Skip to Content

Wiki source code of WebObjects with Scala

Version 407.1 by Ravi Mendis on 2010/01/17 19:19
Show last authors
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 Developing and maintaining a concurrent or multi-threaded WebObjects application can be challenging.
30
31 The lack of static variables means that Scala is inherently thread-safe.
32 It has concurrency that is effectively built-in to the language in the form of Actors.
33
34 So for WebObjects developers, Scala offers itself as a powerful, safe and easy-to-use solution for concurrent applications.
35
36 === Can WebObjects be Programmed In Scala? ===
37
38 Yes. It is very simple.
39 Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
40
41 = WebObjects In Scala =
42
43 The following highlights some of the differences between Java and Scala in WebObjects:
44
45 == EOs in Scala ==
46
47 === Thread-Safe Shared Vars ===
48
49 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.
50 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.
51
52 The following is an example of the use of a //Companion Object// for Talent in Scala instead of Talent static fields in Java.
53
54 Java:
55
56 {{code value="java"}}
57
58 public class _Talent extends EOGenericRecord {
59 public static final String ENTITY_NAME = "Talent";
60
61 {{/code}}
62
63 Scala:
64
65 {{code}}
66
67 object Talent extends EOGenericRecord {
68 val ENTITY_NAME = "Talent"
69
70 {{/code}}
71
72 ==== Compacted imports ====
73
74 Two lines in Java are compacted into one in Scala.
75
76 In Java:
77
78 {{code value="java"}}
79
80 import com.webobjects.eocontrol.EOGenericRecord;
81 import com.webobjects.eocontrol.EORelationshipManipulation;
82
83 {{/code}}
84
85 In Scala:
86
87 {{code}}
88
89 import com.webobjects.eocontrol.{EOGenericRecord, EORelationshipManipulation}
90
91 {{/code}}
92
93 == WOComponents in Scala ==
94
95 ==== Compact Constructors ====
96
97 Scala allows for simpler use of multi-valued constructors than Java.
98
99 In Java:
100
101 {{code value="java"}}
102
103 public class MenuHeader extends WOComponent {
104
105 public MenuHeader(WOContext aContext) {
106 super(aContext);
107 }
108
109 {{/code}}
110
111 In Scala:
112
113 {{code}}
114
115 class MenuHeader(context: WOContext) extends WOComponent(context: WOContext) {
116
117 {{/code}}
118
119 ==== Simplified Exception Handling ====
120
121 Scala doesn't force you to catch exceptions unlike in Java.
122 In addition, the syntax employs Scala's very powerful pattern matching to handle different exceptions.
123
124 In Java:
125
126 {{code value="java"}}
127
128 try {
129 EditPageInterface epi = D2W.factory().editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session());
130 epi.setNextPage(context().page());
131 nextPage = (WOComponent) epi;
132 } catch (IllegalArgumentException e) {
133 ErrorPageInterface epf = D2W.factory().errorPage(session());
134 epf.setMessage(e.toString());
135 epf.setNextPage(context().page());
136 nextPage = (WOComponent) epf;
137 }
138
139 {{/code}}
140
141 In Scala:
142
143 {{code}}
144
145 try {
146 var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(_manipulatedEntityName, session)
147 epi.setNextPage(context.page)
148 nextPage = epi.asInstanceOf[WOComponent]
149 } catch {
150 case e: IllegalArgumentException => {
151 var epf: ErrorPageInterface = D2W.factory.errorPage(session)
152 epf.setMessage(e.toString)
153 epf.setNextPage(context.page)
154 nextPage = epf.asInstanceOf[WOComponent]
155 }
156 }
157
158 {{/code}}
159
160 ==== Scala Annotations vs. Generic Accessors ====
161
162 An example of accessing variables in WebObjects with the following languages:
163
164 |= |= Objective-C |= Java |= Scala
165 |= getter | ##object name## | ##object.name()## | ##object.name##
166 |= setter | ##object setName:aName## | ##object.setName(aName)## | ##object.name = aName##
167
168 Of course in Java, we may generate WebObjects classes with "get" methods as well in order to stick to convention.
169 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.
170
171 E.g, in Main.scala we annotate our component keys with ##@BeanProperty## to automatically create public "set" and "get" methods.
172 These variables can then be accessed via //KVC//.
173
174 {{code}}
175
176 @BeanProperty var username = new String()
177 @BeanProperty var password = new String()
178 @BeanProperty var isAssistantCheckboxVisible = false
179
180 {{/code}}
181
182 == How to Use Scala Collections with EOF ==
183
184 One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map##, ##Seq## and ##Set##.
185 Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
186
187 But one may modify the EO templates to produce API such as:
188
189 {{code}}
190
191 def movies: NSArray[EOGenericRecord] = {
192 storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[EOGenericRecord]]
193 }
194
195 def moviesList: List[EOGenericRecord] = {
196 movies.objects.toList
197 }
198
199 {{/code}}
200
201 == How to Add Scala to a WO Project ==
202
203 {{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
204
205 {{note title="Note"}}
206
207 This is for Eclipse/WOLips IDE
208
209 {{/note}}
210
211 == WO Scala Example ==
212
213 The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
214 All the EO logic and WO components are in Scala.
215 Only the Application class is Java.
216
217 It is based on the D2W Movies example.
218
219 {{attachments patterns=".*zip"}}{{/attachments}}
220
221 === Setup ===
222
223 1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
224 1. Install and start the OpenBase OBMovies database.
225 1. Right-click on Application.java and run as a WOApplication (as usual).
226
227 ==== EO Templates ====
228
229 When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
230
231 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//##
232 1. Change the File Names Extension to "scala"
233 1. In Destination Paths set the Superclass Package (e.g: base)
234 1. Uncheck Java under Options
235
236 == How to Build & Deploy a WebObjects Scala Project with Ant ==
237
238 1. [[Download>>http://www.scala-lang.org/downloads]] and install Scala
239 1. Set ##scala.home## (the location Scala has been installed onto) in the project ##build.properties## file
240 1. [[Add the scalac task and properties>>Configuring Ant to Build Scala with WebObjects]] to the ant build.xml file
241 1. Run from the project directory: ##sudo ant clean install##