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Wiki source code of WebObjects with Scala

Version 400.1 by Ravi Mendis on 2010/01/17 22:07
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1 === What is Scala? ===
2
3 Scala is a language for concurrent computing.
4 In the day and age of multi-core processors, concurrent computing can't be ignored.
5
6 Many of Scala's features have been designed with concurrency in mind.
7 Some of these may not be unfamiliar to Objective-C or WebObjects developers.
8
9 Here's a quick summary:
10
11 |= |= Objective-C |= Java |= Scala
12 |= Mutable/Immuable Datatypes | Collections //e.g: NSArray/NSMutableArray// | No | Yes
13 |= Closures | Blocks (//Extension//) | No | Anonymous Functions
14 |= Static variables | Yes | Yes | No
15 |= Static methods/functions | Yes | Yes | No
16 |= Concurrency | [[Grand Central Dispatch>>http://en.wikipedia.org/wiki/Grand_Central_Dispatch]] (//Extension//)| //Threads// |[[Actors>>http://en.wikipedia.org/wiki/Actor_model]]
17 |= |= Weakly Typed |=--Strongly Typed--|= Strongly Typed
18
19 Other notable features include:
20
21 |= |= Objective-C |= Java |= Scala
22 |= Parametered methods | Yes //e.g: addObject: to~:// | No | Yes //e.g: add(object= ,to=)//
23 |= Class composition | Categories | Interfaces | Traits
24
25 A fuller description of Scala can be found [[here>>http://en.wikipedia.org/wiki/Scala_(programming_language)]].
26
27 === Why Use Scala? ===
28
29 Scala is inherently thread-safe.
30 Because of the lack of static variables developers don't need to worry about synchronising access to mutable shared data.
31 It has concurrency that is effectively built-in to the language.
32
33 So for WebObjects developers, Scala offers itself as a powerful, safe and easy-to-use solution for concurrent applications. (In other words, Scala Actors can be used for problems that would have normally required threads).
34
35 === Can WebObjects be Programmed In Scala? ===
36
37 Yes. It is very simple.
38 Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
39
40 = WebObjects In Scala =
41
42 The following highlights some of the differences between Java and Scala in WebObjects:
43
44 == EOs in Scala ==
45
46 === Thread-Safe Shared Vars ===
47
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.
50
51 The following is an example of the use of a //Companion Object// for Talent in Scala instead of Talent static fields in Java.
52
53 Java:
54
55 {{code value="java"}}
56
57 public class _Talent extends EOGenericRecord {
58 public static final String ENTITY_NAME = "Talent";
59
60 {{/code}}
61
62 Scala:
63
64 {{code}}
65
66 object Talent extends EOGenericRecord {
67 val ENTITY_NAME = "Talent"
68
69 {{/code}}
70
71 ==== Compacted imports ====
72
73 Two lines in Java are compacted into one in Scala.
74
75 In Java:
76
77 {{code value="java"}}
78
79 import com.webobjects.eocontrol.EOGenericRecord;
80 import com.webobjects.eocontrol.EORelationshipManipulation;
81
82 {{/code}}
83
84 In Scala:
85
86 {{code}}
87
88 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
89
90 {{/code}}
91
92 == WOComponents in Scala ==
93
94 ==== Compact Constructors ====
95
96 Scala allows for simpler use of multi-valued constructors than Java.
97
98 In Java:
99
100 {{code value="java"}}
101
102 public class MenuHeader extends WOComponent {
103
104 public MenuHeader(WOContext aContext) {
105 super(aContext);
106 }
107
108 {{/code}}
109
110 In Scala:
111
112 {{code}}
113
114 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
115
116 {{/code}}
117
118 ==== Simplified Exception Handling ====
119
120 Scala doesn't force you to catch exceptions unlike in Java.
121 In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
122
123 In Java:
124
125 {{code value="java"}}
126
127 try {
128 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
129 epi.setNextPage(context().page());
130 nextPage = (WOComponent) epi;
131 } catch (IllegalArgumentException e) {
132 ErrorPageInterface epf = D2W.factory().errorPage(session());
133 epf.setMessage(e.toString());
134 epf.setNextPage(context().page());
135 nextPage = (WOComponent) epf;
136 }
137
138 {{/code}}
139
140 In Scala:
141
142 {{code}}
143
144 try {
145 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
146 epi.setNextPage(context.page)
147 nextPage = epi.asInstanceOf[WOComponent]
148 } catch {
149 case e: IllegalArgumentException => {
150 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
151 epf.setMessage(e.toString)
152 epf.setNextPage(context.page)
153 nextPage = epf.asInstanceOf[WOComponent]
154 }
155 }
156
157 {{/code}}
158
159 ==== Scala Annotations vs. Generic Accessors ====
160
161 An example of accessing variables in WebObjects with the following languages:
162
163 |= |= Objective-C |= Java |= Scala
164 |= getter | ##object name## | ##object.name()## | ##object.name##
165 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
166
167 Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
168 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.
169
170 E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
171 These variables can then be accessed via //KVC//.
172
173 {{code}}
174
175 @BeanProperty var username = new String()
176 @BeanProperty var password = new String()
177 @BeanProperty var isAssistantCheckboxVisible = false
178
179 {{/code}}
180
181 == How to Use Scala Collections with EOF ==
182
183 One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map##, ##Seq## and ##Set##.
184 Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
185
186 But one may modify the EO templates to produce API such as:
187
188 {{code}}
189
190 def movies: NSArray[EOGenericRecord] = {
191 storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[EOGenericRecord]]
192 }
193
194 def moviesList: List[EOGenericRecord] = {
195 movies.objects.toList
196 }
197
198 {{/code}}
199
200 == How to Add Scala to a WO Project ==
201
202 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
203
204 {{note title="Note"}}
205
206 This is for Eclipse/WOLips IDE
207
208 {{/note}}
209
210 == WO Scala Example ==
211
212 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
213 All the EO logic and WO components are in Scala.
214 Only the Application class is Java.
215
216 It is based on the D2W Movies example.
217
218 {{attachments patterns=".*zip"}}{{/attachments}}
219
220 === Setup ===
221
222 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
223 1. Install and start the OpenBase OBMovies database.
224 1. Right-click on Application.java and run as a WOApplication (as usual).
225
226 ==== EO Templates ====
227
228 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
229
230 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//##
231 1. Change the File Names Extension to "scala"
232 1. In Destination Paths set the Superclass Package (e.g: base)
233 1. Uncheck Java under Options
234
235 == How to Build & Deploy a WebObjects Scala Project with Ant ==
236
237 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
238 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
239 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
240 1. Run from the project directory: ##sudo ant clean install##