Skip to Content

Wiki source code of WebObjects with Scala

Version 373.1 by Ravi Mendis on 2009/12/08 19:09
Hide last authors
Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 363.1 3 Scala is a modern language not unlike Groovy.
4 It is said to be more powerful (and faster) than Groovy or Ruby which has been the reason for its adoption at sites like Twitter.
Ravi Mendis 195.1 5
Ravi Mendis 363.1 6 Many of its features and paradigms favor multi-threading and concurrency. Some of these may not be unfamiliar to Objective-C and WebObjects developers. Here's a summary:
Ravi Mendis 294.1 7
Ravi Mendis 338.1 8 |= |= Objective-C |= Java |= Scala
9 |= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | Yes
Ravi Mendis 349.1 10 |= Closures | Blocks (//Extension//) | No | Anonymous Functions
Ravi Mendis 338.1 11 |= Static variables | Yes | Yes | No
12 |= Static methods/functions | Yes | Yes | No
13 |= Concurrency | [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//)| //Threads// |[[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
14 |= |= Weakly Typed |=--Strongly Typed--|= Strongly Typed
Ravi Mendis 294.1 15
16 Other notable features include:
17
Ravi Mendis 338.1 18 |= |= Objective-C |= Java |= Scala
19 |= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
20 |= Class composition | Categories | Interfaces | Traits
Ravi Mendis 294.1 21
Ravi Mendis 338.1 22 A fuller description of Scala can be found [[here>>http://en.wikipedia.org/wiki/Scala_(programming_language)]].
23
Ravi Mendis 195.1 24 === Why Use Scala? ===
25
Ravi Mendis 363.1 26 With Web 2.0, building concurrent WebObjects applications is a must.
Ravi Mendis 338.1 27 Developing and maintaining a concurrent or multi-threaded WebObjects application can be challenging.
Ravi Mendis 195.1 28
Ravi Mendis 363.1 29 Scala offers concurrency that is (effectively) built-in to the language and is inherently thread-safe.
30 In other words, developing Ajax (i.e asynchronous communication) with WO will require concurrent request handling and thread-safe code, for which Scala is a better choice than Java.
Ravi Mendis 318.1 31
Ravi Mendis 363.1 32 In addition it may offer new solutions for concurrency in WebObjects and EOF.
Ravi Mendis 338.1 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 363.1 54 {{code}}
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 363.1 76 {{code}}
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 363.1 99 {{code}}
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 338.1 120 In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
Ravi Mendis 294.1 121
122 In Java:
123
Ravi Mendis 363.1 124 {{code}}
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 369.1 158 ==== Scala Annotations vs. Generic Accessors ====
159
Ravi Mendis 373.1 160 An example of accessing variables in WebObjects with the following languages:
Ravi Mendis 369.1 161
Ravi Mendis 371.1 162 |= |= Objective-C |= Java |= Scala
Ravi Mendis 373.1 163 |= getter | ##object name## | ##object.name()## | ##object.name##
Ravi Mendis 371.1 164 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
Ravi Mendis 369.1 165
Ravi Mendis 373.1 166 Of course in Java, we may generate EO 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
175 var username: String = ""
176 @BeanProperty
177 var password: String = ""
178 @BeanProperty
179 var isAssistantCheckboxVisible: Boolean = false
180
181 {{/code}}
182
Ravi Mendis 353.1 183 == How to Use Scala Collections with EOF ==
Ravi Mendis 351.1 184
185 One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map##, ##Seq## and ##Set##.
186 Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
187
188 But one may modify the EO templates to produce API such as:
189
190 {{code}}
191
192 def movies: NSArray[EOGenericRecord] = {
193 storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[EOGenericRecord]]
194 }
195
196 def moviesList: List[EOGenericRecord] = {
197 movies.objects.toList
198 }
199
200 {{/code}}
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 338.1 206 {{note title="Note"}}
Ravi Mendis 318.1 207
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 318.1 216 Only the Application class is 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 318.1 224 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
Ravi Mendis 353.1 225 1. Install and start the OpenBase OBMovies database.
Ravi Mendis 294.1 226 1. Right-click on Application.java and run as a WOApplication (as usual).
227
Ravi Mendis 318.1 228 ==== EO Templates ====
Ravi Mendis 294.1 229
230 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
231
Ravi Mendis 357.1 232 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 294.1 233 1. Change the File Names Extension to "scala"
Ravi Mendis 367.1 234 1. In Destination Paths set the Superclass Package (e.g: base)
Ravi Mendis 294.1 235 1. Uncheck Java under Options