From 99d6de546c74f0eed230ea8253dda6b85109d2e7 Mon Sep 17 00:00:00 2001
From: Markus Koivisto <markus@vaadin.com>
Date: Fri, 22 Jan 2016 14:55:18 +0200
Subject: Add documentation to master branch

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+---
+title: Vaadin CDI Add-on
+order: 17
+layout: page
+---
+
+[[advanced.cdi]]
+= Vaadin CDI Add-on
+
+((("Contexts and Dependency Injection", id="term.advanced.cdi.cdilong", range="startofrange")))
+
+
+((("CDI", id="term.advanced.cdi.cdi", range="startofrange")))
+
+
+((("Vaadin CDI Add-on", id="term.advanced.cdi.cdiaddon", range="startofrange")))
+
+
+Vaadin CDI add-on makes it easier to use contexts and dependency injection (CDI)
+in Vaadin applications. CDI is a Java EE feature especially targeted for web
+applications, which have well-defined contextual scopes, such as sessions,
+views, requests, and so forth. The lifecycle of objects, such as beans, can be
+managed by binding their lifecycles to such contexts. Vaadin CDI enables these
+features with two additional kinds of Vaadin-specific contextual scopes: UIs and
+navigation views.
+
+To learn more about Vaadin CDI, the link:[Vaadin CDI Tutorial] gives a hands-on
+introduction. The source code of the CDI Tutorial demo is available for browsing
+or cloning at https://github.com/vaadin-samples/cdi-tutorial.
+
+[[advanced.cdi.cdi]]
+== CDI Overview
+
+Contexts and dependency injection, defined in the JSR-299 standard, is a Java EE
+feature that, through a set of services, helps in improving application
+architecture by decoupling the management of service object lifecycles from
+client objects using them. The lifecycle of objects stored in a CDI container is
+defined by a context. The managed objects or beans are accessed using dependency
+injection.
+
+CDI builds on the Java concept of beans, but with somewhat different definition
+and requirements.
+
+Regarding general CDI topics, such as use of qualifiers, interceptors,
+decorators, event notifications, and other CDI features, we refer you to CDI
+documentation.
+
+ifdef::web[]
+* link:http://jaxenter.com/tutorial-introduction-to-cdi-contexts-and-dependency-injection-for-java-ee-jsr-299-104536.html[Introduction
+to CDI]. Pete Muir and Mark Struberg, JAXenter.
+
+* link:http://docs.jboss.org/weld/reference/latest/en-US/html_single/[Weld - CDI
+Reference Implementation]
+
+* link:http://cdi-spec.org/[CDI Specification]
+
+* link:https://vaadin.com/wiki?p_p_id=36&amp;p_p_lifecycle=0&amp;p_p_state=normal&amp;p_p_mode=view&amp;p_p_col_id=row-1&amp;p_p_col_pos=1&amp;p_p_col_count=3&amp;p_r_p_185834411_title=Vaadin+CDI&amp;p_r_p_185834411_nodeName=vaadin.com+wiki&amp;_36_struts_action=%2Fwiki%2Fview[Vaadin
+CDI Tutorial]
+
+endif::web[]
+
+[[advanced.cdi.cdi.injection]]
+=== Dependency Injection
+
+__Dependency injection__ is a way to pass dependencies (service objects) to
+dependent objects (clients) by injecting them in member variables or initializer
+parameters, instead of managing the lifecycle in the clients or passing them
+explicitly as parameters. In CDI, injection of a service object to a client is
+specified by the [classname]#@Inject# annotation.
+
+For example, if we have a UI view that depends on user data, we could inject the
+data in the client as follows:
+
+
+[source, java]
+----
+public class MainView extends CustomComponent implements View {
+    @Inject
+    User user;
+
+    ...
+    @Override
+    public void enter(ViewChangeEvent event) {
+        greeting.setValue("Hello, " + user.getName());
+    }
+}
+----
+
+In addition to injecting managed beans with the annotation, you can query for
+them from the bean manager.
+
+
+[[advanced.cdi.cdi.contexts]]
+=== Contexts and Scopes
+
+__Contexts__ in CDI are services that manage the lifecycle of objects and handle
+their injection. Generally speaking, a context is a situation in which an
+instance is used with a unique identity. Such objects are essentially
+"singletons" in the context. While conventional singletons are application-wide,
+objects managed by a CDI container can be "singletons" in a more narrow
+__scope__: a user session, a particular UI instance associated with the session,
+a view within the UI, or even just a single request. Such a context defines the
+lifecycle of the object: its creation, use, and finally its destruction.
+
+As a very typical example in a web application, you would have a user data
+object associated with a user session.
+
+
+[source, java]
+----
+@SessionScoped
+public class User {
+    private String name;
+
+    public void setName(String name) {this.name = name;}
+    public String getName() {return name;}
+}
+----
+
+Now, when you need to refer to the user, you can use CDI injection to inject the
+session-scoped "singleton" to a member variable or a constructor parameter.
+
+
+[source, java]
+----
+public class MainView extends CustomComponent implements View {
+    @Inject
+    User user;
+
+    ...
+
+    @Override
+    public void enter(ViewChangeEvent event) {
+        greeting.setValue("Hello, " + user.getName());
+    }
+}
+----
+
+
+
+[[advanced.cdi.installation]]
+== Installing Vaadin CDI Add-on
+
+Vaadin CDI requires a Java EE 7 compatible servlet container, such as Glassfish
+or Apache TomEE Web Profile, as mentioned for the reference toolchain in
+<<dummy/../../../framework/getting-started/getting-started-environment#getting-started.environment,"Setting
+up the Development Environment">>.
+
+To install the Vaadin CDI add-on, either define it as an Ivy or Maven dependency
+or download it from the Vaadin Directory add-on page at
+<<,vaadin.com/directory#addon/vaadin-cdi>>. See
+<<dummy/../../../framework/addons/addons-overview.asciidoc#addons.overview,"Using
+Vaadin Add-ons">> for general instructions for installing and using Vaadin
+add-ons.
+
+The Ivy dependency is as follows:
+
+[subs="normal"]
+----
+    &lt;dependency org="com.vaadin" name="vaadin-cdi"
+                rev="[replaceable]#latest.release#"/&gt;
+----
+The Maven dependency is as follows:
+
+[subs="normal"]
+----
+    &lt;dependency&gt;
+        &lt;groupId&gt;com.vaadin&lt;/groupId&gt;
+        &lt;artifactId&gt;vaadin-cdi&lt;/artifactId&gt;
+        &lt;version&gt;[replaceable]#LATEST#&lt;/version&gt;
+    &lt;/dependency&gt;
+    &lt;dependency&gt;
+        &lt;groupId&gt;javax.enterprise&lt;/groupId&gt;
+        &lt;artifactId&gt;cdi-api&lt;/artifactId&gt;
+        &lt;version&gt;[replaceable]#1.2#&lt;/version&gt;
+    &lt;/dependency&gt;
+----
+
+[[advanced.cdi.peparing]]
+== Preparing Application for CDI
+
+A Vaadin application that uses CDI must have a file named [filename]#beans.xml#
+in the [filename]#WEB-INF# directory. The file can be completely empty (it has
+content only in certain limited situations), but it must be present.
+
+The application should not have a servlet extending [classname]#VaadinServlet#,
+as Vaadin servlet has its own [classname]#VaadinCDIServlet# that is deployed
+automatically. If you need multiple servlets or need to customize the Vaadin CDI
+servlet, see <<advanced.cdi.deployment>>.
+
+
+[[advanced.cdi.cdiui]]
+== Injecting a UI with [classname]#@CDIUI#
+
+((("[classname]#@CDIUI#", id="term.advanced.cdi.cdiui", range="startofrange")))
+
+
+Vaadin CDI offers an easier way to instantiate UIs and to define the URL mapping
+for them than the usual ways described in
+<<dummy/../../../framework/application/application-environment#application.environment,"Deploying
+an Application">>. To define a UI class that should be instantiated for a given
+URL, you simply need to annotate the class with [classname]#@CDIUI#. It takes an
+optional URL path as parameter.
+
+
+[source, java]
+----
+@CDIUI("myniceui")
+@Theme("valo")
+public class MyNiceUI extends UI {
+    ...
+----
+
+Giving empty UI path maps the UI to the root of the application context.
+
+
+[source, java]
+----
+@CDIUI("")
+----
+
+If the optional UI path is not given, the path is determined automatically from
+the class name by removing a possible "-UI" suffix in the class name, making it
+lower-case, and for capitalized letters, a hyphen is added. For example, a UI
+with class name [classname]#MyNiceUI# would have path [literal]#++my-nice++#.
+The URL consists of the server address, application context, and the UI path.
+For example, when running a Vaadin application in a development workstation, you
+would have URL such as http://localhost:8080/myproject/my-nice.
+
+UI path mappings are reported in the server log during deployment.
+
+See <<advanced.cdi.deployment>> for how to handle servlet URL mapping of CDI UIs
+when working with multiple servlets in the same web application.
+
+(((range="endofrange", startref="term.advanced.cdi.cdiui")))
+
+[[advanced.cdi.scopes]]
+== Scopes
+
+((("CDI", "scopes", id="term.advanced.cdi.scopes", range="startofrange")))
+
+
+As in programming languages, where a variable name refers to a unique object
+within the scope of the variable, a CDI scope is a context in which an object
+has unique identity. In CDI, objects to be injected are identified by their type
+and any qualifiers they may have. The scope can be defined as an annotation to
+the service class as follows:
+
+
+[source, java]
+----
+@SessionScoped
+public class User {
+    ...
+----
+
+CDI defines a number of scopes. Note that the standard CDI scopes are defined
+under the [package]#javax.enterprise.context# package and Vaadin CDI scopes
+under [package]#com.vaadin.cdi#, while JSF scopes are defined in
+[package]#javax.faces.bean#.
+
+[[advanced.cdi.scopes.ui]]
+=== UI Scope
+
+UI-scoped beans are uniquely identified within a UI instance, that is, a browser
+window or tab.
+
+Vaadin CDI provides two annotations for the UI scope, differing in how they
+enable proxies, as explained later.
+
+[classname]#@UIScoped#([package]#com.vaadin.cdi#):: ((("[classname]#@UIScoped#", id="term.advanced.cdi.scopes.uiscoped", range="startofrange")))
+
+
++
+Injection with this annotation will create a direct reference to the bean rather
+than a proxy. There are some limitations when not using proxies. Circular
+references (injecting A to B and B to A) will not work, and neither do CDI
+interceptors and decorators.
+
+(((range="endofrange", startref="term.advanced.cdi.scopes.uiscoped")))
+[classname]#@NormalUIScoped#([package]#com.vaadin.cdi#):: As [classname]#@UIScoped#, but injecting a managed bean having this annotation
+injects a proxy for the bean instead of a direct reference. This is the normal
+behaviour with CDI, as many CDI features utilize the proxy.
+
+
+
+Defining a CDI view (annotated with [classname]#@CDIView# as described later) as
+[classname]#@UIScoped# makes the view retain the same instance when the user
+navigates away and back to the view.
+
+
+[[advanced.cdi.scopes.view]]
+=== View Scopes
+
+The lifecycle of a view-scoped bean starts when the user navigates to a view
+referring to the object and ends when the user navigates out of the view (or
+when the UI is closed or expires).
+
+Vaadin CDI provides two annotations for the view scope, differing in how they
+enable proxies, as explained later.
+
+[classname]#@ViewScoped#([package]#com.vaadin.cdi#):: Injection with this annotation will create a direct reference to the bean rather
+than a proxy. There are some limitations when not using proxies. Circular
+references (injecting A to B and B to A) will not work, and neither do CDI
+interceptors and decorators.
+
+[classname]#@NormalViewScoped#([package]#com.vaadin.cdi#):: As [classname]#@NormalScoped#, except that injecting with this annotation will
+create a proxy for the contextual instance rather than provide the contextual
+instance itself. See the explanation of proxies below.
+
+
+
+
+[[advanced.cdi.scopes.cdi]]
+=== Standard CDI Scopes
+
+[classname]#@ApplicationScoped#:: ((("[classname]#@ApplicationScoped#", id="term.advanced.cdi.scopes.applicationscoped", range="startofrange")))
+
+
++
+Application-scoped beans are shared by all servlets in the web application, and
+are essentially equal to singletons.//TODO This is just a guess - is it
+true?
+Note that referencing application-scoped beans is not thread-safe and access
+must be synchronized.
+
+(((range="endofrange", startref="term.advanced.cdi.scopes.applicationscoped")))
+[classname]#@SessionScoped#:: ((("[classname]#@SessionScoped#", id="term.advanced.cdi.scopes.sessionscoped", range="startofrange")))
+
+
++
+The lifecycle and visibility of session-scoped beans is bound to a HTTP or user
+session, which in Vaadin applications is associated with the
+[classname]#VaadinSession# (see
+<<dummy/../../../framework/application/application-lifecycle#application.lifecycle.session,"User
+Session">>). This is a very typical scope to store user data, as is done in many
+examples in this section, or database connections. The lifecycle of
+session-scoped beans starts when a user opens the page for a UI in the browser,
+and ends when the session expires after the last UI in the session is closed.
+
+(((range="endofrange", startref="term.advanced.cdi.scopes.sessionscoped")))
+
+
+
+[[advanced.cdi.scopes.proxies]]
+=== Proxies vs Direct References
+
+CDI uses proxy objects to enable many of the CDI features, by hooking into
+message-passing from client to service beans. Under the hood, a proxy is an
+instance of an automatically generated class that extends the proxied bean type,
+so communicating through a proxy occurs transparently, as it has the same
+polymorphic type as the actual bean. Whether proxying is enabled or not is
+defined in the scope: CDI scopes are either __normal scopes__, which can be
+proxied, or __pseudoscopes__, which use direct references to injected beans.
+
+The proxying mechanism creates some requirements for injecting objects in normal
+scope:
+
+* The objects may not be primitive types or arrays
+
+* The bean class must not be final
+
+* The bean class must not have final methods
+
+
+Beans annotated with [classname]#@UIScoped# or [classname]#@ViewScoped# use a
+pseudoscope, and are therefore injected with direct references to the bean
+instances, while [classname]#@NormalUIScoped# and [classname]#@NormalViewScoped#
+beans will use a proxy for communicating with the beans.
+
+When using proxies, be aware that it is not guaranteed that the
+[methodname]#hashCode()# or [methodname]#equals()# will match when comparing a
+proxy to its underlying instance. It is imperative to be aware of this when, for
+example, adding proxies to a [interfacename]#Collection#.
+
+You should avoid using normal scopes with Vaadin components, as proxies may not
+work correctly within the Vaadin framework. If Vaadin CDI plugin detects such
+use, it displays a warning such as the following:
+
+
+----
+INFO: The following Vaadin components are injected
+into normal scoped contexts:
+   @NormalUIScoped       org.example.User
+This approach uses proxy objects and has not been
+extensively tested with the framework. Please report
+any unexpected behavior. Switching to a pseudo-scoped
+context may also resolve potential issues.
+----
+
+
+(((range="endofrange", startref="term.advanced.cdi.scopes")))
+
+[[advanced.cdi.deployment]]
+== Deploying CDI UIs and Servlets
+
+Vaadin CDI hooks into Vaadin framework by using a special
+[classname]#VaadinCDIServlet#. As described earlier, you do not need to map an
+URL path to a UI, as it is handled by Vaadin CDI. However, in the following, we
+go through some cases where you need to customize the servlet or use CDI with
+non-CDI servlets and UIs in a web application.
+
+[[advanced.cdi.deployment.urlmapping]]
+=== Defining Servlet Root with [classname]#@URLMapping#
+
+CDI UIs are managed by a CDI servlet ( [classname]#VaadinCDIServlet#), which is
+by default mapped to the root of the application context. For example, if the
+name of a CDI UI is " [literal]#++my-cdi++#" and application context is
+[literal]#++/myproject++#, the UI would by default have URL "
+[literal]#++/myproject/my-cdi++#". If you do not want to have the servlet mapped
+to context root, you can use the [classname]#@URLMapping# annotation to map all
+CDI UIs to a sub-path. The annotation must be given to only one CDI UI, usually
+the one with the default ("") path.
+
+For example, if we have a root UI and another:
+
+
+[source, java]
+----
+@CDIUI("") // At CDI servlet root
+@URLMapping("mycdiuis") // Define CDI Servlet root
+public class MyCDIRootUI extends UI {...}
+
+@CDIUI("another")
+public class AnotherUI extends UI {...}
+----
+
+These two UIs would have URLs /myproject/mycdiuis and
+/myproject/mycdiuis/another, respectively.
+
+You can also map the CDI servlet to another URL in servlet definition in
+[filename]#web.xml#, as described the following.
+
+
+[[advanced.cdi.servlets.mixing]]
+=== Mixing With Other Servlets
+
+The [classname]#VaadinCDIServlet# is normally used as the default servlet, but
+if you have other servlets in the application, such as for non-CDI UIs, you need
+to define the CDI servlet explicitly in the [filename]#web.xml#. You can map the
+servlet to any URL path, but perhaps typically, you define it as the default
+servlet as follows, and map the other servlets to other URL paths:
+
+[subs="normal"]
+----
+&lt;web-app&gt;
+  ...
+
+  &lt;servlet&gt;
+    &lt;servlet-name&gt;Default&lt;/servlet-name&gt;
+    &lt;servlet-class&gt;
+      com.vaadin.cdi.internal.VaadinCDIServlet
+    &lt;/servlet-class&gt;
+  &lt;/servlet&gt;
+
+  &lt;servlet-mapping&gt;
+    &lt;servlet-name&gt;Default&lt;/servlet-name&gt;
+    &lt;url-pattern&gt;[replaceable]#/mycdiuis/*#&lt;/url-pattern&gt;
+  &lt;/servlet-mapping&gt;
+
+  &lt;servlet-mapping&gt;
+    &lt;servlet-name&gt;Default&lt;/servlet-name&gt;
+    &lt;url-pattern&gt;/VAADIN/*&lt;/url-pattern&gt;
+  &lt;/servlet-mapping&gt;
+&lt;/web-app&gt;
+----
+With such a setting, paths to CDI UIs would have base path
+[filename]#/myapp/mycdiuis#, to which the (optional) UI path would be appended.
+The [filename]#/VAADIN/*# only needs to be mapped to the servlet if there are no
+other Vaadin servlets.
+
+
+[[advanced.cdi.servlets.custom]]
+=== Custom Servlets
+
+When customizing the Vaadin servlet, as outlined in
+<<dummy/../../../framework/application/application-lifecycle#application.lifecycle.servlet-service,"Vaadin
+Servlet, Portlet, and Service">>, you simply need to extend
+[classname]#com.vaadin.cdi.internal.VaadinCDIServlet# instead of
+[classname]#com.vaadin.servlet.VaadinServlet#.
+
+The custom servlet must not have [classname]#@WebServlet# annotation or
+[classname]#@VaadinServletConfiguration#, as you would normally with a Vaadin
+servlet, as described in
+<<dummy/../../../framework/application/application-environment#application.environment,"Deploying
+an Application">>.
+
+
+
+ifdef::web[]
+[[advanced.cdi.navigation]]
+== View Navigation
+
+Vaadin CDI extends the navigation framework in Vaadin, described in
+<<dummy/../../../framework/advanced/advanced-navigator#advanced.navigator,"Navigating
+in an Application">>. It manages CDI views with a special view provider and
+enables view scoping.
+
+[[advanced.cdi.navigation.ui]]
+=== Preparing the UI
+
+You can define navigation for any single-component container, as described in
+<<dummy/../../../framework/advanced/advanced-navigator#advanced.navigator.navigating,"Setting
+Up for Navigation">>, but typically you set up navigation for the entire UI
+content. To use Vaadin CDI views, you need to inject a
+[classname]#CDIViewProvider# in the UI and add it as a provider for the
+navigator.
+
+
+[source, java]
+----
+@CDIUI("mycdiui")
+public class MyCDIUI extends UI {
+    @Inject
+    CDIViewProvider viewProvider;
+    
+    @Override
+    protected void init(VaadinRequest request) {
+        Navigator navigator = new Navigator(this, this);
+        navigator.addProvider(viewProvider);
+
+        // Navigate to start view
+        navigator.navigateTo("");
+    }
+}
+----
+
+
+[[advanced.cdi.navigation.view]]
+=== The View
+
+A view managed by Vaadin CDI only needs to have the [classname]#@CDIView#
+annotation.
+
+
+[source, java]
+----
+@CDIView("main")
+public class MainView extends CustomComponent implements View {
+    ...
+----
+
+The annotation can have the following optional paramers:
+
+value (optional):: Specifies the view name by which it can be accessed programmatically and by the
+URI fragment.
+
+
++
+[source, java]
+----
+@CDIView("main")
+----
++
+If other optional parameters are given, the value must be given by the named
+[parameter]#value# parameter.
+
++
+If the view name is not given, it is derived from the class name by removing a
+possible "View" suffix, making it lower case, and using a dash ("-") to separate
+words originally denoted by capital letters. Thereby, a view class such as
+[classname]#MyFunnyView# would have name " [literal]#++my-funny++#".
+
+supportsParameters:: Specifies whether view parameters can be passed to the view as a suffix to the
+name in the navigation state, that is, in the form of
+[literal]#++viewname+viewparameters++#. The view name is merely a prefix and
+there is no separator nor format for the parameters, but those are left for the
+view to handle. The parameter support mode is disabled by default.
+
+
++
+[source, java]
+----
+@CDIView(value="myview", supportsParameters=true)
+----
++
+You could then navigate to the state with a URI fragment such as
+[literal]#++#!myview/someparameter++# or programmatically with:
+
+
++
+[source, java]
+----
+getUI().getNavigator().navigateTo("myview/someparameter");
+----
++
+The [methodname]#enter()# method of the view gets the URI fragment as parameter
+as is and can interpret it in any application-defined way.
+
++
+Note that in this mode, matching a navigation state to a view is done by the
+prefix of the fragment! Thereby, no other views may start with the name of the
+view as prefix. For example, if the view name is " [literal]#++main++#", you
+must not have a view named " [literal]#++maintenance++#".
+
+uis:: If the application has multiple UIs that use [classname]#CDIViewProvider#, you
+can use this parameter to specify which UIs can show the view.
+
+
++
+[source, java]
+----
+@CDIView(value="myview", uis={MyCDIUI.class})
+----
++
+If the list contains [parameter]#UI.class#, the view is available to all UIs.
+
+
++
+[source, java]
+----
+@CDIView(value="myview", uis={UI.class})
+----
+
+
+In the following, we have a login view that accesses a session-scoped user
+object. Here, we use a constant to define the view name, so that we can use the
+constant when navigating to it.
+
+
+[source, java]
+----
+@CDIView(LoginView.VIEWNAME)
+public class LoginView extends CustomComponent
+                       implements View {
+    public final static String VIEWNAME = "";
+    
+    // Here we inject to the constructor and actually do
+    // not store the injected object to use it later
+    @Inject
+    public LoginView(User user) {
+        VerticalLayout layout = new VerticalLayout();
+        
+        // An input field for editing injected data
+        BeanItem<User> item = new BeanItem<User>(user);
+        TextField username = new TextField("User name",
+                item.getItemProperty("name"));
+        username.setNullRepresentation("");
+        layout.addComponent(username);
+
+        // Login button (authentication omitted) / Java 8
+        layout.addComponent(new Button("Login", e ->
+            getUI().getNavigator().
+                navigateTo(MainView.VIEWNAME)));
+        
+        setCompositionRoot(layout);
+    }
+    
+    @Override
+    public void enter(ViewChangeEvent event) {}
+}
+----
+
+You could now navigate to the view from any other view in the UI with:
+
+
+[source, java]
+----
+getUI().getNavigator().navigateTo(LoginView.VIEWNAME);
+----
+
+
+endif::web[]
+
+ifdef::web[]
+[[advanced.cdi.events]]
+== CDI Events
+
+((("CDI", "events", id="term.advanced.cdi.events", range="startofrange")))
+
+
+CDI events can be used for many purposes in Vaadin applications, such as passing
+messages between different parts of a view, between views, between UIs, or
+between users. Some cases require special consideration, such as when
+communicating between UIs and how injected components should be scoped.
+
+[[advanced.cdi.events.intro]]
+=== Observing Events
+
+Let us consider a case where changes in one part of the UI (or view) require
+updating other parts of the UI. This is typical in master-detail views, for
+updating the master view after editing details, or when handling input from a
+sub-window. While you can handle such a situation with a custom call-back
+listener, CDI event mechanism simplifies the task.
+
+Let us consider the following simple UI containing two panels. The input panel
+will send events, which are received by other parts of the UI, in this case a
+display panel. The panels need to be injected to enable CDI event passing in
+them.
+
+
+[source, java]
+----
+@CDIUI("cdievents")
+@Theme("valo")
+public class CDIEventUI extends UI {
+    @Inject
+    InputPanel inputPanel;
+
+    @Inject
+    DisplayPanel displayPanel;
+
+    @Override
+    protected void init(VaadinRequest request) {
+        Layout content =
+            new HorizontalLayout(inputPanel, displayPanel);
+        setContent(content);
+    }
+}
+----
+
+Now, let us look closer at the sending panel. To send messages, it needs to
+inject a [classname]#javax.enterprise.event.Event# object. As we are injecting
+the event to a component class, we need to specify the full package name to
+avoid confusion with Vaadin [classname]#Component.Event#.
+
+
+[source, java]
+----
+class InputPanel extends Panel {
+    @Inject
+    private javax.enterprise.event.Event<MyEvent> event;
+
+    public InputPanel() {
+        super("Input");
+
+        TextField editor = new TextField();
+        Button save = new Button("Save", e -> // Java 8
+            event.fire(new MyEvent(editor.getValue())));
+
+        setContent(new VerticalLayout(editor, save));
+    }
+}
+----
+
+Firing an event is done with the [methodname]#fire()# method on the injected
+event object. In our example, the event is as follows:
+
+
+[source, java]
+----
+public class MyEvent implements Serializable {
+    private String text;
+    
+    public MyEvent(String text) {
+        this.text = text;
+    }
+    
+    public String getName() {
+        return text;
+    }
+}
+----
+
+The event is received by any method (in an injected object) marked by
+[classname]#@Observes# annotation for the event parameter to observe the event
+type.
+
+
+[source, java]
+----
+@UIScoped
+class DisplayPanel extends Panel {
+    Label display = new Label("-nothing to display-");
+
+    public DisplayPanel() {
+        super("Display");
+        setContent(display);
+    }
+    
+    void myEventObserver(@Observes MyEvent event) {
+        display.setValue("Observed: " + event.getName());
+    }
+}
+----
+
+Such a component that observes events from other components must be scoped to
+the UI or view, as otherwise it will be request-scoped and a new instance is
+created for receiving each event.
+
+The UI with interaction is shown in <<figure.advanced.cdi.events.intro>>.
+
+[[figure.advanced.cdi.events.intro]]
+.Observing CDI Events
+image::img/cdi-events-observing.png[]
+
+Any injection qualifiers defined for the event object in the sender are matched
+in the observers, which feature we will use later to avoid receiving unwanted
+events.
+
+
+[[advanced.cdi.events.broadcasting]]
+=== Communicating Between UIs
+
+((("broadcasting", id="term.advanced.cdi.events.broadcasting", range="startofrange")))
+
+
+CDI events are not propagated to inactive contexts, and only the context of the
+currently processed UI is active. Further, as explained in
+<<dummy/../../../framework/advanced/advanced-push#advanced.push.running,"Accessing
+UI from Another Thread">>, other Vaadin UIs may not be accessed without proper
+synchronization, as their requests are processed concurrently in different
+server threads. Therefore, you need to pass the events through an
+application-scoped messaging service and synchronize the access to other UIs by
+using the [methodname]#access()# method.
+
+In
+<<dummy/../../../framework/advanced/advanced-push#advanced.push.pusharound,"Broadcasting
+to Other Users">> we looked into how to pass messages to all other UIs using a
+broadcasting service. In that example, we used static variables and methods to
+store references and to access the service. With CDI, we can let the context
+manage its lifecycle, access it by injection, and pass messages by CDI events.
+By scoping the messaging service to application, we essentially make it a
+singleton.
+
+
+[source, java]
+----
+@ApplicationScoped
+public class CDIBroadcaster implements Serializable {
+----
+
+As we can not let CDI deliver the messages, the messaging service needs to keep
+book of the messaging clients (UIs) waiting to receive messages.
+
+
+[source, java]
+----
+    private Collection<UI> uis = new HashSet<UI>();
+    
+    public synchronized void register(UI listener) {
+        uis.add(listener);
+    }
+    
+    public synchronized void unregister(UI listener) {
+        uis.remove(listener);
+    }
+----
+
+The main logic of the messaging service is to observe messages and fire them in
+the recipient UIs. As we are broadcasting to all UIs here, we again use an
+executor service to execute the code. To lock on the session when accessing the
+UIs, we use the [methodname]#access()# method.
+
+
+[source, java]
+----
+    // Inject event to be fired
+    @Inject
+    private javax.enterprise.event.Event<BroadcastMessage>
+            messageEvent;
+
+    ExecutorService executorService =
+        Executors.newSingleThreadExecutor();
+
+    // Observe messages (only from clients)
+    @SuppressWarnings("unused")
+    private synchronized void observeMessage(
+            @Observes @OriginalSender
+            final BroadcastMessage message) {
+        for (final UI listener: uis)
+            executorService.execute(() ->
+                listener.access(()->
+                    messageEvent.fire(message)));
+    }
+}
+----
+
+Here we use a [classname]#@OriginalSender# qualifier to receive events only from
+a client (original sender), not from the messaging service itself, which would
+cause an infinite event loop. The qualifier is defined as follows:
+
+((("CDI", "qualifiers")))
+
+[source, java]
+----
+@Qualifier
+@Retention(RUNTIME)
+@Target({PARAMETER, FIELD})
+public @interface OriginalSender {}
+----
+
+The message type is a simple POJO as follows:
+
+
+[source, java]
+----
+public class BroadcastMessage {
+    private String text;
+    private Object sender; // For checking if sent by self
+
+    ... constructor, getters, and setters ...
+}
+----
+
+Let us take a look at the UI class, which manages both the messaging service and
+the client components. The UI just needs to register itself in the messaging
+service and build the UI, including the UI components doing messaging. We could,
+of course, do that also at view level.
+
+((("[classname]#@Push#")))
+
+[source, java]
+----
+@CDIUI("cdichat")
+@Push
+public class CDIChatUI extends UI {
+    @Inject
+    CDIBroadcaster broadcaster;
+    
+    @Inject
+    ChatBox chatbox;
+
+    @Override
+    protected void init(VaadinRequest request) {
+        setContent(chatbox);
+        
+        // Register to receive broadcasts
+        broadcaster.register(this);
+    }
+
+    // Must also unregister when the UI expires or is closed    
+    @Override
+    public void detach() {
+        broadcaster.unregister(this);
+        super.detach();
+    }
+}
+----
+
+Now for an actual messaging client, we look at the chat box component. Most of
+the UI code is omitted from the example. As noted earlier, the component
+receiving events must be scoped to the UI, to avoid creation of invalid
+instances.
+
+((("[classname]#@UIScoped#")))
+
+[source, java]
+----
+@UIScoped
+class ChatBox extends CustomComponent {
+    VerticalLayout messages = new VerticalLayout();
+    
+    public ChatBox(CDIChatUI cdiChatUI) {
+        ... build the composite ...
+
+        TextField input = new TextField();
+
+        Button send = new Button("Send", e -> { // Java 8
+            // Broadcast the input
+            broadcast(input.getValue());
+            addMessage(input.getValue()); // Add to self
+        });
+        ...
+    }
+    
+    @Inject
+    @OriginalSender
+    private javax.enterprise.event.Event<BroadcastMessage>
+        messageEvent;
+    
+    // Sends a message
+    private void broadcast(String msg) {
+        messageEvent.fire(new BroadcastMessage(msg, this));
+    }
+
+    // Receives messages
+    @SuppressWarnings("unused")
+    private void observeMessage(
+            @Observes BroadcastMessage event) {
+        if (event.getSender() != this)
+            addMessage(event.getText());
+    }
+
+    private void addMessage(String msg) {
+        messages.addComponent(new Label(msg));
+    }
+}
+----
+
+((("CDI", "qualifiers")))
+Note that the client object is completely unaware of the fact that the messages
+are delivered through a messaging service; we have successfully decoupled the
+messaging logic required by Vaadin UIs from the component. Only the requirement
+for using the event qualifier remains (notice that its use is not checked at
+compile time).
+
+(((range="endofrange", startref="term.advanced.cdi.events.broadcasting")))
+
+(((range="endofrange", startref="term.advanced.cdi.events")))
+endif::web[]
+
+(((range="endofrange", startref="term.advanced.cdi.cdilong")))
+(((range="endofrange", startref="term.advanced.cdi.cdi")))
+(((range="endofrange", startref="term.advanced.cdi.cdiaddon")))
+
+
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