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Wiki source code of WebObjects with Scala

Version 348.1 by Ravi Mendis on 2009/10/12 21:31
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Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
Ravi Mendis 338.1 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 338.1 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 347.1 10 |= Closures | Blocks (//Extension//) | No | Anon. 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 338.1 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 338.1 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 338.1 32 In addition it may offer new solutions for concurrency in WebObjects and EOF.
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 339.1 50 In Java:
Ravi Mendis 294.1 51
Ravi Mendis 338.1 52 {{code}}
Ravi Mendis 308.1 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 339.1 59 In Scala:
Ravi Mendis 294.1 60
61 {{code}}
62
Ravi Mendis 339.1 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 338.1 74 {{code}}
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 338.1 97 {{code}}
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 338.1 118 In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
Ravi Mendis 294.1 119
120 In Java:
121
Ravi Mendis 338.1 122 {{code}}
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 == How to Add Scala to a WO Project ==
Ravi Mendis 308.1 157
158 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
159
Ravi Mendis 338.1 160 {{note title="Note"}}
Ravi Mendis 318.1 161
162 This is for Eclipse/WOLips IDE
163
164 {{/note}}
165
Ravi Mendis 290.1 166 == WO Scala Example ==
167
Ravi Mendis 343.1 168 The following example is a mixed Java/Scala version of the WO Movies D2W app.
Ravi Mendis 292.1 169 All the EO logic and WO components are in Scala.
Ravi Mendis 318.1 170 Only the Application class is Java.
Ravi Mendis 292.1 171
Ravi Mendis 290.1 172 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 173
174 === Setup ===
175
Ravi Mendis 318.1 176 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
Ravi Mendis 339.1 177 1. Install and run the OpenBase OBMovies database.
Ravi Mendis 294.1 178 1. Right-click on Application.java and run as a WOApplication (as usual).
179
Ravi Mendis 318.1 180 ==== EO Templates ====
Ravi Mendis 294.1 181
Ravi Mendis 339.1 182 See: [[Scala templates>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]]
183
Ravi Mendis 294.1 184 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
185
186 1. Change the File Names Extension to "scala"
187 1. Uncheck Java under Options