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Wiki source code of WebObjects with Scala

Version 517.1 by Ravi Mendis on 2010/04/06 18:25
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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 517.1 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
18
Ravi Mendis 294.1 19 Other notable features include:
20
Ravi Mendis 517.1 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 515.1 43 === Thread-Safe Shared Vars ===
Ravi Mendis 294.1 44
Ravi Mendis 515.1 45 Scala doesn't have static variables or methods. However, a class can have a //Companion Object// that will allow you to achieve something equivalent to static variables.
46 One of the advantages of this approach is that it is **thread-safe**, so you don't have to worry about synchronizing access to these fields in a concurrent application.
Ravi Mendis 294.1 47
Ravi Mendis 517.1 48 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 49
Ravi Mendis 517.1 50 Java:
Ravi Mendis 294.1 51
Ravi Mendis 517.1 52 {{code value="java"}}
53
Ravi Mendis 369.1 54 public class _Talent extends EOGenericRecord {
Ravi Mendis 294.1 55 public static final String ENTITY_NAME = "Talent";
56
57 {{/code}}
58
Ravi Mendis 517.1 59 Scala:
Ravi Mendis 294.1 60
61 {{code}}
62
Ravi Mendis 517.1 63 object Talent extends EOGenericRecord {
Ravi Mendis 294.1 64 val ENTITY_NAME = "Talent"
65
66 {{/code}}
67
Ravi Mendis 517.1 68 This value will be accessed exactly the same way in both languages:
69
70 {{code}}
71
72 Talent.ENTITY_NAME
73
74 {{/code}}
75
Ravi Mendis 318.1 76 ==== Compacted imports ====
Ravi Mendis 308.1 77
Ravi Mendis 513.1 78 Two lines in Java are compacted into one in Scala.
79
Ravi Mendis 294.1 80 In Java:
81
Ravi Mendis 517.1 82 {{code value="java"}}
Ravi Mendis 294.1 83
84 import com.webobjects.eocontrol.EOGenericRecord;
85 import com.webobjects.eocontrol.EORelationshipManipulation;
86
87 {{/code}}
88
89 In Scala:
90
91 {{code}}
92
93 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
94
95 {{/code}}
96
97 == WOComponents in Scala ==
98
99 ==== Compact Constructors ====
100
101 Scala allows for simpler use of multi-valued constructors than Java.
102
103 In Java:
104
Ravi Mendis 517.1 105 {{code value="java"}}
Ravi Mendis 294.1 106
107 public class MenuHeader extends WOComponent {
108
109 public MenuHeader(WOContext aContext) {
110 super(aContext);
111 }
112
113 {{/code}}
114
115 In Scala:
116
117 {{code}}
118
Ravi Mendis 312.1 119 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
Ravi Mendis 294.1 120
121 {{/code}}
122
123 ==== Simplified Exception Handling ====
124
125 Scala doesn't force you to catch exceptions unlike in Java.
Ravi Mendis 517.1 126 In addition, the syntax employs Scala's very powerful **pattern matching** to handle exceptions.
Ravi Mendis 294.1 127
128 In Java:
129
Ravi Mendis 517.1 130 {{code value="java"}}
Ravi Mendis 294.1 131
132 try {
133 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
134 epi.setNextPage(context().page());
135 nextPage = (WOComponent) epi;
136 } catch (IllegalArgumentException e) {
137 ErrorPageInterface epf = D2W.factory().errorPage(session());
138 epf.setMessage(e.toString());
139 epf.setNextPage(context().page());
140 nextPage = (WOComponent) epf;
141 }
142
143 {{/code}}
144
145 In Scala:
146
147 {{code}}
148
149 try {
150 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
151 epi.setNextPage(context.page)
152 nextPage = epi.asInstanceOf[WOComponent]
153 } catch {
154 case e: IllegalArgumentException => {
155 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
156 epf.setMessage(e.toString)
157 epf.setNextPage(context.page)
158 nextPage = epf.asInstanceOf[WOComponent]
159 }
160 }
161
162 {{/code}}
163
Ravi Mendis 517.1 164 ==== Scala Annotations vs. Generated Accessors ====
165
166 An example of accessing variables in WebObjects with the following languages:
167
168 |= |= Objective-C |= Java |= Scala
169 |= getter | ##object name## | ##object.name()## | ##object.name##
170 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
171
172 Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
173 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.
174
175 E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
176 These variables can then be accessed via //KVC//.
177
178 {{code}}
179
180 import scala.reflect.BeanProperty
181
182 @BeanProperty var username = new String()
183 @BeanProperty var password = new String()
184 @BeanProperty var isAssistantCheckboxVisible = false
185
186 {{/code}}
187
188 == How to Use Scala Collections with EOF ==
189
190 One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map## and ##Set##.
191 Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
192
193 But one may modify the EO templates to produce API such as:
194
195 {{code}}
196
197 def movies: NSArray[Studio] = {
198 storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[Studio]]
199 }
200
201 def moviesList: List[Studio] = {
202 movies.objects.toList
203 }
204
205 {{/code}}
206
Ravi Mendis 513.1 207 == How to Add Scala to a WO Project ==
Ravi Mendis 308.1 208
209 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
210
Ravi Mendis 517.1 211 {{note}}
Ravi Mendis 513.1 212
213 This is for Eclipse/WOLips IDE
214
215 {{/note}}
216
Ravi Mendis 290.1 217 == WO Scala Example ==
218
Ravi Mendis 517.1 219 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
Ravi Mendis 292.1 220 All the EO logic and WO components are in Scala.
Ravi Mendis 513.1 221 Only the Application class is Java.
Ravi Mendis 292.1 222
Ravi Mendis 517.1 223 It is based on the D2W Movies example.
224
Ravi Mendis 290.1 225 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 226
227 === Setup ===
228
Ravi Mendis 515.1 229 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
Ravi Mendis 517.1 230 1. Install and start the OpenBase OBMovies database.
Ravi Mendis 294.1 231 1. Right-click on Application.java and run as a WOApplication (as usual).
232
Ravi Mendis 515.1 233 ==== EO Templates ====
Ravi Mendis 294.1 234
235 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
236
Ravi Mendis 517.1 237 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 294.1 238 1. Change the File Names Extension to "scala"
Ravi Mendis 517.1 239 1. In Destination Paths set the Superclass Package (e.g: base)
Ravi Mendis 294.1 240 1. Uncheck Java under Options
Ravi Mendis 517.1 241
242 == How to Build & Deploy a WebObjects Scala Project with Ant ==
243
244 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
245 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
246 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
247 1. Run from the project directory: ##sudo ant clean install##
248
249 == Caveats ==
250
251 {{warning}}
252
253 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.
254
255 {{/warning}}