leverage Java expertise. Build upon your Java skills. Powerful: The swiss army knife of the Java hacker!
  79. 79. Swiss army knife, indeed Ain't this groovy or what? db.groovy 1 @GrabConfig(systemClassLoader=true) 2 @Grab(group='mysql', module='mysql−connector−java', version=' 5.1.6') 3 import groovy.sql.Sql 4 def query="select count(*) as c, date(creationDate) as d from dofields group by d order by c desc limit 10" 5 def url="jdbc:mysql://localhost:3306/test_db?characterEncoding= utf−8" 6 def (u,p)=["test","test"] 7 try { 8 def sql = Sql.newInstance(url,u,p,"com.mysql.jdbc.Driver") 9 sql.eachRow(query) { println("${it.c}:${it.d}") } 10 } 11 catch(e) { e.printStackTrace() }
  80. 80. Output Run it groovy db Output 1 9427:2004−08−20 2 6615:2004−10−29 3 5498:2004−10−08 4 5103:2004−08−31 5 4864:2004−10−14 6 4675:2004−10−31 7 4583:2004−10−05 8 4570:2004−08−21 9 4339:2004−09−30 10 4235:2004−10−30
  81. 81. Groovy rocks!
  82. 82. We 've only scratched the surface Groovy topics not covered Metaprogramming Grape Builders Working with XML Working with SQL Testing And much, much more... Perhaps in a 2nd part?
  83. 83. What about performance? Programmers have spent far too much time worrying about efficiency in the wrong places at the wrong times; premature optimization is the root of all evil. Donald E. Knuth ACM Turing Award, 1974
  84. 84. Put in other terms The reason to use Groovy should be because it improves your performance not the computer's. matthew@stackoverflow
  85. 85. About Groovy Performance Sorry, it hasn't bothered me yet. Groovy 2.x introduced the @CompileStatic annotation. Most of Groovy method calls are compiled into direct JVM bytecode method calls. People report that Groovy reaches to almost identical performance with Java. Start with Groovy and (re)write your performance-critical classes in Java as you grow. You can find various benchmarks and performance comparisons on the web. Any volunteers for benchmarking, should we do a 2nd part?
  86. 86. Resources 1. Programming Groovy 2, V. Subramaniam, The Pragmatic Bookshelf, 978-1-937785-30-7, 2013 2. Groovy in Action, D. Koenig, A. Glover, P. King, G. Laforge and J. Skeet, Manning Publications, 1-932394-84-2, 2007 3. Groovy Web Site http://groovy.codehaus.org 4. Groovy language documentation beta http://beta.groovy-lang.org/docs/ groovy-2.3.0/html/documentation/
  87. 87. Thank you Questions? Proudly powered by: LATEX Using the Beamer class & the Wronki theme (slightly modified).

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