Skip to Content

Changes for page WebObjects with Scala

Last modified by Ravi Mendis on 2011/05/10 02:10
From version 90.1
edited by Ravi Mendis
on 2009/12/08 19:13
Change comment: There is no comment for this version
To version 24.1
edited by Ravi Mendis
on 2009/09/15 20:26
Change comment: There is no comment for this version

Summary

Details

Page properties
Content
... ... @@ -1,232 +1,55 @@
1 1  === What is Scala? ===
2 2  
3 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.
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 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:
6 +|= |= Objective-C |= Java |= Scala
7 +|= Mutable/Immuable Datatypes |Collections (e.g: //NSArray/NSMutableArray//) | No | //All datatypes//
8 +|= Closures | (//extensions//) | No | //Built-in//
9 +|= Static variables | Yes | Yes | No
10 +|= Static methods/functions | Yes | Yes | No
11 +|= Concurrency | Grand Central Dispatch (//extensions//) | //Threads// | Actors
7 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 24  === Why Use Scala? ===
25 25  
26 26  With Web 2.0, building concurrent WebObjects applications is a must.
27 27  Developing and maintaining a concurrent or multi-threaded WebObjects application can be challenging.
28 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.
18 +Scala offers concurrency built into the language.
19 +So it may offer new solutions to allowing concurrency in WebObjects.
31 31  
32 -In addition it may offer new solutions for concurrency in WebObjects and EOF.
21 +=== Can WebObjects be Programmed With Scala? ===
33 33  
34 -=== Can WebObjects be Programmed In Scala? ===
35 -
36 36  Yes. It is very simple.
37 37  Scala compiles to java bytecode. Hence using it with WebObjects is fairly straightforward.
38 38  
39 -= WebObjects In Scala =
26 +== How to Develop WebObjects With Scala ==
40 40  
41 -The following highlights some of the differences between Java and Scala in WebObjects:
28 +1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
29 +1. Add Scala support to your project
30 +11. Right-click your project in the WO Explorer
31 +11. In the context menu select Scala -> Add Scala Nature
32 +1. Convert or use ##.scala## instead of ##.java## source
42 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 WebObjects 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 var username = new String()
175 -@BeanProperty var password = new String()
176 -@BeanProperty var isAssistantCheckboxVisible = false
177 -
178 -{{/code}}
179 -
180 -== How to Use Scala Collections with EOF ==
181 -
182 -One of the benefits of Scala is its very powerful, concurrency-ready collection classes - primarily ##List##, ##Map##, ##Seq## and ##Set##.
183 -Employing these instead of ##NSArray## and ##NSDictionary## in WebObjects/EOF may be challenging.
184 -
185 -But one may modify the EO templates to produce API such as:
186 -
187 -{{code}}
188 -
189 -def movies: NSArray[EOGenericRecord] = {
190 - storedValueForKey(_Studio.Keys.MOVIES).asInstanceOf[NSArray[EOGenericRecord]]
191 -}
192 -
193 -def moviesList: List[EOGenericRecord] = {
194 - movies.objects.toList
195 -}
196 -
197 -{{/code}}
198 -
199 -== How to Add Scala to a WO Project ==
200 -
201 -{{include value="WOL:Adding Scala Support to a WOLips Project"}}{{/include}}
202 -
203 203  {{note title="Note"}}
204 204  
205 -This is for Eclipse/WOLips IDE
36 +This is for Eclipse/WOLips developers
206 206  
207 207  {{/note}}
208 208  
209 209  == WO Scala Example ==
210 210  
211 -The following example is an almost 100% Scala WO app. In reality it is a mixed Java/Scala app:
42 +The following is a mixed Java/Scala version of the WO Movies D2W app.
212 212  All the EO logic and WO components are in Scala.
213 213  Only the Application class is Java.
214 214  
215 -It is based on the D2W Movies example.
216 -
217 217  {{attachments patterns=".*zip"}}{{/attachments}}
218 218  
219 219  === Setup ===
220 220  
221 -1. [[Install the Scala eclipse IDE>>http://www.scala-lang.org/node/94]]
222 -1. Install and start the OpenBase OBMovies database.
50 +1. Install and run the OpenBase OBMovies database.
223 223  1. Right-click on Application.java and run as a WOApplication (as usual).
224 224  
225 225  ==== EO Templates ====
226 226  
227 -When you create your ##.eogen## file, be sure to make the following changes in the EOGenerator Editor:
228 -
229 -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//##
230 -1. Change the File Names Extension to "scala"
231 -1. In Destination Paths set the Superclass Package (e.g: base)
232 -1. Uncheck Java under Options
55 +See: [[Scala templates>>http://wiki.objectstyle.org/confluence/display/WOL/EOGenerator+Templates+and+Additions]]