Skip to Content

Wiki source code of WebObjects with Scala

Version 319.1 by Ravi Mendis on 2010/01/20 01:23
Hide last authors
Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 318.1 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.
Ravi Mendis 195.1 5
Ravi Mendis 318.1 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 318.1 9 Here's a quick summary:
Ravi Mendis 294.1 10
Ravi Mendis 318.1 11 |= |= Objective-C |= Java |= Scala
12 |= 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
Ravi Mendis 294.1 19 Other notable features include:
20
Ravi Mendis 318.1 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
Ravi Mendis 318.1 27 Scala is inherently thread-safe.
28 It has concurrency that is effectively built-in to the language.
Ravi Mendis 195.1 29
Ravi Mendis 318.1 30 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).
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 318.1 43 === Thread-Safe Shared Vars ===
Ravi Mendis 294.1 44
Ravi Mendis 318.1 45 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.
46 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 47
Ravi Mendis 308.1 48 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 49
Ravi Mendis 308.1 50 Java:
51
52 {{code value="java"}}
53
Ravi Mendis 318.1 54 public class _Talent extends EOGenericRecord {
Ravi Mendis 294.1 55 public static final String ENTITY_NAME = "Talent";
56
57 {{/code}}
58
Ravi Mendis 308.1 59 Scala:
Ravi Mendis 294.1 60
61 {{code}}
62
Ravi Mendis 318.1 63 object Talent extends EOGenericRecord {
Ravi Mendis 294.1 64 val ENTITY_NAME = "Talent"
65
66 {{/code}}
67
Ravi Mendis 318.1 68 ==== Compacted imports ====
Ravi Mendis 308.1 69
Ravi Mendis 318.1 70 Two lines in Java are compacted into one in Scala.
Ravi Mendis 308.1 71
Ravi Mendis 294.1 72 In Java:
73
Ravi Mendis 308.1 74 {{code value="java"}}
Ravi Mendis 294.1 75
76 import com.webobjects.eocontrol.EOGenericRecord;
77 import com.webobjects.eocontrol.EORelationshipManipulation;
78
79 {{/code}}
80
81 In Scala:
82
83 {{code}}
84
85 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
86
87 {{/code}}
88
89 == WOComponents in Scala ==
90
91 ==== Compact Constructors ====
92
93 Scala allows for simpler use of multi-valued constructors than Java.
94
95 In Java:
96
Ravi Mendis 308.1 97 {{code value="java"}}
Ravi Mendis 294.1 98
99 public class MenuHeader extends WOComponent {
100
101 public MenuHeader(WOContext aContext) {
102 super(aContext);
103 }
104
105 {{/code}}
106
107 In Scala:
108
109 {{code}}
110
Ravi Mendis 312.1 111 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
Ravi Mendis 294.1 112
113 {{/code}}
114
115 ==== Simplified Exception Handling ====
116
117 Scala doesn't force you to catch exceptions unlike in Java.
Ravi Mendis 308.1 118 In addition, the syntax employs Scala's very powerful **pattern matching** to handle exceptions.
Ravi Mendis 294.1 119
120 In Java:
121
Ravi Mendis 308.1 122 {{code value="java"}}
Ravi Mendis 294.1 123
124 try {
125 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
126 epi.setNextPage(context().page());
127 nextPage = (WOComponent) epi;
128 } catch (IllegalArgumentException e) {
129 ErrorPageInterface epf = D2W.factory().errorPage(session());
130 epf.setMessage(e.toString());
131 epf.setNextPage(context().page());
132 nextPage = (WOComponent) epf;
133 }
134
135 {{/code}}
136
137 In Scala:
138
139 {{code}}
140
141 try {
142 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
143 epi.setNextPage(context.page)
144 nextPage = epi.asInstanceOf[WOComponent]
145 } catch {
146 case e: IllegalArgumentException => {
147 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
148 epf.setMessage(e.toString)
149 epf.setNextPage(context.page)
150 nextPage = epf.asInstanceOf[WOComponent]
151 }
152 }
153
154 {{/code}}
155
Ravi Mendis 318.1 156 ==== Scala Annotations vs. Generic Accessors ====
Ravi Mendis 294.1 157
Ravi Mendis 318.1 158 An example of accessing variables in WebObjects with the following languages:
Ravi Mendis 294.1 159
Ravi Mendis 318.1 160 |= |= Objective-C |= Java |= Scala
161 |= getter | ##object name## | ##object.name()## | ##object.name##
162 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
Ravi Mendis 195.1 163
Ravi Mendis 308.1 164 Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
165 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.
Ravi Mendis 195.1 166
Ravi Mendis 308.1 167 E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
168 These variables can then be accessed via //KVC//.
Ravi Mendis 290.1 169
Ravi Mendis 308.1 170 {{code}}
171
172 @BeanProperty var username = new String()
173 @BeanProperty var password = new String()
174 @BeanProperty var isAssistantCheckboxVisible = false
175
176 {{/code}}
177
178 == How to Use Scala Collections with EOF ==
179
Ravi Mendis 318.1 180 One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map##, ##Seq## and ##Set##.
181 Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
Ravi Mendis 308.1 182
Ravi Mendis 318.1 183 But one may modify the EO templates to produce API such as:
Ravi Mendis 308.1 184
Ravi Mendis 318.1 185 {{code}}
Ravi Mendis 308.1 186
Ravi Mendis 318.1 187 def movies: NSArray[EOGenericRecord] = {
188 storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[EOGenericRecord]]
189 }
190
191 def moviesList: List[EOGenericRecord] = {
192 movies.objects.toList
193 }
194
Ravi Mendis 308.1 195 {{/code}}
196
Ravi Mendis 318.1 197 == How to Add Scala to a WO Project ==
Ravi Mendis 308.1 198
199 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
200
Ravi Mendis 318.1 201 {{note title="Note"}}
202
203 This is for Eclipse/WOLips IDE
204
205 {{/note}}
206
Ravi Mendis 290.1 207 == WO Scala Example ==
208
Ravi Mendis 308.1 209 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
Ravi Mendis 292.1 210 All the EO logic and WO components are in Scala.
Ravi Mendis 318.1 211 Only the Application class is Java.
Ravi Mendis 292.1 212
Ravi Mendis 308.1 213 It is based on the D2W Movies example.
214
Ravi Mendis 290.1 215 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 216
217 === Setup ===
218
Ravi Mendis 318.1 219 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
220 1. Install and start the OpenBase OBMovies database.
Ravi Mendis 294.1 221 1. Right-click on Application.java and run as a WOApplication (as usual).
222
Ravi Mendis 318.1 223 ==== EO Templates ====
Ravi Mendis 294.1 224
225 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
226
Ravi Mendis 318.1 227 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 294.1 228 1. Change the File Names Extension to "scala"
Ravi Mendis 308.1 229 1. In Destination Paths set the Superclass Package (e.g: base)
Ravi Mendis 294.1 230 1. Uncheck Java under Options
Ravi Mendis 308.1 231
232 == How to Build & Deploy a WebObjects Scala Project with Ant ==
233
234 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
235 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
236 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
237 1. Run from the project directory: ##sudo ant clean install##