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Wiki source code of WebObjects with Scala

Version 503.1 by Ravi Mendis on 2010/12/24 01:33
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Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 497.1 3 [[Scala>>http://www.scala-lang.org/]] is a modern, multi-paradigm JVM language that is most often compared to [[Groovy>>http://en.wikipedia.org/wiki/Groovy_(programming_language)]], [[Clojure>>http://en.wikipedia.org/wiki/Clojure]] or [[Erlang>>http://en.wikipedia.org/wiki/Erlang_(programming_language)]]. Its [[functional language>>http://en.wikipedia.org/wiki/Functional_programming]] foundations and built-in Actors library make it especially attractive for concurrent computing. (Scala is an abbreviation for "scalable" hinting at its design goals). In this day and age of multi-core processors concurrent computing can not be ignored.
Ravi Mendis 195.1 4
Ravi Mendis 497.1 5 Many of the design features of Scala have been chosen with concurrency in mind, some of which may not be unfamiliar to Objective-C or WebObjects developers. Here's a summary:
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Ravi Mendis 435.1 7 |= |= Objective-C |= Java |= Scala
Ravi Mendis 501.1 8 |= Immutability | Partial - via collections //e.g: NSArray/NSMutableArray// | No | Yes
9 |= Closures | Yes - via Blocks (//Extension//) | No | Yes - via Anonymous Functions
Ravi Mendis 435.1 10 |= Static variables | Yes | Yes | No
Ravi Mendis 497.1 11 |= Static methods or functions | Yes | Yes | No
Ravi Mendis 501.1 12 |= Concurrency | Yes - via [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//) | //Yes - via Threads// | Yes - via [[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
Ravi Mendis 435.1 13 |= |= Weakly Typed |= --Strongly Typed-- |= Strongly Typed
Ravi Mendis 294.1 14
15 Other notable features include:
16
Ravi Mendis 435.1 17 |= |= Objective-C |= Java |= Scala
18 |= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
Ravi Mendis 503.1 19 |= Class composition | Yes - via Categories | Yes - via Interfaces | Yes - via Traits
Ravi Mendis 294.1 20
Ravi Mendis 195.1 21 === Why Use Scala? ===
22
Ravi Mendis 487.1 23 For WebObjects developers, Scala offers itself as a powerful, safe and easy-to-use solution for [[concurrent computing>>Building Concurrent Applications with WebObjects and Scala]]. (In other words, Scala Actors can be used for problems that would have normally required threads).
Ravi Mendis 195.1 24
Ravi Mendis 294.1 25 === Can WebObjects be Programmed In Scala? ===
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Ravi Mendis 288.1 27 Yes. It is very simple.
Ravi Mendis 495.1 28 By virtue of being a JVM-language, Scala compiles to java bytecode.
Ravi Mendis 195.1 29
Ravi Mendis 455.1 30 Furthermore, being a multi-paradigm language grants Scala easy WebObjects-interoperability.
Ravi Mendis 445.1 31
Ravi Mendis 455.1 32 ===== Caveats =====
33
Ravi Mendis 495.1 34 Legacy tool support is often cited as a weak point. The [[Eclipse Scala plugin>>http://www.scala-ide.org]] has been found to be slow at times and sometimes buggy.
Ravi Mendis 455.1 35
Ravi Mendis 294.1 36 = WebObjects In Scala =
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Ravi Mendis 294.1 38 The following highlights some of the differences between Java and Scala in WebObjects:
Ravi Mendis 195.1 39
Ravi Mendis 294.1 40 == EOs in Scala ==
41
Ravi Mendis 435.1 42 === Thread-Safe Shared Vars ===
Ravi Mendis 294.1 43
Ravi Mendis 481.1 44 Scala doesn't have static variables or methods. Instead Scala employs the [[Singleton Pattern>>http://en.wikipedia.org/wiki/Singleton_pattern]] which is built into the language and is **thread-safe**: a class can have a //Companion Object// that will allow you to achieve something equivalent to static variables - but better.
Ravi Mendis 294.1 45
Ravi Mendis 479.1 46 You don't have to worry about synchronizing access to shared mutable fields in a concurrent application.
Ravi Mendis 495.1 47 (This is not however true when for example you have a ##val## declared as a ##NSMutableArray##. You will still have to synchronize when adding to or removing from this mutable field).
Ravi Mendis 435.1 48
Ravi Mendis 359.1 49 The following is an example of the use of a //Companion Object// for Talent in Scala instead of Talent static fields in Java.
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Ravi Mendis 355.1 51 Java:
52
Ravi Mendis 393.1 53 {{code value="java"}}
Ravi Mendis 308.1 54
Ravi Mendis 369.1 55 public class _Talent extends EOGenericRecord {
Ravi Mendis 294.1 56 public static final String ENTITY_NAME = "Talent";
57
58 {{/code}}
59
Ravi Mendis 355.1 60 Scala:
Ravi Mendis 294.1 61
62 {{code}}
63
Ravi Mendis 495.1 64 object Talent {
Ravi Mendis 294.1 65 val ENTITY_NAME = "Talent"
66
67 {{/code}}
68
Ravi Mendis 435.1 69 This value will be accessed exactly the same way in both languages:
70
71 {{code}}
72
73 Talent.ENTITY_NAME
74
75 {{/code}}
76
Ravi Mendis 318.1 77 ==== Compacted imports ====
Ravi Mendis 308.1 78
Ravi Mendis 294.1 79 In Java:
80
Ravi Mendis 393.1 81 {{code value="java"}}
Ravi Mendis 294.1 82
83 import com.webobjects.eocontrol.EOGenericRecord;
84 import com.webobjects.eocontrol.EORelationshipManipulation;
85
86 {{/code}}
87
88 In Scala:
89
90 {{code}}
91
92 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
93
94 {{/code}}
95
96 == WOComponents in Scala ==
97
98 ==== Compact Constructors ====
99
100 Scala allows for simpler use of multi-valued constructors than Java.
101
102 In Java:
103
Ravi Mendis 393.1 104 {{code value="java"}}
Ravi Mendis 294.1 105
106 public class MenuHeader extends WOComponent {
107
108 public MenuHeader(WOContext aContext) {
109 super(aContext);
110 }
111
112 {{/code}}
113
114 In Scala:
115
116 {{code}}
117
Ravi Mendis 312.1 118 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
Ravi Mendis 294.1 119
120 {{/code}}
121
122 ==== Simplified Exception Handling ====
123
124 Scala doesn't force you to catch exceptions unlike in Java.
Ravi Mendis 431.1 125 In addition, the syntax employs Scala's very powerful **pattern matching** to handle exceptions.
Ravi Mendis 294.1 126
127 In Java:
128
Ravi Mendis 393.1 129 {{code value="java"}}
Ravi Mendis 294.1 130
131 try {
132 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
133 epi.setNextPage(context().page());
134 nextPage = (WOComponent) epi;
135 } catch (IllegalArgumentException e) {
136 ErrorPageInterface epf = D2W.factory().errorPage(session());
137 epf.setMessage(e.toString());
138 epf.setNextPage(context().page());
139 nextPage = (WOComponent) epf;
140 }
141
142 {{/code}}
143
144 In Scala:
145
146 {{code}}
147
148 try {
149 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
150 epi.setNextPage(context.page)
151 nextPage = epi.asInstanceOf[WOComponent]
152 } catch {
153 case e: IllegalArgumentException => {
154 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
155 epf.setMessage(e.toString)
156 epf.setNextPage(context.page)
157 nextPage = epf.asInstanceOf[WOComponent]
158 }
159 }
160
161 {{/code}}
162
Ravi Mendis 435.1 163 ==== Scala Annotations vs. Generated Accessors ====
Ravi Mendis 381.1 164
Ravi Mendis 497.1 165 An example of accessing variables in WebObjects with the following languages:
Ravi Mendis 381.1 166
Ravi Mendis 435.1 167 |= |= Objective-C |= Java |= Scala
168 |= getter | ##object name## | ##object.name()## | ##object.name##
169 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
Ravi Mendis 381.1 170
Ravi Mendis 385.1 171 Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
172 In scala there is an additional convenience we may use to produce "get" and "set" methods in addition to the default Scala accessors - Scala Annotations.
173
174 E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
175 These variables can then be accessed via //KVC//.
176
177 {{code}}
178
Ravi Mendis 435.1 179 import scala.reflect.BeanProperty
180
Ravi Mendis 385.1 181 @BeanProperty var username = new String()
182 @BeanProperty var password = new String()
183 @BeanProperty var isAssistantCheckboxVisible = false
184
185 {{/code}}
186
Ravi Mendis 353.1 187 == How to Use Scala Collections with EOF ==
Ravi Mendis 351.1 188
Ravi Mendis 445.1 189 To use the Scala Collections API with an NSArray or NSDictionary you simply need to add an import:
Ravi Mendis 351.1 190
Ravi Mendis 445.1 191 {{code value="java"}}
Ravi Mendis 351.1 192
Ravi Mendis 445.1 193 import scala.collection.JavaConversions._
194
195 {{/code}}
196
Ravi Mendis 495.1 197 After that, you may access the typical Scala collection methods directly on NSArray.  This employs a feature of Scala known as implicit conversions to automagically cast a NSArray (a Java Iterable) into a Scala Iterable while leaving the actual object unchanged.
Ravi Mendis 445.1 198
Ravi Mendis 495.1 199 == How to Add Scala to a WO Project (in Eclipse) ==
Ravi Mendis 308.1 200
201 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
202
Ravi Mendis 290.1 203 == WO Scala Example ==
204
Ravi Mendis 353.1 205 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
Ravi Mendis 292.1 206 All the EO logic and WO components are in Scala.
Ravi Mendis 435.1 207 Only the Application class remains Java.
Ravi Mendis 292.1 208
Ravi Mendis 353.1 209 It is based on the D2W Movies example.
210
Ravi Mendis 290.1 211 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 212
213 === Setup ===
214
Ravi Mendis 435.1 215 1. [[Install the Scala eclipse IDE>>http://www.scala-ide.org/]]
Ravi Mendis 294.1 216 1. Right-click on Application.java and run as a WOApplication (as usual).
217
Ravi Mendis 491.1 218 {{note}}
219
John Huss 437.1 220 Application can be made into a Scala class as well, but then you will have to create a launcher in Eclipse manually.
221
Ravi Mendis 491.1 222 {{/note}}
223
Ravi Mendis 435.1 224 == EO Templates ==
Ravi Mendis 294.1 225
226 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
227
Ravi Mendis 435.1 228 1. Point to the local [[Scala versions>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]] of the .eotemplate files for ##Entity## and ##Entity##
Ravi Mendis 294.1 229 1. Change the File Names Extension to "scala"
Ravi Mendis 367.1 230 1. In Destination Paths set the Superclass Package (e.g: base)
Ravi Mendis 294.1 231 1. Uncheck Java under Options
Ravi Mendis 385.1 232
233 == How to Build & Deploy a WebObjects Scala Project with Ant ==
234
235 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
Ravi Mendis 393.1 236 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
237 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
238 1. Run from the project directory: ##sudo ant clean install##