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Wiki source code of WebObjects with Scala

Version 401.1 by Ravi Mendis on 2010/01/17 19:18
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Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 401.1 3 Scala is a modern language not unlike Groovy.
4 It is said to be more powerful and faster than Groovy or Ruby.
5 This's been the reason for its adoption at sites like Twitter.
6
Ravi Mendis 393.1 7 Scala is a language for concurrent computing.
8 In the day and age of multi-core processors, concurrent computing can't be ignored.
Ravi Mendis 195.1 9
Ravi Mendis 399.1 10 Many of Scala's features have been designed with concurrency in mind.
Ravi Mendis 393.1 11 Some of these may not be unfamiliar to Objective-C or WebObjects developers.
Ravi Mendis 294.1 12
Ravi Mendis 393.1 13 Here's a quick summary:
14
Ravi Mendis 338.1 15 |= |= Objective-C |= Java |= Scala
16 |= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | Yes
Ravi Mendis 349.1 17 |= Closures | Blocks (//Extension//) | No | Anonymous Functions
Ravi Mendis 338.1 18 |= Static variables | Yes | Yes | No
19 |= Static methods/functions | Yes | Yes | No
20 |= Concurrency | [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//)| //Threads// |[[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
21 |= |= Weakly Typed |=--Strongly Typed--|= Strongly Typed
Ravi Mendis 294.1 22
23 Other notable features include:
24
Ravi Mendis 338.1 25 |= |= Objective-C |= Java |= Scala
26 |= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
27 |= Class composition | Categories | Interfaces | Traits
Ravi Mendis 294.1 28
Ravi Mendis 338.1 29 A fuller description of Scala can be found [[here>>http://en.wikipedia.org/wiki/Scala_(programming_language)]].
30
Ravi Mendis 195.1 31 === Why Use Scala? ===
32
Ravi Mendis 401.1 33 Developing and maintaining a concurrent or multi-threaded WebObjects application can be challenging.
Ravi Mendis 195.1 34
Ravi Mendis 401.1 35 The lack of static variables means that Scala is inherently thread-safe.
36 It has concurrency that is effectively built-in to the language in the form of Actors.
Ravi Mendis 318.1 37
Ravi Mendis 401.1 38 So for WebObjects developers, Scala offers itself as a powerful, safe and easy-to-use solution for concurrent applications.
39
Ravi Mendis 294.1 40 === Can WebObjects be Programmed In Scala? ===
Ravi Mendis 195.1 41
Ravi Mendis 288.1 42 Yes. It is very simple.
Ravi Mendis 318.1 43 Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
Ravi Mendis 195.1 44
Ravi Mendis 294.1 45 = WebObjects In Scala =
Ravi Mendis 195.1 46
Ravi Mendis 294.1 47 The following highlights some of the differences between Java and Scala in WebObjects:
Ravi Mendis 195.1 48
Ravi Mendis 294.1 49 == EOs in Scala ==
50
Ravi Mendis 318.1 51 === Thread-Safe Shared Vars ===
Ravi Mendis 294.1 52
Ravi Mendis 318.1 53 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.
54 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 55
Ravi Mendis 359.1 56 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 294.1 57
Ravi Mendis 355.1 58 Java:
59
Ravi Mendis 393.1 60 {{code value="java"}}
Ravi Mendis 308.1 61
Ravi Mendis 369.1 62 public class _Talent extends EOGenericRecord {
Ravi Mendis 294.1 63 public static final String ENTITY_NAME = "Talent";
64
65 {{/code}}
66
Ravi Mendis 355.1 67 Scala:
Ravi Mendis 294.1 68
69 {{code}}
70
Ravi Mendis 369.1 71 object Talent extends EOGenericRecord {
Ravi Mendis 294.1 72 val ENTITY_NAME = "Talent"
73
74 {{/code}}
75
Ravi Mendis 318.1 76 ==== Compacted imports ====
Ravi Mendis 308.1 77
Ravi Mendis 318.1 78 Two lines in Java are compacted into one in Scala.
Ravi Mendis 308.1 79
Ravi Mendis 294.1 80 In Java:
81
Ravi Mendis 393.1 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 393.1 105 {{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 395.1 126 In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
Ravi Mendis 294.1 127
128 In Java:
129
Ravi Mendis 393.1 130 {{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 381.1 164 ==== Scala Annotations vs. Generic Accessors ====
165
Ravi Mendis 385.1 166 An example of accessing variables in WebObjects with the following languages:
Ravi Mendis 381.1 167
Ravi Mendis 385.1 168 |= |= Objective-C |= Java |= Scala
169 |= getter | ##object name## | ##object.name()## | ##object.name##
170 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
Ravi Mendis 381.1 171
Ravi Mendis 385.1 172 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 @BeanProperty var username = new String()
181 @BeanProperty var password = new String()
182 @BeanProperty var isAssistantCheckboxVisible = false
183
184 {{/code}}
185
Ravi Mendis 353.1 186 == How to Use Scala Collections with EOF ==
Ravi Mendis 351.1 187
188 One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map##, ##Seq## and ##Set##.
189 Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
190
191 But one may modify the EO templates to produce API such as:
192
193 {{code}}
194
195 def movies: NSArray[EOGenericRecord] = {
196 storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[EOGenericRecord]]
197 }
198
199 def moviesList: List[EOGenericRecord] = {
200 movies.objects.toList
201 }
202
203 {{/code}}
204
Ravi Mendis 318.1 205 == How to Add Scala to a WO Project ==
Ravi Mendis 308.1 206
207 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
208
Ravi Mendis 338.1 209 {{note title="Note"}}
Ravi Mendis 318.1 210
211 This is for Eclipse/WOLips IDE
212
213 {{/note}}
214
Ravi Mendis 290.1 215 == WO Scala Example ==
216
Ravi Mendis 353.1 217 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
Ravi Mendis 292.1 218 All the EO logic and WO components are in Scala.
Ravi Mendis 318.1 219 Only the Application class is Java.
Ravi Mendis 292.1 220
Ravi Mendis 353.1 221 It is based on the D2W Movies example.
222
Ravi Mendis 290.1 223 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 224
225 === Setup ===
226
Ravi Mendis 318.1 227 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
Ravi Mendis 353.1 228 1. Install and start the OpenBase OBMovies database.
Ravi Mendis 294.1 229 1. Right-click on Application.java and run as a WOApplication (as usual).
230
Ravi Mendis 318.1 231 ==== EO Templates ====
Ravi Mendis 294.1 232
233 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
234
Ravi Mendis 357.1 235 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##