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Wiki source code of WebObjects with Scala

Version 486.1 by Ravi Mendis on 2010/12/24 00:07
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Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 485.1 3 [[Scala>>http://en.wikipedia.org/wiki/Scala_(programming_language)]] 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 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 477.1 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:
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Ravi Mendis 435.1 7 |= |= Objective-C |= Java |= Scala
Ravi Mendis 455.1 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
Ravi Mendis 477.1 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 477.1 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).
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 477.1 31 Scala compiles to java bytecode.
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Ravi Mendis 455.1 33 Furthermore, being a multi-paradigm language grants Scala easy WebObjects-interoperability.
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Ravi Mendis 455.1 35 ===== Caveats =====
36
Ravi Mendis 477.1 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 455.1 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 ===
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Ravi Mendis 481.1 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.
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Ravi Mendis 479.1 49 You don't have to worry about synchronizing access to shared mutable fields in a concurrent application.
Ravi Mendis 481.1 50 This is not however true for mutable ##val## e.g: ##NSMutableArray##, ##scala.collection.mutable.ListBuffer## which you will have to synchronize the adding to or removing from.
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Ravi Mendis 359.1 52 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 54 Java:
55
Ravi Mendis 393.1 56 {{code value="java"}}
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Ravi Mendis 369.1 58 public class _Talent extends EOGenericRecord {
Ravi Mendis 294.1 59 public static final String ENTITY_NAME = "Talent";
60
61 {{/code}}
62
Ravi Mendis 355.1 63 Scala:
Ravi Mendis 294.1 64
65 {{code}}
66
Ravi Mendis 477.1 67 object Talent extends EOGenericRecord {
Ravi Mendis 294.1 68 val ENTITY_NAME = "Talent"
69
70 {{/code}}
71
Ravi Mendis 435.1 72 This value will be accessed exactly the same way in both languages:
73
74 {{code}}
75
76 Talent.ENTITY_NAME
77
78 {{/code}}
79
Ravi Mendis 318.1 80 ==== Compacted imports ====
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Ravi Mendis 477.1 82 Two lines in Java are compacted into one in Scala.
83
Ravi Mendis 294.1 84 In Java:
85
Ravi Mendis 393.1 86 {{code value="java"}}
Ravi Mendis 294.1 87
88 import com.webobjects.eocontrol.EOGenericRecord;
89 import com.webobjects.eocontrol.EORelationshipManipulation;
90
91 {{/code}}
92
93 In Scala:
94
95 {{code}}
96
97 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
98
99 {{/code}}
100
101 == WOComponents in Scala ==
102
103 ==== Compact Constructors ====
104
105 Scala allows for simpler use of multi-valued constructors than Java.
106
107 In Java:
108
Ravi Mendis 393.1 109 {{code value="java"}}
Ravi Mendis 294.1 110
111 public class MenuHeader extends WOComponent {
112
113 public MenuHeader(WOContext aContext) {
114 super(aContext);
115 }
116
117 {{/code}}
118
119 In Scala:
120
121 {{code}}
122
Ravi Mendis 312.1 123 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
Ravi Mendis 294.1 124
125 {{/code}}
126
127 ==== Simplified Exception Handling ====
128
129 Scala doesn't force you to catch exceptions unlike in Java.
Ravi Mendis 431.1 130 In addition, the syntax employs Scala's very powerful **pattern matching** to handle exceptions.
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132 In Java:
133
Ravi Mendis 393.1 134 {{code value="java"}}
Ravi Mendis 294.1 135
136 try {
137 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
138 epi.setNextPage(context().page());
139 nextPage = (WOComponent) epi;
140 } catch (IllegalArgumentException e) {
141 ErrorPageInterface epf = D2W.factory().errorPage(session());
142 epf.setMessage(e.toString());
143 epf.setNextPage(context().page());
144 nextPage = (WOComponent) epf;
145 }
146
147 {{/code}}
148
149 In Scala:
150
151 {{code}}
152
153 try {
154 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
155 epi.setNextPage(context.page)
156 nextPage = epi.asInstanceOf[WOComponent]
157 } catch {
158 case e: IllegalArgumentException => {
159 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
160 epf.setMessage(e.toString)
161 epf.setNextPage(context.page)
162 nextPage = epf.asInstanceOf[WOComponent]
163 }
164 }
165
166 {{/code}}
167
Ravi Mendis 435.1 168 ==== Scala Annotations vs. Generated Accessors ====
Ravi Mendis 381.1 169
Ravi Mendis 385.1 170 An example of accessing variables in WebObjects with the following languages:
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Ravi Mendis 435.1 172 |= |= Objective-C |= Java |= Scala
173 |= getter | ##object name## | ##object.name()## | ##object.name##
174 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
Ravi Mendis 381.1 175
Ravi Mendis 385.1 176 Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
177 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.
178
179 E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
180 These variables can then be accessed via //KVC//.
181
182 {{code}}
183
Ravi Mendis 435.1 184 import scala.reflect.BeanProperty
185
Ravi Mendis 385.1 186 @BeanProperty var username = new String()
187 @BeanProperty var password = new String()
188 @BeanProperty var isAssistantCheckboxVisible = false
189
190 {{/code}}
191
Ravi Mendis 353.1 192 == How to Use Scala Collections with EOF ==
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Ravi Mendis 445.1 194 To use the Scala Collections API with an NSArray or NSDictionary you simply need to add an import:
Ravi Mendis 351.1 195
Ravi Mendis 445.1 196 {{code value="java"}}
Ravi Mendis 351.1 197
Ravi Mendis 445.1 198 import scala.collection.JavaConversions._
199
200 {{/code}}
201
202 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.
203
Ravi Mendis 477.1 204 == How to Add Scala to a WO Project ==
Ravi Mendis 308.1 205
206 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
207
Ravi Mendis 477.1 208 {{note}}
209
210 This is for Eclipse/WOLips IDE
211
212 {{/note}}
213
Ravi Mendis 290.1 214 == WO Scala Example ==
215
Ravi Mendis 353.1 216 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
Ravi Mendis 292.1 217 All the EO logic and WO components are in Scala.
Ravi Mendis 435.1 218 Only the Application class remains Java.
Ravi Mendis 292.1 219
Ravi Mendis 353.1 220 It is based on the D2W Movies example.
221
Ravi Mendis 290.1 222 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 223
224 === Setup ===
225
Ravi Mendis 435.1 226 1. [[Install the Scala eclipse IDE>>http://www.scala-ide.org/]]
Ravi Mendis 294.1 227 1. Right-click on Application.java and run as a WOApplication (as usual).
228
John Huss 437.1 229 Application can be made into a Scala class as well, but then you will have to create a launcher in Eclipse manually.
230
Ravi Mendis 435.1 231 == EO Templates ==
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233 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
234
Ravi Mendis 435.1 235 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 294.1 236 1. Change the File Names Extension to "scala"
Ravi Mendis 367.1 237 1. In Destination Paths set the Superclass Package (e.g: base)
Ravi Mendis 294.1 238 1. Uncheck Java under Options
Ravi Mendis 385.1 239
240 == How to Build & Deploy a WebObjects Scala Project with Ant ==
241
242 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
Ravi Mendis 393.1 243 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
244 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
245 1. Run from the project directory: ##sudo ant clean install##