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Wiki source code of WebObjects with Scala

Version 314.1 by Ravi Mendis on 2011/05/10 02:06
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Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 314.1 3 [[Scala>>http://www.scala-lang.org/]] is a modern, multi-paradigm JVM language that is most often compared to [[Groovy>>http://en.wikipedia.org/wiki/Groovy_(programming_language)]], [[Clojure>>http://en.wikipedia.org/wiki/Clojure]] or [[Erlang>>http://en.wikipedia.org/wiki/Erlang_(programming_language)]]. Its [[functional language>>http://en.wikipedia.org/wiki/Functional_programming]] foundations and built-in [[Actors>>http://en.wikipedia.org/wiki/Actor_model]] library make it especially attractive for concurrent computing. (Scala is an abbreviation for "scalable" hinting at its design goals).
Ravi Mendis 195.1 4
Ravi Mendis 308.1 5 In this day and age of multi-core processors concurrent computing can not be ignored. Many of the design features of Scala have been chosen with concurrency in mind, some of which may not be unfamiliar to Objective-C or WebObjects developers. Here's a summary:
Ravi Mendis 294.1 6
Ravi Mendis 308.1 7 |= |= Objective-C |= Java |= Scala
8 |= Immutability | Partial - via collections //e.g: NSArray/NSMutableArray// | No | Yes
9 |= Closures | Yes - via Blocks (//Extension//) | No | Yes - via Anonymous Functions
10 |= Static variables | Yes | Yes | No
11 |= Static methods | Yes | Yes | No
12 |= Concurrency | Yes - via [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//) | //Yes - via Threads// | Yes - via [[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
13 |= |= Weakly Typed |= --Strongly Typed-- |= Strongly Typed
Ravi Mendis 294.1 14
15 Other notable features include:
16
Ravi Mendis 308.1 17 |= |= Objective-C |= Java |= Scala
18 |= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
19 |= Class composition | Yes - via Categories | Yes - via Interfaces | Yes - via [[Traits>>http://en.wikipedia.org/wiki/Trait_(computer_science)]]
Ravi Mendis 294.1 20
Ravi Mendis 195.1 21 === Why Use Scala? ===
22
Ravi Mendis 308.1 23 For WebObjects developers, Scala offers itself as a powerful, safe and easy-to-use solution for [[concurrent computing>>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 25 === Can WebObjects be Programmed In Scala? ===
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Ravi Mendis 288.1 27 Yes. It is very simple.
Ravi Mendis 308.1 28 By virtue of being a JVM-language, Scala compiles to java bytecode.
Ravi Mendis 195.1 29
Ravi Mendis 308.1 30 Furthermore, being a multi-paradigm language grants Scala easy WebObjects-interoperability.
31
32 ===== Caveats =====
33
34 Legacy tool support is often cited as a weak point. The [[Eclipse Scala plugin>>http://www.scala-ide.org]] has been found to be slow at times and sometimes buggy.
35
Ravi Mendis 294.1 36 = WebObjects In Scala =
Ravi Mendis 195.1 37
Ravi Mendis 294.1 38 The following highlights some of the differences between Java and Scala in WebObjects:
Ravi Mendis 195.1 39
Ravi Mendis 294.1 40 == EOs in Scala ==
41
Ravi Mendis 308.1 42 === Thread-Safe Shared Vars ===
Ravi Mendis 294.1 43
Ravi Mendis 308.1 44 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.
Ravi Mendis 294.1 45
Ravi Mendis 308.1 46 You don't have to worry about synchronizing access to shared mutable fields in a concurrent application.
47 (This is not however true when for example you have a ##val## declared as a ##NSMutableArray##. You will still have to synchronize when adding to or removing from this mutable field).
Ravi Mendis 294.1 48
Ravi Mendis 308.1 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 308.1 51 Java:
52
53 {{code value="java"}}
54
55 public class Talent extends EOGenericRecord {
Ravi Mendis 294.1 56 public static final String ENTITY_NAME = "Talent";
Ravi Mendis 314.1 57 }
Ravi Mendis 294.1 58
59 {{/code}}
60
Ravi Mendis 308.1 61 Scala:
Ravi Mendis 294.1 62
63 {{code}}
64
Ravi Mendis 308.1 65 object Talent {
Ravi Mendis 294.1 66 val ENTITY_NAME = "Talent"
Ravi Mendis 314.1 67 }
Ravi Mendis 294.1 68
69 {{/code}}
70
Ravi Mendis 308.1 71 This value will be accessed exactly the same way in both languages:
72
73 {{code}}
74
75 Talent.ENTITY_NAME
76
77 {{/code}}
78
Ravi Mendis 294.1 79 ==== Compacted imports ====
80
81 In Java:
82
Ravi Mendis 308.1 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 308.1 106 {{code value="java"}}
Ravi Mendis 294.1 107
108 public class MenuHeader extends WOComponent {
109
110 public MenuHeader(WOContext aContext) {
111 super(aContext);
112 }
Ravi Mendis 314.1 113 }
Ravi Mendis 294.1 114
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 308.1 128 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 308.1 132 {{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 308.1 166 ==== Scala Annotations vs. Generated Accessors ====
Ravi Mendis 294.1 167
Ravi Mendis 308.1 168 Here's an example of accessing variables in the following languages:
Ravi Mendis 294.1 169
Ravi Mendis 308.1 170 |= |= 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 195.1 173
Ravi Mendis 308.1 174 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.
Ravi Mendis 195.1 176
Ravi Mendis 308.1 177 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//.
Ravi Mendis 290.1 179
Ravi Mendis 308.1 180 {{code}}
181
182 import scala.reflect.BeanProperty
183
184 @BeanProperty var username = new String()
185 @BeanProperty var password = new String()
186 @BeanProperty var isAssistantCheckboxVisible = false
187
188 {{/code}}
189
190 == How to Use Scala Collections with EOF ==
191
192 To use the Scala Collections API with an NSArray or NSDictionary you simply need to add an import:
193
194 {{code value="java"}}
195
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.
201
202 == How to Add Scala to a WO Project (in Eclipse) ==
203
204 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
205
Ravi Mendis 290.1 206 == WO Scala Example ==
207
Ravi Mendis 308.1 208 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
Ravi Mendis 292.1 209 All the EO logic and WO components are in Scala.
Ravi Mendis 308.1 210 Only the Application class remains Java.
Ravi Mendis 292.1 211
Ravi Mendis 308.1 212 It is based on the D2W Movies example.
213
Ravi Mendis 290.1 214 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 215
216 === Setup ===
217
Ravi Mendis 310.1 218 1. [[Install the Scala eclipse IDE>>http://download.scala-ide.org/]]
Ravi Mendis 294.1 219 1. Right-click on Application.java and run as a WOApplication (as usual).
220
Ravi Mendis 308.1 221 {{note}}
Ravi Mendis 294.1 222
Ravi Mendis 308.1 223 Application can be made into a Scala class as well, but then you will have to create a launcher in Eclipse manually.
Ravi Mendis 294.1 224
Ravi Mendis 308.1 225 {{/note}}
226
227 == EO Templates ==
228
Ravi Mendis 294.1 229 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
230
Ravi Mendis 308.1 231 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 294.1 232 1. Change the File Names Extension to "scala"
Ravi Mendis 308.1 233 1. In Destination Paths set the Superclass Package (e.g: base)
Ravi Mendis 294.1 234 1. Uncheck Java under Options
Ravi Mendis 308.1 235
236 == How to Build & Deploy a WebObjects Scala Project with Ant ==
237
238 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
239 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
240 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
241 1. Run from the project directory: ##sudo ant clean install##