netbeans.apache.org/src/content/wiki/DevFaqModuleLoadUnloadNotification.asciidoc

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= DevFaqModuleLoadUnloadNotification
:jbake-type: wiki
:jbake-tags: wiki, devfaq, needsreview
:jbake-status: published
:keywords: Apache NetBeans wiki DevFaqModuleLoadUnloadNotification
:description: Apache NetBeans wiki DevFaqModuleLoadUnloadNotification
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=== How can code in one module be notified when other modules are loaded or unloaded?

Let's begin by stating that you probably do not _need_ to know when other modules are loaded or unloaded.
The module system takes care of dependency management for you,
so your module should never be loaded unless all of its stated dependencies are loaded too.

The normal means of communicating between modules about available services
(which you could consider _indirect dependencies_) is using the Lookup API.
If what you really wanted was to know when a _service_ became available,
you do not need to listen to module load or unload events as such;
which module hosts the service is not of direct interest.
Instead:

1. Define a service `some.Interface` in some module.
2. Implement that interface using `some.Implementation` in some other module. Register it with `@ServiceProvider(service=Interface.class)`.
3. In some module consuming the service, use
[source,java]
----

 import some.Interface;
 // ...
 private static final Lookup.Result<Interface> services =
     Lookup.getDefault().lookupResult(Interface.class);
 static {
     services.addLookupListener(new LookupListener() {
         public void resultChanged(LookupEvent ev) {
             // some module was loaded or unloaded!
         }
     });
 }
 // ...
 for (Interface service : services.allInstances()) {
     // use a currently available service
 } 
----

If you simply want to run some code when _your_ module loads or unloads,
registering an instance of
link:http://bits.netbeans.org/dev/javadoc/org-openide-modules/org/openide/modules/ModuleInstall.html[ModuleInstall]
will do the trick.
There is even a wizard in the IDE for setting this up.

But in the very rare case that you want to be notified when _other_ modules are loaded or unloaded,
it is possible because:

1. You can use link:http://bits.netbeans.org/dev/javadoc/org-openide-util/org/openide/util/Lookup.Result.html[Lookup.Result] to listen to changes in the contents of a `Lookup`, even the global lookup.
2. Every module installs an instance of link:http://bits.netbeans.org/dev/javadoc/org-openide-modules/org/openide/modules/ModuleInfo.html[ModuleInfo] into the default `Lookup` so the module system (or other code) can find out details about the module including its code name base, version numbers and display name.

By using these two facts together, it is possible to listen to changes in the installed modules by running code like this at some point in the application's lifecycle (link:DevFaqAppLifecycleHooks.asciidoc[DevFaqAppLifecycleHooks]):

[source,java]
----

 final Lookup.Result<ModuleInfo> result =
     Lookup.getDefault().lookupResult(ModuleInfo.class);
 result.addLookupListener(new LookupListener() {
     public void resultChanged(LookupEvent event) {
         // it seems a module was installed or removed
     }
 });
----

Once you detect that a module has been created you may also want to register a `PropertyChangeListener` and listen to `ModuleInfo.PROP_ENABLED`.
(A module present in the installation will provide a `ModuleInfo` but `isEnabled` might be false if it is not currently loaded.)

<hr/>
Applies to: NetBeans 6.7 and later

=== Apache Migration Information

The content in this page was kindly donated by Oracle Corp. to the
Apache Software Foundation.

This page was exported from link:http://wiki.netbeans.org/DevFaqModuleLoadUnloadNotification[http://wiki.netbeans.org/DevFaqModuleLoadUnloadNotification] , 
that was last modified by NetBeans user Jglick 
on 2009-12-03T14:18:59Z.


*NOTE:* This document was automatically converted to the AsciiDoc format on 2018-02-07, and needs to be reviewed.