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Wiki source code of WebObjects with Scala

Version 528.1 by Ravi Mendis on 2010/08/12 03:14
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Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 517.1 3 [[Scala>>http://en.wikipedia.org/wiki/Scala_(programming_language)]] is a language for concurrent computing.
4 In this day and age of multi-core processors, concurrent computing can't be ignored.
Ravi Mendis 195.1 5
Ravi Mendis 517.1 6 Many of Scala's features have been designed with concurrency in mind.
7 Some of these may not be unfamiliar to Objective-C or WebObjects developers.
Ravi Mendis 294.1 8
Ravi Mendis 517.1 9 Here's a quick summary:
Ravi Mendis 513.1 10
Ravi Mendis 519.1 11 |= |= Objective-C |= Java |= Scala
12 |= Separation of Mutable & Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | Yes
13 |= Closures | Blocks (//Extension//) | No | Anonymous Functions
14 |= Static variables | Yes | Yes | No
15 |= Static methods or functions | Yes | Yes | No
16 |= Concurrency | [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//) | //Threads// | [[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
17 |= |= Weakly Typed |= --Strongly Typed-- |= Strongly Typed
Ravi Mendis 517.1 18
Ravi Mendis 294.1 19 Other notable features include:
20
Ravi Mendis 519.1 21 |= |= Objective-C |= Java |= Scala
22 |= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
23 |= Class composition | Categories | Interfaces | Traits
Ravi Mendis 294.1 24
Ravi Mendis 195.1 25 === Why Use Scala? ===
26
Ravi Mendis 517.1 27 Scala is inherently thread-safe.
28 It has concurrency that is effectively built-in to the language.
Ravi Mendis 195.1 29
Ravi Mendis 517.1 30 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 513.1 31
Ravi Mendis 294.1 32 === Can WebObjects be Programmed In Scala? ===
Ravi Mendis 195.1 33
Ravi Mendis 288.1 34 Yes. It is very simple.
Ravi Mendis 513.1 35 Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
Ravi Mendis 195.1 36
Ravi Mendis 294.1 37 = WebObjects In Scala =
Ravi Mendis 195.1 38
Ravi Mendis 294.1 39 The following highlights some of the differences between Java and Scala in WebObjects:
Ravi Mendis 195.1 40
Ravi Mendis 294.1 41 == EOs in Scala ==
42
Ravi Mendis 519.1 43 === Thread-Safe Shared Vars ===
Ravi Mendis 294.1 44
Ravi Mendis 519.1 45 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 46
Ravi Mendis 519.1 47 So you don't have to worry about synchronizing access to shared mutable fields in a concurrent application.
48
Ravi Mendis 517.1 49 The following is an example of the use of a //Companion Object// for Talent in Scala instead of Talent static fields in Java.
Ravi Mendis 435.1 50
Ravi Mendis 517.1 51 Java:
Ravi Mendis 294.1 52
Ravi Mendis 517.1 53 {{code value="java"}}
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 517.1 60 Scala:
Ravi Mendis 294.1 61
62 {{code}}
63
Ravi Mendis 517.1 64 object Talent extends EOGenericRecord {
Ravi Mendis 294.1 65 val ENTITY_NAME = "Talent"
66
67 {{/code}}
68
Ravi Mendis 517.1 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 513.1 79 Two lines in Java are compacted into one in Scala.
80
Ravi Mendis 294.1 81 In Java:
82
Ravi Mendis 517.1 83 {{code value="java"}}
Ravi Mendis 294.1 84
85 import com.webobjects.eocontrol.EOGenericRecord;
86 import com.webobjects.eocontrol.EORelationshipManipulation;
87
88 {{/code}}
89
90 In Scala:
91
92 {{code}}
93
94 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
95
96 {{/code}}
97
98 == WOComponents in Scala ==
99
100 ==== Compact Constructors ====
101
102 Scala allows for simpler use of multi-valued constructors than Java.
103
104 In Java:
105
Ravi Mendis 517.1 106 {{code value="java"}}
Ravi Mendis 294.1 107
108 public class MenuHeader extends WOComponent {
109
110 public MenuHeader(WOContext aContext) {
111 super(aContext);
112 }
113
114 {{/code}}
115
116 In Scala:
117
118 {{code}}
119
Ravi Mendis 312.1 120 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
Ravi Mendis 294.1 121
122 {{/code}}
123
124 ==== Simplified Exception Handling ====
125
126 Scala doesn't force you to catch exceptions unlike in Java.
Ravi Mendis 517.1 127 In addition, the syntax employs Scala's very powerful **pattern matching** to handle exceptions.
Ravi Mendis 294.1 128
129 In Java:
130
Ravi Mendis 517.1 131 {{code value="java"}}
Ravi Mendis 294.1 132
133 try {
134 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
135 epi.setNextPage(context().page());
136 nextPage = (WOComponent) epi;
137 } catch (IllegalArgumentException e) {
138 ErrorPageInterface epf = D2W.factory().errorPage(session());
139 epf.setMessage(e.toString());
140 epf.setNextPage(context().page());
141 nextPage = (WOComponent) epf;
142 }
143
144 {{/code}}
145
146 In Scala:
147
148 {{code}}
149
150 try {
151 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
152 epi.setNextPage(context.page)
153 nextPage = epi.asInstanceOf[WOComponent]
154 } catch {
155 case e: IllegalArgumentException => {
156 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
157 epf.setMessage(e.toString)
158 epf.setNextPage(context.page)
159 nextPage = epf.asInstanceOf[WOComponent]
160 }
161 }
162
163 {{/code}}
164
Ravi Mendis 517.1 165 ==== Scala Annotations vs. Generated Accessors ====
166
167 An example of accessing variables in WebObjects with the following languages:
168
Ravi Mendis 519.1 169 |= |= Objective-C |= Java |= Scala
170 |= getter | ##object name## | ##object.name()## | ##object.name##
171 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
Ravi Mendis 517.1 172
173 Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
174 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.
175
176 E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
177 These variables can then be accessed via //KVC//.
178
179 {{code}}
180
181 import scala.reflect.BeanProperty
182
183 @BeanProperty var username = new String()
184 @BeanProperty var password = new String()
185 @BeanProperty var isAssistantCheckboxVisible = false
186
187 {{/code}}
188
189 == How to Use Scala Collections with EOF ==
190
191 One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map## and ##Set##.
192 Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
193
194 But one may modify the EO templates to produce API such as:
195
196 {{code}}
197
Ravi Mendis 525.1 198 import scala.collection.JavaConversions._
199
200 def movies = {
201 storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[Movie]]
Ravi Mendis 517.1 202 }
Ravi Mendis 519.1 203
Ravi Mendis 525.1 204 def moviesList = {
205 movies.asInstanceOf[java.lang.Iterable[Movie]].toList
Ravi Mendis 517.1 206 }
207
208 {{/code}}
209
Ravi Mendis 525.1 210 This employs a feature of Scala known as **implicit conversions** to automagically convert a NSArray (a Java Iterable) into a Scala Iterable.
211
Ravi Mendis 513.1 212 == How to Add Scala to a WO Project ==
Ravi Mendis 308.1 213
214 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
215
Ravi Mendis 517.1 216 {{note}}
Ravi Mendis 513.1 217
218 This is for Eclipse/WOLips IDE
219
220 {{/note}}
221
Ravi Mendis 290.1 222 == WO Scala Example ==
223
Ravi Mendis 517.1 224 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
Ravi Mendis 292.1 225 All the EO logic and WO components are in Scala.
Ravi Mendis 513.1 226 Only the Application class is Java.
Ravi Mendis 292.1 227
Ravi Mendis 517.1 228 It is based on the D2W Movies example.
229
Ravi Mendis 290.1 230 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 231
232 === Setup ===
233
Ravi Mendis 521.1 234 1. [[Install the Scala eclipse IDE>>http://www.scala-ide.org/]]
Ravi Mendis 527.1 235 1. Install and start the OpenBase OBMovies database.
Ravi Mendis 294.1 236 1. Right-click on Application.java and run as a WOApplication (as usual).
237
Ravi Mendis 515.1 238 ==== EO Templates ====
Ravi Mendis 294.1 239
240 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
241
Ravi Mendis 519.1 242 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 294.1 243 1. Change the File Names Extension to "scala"
Ravi Mendis 517.1 244 1. In Destination Paths set the Superclass Package (e.g: base)
Ravi Mendis 294.1 245 1. Uncheck Java under Options
Ravi Mendis 517.1 246
247 == How to Build & Deploy a WebObjects Scala Project with Ant ==
248
249 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
250 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
251 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
252 1. Run from the project directory: ##sudo ant clean install##
253
254 == Caveats ==
255
256 {{warning}}
257
258 Currently mixed Scala and Java projects aren't supported by the Scala Eclipse IDE, though it is possible to do so providing your project is either mostly Java or mostly Scala.
259
260 {{/warning}}