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Wiki source code of WebObjects with Scala

Version 437.1 by John Huss on 2010/12/03 16:40
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Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
John Huss 437.1 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.
Ravi Mendis 431.1 4 In this day and age of multi-core processors, concurrent computing can't be ignored.
Ravi Mendis 195.1 5
John Huss 437.1 6 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.
Ravi Mendis 431.1 7 Some of these may not be unfamiliar to Objective-C or WebObjects developers.
Ravi Mendis 294.1 8
Ravi Mendis 431.1 9 Here's a quick summary:
10
Ravi Mendis 435.1 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 294.1 18
19 Other notable features include:
20
Ravi Mendis 435.1 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
John Huss 437.1 27 Scala can help you to write thread-safe code.
28 It has concurrency that is built-in to the standard library, primarily via Actors.
Ravi Mendis 195.1 29
Ravi Mendis 435.1 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 318.1 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 318.1 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 435.1 43 === Thread-Safe Shared Vars ===
Ravi Mendis 294.1 44
John Huss 437.1 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. Is this true?  I don't think Scala "object" instances (with the object keyword) are guaranteed to be thread-safe; they are just singletons
Ravi Mendis 294.1 46
Ravi Mendis 435.1 47 So you don't have to worry about synchronizing access to shared mutable fields in a concurrent application.
48
Ravi Mendis 359.1 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 294.1 50
Ravi Mendis 355.1 51 Java:
52
Ravi Mendis 393.1 53 {{code value="java"}}
Ravi Mendis 308.1 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 355.1 60 Scala:
Ravi Mendis 294.1 61
62 {{code}}
63
Ravi Mendis 369.1 64 object Talent extends EOGenericRecord {
Ravi Mendis 294.1 65 val ENTITY_NAME = "Talent"
66
67 {{/code}}
68
Ravi Mendis 435.1 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 318.1 79 Two lines in Java are compacted into one in Scala.
Ravi Mendis 308.1 80
Ravi Mendis 294.1 81 In Java:
82
Ravi Mendis 393.1 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 393.1 106 {{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 431.1 127 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 393.1 131 {{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 435.1 165 ==== Scala Annotations vs. Generated Accessors ====
Ravi Mendis 381.1 166
Ravi Mendis 385.1 167 An example of accessing variables in WebObjects with the following languages:
Ravi Mendis 381.1 168
Ravi Mendis 435.1 169 |= |= 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 381.1 172
Ravi Mendis 385.1 173 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
Ravi Mendis 435.1 181 import scala.reflect.BeanProperty
182
Ravi Mendis 385.1 183 @BeanProperty var username = new String()
184 @BeanProperty var password = new String()
185 @BeanProperty var isAssistantCheckboxVisible = false
186
187 {{/code}}
188
Ravi Mendis 353.1 189 == How to Use Scala Collections with EOF ==
Ravi Mendis 351.1 190
John Huss 437.1 191 To use the Scala Collections API with an NSArray or NSDictionary you simply need to add an import:import scala.collection.JavaConversions.
Ravi Mendis 351.1 192
John Huss 437.1 193 Then you can 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.
Ravi Mendis 351.1 194
Ravi Mendis 318.1 195 == How to Add Scala to a WO Project ==
Ravi Mendis 308.1 196
197 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
198
Ravi Mendis 435.1 199 {{note}}
Ravi Mendis 318.1 200
201 This is for Eclipse/WOLips IDE
202
203 {{/note}}
204
Ravi Mendis 290.1 205 == WO Scala Example ==
206
Ravi Mendis 353.1 207 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
Ravi Mendis 292.1 208 All the EO logic and WO components are in Scala.
Ravi Mendis 435.1 209 Only the Application class remains Java.
Ravi Mendis 292.1 210
Ravi Mendis 353.1 211 It is based on the D2W Movies example.
212
Ravi Mendis 290.1 213 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 214
215 === Setup ===
216
Ravi Mendis 435.1 217 1. [[Install the Scala eclipse IDE>>http://www.scala-ide.org/]]
Ravi Mendis 294.1 218 1. Right-click on Application.java and run as a WOApplication (as usual).
219
John Huss 437.1 220 Application can be made into a Scala class as well, but then you will have to create a launcher in Eclipse manually.
221
Ravi Mendis 435.1 222 == EO Templates ==
Ravi Mendis 294.1 223
224 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
225
Ravi Mendis 435.1 226 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 294.1 227 1. Change the File Names Extension to "scala"
Ravi Mendis 367.1 228 1. In Destination Paths set the Superclass Package (e.g: base)
Ravi Mendis 294.1 229 1. Uncheck Java under Options
Ravi Mendis 385.1 230
231 == How to Build & Deploy a WebObjects Scala Project with Ant ==
232
233 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
Ravi Mendis 393.1 234 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
235 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
236 1. Run from the project directory: ##sudo ant clean install##