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Wiki source code of WebObjects with Scala

Version 453.1 by Ravi Mendis on 2010/12/23 06:51
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Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 453.1 3 [[Scala>>http://en.wikipedia.org/wiki/Scala_(programming_language)]] is a JVM language that is a hybrid of Object-Oriented and Functional styles. It is useful as complete general purpose replacement for Java. But its built-in Actors library makes it especially attractive for concurrent computing. In this day and age of multi-core processors, concurrent computing can't be ignored.
Ravi Mendis 195.1 4
Ravi Mendis 453.1 5 Many of Scala's features have been designed with concurrency in mind, primarily a preference for immutability and the use of other functional language paradigms.
6 Some of these may not be unfamiliar to Objective-C or WebObjects developers.
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Ravi Mendis 453.1 8 Here's a quick summary:
9
Ravi Mendis 435.1 10 |= |= Objective-C |= Java |= Scala
Ravi Mendis 453.1 11 |= Separation of Mutable & Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | Yes
Ravi Mendis 435.1 12 |= Closures | Blocks (//Extension//) | No | Anonymous Functions
13 |= Static variables | Yes | Yes | No
14 |= Static methods or functions | Yes | Yes | No
15 |= Concurrency | [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//) | //Threads// | [[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
16 |= |= Weakly Typed |= --Strongly Typed-- |= Strongly Typed
Ravi Mendis 294.1 17
18 Other notable features include:
19
Ravi Mendis 435.1 20 |= |= Objective-C |= Java |= Scala
21 |= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
22 |= Class composition | Categories | Interfaces | Traits
Ravi Mendis 294.1 23
Ravi Mendis 195.1 24 === Why Use Scala? ===
25
John Huss 437.1 26 Scala can help you to write thread-safe code.
27 It has concurrency that is built-in to the standard library, primarily via Actors.
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Ravi Mendis 435.1 29 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).
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Ravi Mendis 294.1 31 === Can WebObjects be Programmed In Scala? ===
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Ravi Mendis 288.1 33 Yes. It is very simple.
Ravi Mendis 449.1 34 Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
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Ravi Mendis 453.1 36 However, tool support is a weak point. You should use Eclipse 3.6 with bundle-less WO builds.  If your Application class is in Scala then you will have to create an Eclipse launch configuration manually. One weird thing is that once you add the Scala nature to a WO project WOD completion will stop working - this is unfortunate. Also the [[Scala plugin>>http://www.scala-ide.org]] is rather slow and still very buggy.
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Ravi Mendis 294.1 38 = WebObjects In Scala =
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Ravi Mendis 294.1 40 The following highlights some of the differences between Java and Scala in WebObjects:
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Ravi Mendis 294.1 42 == EOs in Scala ==
43
Ravi Mendis 435.1 44 === Thread-Safe Shared Vars ===
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John Huss 437.1 46 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. Is this true?  I don't think Scala "object" instances (with the object keyword) are guaranteed to be thread-safe; they are just singletons
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Ravi Mendis 435.1 48 So you don't have to worry about synchronizing access to shared mutable fields in a concurrent application.
49
Ravi Mendis 359.1 50 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 52 Java:
53
Ravi Mendis 393.1 54 {{code value="java"}}
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Ravi Mendis 369.1 56 public class _Talent extends EOGenericRecord {
Ravi Mendis 294.1 57 public static final String ENTITY_NAME = "Talent";
58
59 {{/code}}
60
Ravi Mendis 355.1 61 Scala:
Ravi Mendis 294.1 62
63 {{code}}
64
Ravi Mendis 369.1 65 object Talent extends EOGenericRecord {
Ravi Mendis 294.1 66 val ENTITY_NAME = "Talent"
67
68 {{/code}}
69
Ravi Mendis 435.1 70 This value will be accessed exactly the same way in both languages:
71
72 {{code}}
73
74 Talent.ENTITY_NAME
75
76 {{/code}}
77
Ravi Mendis 318.1 78 ==== Compacted imports ====
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Ravi Mendis 318.1 80 Two lines in Java are compacted into one in Scala.
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Ravi Mendis 294.1 82 In Java:
83
Ravi Mendis 393.1 84 {{code value="java"}}
Ravi Mendis 294.1 85
86 import com.webobjects.eocontrol.EOGenericRecord;
87 import com.webobjects.eocontrol.EORelationshipManipulation;
88
89 {{/code}}
90
91 In Scala:
92
93 {{code}}
94
95 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
96
97 {{/code}}
98
99 == WOComponents in Scala ==
100
101 ==== Compact Constructors ====
102
103 Scala allows for simpler use of multi-valued constructors than Java.
104
105 In Java:
106
Ravi Mendis 393.1 107 {{code value="java"}}
Ravi Mendis 294.1 108
109 public class MenuHeader extends WOComponent {
110
111 public MenuHeader(WOContext aContext) {
112 super(aContext);
113 }
114
115 {{/code}}
116
117 In Scala:
118
119 {{code}}
120
Ravi Mendis 312.1 121 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
Ravi Mendis 294.1 122
123 {{/code}}
124
125 ==== Simplified Exception Handling ====
126
127 Scala doesn't force you to catch exceptions unlike in Java.
Ravi Mendis 431.1 128 In addition, the syntax employs Scala's very powerful **pattern matching** to handle exceptions.
Ravi Mendis 294.1 129
130 In Java:
131
Ravi Mendis 393.1 132 {{code value="java"}}
Ravi Mendis 294.1 133
134 try {
135 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
136 epi.setNextPage(context().page());
137 nextPage = (WOComponent) epi;
138 } catch (IllegalArgumentException e) {
139 ErrorPageInterface epf = D2W.factory().errorPage(session());
140 epf.setMessage(e.toString());
141 epf.setNextPage(context().page());
142 nextPage = (WOComponent) epf;
143 }
144
145 {{/code}}
146
147 In Scala:
148
149 {{code}}
150
151 try {
152 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
153 epi.setNextPage(context.page)
154 nextPage = epi.asInstanceOf[WOComponent]
155 } catch {
156 case e: IllegalArgumentException => {
157 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
158 epf.setMessage(e.toString)
159 epf.setNextPage(context.page)
160 nextPage = epf.asInstanceOf[WOComponent]
161 }
162 }
163
164 {{/code}}
165
Ravi Mendis 435.1 166 ==== Scala Annotations vs. Generated Accessors ====
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Ravi Mendis 385.1 168 An example of accessing variables in WebObjects with the following languages:
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Ravi Mendis 435.1 170 |= |= Objective-C |= Java |= Scala
171 |= getter | ##object name## | ##object.name()## | ##object.name##
172 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
Ravi Mendis 381.1 173
Ravi Mendis 385.1 174 Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
175 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.
176
177 E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
178 These variables can then be accessed via //KVC//.
179
180 {{code}}
181
Ravi Mendis 435.1 182 import scala.reflect.BeanProperty
183
Ravi Mendis 385.1 184 @BeanProperty var username = new String()
185 @BeanProperty var password = new String()
186 @BeanProperty var isAssistantCheckboxVisible = false
187
188 {{/code}}
189
Ravi Mendis 353.1 190 == How to Use Scala Collections with EOF ==
Ravi Mendis 351.1 191
Ravi Mendis 445.1 192 To use the Scala Collections API with an NSArray or NSDictionary you simply need to add an import:
Ravi Mendis 351.1 193
Ravi Mendis 445.1 194 {{code value="java"}}
Ravi Mendis 351.1 195
Ravi Mendis 445.1 196 import scala.collection.JavaConversions._
197
198 {{/code}}
199
200 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.
201
Ravi Mendis 318.1 202 == How to Add Scala to a WO Project ==
Ravi Mendis 308.1 203
204 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
205
Ravi Mendis 435.1 206 {{note}}
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208 This is for Eclipse/WOLips IDE
209
210 {{/note}}
211
Ravi Mendis 290.1 212 == WO Scala Example ==
213
Ravi Mendis 353.1 214 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
Ravi Mendis 292.1 215 All the EO logic and WO components are in Scala.
Ravi Mendis 435.1 216 Only the Application class remains Java.
Ravi Mendis 292.1 217
Ravi Mendis 353.1 218 It is based on the D2W Movies example.
219
Ravi Mendis 290.1 220 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 221
222 === Setup ===
223
Ravi Mendis 435.1 224 1. [[Install the Scala eclipse IDE>>http://www.scala-ide.org/]]
Ravi Mendis 294.1 225 1. Right-click on Application.java and run as a WOApplication (as usual).
226
John Huss 437.1 227 Application can be made into a Scala class as well, but then you will have to create a launcher in Eclipse manually.
228
Ravi Mendis 435.1 229 == EO Templates ==
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231 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
232
Ravi Mendis 435.1 233 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 294.1 234 1. Change the File Names Extension to "scala"
Ravi Mendis 367.1 235 1. In Destination Paths set the Superclass Package (e.g: base)
Ravi Mendis 294.1 236 1. Uncheck Java under Options
Ravi Mendis 385.1 237
238 == How to Build & Deploy a WebObjects Scala Project with Ant ==
239
240 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
Ravi Mendis 393.1 241 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
242 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
243 1. Run from the project directory: ##sudo ant clean install##