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Wiki source code of WebObjects with Scala

Version 432.1 by Ravi Mendis on 2010/01/18 00:11
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Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 431.1 3 Scala 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 431.1 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 431.1 9 Here's a quick summary:
10
Ravi Mendis 338.1 11 |= |= Objective-C |= Java |= Scala
12 |= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | Yes
Ravi Mendis 349.1 13 |= Closures | Blocks (//Extension//) | No | Anonymous Functions
Ravi Mendis 338.1 14 |= Static variables | Yes | Yes | No
15 |= Static methods/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 338.1 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 338.1 25 A fuller description of Scala can be found [[here>>http://en.wikipedia.org/wiki/Scala_(programming_language)]].
26
Ravi Mendis 195.1 27 === Why Use Scala? ===
28
Ravi Mendis 431.1 29 Scala is inherently thread-safe.
30 It has concurrency that is effectively built-in to the language.
Ravi Mendis 195.1 31
Ravi Mendis 431.1 32 So for WebObjects developers, Scala offers itself as a powerful, safe and easy-to-use solution for concurrent applications. (In other words, Scala Actors can be used for problems that would have normally required threads).
Ravi Mendis 318.1 33
Ravi Mendis 294.1 34 === Can WebObjects be Programmed In Scala? ===
Ravi Mendis 195.1 35
Ravi Mendis 288.1 36 Yes. It is very simple.
Ravi Mendis 318.1 37 Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
Ravi Mendis 195.1 38
Ravi Mendis 294.1 39 = WebObjects In Scala =
Ravi Mendis 195.1 40
Ravi Mendis 294.1 41 The following highlights some of the differences between Java and Scala in WebObjects:
Ravi Mendis 195.1 42
Ravi Mendis 294.1 43 == EOs in Scala ==
44
Ravi Mendis 318.1 45 === Thread-Safe Shared Vars ===
Ravi Mendis 294.1 46
Ravi Mendis 318.1 47 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.
48 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 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.
Ravi Mendis 294.1 51
Ravi Mendis 355.1 52 Java:
53
Ravi Mendis 393.1 54 {{code value="java"}}
Ravi Mendis 308.1 55
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 318.1 70 ==== Compacted imports ====
Ravi Mendis 308.1 71
Ravi Mendis 318.1 72 Two lines in Java are compacted into one in Scala.
Ravi Mendis 308.1 73
Ravi Mendis 294.1 74 In Java:
75
Ravi Mendis 393.1 76 {{code value="java"}}
Ravi Mendis 294.1 77
78 import com.webobjects.eocontrol.EOGenericRecord;
79 import com.webobjects.eocontrol.EORelationshipManipulation;
80
81 {{/code}}
82
83 In Scala:
84
85 {{code}}
86
87 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
88
89 {{/code}}
90
91 == WOComponents in Scala ==
92
93 ==== Compact Constructors ====
94
95 Scala allows for simpler use of multi-valued constructors than Java.
96
97 In Java:
98
Ravi Mendis 393.1 99 {{code value="java"}}
Ravi Mendis 294.1 100
101 public class MenuHeader extends WOComponent {
102
103 public MenuHeader(WOContext aContext) {
104 super(aContext);
105 }
106
107 {{/code}}
108
109 In Scala:
110
111 {{code}}
112
Ravi Mendis 312.1 113 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
Ravi Mendis 294.1 114
115 {{/code}}
116
117 ==== Simplified Exception Handling ====
118
119 Scala doesn't force you to catch exceptions unlike in Java.
Ravi Mendis 431.1 120 In addition, the syntax employs Scala's very powerful **pattern matching** to handle exceptions.
Ravi Mendis 294.1 121
122 In Java:
123
Ravi Mendis 393.1 124 {{code value="java"}}
Ravi Mendis 294.1 125
126 try {
127 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
128 epi.setNextPage(context().page());
129 nextPage = (WOComponent) epi;
130 } catch (IllegalArgumentException e) {
131 ErrorPageInterface epf = D2W.factory().errorPage(session());
132 epf.setMessage(e.toString());
133 epf.setNextPage(context().page());
134 nextPage = (WOComponent) epf;
135 }
136
137 {{/code}}
138
139 In Scala:
140
141 {{code}}
142
143 try {
144 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
145 epi.setNextPage(context.page)
146 nextPage = epi.asInstanceOf[WOComponent]
147 } catch {
148 case e: IllegalArgumentException => {
149 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
150 epf.setMessage(e.toString)
151 epf.setNextPage(context.page)
152 nextPage = epf.asInstanceOf[WOComponent]
153 }
154 }
155
156 {{/code}}
157
Ravi Mendis 381.1 158 ==== Scala Annotations vs. Generic Accessors ====
159
Ravi Mendis 385.1 160 An example of accessing variables in WebObjects with the following languages:
Ravi Mendis 381.1 161
Ravi Mendis 385.1 162 |= |= Objective-C |= Java |= Scala
163 |= getter | ##object name## | ##object.name()## | ##object.name##
164 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
Ravi Mendis 381.1 165
Ravi Mendis 385.1 166 Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
167 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.
168
169 E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
170 These variables can then be accessed via //KVC//.
171
172 {{code}}
173
174 @BeanProperty var username = new String()
175 @BeanProperty var password = new String()
176 @BeanProperty var isAssistantCheckboxVisible = false
177
178 {{/code}}
179
Ravi Mendis 353.1 180 == How to Use Scala Collections with EOF ==
Ravi Mendis 351.1 181
182 One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map##, ##Seq## and ##Set##.
183 Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
184
185 But one may modify the EO templates to produce API such as:
186
187 {{code}}
188
189 def movies: NSArray[EOGenericRecord] = {
190 storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[EOGenericRecord]]
191 }
192
193 def moviesList: List[EOGenericRecord] = {
194 movies.objects.toList
195 }
196
197 {{/code}}
198
Ravi Mendis 318.1 199 == How to Add Scala to a WO Project ==
Ravi Mendis 308.1 200
201 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
202
Ravi Mendis 338.1 203 {{note title="Note"}}
Ravi Mendis 318.1 204
205 This is for Eclipse/WOLips IDE
206
207 {{/note}}
208
Ravi Mendis 290.1 209 == WO Scala Example ==
210
Ravi Mendis 353.1 211 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
Ravi Mendis 292.1 212 All the EO logic and WO components are in Scala.
Ravi Mendis 318.1 213 Only the Application class is Java.
Ravi Mendis 292.1 214
Ravi Mendis 353.1 215 It is based on the D2W Movies example.
216
Ravi Mendis 290.1 217 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 218
219 === Setup ===
220
Ravi Mendis 318.1 221 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
Ravi Mendis 353.1 222 1. Install and start the OpenBase OBMovies database.
Ravi Mendis 294.1 223 1. Right-click on Application.java and run as a WOApplication (as usual).
224
Ravi Mendis 318.1 225 ==== EO Templates ====
Ravi Mendis 294.1 226
227 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
228
Ravi Mendis 357.1 229 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 294.1 230 1. Change the File Names Extension to "scala"
Ravi Mendis 367.1 231 1. In Destination Paths set the Superclass Package (e.g: base)
Ravi Mendis 294.1 232 1. Uncheck Java under Options
Ravi Mendis 385.1 233
234 == How to Build & Deploy a WebObjects Scala Project with Ant ==
235
236 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
Ravi Mendis 393.1 237 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
238 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
239 1. Run from the project directory: ##sudo ant clean install##