Skip to Content

Wiki source code of WebObjects with Scala

Version 196.1 by Ravi Mendis on 2009/09/16 19:03
Show last authors
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 Rails which has been the reason for its adoption at sites like Twitter.
5
6 Many of its features and paradigms favor multi-threaded and concurrent development which 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
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 So it may offer new solutions for concurrency in WebObjects.
31
32 === Can WebObjects be Programmed In Scala? ===
33
34 Yes. It is very simple.
35 Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
36
37 = WebObjects In Scala =
38
39 The following is an in-depth explanation of differences between Java and Scala in WebObjects:
40
41 == EOs in Scala ==
42
43 === Thread-Safe Shared Constants and Vars ===
44
45 Scala doesn't have static variables or methods. However, every class does 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
158 {{note title="Note"}}
159
160 This is for Eclipse/WOLips IDE
161
162 {{/note}}
163
164 == WO Scala Example ==
165
166 The following is a mixed Java/Scala version of the WO Movies D2W app.
167 All the EO logic and WO components are in Scala.
168 Only the Application class is Java.
169
170 {{attachments patterns=".*zip"}}{{/attachments}}
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