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Wiki source code of WebObjects with Scala

Version 296.1 by Ravi Mendis on 2009/09/16 23:19
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Ravi Mendis 21.1 1 === What is Scala? ===
Ravi Mendis 195.1 2
3 Scala is a modern language not unlike Groovy.
Ravi Mendis 294.1 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 294.1 6 Many of its features and paradigms favor multi-threading and concurrency. These may not be unfamiliar to Objective-C and WebObjects developers. Here's a summary:
7
8 |= |= Objective-C |= Java |= Scala
9 |= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | //All datatypes//
10 |= Closures | Blocks (//Extension//) | No | //Built-in//
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
15
16 Other notable features include:
17
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
21
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 294.1 26 With Web 2.0, building concurrent WebObjects applications is a must.
Ravi Mendis 195.1 27 Developing and maintaining a concurrent or multi-threaded WebObjects application can be challenging.
28
Ravi Mendis 294.1 29 Scala offers concurrency that is (effectively) built-in to the language and is inherently thread-safe.
30 So it may offer new solutions for concurrency in WebObjects.
Ravi Mendis 195.1 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.
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
43 === Thread-Safe Shared Constants and Vars ===
44
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.
47
48 In Java:
49
50 {{code}}
51
52 public class _Talent extends EOGenericRecord {
53 public static final String ENTITY_NAME = "Talent";
54
55 {{/code}}
56
57 In Scala:
58
59 {{code}}
60
61 object _Talent extends EOGenericRecord {
62 val ENTITY_NAME = "Talent"
63
64 {{/code}}
65
66 ==== Compacted imports ====
67
68 Two lines in Java is compacted into one in Scala.
69
70 In Java:
71
72 {{code}}
73
74 import com.webobjects.eocontrol.EOGenericRecord;
75 import com.webobjects.eocontrol.EORelationshipManipulation;
76
77 {{/code}}
78
79 In Scala:
80
81 {{code}}
82
83 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
84
85 {{/code}}
86
87 == WOComponents in Scala ==
88
89 ==== Compact Constructors ====
90
91 Scala allows for simpler use of multi-valued constructors than Java.
92
93 In Java:
94
95 {{code}}
96
97 public class MenuHeader extends WOComponent {
98
99 public MenuHeader(WOContext aContext) {
100 super(aContext);
101 }
102
103 {{/code}}
104
105 In Scala:
106
107 {{code}}
108
109 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
110
111 {{/code}}
112
113 ==== Simplified Exception Handling ====
114
115 Scala doesn't force you to catch exceptions unlike in Java.
116 In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
117
118 In Java:
119
120 {{code}}
121
122 try {
123 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
124 epi.setNextPage(context().page());
125 nextPage = (WOComponent) epi;
126 } catch (IllegalArgumentException e) {
127 ErrorPageInterface epf = D2W.factory().errorPage(session());
128 epf.setMessage(e.toString());
129 epf.setNextPage(context().page());
130 nextPage = (WOComponent) epf;
131 }
132
133 {{/code}}
134
135 In Scala:
136
137 {{code}}
138
139 try {
140 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
141 epi.setNextPage(context.page)
142 nextPage = epi.asInstanceOf[WOComponent]
143 } catch {
144 case e: IllegalArgumentException => {
145 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
146 epf.setMessage(e.toString)
147 epf.setNextPage(context.page)
148 nextPage = epf.asInstanceOf[WOComponent]
149 }
150 }
151
152 {{/code}}
153
154 == How to Add Scala to a WO Project ==
155
156 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
157
Ravi Mendis 195.1 158 {{note title="Note"}}
159
Ravi Mendis 294.1 160 This is for Eclipse/WOLips IDE
Ravi Mendis 195.1 161
162 {{/note}}
Ravi Mendis 290.1 163
164 == WO Scala Example ==
165
Ravi Mendis 294.1 166 The following example is a mixed Java/Scala version of the WO Movies D2W app.
Ravi Mendis 292.1 167 All the EO logic and WO components are in Scala.
168 Only the Application class is Java.
169
Ravi Mendis 290.1 170 {{attachments patterns=".*zip"}}{{/attachments}}
Ravi Mendis 294.1 171
172 === Setup ===
173
174 1. Install and run the OpenBase OBMovies database.
175 1. Right-click on Application.java and run as a WOApplication (as usual).
176
177 ==== EO Templates ====
178
179 See: [[Scala templates>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]]
180
181 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
182
183 1. Change the File Names Extension to "scala"
184 1. Uncheck Java under Options