{"id":2158,"date":"2015-12-01T15:35:25","date_gmt":"2015-12-01T13:35:25","guid":{"rendered":"http:\/\/hasselba.ch\/blog\/?p=2158"},"modified":"2015-12-01T15:36:20","modified_gmt":"2015-12-01T13:36:20","slug":"things-i-never-blogged-about-the-eventbus","status":"publish","type":"post","link":"https:\/\/hasselba.ch\/blog\/?p=2158","title":{"rendered":"Things I never blogged about: XPages & Google’s EventBus"},"content":{"rendered":"

This is another topic I wanted to blog about for a long time: The use of Google’s EventBus<\/a> in XPages applications. EventBus<\/em> is a replacement for the Java in-process event distribution. It makes life a lot easier.<\/p>\n

My first plan was to add the guava.jar<\/a> into an OSGi plugin because of security reasons (otherwise you have to use the „grant{ permission java.security.AllPermission;}<\/em>„) but I never had the time. That’s why I created a simple example which uses the jar in the lib\/ext<\/em> folder instead.<\/p>\n

To use the EventBus<\/em> in an application, you first have to define an event. This simple example has a message only, but you can add any properties you want.<\/p>\n

package ch.hasselba.xpages;\r\n\r\npublic class FrontendEvent {\r\n\r\n\u00a0\u00a0 \u00a0private final String message;\r\n\r\n\u00a0\u00a0 \u00a0public FrontendEvent(final String message) {\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0this.message = message;\r\n\u00a0\u00a0 \u00a0}\r\n\r\n\u00a0\u00a0 \u00a0public String getMessage() {\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0return message;\r\n\u00a0\u00a0 \u00a0}\r\n\r\n}<\/code><\/pre>\n
Then we need a subscriber. For this we have to add the annotation @Subscribe<\/em> to a method of a managed bean which should handle an event.\u00a0The class type of the parameter tells the EventBus<\/em> what kind of event our method should handle.<\/p>\n
This is a managed bean which stores the last message sent over the EventBus<\/em>:<\/p>\n
package ch.hasselba.xpages;\r\n\r\nimport com.google.common.eventbus.Subscribe;\r\n\r\npublic class EventSubscriber {\r\n\r\n\u00a0\u00a0 \u00a0private String message;\r\n\r\n\u00a0\u00a0 \u00a0@Subscribe\r\n\u00a0\u00a0 \u00a0public void handleEvent(FrontendEvent event) {\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0this.message = event.getMessage();\r\n\u00a0\u00a0 \u00a0}\r\n\r\n\u00a0\u00a0 \u00a0public void getMessage(String msg) {\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0this.message = msg;\r\n\u00a0\u00a0 \u00a0}\r\n\r\n\u00a0\u00a0 \u00a0public String getMessage() {\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0return this.message;\r\n\u00a0\u00a0 \u00a0}\r\n}<\/code><\/pre>\n
Then we have to create a managed bean which has an instance of EventBus<\/em>, the FrontendEventBus.<\/em> The bus has a managed property subscribers<\/em>. As soon the bean is instantiated, the managed property is called and the list of objects is registered to the EventBus<\/em> instance.<\/p>\n
package ch.hasselba.xpages;\r\n\r\nimport java.io.Serializable;\r\nimport java.util.ArrayList;\r\n\r\nimport com.google.common.eventbus.EventBus;\r\nimport com.google.common.eventbus.SubscriberExceptionContext;\r\nimport com.google.common.eventbus.SubscriberExceptionHandler;\r\n\r\n@SuppressWarnings(\"serial\")\r\npublic class FrontendEventBus implements SubscriberExceptionHandler,\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0Serializable {\r\n\r\n\u00a0\u00a0 \u00a0final EventBus eventBus = new EventBus();\r\n\u00a0\u00a0 \u00a0ArrayList<Object> subscribers;\r\n\r\n\u00a0\u00a0 \u00a0\/**\r\n\u00a0\u00a0 \u00a0 * registers all subscribing managed beans from faces-config.xml\r\n\u00a0\u00a0 \u00a0 * \r\n\u00a0\u00a0 \u00a0 * @param subscribers\r\n\u00a0\u00a0 \u00a0 *\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 ArrayList with references to managed beans\r\n\u00a0\u00a0 \u00a0 *\/\r\n\u00a0\u00a0 \u00a0public void setSubscribers(ArrayList<Object> subscribers) {\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0this.subscribers = subscribers;\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0for (Object subscriber : subscribers) {\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0register(subscriber);\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0}\r\n\u00a0\u00a0 \u00a0}\r\n\r\n\u00a0\u00a0 \u00a0public void post(final Object event) {\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0eventBus.post(event);\r\n\u00a0\u00a0 \u00a0}\r\n\r\n\u00a0\u00a0 \u00a0public void register(final Object object) {\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0eventBus.register(object);\r\n\u00a0\u00a0 \u00a0}\r\n\r\n\u00a0\u00a0 \u00a0public void unregister(final Object object) {\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0eventBus.unregister(object);\r\n\u00a0\u00a0 \u00a0}\r\n\r\n\u00a0\u00a0 \u00a0public final void handleException(Throwable exception,\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0SubscriberExceptionContext context) {\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0exception.printStackTrace();\r\n\r\n\u00a0\u00a0 \u00a0}\r\n\r\n}\r\n<\/code><\/pre>\n
There is only one problem: If a bean is in a lower scope, the initialization will fail. In this case we have to do the opposite to attach a subscriber to the bus. Instead of telling the bus which subscriber we want to register, we are telling the subscriber which bus to attach to.<\/p>\n
package ch.hasselba.xpages;\r\n\r\npublic class EventSubscriberRequestScope extends EventSubscriber {\r\n\r\n\u00a0\u00a0 \u00a0\/**\r\n\u00a0\u00a0 \u00a0 * registers the current instance to the event bus\r\n\u00a0\u00a0 \u00a0 * \r\n\u00a0\u00a0 \u00a0 * @param eventBus\r\n\u00a0\u00a0 \u00a0 *\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 the frontend event bus\r\n\u00a0\u00a0 \u00a0 *\/\r\n\u00a0\u00a0 \u00a0public void setEventBus(FrontendEventBus eventBus) {\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0eventBus.register(this);\r\n\u00a0\u00a0 \u00a0}\r\n\r\n}<\/code><\/pre>\n
As soon the bean is instantiated, the managed property will have an instance of our FrontendEventBus<\/em> and the bean can register itself.<\/p>\n
The faces-config.xml<\/em> looks like this:<\/p>\n
<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n<faces-config>\r\n\r\n\u00a0\u00a0 \u00a0<managed-bean>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<managed-bean-name>frontendEventBus<\/managed-bean-name>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<managed-bean-class>ch.hasselba.xpages.FrontendEventBus<\/managed-bean-class>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<managed-bean-scope>session<\/managed-bean-scope>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<managed-property>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<property-name>subscribers<\/property-name>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<list-entries>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<value-class>java.lang.Object<\/value-class>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<value>#{eventSubscriber}<\/value>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<\/list-entries>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<\/managed-property>\r\n\u00a0\u00a0 \u00a0<\/managed-bean>\r\n\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0 \u00a0<managed-bean>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<managed-bean-name>eventSubscriber<\/managed-bean-name>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<managed-bean-class>ch.hasselba.xpages.EventSubscriber<\/managed-bean-class>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<managed-bean-scope>session<\/managed-bean-scope>\r\n\u00a0\u00a0 \u00a0<\/managed-bean>\r\n\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0 \u00a0<managed-bean>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<managed-bean-name>eventSubscriberRequestScope<\/managed-bean-name>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<managed-bean-class>ch.hasselba.xpages.EventSubscriberRequestScope<\/managed-bean-class>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<managed-bean-scope>request<\/managed-bean-scope>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<managed-property>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<property-name>eventBus<\/property-name>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<value>#{frontendEventBus}<\/value>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<\/managed-property>\r\n\u00a0\u00a0 \u00a0<\/managed-bean>\r\n\u00a0\u00a0\u00a0 \r\n<\/faces-config><\/code><\/pre>\n
The first subscribing bean is in the same scope as the FrontendEventBus<\/em>, but the second one is a request scoped bean.<\/p>\n
Now it’s time to send an event. This can be realized by creating a new instance of our FrontendEvent<\/em> we have created earlier and posting it to the bus.<\/p>\n
<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n<xp:view xmlns:xp=\"http:\/\/www.ibm.com\/xsp\/core\">\r\n\r\n\u00a0\u00a0 \u00a0<xp:button\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0id=\"button1\" value=\"Click me\">\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<xp:eventHandler\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0event=\"onclick\"\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0submit=\"true\"\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0refreshMode=\"complete\">\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<xp:this.action>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<![CDATA[#{javascript:importPackage( ch.hasselba.xpages );\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0var msg = \"Timestamp: \" + java.lang.System.currentTimeMillis();\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0var se = new ch.hasselba.xpages.FrontendEvent( msg );\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0frontendEventBus.post( se );\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0}]]>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<\/xp:this.action>\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0<\/xp:eventHandler>\r\n\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0 \u00a0<\/xp:button>\r\n\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0 \u00a0<br \/>\r\n\u00a0\u00a0 \u00a0<br \/>\r\n\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0 \u00a0<xp:label\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0value=\"#{eventSubscriber.message}\"\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0id=\"labelSubscriberMessage\">\r\n\u00a0\u00a0 \u00a0<\/xp:label>\r\n\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0 \u00a0<br \/>\r\n\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0 \u00a0<xp:label\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0value=\"#{eventSubscriberRequestScope.message}\"\r\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0id=\"labelSubscriberRequestScope\">\r\n\u00a0\u00a0 \u00a0<\/xp:label>\r\n\u00a0\u00a0 \u00a0\r\n<\/xp:view><\/code><\/pre>\n
As soon the button is clicked, both beans are receiving the event and updating their message.<\/p>\n
\"2015-12-01<\/a><\/p>\n
Hope someone finds it usefull.<\/p>\n","protected":false},"excerpt":{"rendered":"
This is another topic I wanted to blog about for a long time: The use of Google’s EventBus in XPages applications. EventBus is a replacement for the Java in-process event distribution. It makes life a lot easier. My first plan … Weiterlesen →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[89,26,74],"tags":[],"class_list":["post-2158","post","type-post","status-publish","format-standard","hentry","category-java","category-jsf","category-xpages"],"_links":{"self":[{"href":"https:\/\/hasselba.ch\/blog\/index.php?rest_route=\/wp\/v2\/posts\/2158","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/hasselba.ch\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/hasselba.ch\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/hasselba.ch\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/hasselba.ch\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2158"}],"version-history":[{"count":7,"href":"https:\/\/hasselba.ch\/blog\/index.php?rest_route=\/wp\/v2\/posts\/2158\/revisions"}],"predecessor-version":[{"id":2197,"href":"https:\/\/hasselba.ch\/blog\/index.php?rest_route=\/wp\/v2\/posts\/2158\/revisions\/2197"}],"wp:attachment":[{"href":"https:\/\/hasselba.ch\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2158"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/hasselba.ch\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2158"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/hasselba.ch\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2158"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}