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Wiki source code of WebObjects with Scala

Version 341.1 by Ravi Mendis on 2009/10/13 18:52
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1 === What is Scala? ===
2
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.
5
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:
7
8 |= |= Objective-C |= Java |= Scala
9 |= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | Yes
10 |= Closures | Blocks (//Extension//) | No | Anonymous Functions
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
24 === Why Use Scala? ===
25
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.
28
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.
31
32 In addition it may offer new solutions for concurrency in WebObjects and EOF.
33
34 === Can WebObjects be Programmed In Scala? ===
35
36 Yes. It is very simple.
37 Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
38
39 = WebObjects In Scala =
40
41 The following highlights some of the differences between Java and Scala in WebObjects:
42
43 == EOs in Scala ==
44
45 === Thread-Safe Shared Vars ===
46
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.
49
50 In Java:
51
52 {{code}}
53
54 public class _Talent extends EOGenericRecord {
55 public static final String ENTITY_NAME = "Talent";
56
57 {{/code}}
58
59 In Scala:
60
61 {{code}}
62
63 object _Talent extends EOGenericRecord {
64 val ENTITY_NAME = "Talent"
65
66 {{/code}}
67
68 ==== Compacted imports ====
69
70 Two lines in Java are compacted into one in Scala.
71
72 In Java:
73
74 {{code}}
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
97 {{code}}
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
111 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
112
113 {{/code}}
114
115 ==== Simplified Exception Handling ====
116
117 Scala doesn't force you to catch exceptions unlike in Java.
118 In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
119
120 In Java:
121
122 {{code}}
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
156 == How to Use Scala Collections with EOF ==
157
158 One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map##, ##Seq## and ##Set##.
159 Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
160
161 But one may modify the EO templates to produce API such as:
162
163 {{code}}
164
165 def movies: NSArray[EOGenericRecord] = {
166 storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[EOGenericRecord]]
167 }
168
169 def moviesList: List[EOGenericRecord] = {
170 movies.objects.toList
171 }
172
173 {{/code}}
174
175 == How to Add Scala to a WO Project ==
176
177 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
178
179 {{note title="Note"}}
180
181 This is for Eclipse/WOLips IDE
182
183 {{/note}}
184
185 == WO Scala Example ==
186
187 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
188 All the EO logic and WO components are in Scala.
189 Only the Application class is Java.
190
191 It is based on the D2W Movies example.
192
193 {{attachments patterns=".*zip"}}{{/attachments}}
194
195 === Setup ===
196
197 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
198 1. Install and run the OpenBase OBMovies database.
199 1. Right-click on Application.java and run as a WOApplication (as usual).
200
201 ==== EO Templates ====
202
203 See: [[Scala templates>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]]
204
205 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
206
207 1. Change the File Names Extension to "scala"
208 1. Uncheck Java under Options