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Wiki source code of Creating Plugins

Last modified by Simon Urli on 2023/10/10
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1 {{box cssClass="floatinginfobox" title="**Contents**"}}
2 {{toc/}}
3 {{/box}}
4
5 {{warning}}
6 Plugins are the old way of writing XWiki extensions. The new way is to [[write a Component>>xwiki:Documentation.DevGuide.Tutorials.WritingComponents]].
7 {{/warning}}
8
9 Plugins are quite handy when you want to interact with third-party code from the Velocity context. Check the [[Extensions wiki>>extensions:Main.WebHome]] for a list of existing plugins.
10
11 Here are the steps to develop a "Hello World" plugin and more.
12
13 = The plugin architecture =
14
15 Basically, a plugin is composed of two parts:
16
17 * The **plugin** itself: it must implement the [[XWikiPluginInterface>>https://fisheye2.atlassian.com/browse/xwiki/xwiki-platform/core/trunk/xwiki-core/src/main/java/com/xpn/xwiki/plugin/XWikiPluginInterface.java]] interface. For simplicity you can also extend the [[XWikiDefaultPlugin>>https://fisheye2.atlassian.com/browse/xwiki/xwiki-platform/core/trunk/xwiki-core/src/main/java/com/xpn/xwiki/plugin/XWikiDefaultPlugin.java]] class which is an adapter to the XWikiPluginInterface. The plugin contains the core functions of your plugin. They will not be accessible from scripting (without programming rights).
18 * Its **API**: it should extend the [[Api>>https://fisheye2.atlassian.com/browse/xwiki/xwiki-platform/core/trunk/xwiki-core/src/main/java/com/xpn/xwiki/api/Api.java]] class. Will contain all the public methods, accessible from scripting.
19
20 Although you can write the functionality inside the API, this is not recommended; the plugin functionality is written in the //hidden// part ("hidden" as in "not publicly accessible"), and the API can filter the access to privileged users, beautify the method names or parameter list, etc., or simply forward the call to the hidden part.
21
22 == Plugin lifecycle ==
23
24 When the XWiki engine is initialized, the Plugin Manager calls the class constructor for all the enabled plugins (classes implementing the com.xpn.xwiki.plugin.XWikiPluginInterface). For each plugin the class constructor is called only once, and the plugin manager calls the init(XWikiContext) method of the plugin. Each time a plugin is referenced by a Velocity script, for example, when you call a method served by the plugin API:
25
26 {{code}}
27 #set($helloWorldText = "$xwiki.helloworld.hello()")
28 {{/code}}
29
30 or when you ask the XWiki instance for the plugin API object :
31
32 {{code}}
33 #set($pluginObject = $xwiki.getPlugin("helloworld")
34
35 #* the name given as argument of getPlugin() should be
36 the one returned by the getName() method of the Plugin class.
37 *#
38 {{/code}}
39
40 XWiki calls the getPluginApi() method for the plugin's instance, which itself creates an instance of the class com.xpn.xwiki.plugin.PluginApi. This is why you should not store things in fields of the class extending PluginApi in your plugin, since the usual behavior for the getPluginApi() method is to create a new instance of the PluginApi class every time Velocity needs to access the API for your plugin. This is not true if you store the returned plugin API in a variable, for example:
41
42 {{code}}
43 #set($myPluginApi = $xwiki.helloworld)
44 {{/code}}
45
46 The myPluginApi variable will point to the same object as long as the variable exists. You can declare fields in your plugin class instead, since there is only one instance of this class, whose lifecycle spans over the entire servlet's lifecycle.
47
48 = Write the plugin =
49
50 {{warning}}
51 Before starting to create plugins, you need to setup your environment correctly and learn the basics of working with the API:
52
53 To learn how to find classes, in what modules classes reside and what modules to import, use [[API Reference>>https://www.xwiki.org/xwiki/bin/view/Documentation/DevGuide/API/]] page.
54 To be able to build the plugin, you need to setup your environment according to the [[Building XWiki from sources>>https://dev.xwiki.org/xwiki/bin/view/Community/Building/]] guide.
55
56 These two should be enough to let you follow and finish this tutorial, and let you start making your own plugins.
57 {{/warning}}
58
59 First of all let's **declare our plugin class**:
60
61 {{code language="java"}}
62 public class HelloWorldPlugin extends XWikiDefaultPlugin {...}
63 {{/code}}
64
65 Then let's **implement the needed constructor**:
66
67 {{code language="java"}}
68 public HelloWorldPlugin(String name, String className, XWikiContext context) {
69 super(name,className,context);
70 }
71 {{/code}}
72
73 **Set a method to get the name of the plugin**. That's how we will call it from Velocity. For example, we will be able to use our plugin with ##$xwiki.helloworld.myMethod()##;
74
75 {{code language="java"}}
76 public String getName() {
77 return "helloworld";
78 }
79 {{/code}}
80
81 **Write a method to get the plugin API**. Don't forget to cast the plugin.
82
83 {{code language="java"}}
84 public Api getPluginApi(XWikiPluginInterface plugin, XWikiContext context) {
85 return new HelloWorldPluginApi((HelloWorldPlugin) plugin, context);
86 }
87 {{/code}}
88
89 **Overload the cache flush method** (optional):
90
91 {{code language="java"}}
92 public void flushCache() {}
93 {{/code}}
94
95 Optionally, we can **create a [[log4j>>http://logging.apache.org/log4j/1.2/apidocs/index.html]] instance** for the plugin:
96
97 {{code language="java"}}
98 private static final Log LOG = LogFactory.getLog(HelloWorldPlugin.class);
99 {{/code}}
100
101 This is very useful for debugging. The logger could be invoked from any method like:
102
103 {{code language="java"}}
104 public String getName() {
105 LOG.debug("Entered method getName");
106 return "helloworld";
107 }
108 {{/code}}
109
110 Then, to enable logging at a specific level for your plugin, edit //webapps/xwiki/WEB-INF/classes/log4j.properties// and add, for example:
111
112 {{code}}
113 log4j.com.xpn.xwiki.plugin.helloworld.HelloWorldPlugin=debug
114 {{/code}}
115
116 You'll then be able to follow your plugin's log messages by tailing your ##xwiki.log## file. Note that you'll need to restart the app server for changes to ##log4j.properties## to take effect.
117
118 And finally, **write a method to init the context**:
119
120 {{code language="java"}}
121 public void init(XWikiContext context) {
122 super.init(context);
123 }
124 {{/code}}
125
126 Here is the code you should have now:
127
128 {{code language="java"}}
129 package com.xpn.xwiki.plugin.helloworld;
130
131 import org.apache.commons.logging.Log;
132 import org.apache.commons.logging.LogFactory;
133
134 import com.xpn.xwiki.XWikiContext;
135 import com.xpn.xwiki.api.Api;
136 import com.xpn.xwiki.plugin.XWikiDefaultPlugin;
137 import com.xpn.xwiki.plugin.XWikiPluginInterface;
138
139 public class HelloWorldPlugin extends XWikiDefaultPlugin {
140
141 private static Log LOG = LogFactory.getLog(HelloWorldPlugin.class);
142
143 public HelloWorldPlugin(String name, String className, XWikiContext context) {
144 super(name,className,context);
145 init(context);
146 }
147
148 public String getName() {
149 return "helloworld";
150 }
151
152 public Api getPluginApi(XWikiPluginInterface plugin, XWikiContext context) {
153 return new HelloWorldPluginApi((HelloWorldPlugin) plugin, context);
154 }
155
156 public void flushCache() {
157 }
158
159 public void init(XWikiContext context) {
160 super.init(context);
161 }
162 }
163 {{/code}}
164
165 = Write the API =
166
167 Let's write the API class which will contain the methods that can be called from Velocity.
168
169 Firstly, **class declaration**:
170
171 {{code language="java"}}
172 public class HelloWorldPluginApi extends Api {...}
173 {{/code}}
174
175 Then, **plugin field declaration**. It will let our API to call backend methods.
176
177 {{code language="java"}}
178 private HelloWorldPlugin plugin;
179 {{/code}}
180
181 **Required constructor**
182
183 {{code language="java"}}
184 public HelloWorldPluginApi(HelloWorldPlugin plugin, XWikiContext context) {
185 super(context);
186 setPlugin(plugin);
187 }
188 {{/code}}
189
190 Classic **plugin getter and setter**. These methods are not required at all, on the contrary, they should not be defined, unless they are really needed.
191
192 {{code language="java"}}
193 public HelloWorldPlugin getPlugin(){
194 return (hasProgrammingRights() ? plugin : null);
195 // Uncomment for allowing unrestricted access to the plugin
196 // return plugin;
197 }
198
199 public void setPlugin(HelloWorldPlugin plugin) {
200 this.plugin = plugin;
201 }
202 {{/code}}
203
204 Here is the key **API method**. Here is the one that you will call from velocity. You can define any number of them and call your plugin backend from them.
205
206 {{code language="java"}}
207 public String hello() {
208 return "Hello World!";
209 }
210 {{/code}}
211
212 You can also have void methods:
213
214 {{code language="java"}}
215 public void updatePage() {
216 //...
217 }
218 {{/code}}
219
220 Here is the complete API code:
221
222 {{code language="java"}}
223 package com.xpn.xwiki.plugin.helloworld;
224
225 import com.xpn.xwiki.XWikiContext;
226 import com.xpn.xwiki.api.Api;
227
228 public class HelloWorldPluginApi extends Api {
229 private HelloWorldPlugin plugin;
230
231 public HelloWorldPluginApi(HelloWorldPlugin plugin, XWikiContext context) {
232 super(context);
233 setPlugin(plugin);
234 }
235
236 public HelloWorldPlugin getPlugin(){
237 return (hasProgrammingRights() ? plugin : null);
238 // Uncomment for allowing unrestricted access to the plugin
239 // return plugin;
240 }
241
242 public void setPlugin(HelloWorldPlugin plugin) {
243 this.plugin = plugin;
244 }
245
246 public String hello() {
247 return "Hello World!";
248 }
249
250 public void updatePage() {
251 //...
252 }
253 }
254 {{/code}}
255
256 = Integrate the plugin in your XWiki installation =
257
258 First of all you need to **copy your classes to the XWiki servlet installation**. Don't forget to be consistent with your package tree. With a Linux Tomcat installation, you'll need to follow these steps which you should be able to reproduce easily in your favourite operating system:
259
260 {{code}}
261 go to the tomcat installation folder (or whatever container you are using)
262 $ cd myTomcatInstallation
263 go to the xwiki WEB-INF directory
264 $ cd webapps/xwiki/WEB-INF
265 create the classes tree, compliant to the "package" directive that you set in the plugin source files
266 $ mkdir classes/com/xpn/xwiki/plugin/helloworld
267 And then copy the class files to this location
268 $ cp myPluginsFolder/HelloWorldPlugin.class classes/com/xpn/xwiki/plugin/helloworld
269 $ cp myPluginsFolder/HelloWorldPluginAPI.class classes/com/xpn/xwiki/plugin/helloworld
270 {{/code}}
271
272 Alternatively, you can jar up your classes (with the required directory structure) and place the jar in //webapps/xwiki/WEB-INF/lib//. This is a more agreeable way of distributing your plugin.
273
274 Finally you need to **register your plugin** in the ##xwiki.cfg## file located in //WEB-INF//:
275
276 {{code}}
277 xwiki.plugins=com.xpn.xwiki.plugin.calendar.CalendarPlugin,\
278 ...,\
279 com.xpn.xwiki.plugin.helloworld.HelloWorldPlugin
280 {{/code}}
281
282 {{info}}
283 Here you need to specify the plugin class. The class that extends the XWikiDefaultPlugin or implements the XWikiPluginInterface, not groupId and artifactId of the pom.
284 {{/info}}
285
286 Don't forget to restart your servlet container after this. XWiki has to re-read the configuration file.
287
288 = Use the plugin =
289
290 Here is the simplest part. Edit a page and write: {{code}}My plugin says: "$xwiki.helloworld.hello()"{{/code}}.
291 It should be rendered like this: {{code}}My plugin says: "Hello World!"{{/code}}.
292 You can also call void methods specified in the API class :
293
294 {{code}}
295 $xwiki.helloworld.updatePage()
296 The page has been updated.
297 {{/code}}
298
299 = Examples =
300
301 Here are some examples of what you can do with plugins. You should actually check the [[API Guide>>xwiki:Documentation.DevGuide.APIGuide]], since it contains examples on how to use the XWiki API. The examples in the API Guide are written in Velocity, and are thus easily applicable to Java.
302
303 == Accessing pages, objects and object properties from pages ==
304
305 This is something you can do from Velocity as well, but when you need to perform complex treatments on your XWiki pages, you need to do it from a java plugin.
306
307 The class representing a document in the XWiki Java model is ##com.xpn.xwiki.doc.XWikiDocument##. The class representing an object in the XWiki Java model is ##com.xpn.xwiki.objects.BaseObject##.
308
309 If you need to access existing documents from your plugin, you use the XWiki class, ##com.xpn.xwiki.XWiki##, which has a getDocument() method. You can retrieve the current Xwiki instance by using the ##com.xpn.xwiki.XWikiContext## class, which has a getWiki() method.
310
311 The rule, in plugin programming, is to pass the current context as a ##com.xpn.xwiki.XWikiContext## function parameter, between the different methods of your plugin class. The plugin API class also has a context property pointing to the current context.
312
313 {{code}}
314 // You need the current context, which you always have in a plugin anyway
315 com.xpn.xwiki.doc.XWikiDocument doc = context.getDoc(); // current document;
316 com.xpn.xwiki.doc.XWikiDocument doc = context.getWiki().getDocument("theSpace.theDoc", context); // any document
317 com.xpn.xwiki.objects.BaseObject meta;
318 meta = doc.getObject("fooSpace.fooClass");
319 String docType = (String)meta.getStringValue("type"); //if the class of the object has a property named "type", which can accept a text value...
320 meta.set("type", "newValue", context);
321 {{/code}}
322
323 If you need to access the parent of an XWiki document, you should use the getDocument() method of the XWiki class, as seen in the example above, with, as parameter value, the parent's full name returned by the getParent() method of the XWikiDocument class.
324
325 {{code}}
326 com.xpn.xwiki.doc.XWikiDocument parentDocument = context.getWiki().getDocument(childDocument.getParent());
327 {{/code}}
328
329 You should not use ##XWikiDocument.getParentDoc## since it only returns a blank XWikiDocument object set with the same full name as the parent's full name.

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