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Wiki source code of WebObjects with Scala

Version 527.1 by Ravi Mendis on 2010/08/12 03:14
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1 === What is Scala? ===
2
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.
5
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.
8
9 Here's a quick summary:
10
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
19 Other notable features include:
20
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
24
25 === Why Use Scala? ===
26
27 Scala is inherently thread-safe.
28 It has concurrency that is effectively built-in to the language.
29
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).
31
32 === Can WebObjects be Programmed In Scala? ===
33
34 Yes. It is very simple.
35 Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
36
37 = WebObjects In Scala =
38
39 The following highlights some of the differences between Java and Scala in WebObjects:
40
41 == EOs in Scala ==
42
43 === Thread-Safe Shared Vars ===
44
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.
46
47 So you don't have to worry about synchronizing access to shared mutable fields in a concurrent application.
48
49 The following is an example of the use of a //Companion Object// for Talent in Scala instead of Talent static fields in Java.
50
51 Java:
52
53 {{code value="java"}}
54
55 public class _Talent extends EOGenericRecord {
56 public static final String ENTITY_NAME = "Talent";
57
58 {{/code}}
59
60 Scala:
61
62 {{code}}
63
64 object Talent extends EOGenericRecord {
65 val ENTITY_NAME = "Talent"
66
67 {{/code}}
68
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
77 ==== Compacted imports ====
78
79 Two lines in Java are compacted into one in Scala.
80
81 In Java:
82
83 {{code value="java"}}
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
106 {{code value="java"}}
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
120 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
121
122 {{/code}}
123
124 ==== Simplified Exception Handling ====
125
126 Scala doesn't force you to catch exceptions unlike in Java.
127 In addition, the syntax employs Scala's very powerful **pattern matching** to handle exceptions.
128
129 In Java:
130
131 {{code value="java"}}
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
165 ==== Scala Annotations vs. Generated Accessors ====
166
167 An example of accessing variables in WebObjects with the following languages:
168
169 |= |= Objective-C |= Java |= Scala
170 |= getter | ##object name## | ##object.name()## | ##object.name##
171 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
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
198 import scala.collection.JavaConversions._
199
200 def movies = {
201 storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[Movie]]
202 }
203
204 def moviesList = {
205 movies.asInstanceOf[java.lang.Iterable[Movie]].toList
206 }
207
208 {{/code}}
209
210 This employs a feature of Scala known as **implicit conversions** to automagically convert a NSArray (a Java Iterable) into a Scala Iterable.
211
212 == How to Add Scala to a WO Project ==
213
214 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
215
216 {{note}}
217
218 This is for Eclipse/WOLips IDE
219
220 {{/note}}
221
222 == WO Scala Example ==
223
224 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
225 All the EO logic and WO components are in Scala.
226 Only the Application class is Java.
227
228 It is based on the D2W Movies example.
229
230 {{attachments patterns=".*zip"}}{{/attachments}}
231
232 === Setup ===
233
234 1. [[Install the Scala eclipse IDE>>http://www.scala-ide.org/]]
235 1. Install and start the OpenBase OBMovies database.
236 1. Right-click on Application.java and run as a WOApplication (as usual).
237
238 ==== EO Templates ====
239
240 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
241
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##
243 1. Change the File Names Extension to "scala"
244 1. In Destination Paths set the Superclass Package (e.g: base)
245 1. Uncheck Java under Options
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}}