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Wiki source code of WebObjects with Scala

Version 448.1 by Ravi Mendis on 2010/12/23 23:48
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Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 445.1 3 [[Scala>>http://en.wikipedia.org/wiki/Scala_(programming_language)]] is a JVM language that is a hybrid of Object-Oriented and Functional styles. Its [[functional language>>http://en.wikipedia.org/wiki/Functional_programming]] foundations and built-in Actors library makes it especially attractive for concurrent computing. In this day and age of multi-core processors concurrent computing can not be ignored.
Ravi Mendis 195.1 4
Ravi Mendis 445.1 5 Many of Scala's features have been designed with concurrency in mind, some of which may not be unfamiliar to Objective-C or WebObjects developers. Here's a summary:
Ravi Mendis 294.1 6
Ravi Mendis 435.1 7 |= |= Objective-C |= Java |= Scala
Ravi Mendis 445.1 8 |= Immutability | Collections //e.g: NSArray/NSMutableArray// | No | Yes
Ravi Mendis 435.1 9 |= Closures | Blocks (//Extension//) | No | Anonymous Functions
10 |= Static variables | Yes | Yes | No
11 |= Static methods or functions | Yes | Yes | No
12 |= Concurrency | [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//) | //Threads// | [[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
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=)//
19 |= Class composition | Categories | Interfaces | Traits
Ravi Mendis 294.1 20
Ravi Mendis 195.1 21 === Why Use Scala? ===
22
John Huss 437.1 23 Scala can help you to write thread-safe code.
24 It has concurrency that is built-in to the standard library, primarily via Actors.
Ravi Mendis 195.1 25
Ravi Mendis 435.1 26 So for WebObjects developers, Scala offers itself as a powerful, safe and easy-to-use solution for [[concurrent applications>>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 318.1 27
Ravi Mendis 294.1 28 === Can WebObjects be Programmed In Scala? ===
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Ravi Mendis 288.1 30 Yes. It is very simple.
Ravi Mendis 445.1 31 Scala compiles to java bytecode.
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Ravi Mendis 445.1 33 Furthermore, being a multi-paradigm language grants Scala easy WebObjects-interoperability.
Ravi Mendis 439.1 34
Ravi Mendis 445.1 35 ===== Caveats =====
36
Ravi Mendis 447.1 37 Tool support is a weak point. If your Application class is in Scala then you will have to create an Eclipse launch configuration manually. Also the [[Scala plugin>>http://www.scala-ide.org]] is rather slow and still very buggy.
Ravi Mendis 445.1 38
Ravi Mendis 294.1 39 = WebObjects In Scala =
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Ravi Mendis 294.1 41 The following highlights some of the differences between Java and Scala in WebObjects:
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Ravi Mendis 294.1 43 == EOs in Scala ==
44
Ravi Mendis 435.1 45 === Thread-Safe Shared Vars ===
Ravi Mendis 294.1 46
John Huss 437.1 47 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. Is this true?  I don't think Scala "object" instances (with the object keyword) are guaranteed to be thread-safe; they are just singletons
Ravi Mendis 294.1 48
Ravi Mendis 435.1 49 So you don't have to worry about synchronizing access to shared mutable fields in a concurrent application.
50
Ravi Mendis 359.1 51 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 53 Java:
54
Ravi Mendis 393.1 55 {{code value="java"}}
Ravi Mendis 308.1 56
Ravi Mendis 369.1 57 public class _Talent extends EOGenericRecord {
Ravi Mendis 294.1 58 public static final String ENTITY_NAME = "Talent";
59
60 {{/code}}
61
Ravi Mendis 355.1 62 Scala:
Ravi Mendis 294.1 63
64 {{code}}
65
Ravi Mendis 369.1 66 object Talent extends EOGenericRecord {
Ravi Mendis 294.1 67 val ENTITY_NAME = "Talent"
68
69 {{/code}}
70
Ravi Mendis 435.1 71 This value will be accessed exactly the same way in both languages:
72
73 {{code}}
74
75 Talent.ENTITY_NAME
76
77 {{/code}}
78
Ravi Mendis 318.1 79 ==== Compacted imports ====
Ravi Mendis 308.1 80
Ravi Mendis 318.1 81 Two lines in Java are compacted into one in Scala.
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Ravi Mendis 294.1 83 In Java:
84
Ravi Mendis 393.1 85 {{code value="java"}}
Ravi Mendis 294.1 86
87 import com.webobjects.eocontrol.EOGenericRecord;
88 import com.webobjects.eocontrol.EORelationshipManipulation;
89
90 {{/code}}
91
92 In Scala:
93
94 {{code}}
95
96 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
97
98 {{/code}}
99
100 == WOComponents in Scala ==
101
102 ==== Compact Constructors ====
103
104 Scala allows for simpler use of multi-valued constructors than Java.
105
106 In Java:
107
Ravi Mendis 393.1 108 {{code value="java"}}
Ravi Mendis 294.1 109
110 public class MenuHeader extends WOComponent {
111
112 public MenuHeader(WOContext aContext) {
113 super(aContext);
114 }
115
116 {{/code}}
117
118 In Scala:
119
120 {{code}}
121
Ravi Mendis 312.1 122 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
Ravi Mendis 294.1 123
124 {{/code}}
125
126 ==== Simplified Exception Handling ====
127
128 Scala doesn't force you to catch exceptions unlike in Java.
Ravi Mendis 431.1 129 In addition, the syntax employs Scala's very powerful **pattern matching** to handle exceptions.
Ravi Mendis 294.1 130
131 In Java:
132
Ravi Mendis 393.1 133 {{code value="java"}}
Ravi Mendis 294.1 134
135 try {
136 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
137 epi.setNextPage(context().page());
138 nextPage = (WOComponent) epi;
139 } catch (IllegalArgumentException e) {
140 ErrorPageInterface epf = D2W.factory().errorPage(session());
141 epf.setMessage(e.toString());
142 epf.setNextPage(context().page());
143 nextPage = (WOComponent) epf;
144 }
145
146 {{/code}}
147
148 In Scala:
149
150 {{code}}
151
152 try {
153 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
154 epi.setNextPage(context.page)
155 nextPage = epi.asInstanceOf[WOComponent]
156 } catch {
157 case e: IllegalArgumentException => {
158 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
159 epf.setMessage(e.toString)
160 epf.setNextPage(context.page)
161 nextPage = epf.asInstanceOf[WOComponent]
162 }
163 }
164
165 {{/code}}
166
Ravi Mendis 435.1 167 ==== Scala Annotations vs. Generated Accessors ====
Ravi Mendis 381.1 168
Ravi Mendis 385.1 169 An example of accessing variables in WebObjects with the following languages:
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Ravi Mendis 435.1 171 |= |= Objective-C |= Java |= Scala
172 |= getter | ##object name## | ##object.name()## | ##object.name##
173 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
Ravi Mendis 381.1 174
Ravi Mendis 385.1 175 Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
176 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.
177
178 E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
179 These variables can then be accessed via //KVC//.
180
181 {{code}}
182
Ravi Mendis 435.1 183 import scala.reflect.BeanProperty
184
Ravi Mendis 385.1 185 @BeanProperty var username = new String()
186 @BeanProperty var password = new String()
187 @BeanProperty var isAssistantCheckboxVisible = false
188
189 {{/code}}
190
Ravi Mendis 353.1 191 == How to Use Scala Collections with EOF ==
Ravi Mendis 351.1 192
Ravi Mendis 445.1 193 To use the Scala Collections API with an NSArray or NSDictionary you simply need to add an import:
Ravi Mendis 351.1 194
Ravi Mendis 445.1 195 {{code value="java"}}
Ravi Mendis 351.1 196
Ravi Mendis 445.1 197 import scala.collection.JavaConversions._
198
199 {{/code}}
200
201 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.  Alternatively, you could generate an actual new scala.List instance by calling myNSArray.toList.
202
Ravi Mendis 318.1 203 == How to Add Scala to a WO Project ==
Ravi Mendis 308.1 204
205 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
206
Ravi Mendis 435.1 207 {{note}}
Ravi Mendis 318.1 208
209 This is for Eclipse/WOLips IDE
210
211 {{/note}}
212
Ravi Mendis 290.1 213 == WO Scala Example ==
214
Ravi Mendis 353.1 215 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
Ravi Mendis 292.1 216 All the EO logic and WO components are in Scala.
Ravi Mendis 435.1 217 Only the Application class remains Java.
Ravi Mendis 292.1 218
Ravi Mendis 353.1 219 It is based on the D2W Movies example.
220
Ravi Mendis 290.1 221 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 222
223 === Setup ===
224
Ravi Mendis 435.1 225 1. [[Install the Scala eclipse IDE>>http://www.scala-ide.org/]]
Ravi Mendis 294.1 226 1. Right-click on Application.java and run as a WOApplication (as usual).
227
John Huss 437.1 228 Application can be made into a Scala class as well, but then you will have to create a launcher in Eclipse manually.
229
Ravi Mendis 435.1 230 == EO Templates ==
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232 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
233
Ravi Mendis 435.1 234 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 294.1 235 1. Change the File Names Extension to "scala"
Ravi Mendis 367.1 236 1. In Destination Paths set the Superclass Package (e.g: base)
Ravi Mendis 294.1 237 1. Uncheck Java under Options
Ravi Mendis 385.1 238
239 == How to Build & Deploy a WebObjects Scala Project with Ant ==
240
241 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
Ravi Mendis 393.1 242 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
243 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
244 1. Run from the project directory: ##sudo ant clean install##