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Wiki source code of WebObjects with Scala

Version 373.1 by Ravi Mendis on 2009/12/08 19:09
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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 The following is an example of the use of a //Companion Object// for Talent in Scala instead of Talent static fields in Java.
51
52 Java:
53
54 {{code}}
55
56 public class _Talent extends EOGenericRecord {
57 public static final String ENTITY_NAME = "Talent";
58
59 {{/code}}
60
61 Scala:
62
63 {{code}}
64
65 object Talent extends EOGenericRecord {
66 val ENTITY_NAME = "Talent"
67
68 {{/code}}
69
70 ==== Compacted imports ====
71
72 Two lines in Java are compacted into one in Scala.
73
74 In Java:
75
76 {{code}}
77
78 import com.webobjects.eocontrol.EOGenericRecord;
79 import com.webobjects.eocontrol.EORelationshipManipulation;
80
81 {{/code}}
82
83 In Scala:
84
85 {{code}}
86
87 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
88
89 {{/code}}
90
91 == WOComponents in Scala ==
92
93 ==== Compact Constructors ====
94
95 Scala allows for simpler use of multi-valued constructors than Java.
96
97 In Java:
98
99 {{code}}
100
101 public class MenuHeader extends WOComponent {
102
103 public MenuHeader(WOContext aContext) {
104 super(aContext);
105 }
106
107 {{/code}}
108
109 In Scala:
110
111 {{code}}
112
113 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
114
115 {{/code}}
116
117 ==== Simplified Exception Handling ====
118
119 Scala doesn't force you to catch exceptions unlike in Java.
120 In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
121
122 In Java:
123
124 {{code}}
125
126 try {
127 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
128 epi.setNextPage(context().page());
129 nextPage = (WOComponent) epi;
130 } catch (IllegalArgumentException e) {
131 ErrorPageInterface epf = D2W.factory().errorPage(session());
132 epf.setMessage(e.toString());
133 epf.setNextPage(context().page());
134 nextPage = (WOComponent) epf;
135 }
136
137 {{/code}}
138
139 In Scala:
140
141 {{code}}
142
143 try {
144 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
145 epi.setNextPage(context.page)
146 nextPage = epi.asInstanceOf[WOComponent]
147 } catch {
148 case e: IllegalArgumentException => {
149 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
150 epf.setMessage(e.toString)
151 epf.setNextPage(context.page)
152 nextPage = epf.asInstanceOf[WOComponent]
153 }
154 }
155
156 {{/code}}
157
158 ==== Scala Annotations vs. Generic Accessors ====
159
160 An example of accessing variables in WebObjects with the following languages:
161
162 |= |= Objective-C |= Java |= Scala
163 |= getter | ##object name## | ##object.name()## | ##object.name##
164 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
165
166 Of course in Java, we may generate EO classes with "get" methods as well in order to stick to convention.
167 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.
168
169 E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
170 These variables can then be accessed via //KVC//.
171
172 {{code}}
173
174 @BeanProperty
175 var username: String = ""
176 @BeanProperty
177 var password: String = ""
178 @BeanProperty
179 var isAssistantCheckboxVisible: Boolean = false
180
181 {{/code}}
182
183 == How to Use Scala Collections with EOF ==
184
185 One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map##, ##Seq## and ##Set##.
186 Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
187
188 But one may modify the EO templates to produce API such as:
189
190 {{code}}
191
192 def movies: NSArray[EOGenericRecord] = {
193 storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[EOGenericRecord]]
194 }
195
196 def moviesList: List[EOGenericRecord] = {
197 movies.objects.toList
198 }
199
200 {{/code}}
201
202 == How to Add Scala to a WO Project ==
203
204 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
205
206 {{note title="Note"}}
207
208 This is for Eclipse/WOLips IDE
209
210 {{/note}}
211
212 == WO Scala Example ==
213
214 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
215 All the EO logic and WO components are in Scala.
216 Only the Application class is Java.
217
218 It is based on the D2W Movies example.
219
220 {{attachments patterns=".*zip"}}{{/attachments}}
221
222 === Setup ===
223
224 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
225 1. Install and start the OpenBase OBMovies database.
226 1. Right-click on Application.java and run as a WOApplication (as usual).
227
228 ==== EO Templates ====
229
230 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
231
232 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//##
233 1. Change the File Names Extension to "scala"
234 1. In Destination Paths set the Superclass Package (e.g: base)
235 1. Uncheck Java under Options