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Wiki source code of WebObjects with Scala

Version 516.1 by Ravi Mendis on 2009/09/30 18:01
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Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 515.1 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 515.1 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 515.1 8 |= |= Objective-C |= Java |= Scala
9 |= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | Yes
10 |= Closures | Blocks (//Extension//) | No | Yes
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 513.1 15
Ravi Mendis 294.1 16 Other notable features include:
17
Ravi Mendis 515.1 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 515.1 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 515.1 26 With Web 2.0, building concurrent WebObjects applications is a must.
27 Developing and maintaining a concurrent or multi-threaded WebObjects application can be challenging.
Ravi Mendis 195.1 28
Ravi Mendis 515.1 29 Scala offers concurrency that is (effectively) built-in to the language and is inherently thread-safe.
Ravi Mendis 513.1 30
Ravi Mendis 515.1 31 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.
32
33 In addition it may offer new solutions for concurrency in WebObjects and EOF.
34
Ravi Mendis 294.1 35 === Can WebObjects be Programmed In Scala? ===
Ravi Mendis 195.1 36
Ravi Mendis 288.1 37 Yes. It is very simple.
Ravi Mendis 513.1 38 Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
Ravi Mendis 195.1 39
Ravi Mendis 294.1 40 = WebObjects In Scala =
Ravi Mendis 195.1 41
Ravi Mendis 294.1 42 The following highlights some of the differences between Java and Scala in WebObjects:
Ravi Mendis 195.1 43
Ravi Mendis 294.1 44 == EOs in Scala ==
45
Ravi Mendis 515.1 46 === Thread-Safe Shared Vars ===
Ravi Mendis 294.1 47
Ravi Mendis 515.1 48 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.
49 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 50
Ravi Mendis 515.1 51 In Java:
Ravi Mendis 435.1 52
Ravi Mendis 515.1 53 {{code}}
Ravi Mendis 294.1 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 515.1 60 In Scala:
Ravi Mendis 294.1 61
62 {{code}}
63
Ravi Mendis 515.1 64 object _Talent extends EOGenericRecord {
Ravi Mendis 294.1 65 val ENTITY_NAME = "Talent"
66
67 {{/code}}
68
Ravi Mendis 318.1 69 ==== Compacted imports ====
Ravi Mendis 308.1 70
Ravi Mendis 513.1 71 Two lines in Java are compacted into one in Scala.
72
Ravi Mendis 294.1 73 In Java:
74
Ravi Mendis 515.1 75 {{code}}
Ravi Mendis 294.1 76
77 import com.webobjects.eocontrol.EOGenericRecord;
78 import com.webobjects.eocontrol.EORelationshipManipulation;
79
80 {{/code}}
81
82 In Scala:
83
84 {{code}}
85
86 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
87
88 {{/code}}
89
90 == WOComponents in Scala ==
91
92 ==== Compact Constructors ====
93
94 Scala allows for simpler use of multi-valued constructors than Java.
95
96 In Java:
97
Ravi Mendis 515.1 98 {{code}}
Ravi Mendis 294.1 99
100 public class MenuHeader extends WOComponent {
101
102 public MenuHeader(WOContext aContext) {
103 super(aContext);
104 }
105
106 {{/code}}
107
108 In Scala:
109
110 {{code}}
111
Ravi Mendis 312.1 112 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
Ravi Mendis 294.1 113
114 {{/code}}
115
116 ==== Simplified Exception Handling ====
117
118 Scala doesn't force you to catch exceptions unlike in Java.
Ravi Mendis 515.1 119 In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
Ravi Mendis 294.1 120
121 In Java:
122
Ravi Mendis 515.1 123 {{code}}
Ravi Mendis 294.1 124
125 try {
126 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
127 epi.setNextPage(context().page());
128 nextPage = (WOComponent) epi;
129 } catch (IllegalArgumentException e) {
130 ErrorPageInterface epf = D2W.factory().errorPage(session());
131 epf.setMessage(e.toString());
132 epf.setNextPage(context().page());
133 nextPage = (WOComponent) epf;
134 }
135
136 {{/code}}
137
138 In Scala:
139
140 {{code}}
141
142 try {
143 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
144 epi.setNextPage(context.page)
145 nextPage = epi.asInstanceOf[WOComponent]
146 } catch {
147 case e: IllegalArgumentException => {
148 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
149 epf.setMessage(e.toString)
150 epf.setNextPage(context.page)
151 nextPage = epf.asInstanceOf[WOComponent]
152 }
153 }
154
155 {{/code}}
156
Ravi Mendis 513.1 157 == How to Add Scala to a WO Project ==
Ravi Mendis 308.1 158
159 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
160
Ravi Mendis 515.1 161 {{note title="Note"}}
Ravi Mendis 513.1 162
163 This is for Eclipse/WOLips IDE
164
165 {{/note}}
166
Ravi Mendis 290.1 167 == WO Scala Example ==
168
Ravi Mendis 515.1 169 The following example is a mixed Java/Scala version of the WO Movies D2W app.
Ravi Mendis 292.1 170 All the EO logic and WO components are in Scala.
Ravi Mendis 513.1 171 Only the Application class is Java.
Ravi Mendis 292.1 172
Ravi Mendis 290.1 173 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 174
175 === Setup ===
176
Ravi Mendis 515.1 177 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
178 1. Install and run the OpenBase OBMovies database.
Ravi Mendis 294.1 179 1. Right-click on Application.java and run as a WOApplication (as usual).
180
Ravi Mendis 515.1 181 ==== EO Templates ====
Ravi Mendis 294.1 182
Ravi Mendis 515.1 183 See: [[Scala templates>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]]
184
Ravi Mendis 294.1 185 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
186
187 1. Change the File Names Extension to "scala"
188 1. Uncheck Java under Options