OSGi 系列（十四）之 Event Admin Service

OSGi 系列（十四）之 Event Admin Service

OSGi 的 Event Admin 服务规范提供了开发者基于发布/订阅模型，通过事件机制实现 Bundle 间协作的标准通讯方式。

事件发布者使用 Event Admin 服务发送基于主题 (Topic) 的事件，任何对某一主题感兴趣的事件订阅者都会收到该事件，并且做出相应的反应。

1. Event Admin Service 介绍

(1) Event Admin Service 规范

compendium 规范提供了 Event Admin Service 服务，具体规范见 org.osgi.service.event

(2) Topic 的规范

• /不能用于开头或者结尾
• 可以使用 A-Z,a-z,0-9,-,_

2. 快速入门

2.1 环境准备

<dependency>
    <groupId>org.osgi</groupId>
    <artifactId>org.osgi.core</artifactId>
    <version>5.0.0</version>
</dependency>
<dependency>
    <groupId>org.osgi</groupId>
    <artifactId>org.osgi.compendium</artifactId>
    <version>5.0.0</version>
</dependency>

2.2 新建 2 个 bundle，一个发布事件(osgi-event-publish)，一个接收事件(osgi-event-subscribe)

2.3 发布事件(osgi-event-publish)

import java.util.HashMap;
import java.util.Map;

import org.osgi.service.event.Event;
import org.osgi.service.event.EventAdmin;

public class EventPublish {

    private EventAdmin eventAdmin;
    
    public void publish() {
        Map<String, String> content = new HashMap<>();
        content.put("phone", "10086");
        content.put("content", "ye");
        eventAdmin.postEvent(new Event("send/10086", content));
    }

    public void setEventAdmin(EventAdmin eventAdmin) {
        this.eventAdmin = eventAdmin;
    }
}

blueprint.xml 配制

<?xml version="1.0" encoding="UTF-8"?>
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://www.osgi.org/xmlns/blueprint/v1.0.0 http://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">
    
    <reference id="eventAdmin" interface="org.osgi.service.event.EventAdmin" />

    <bean class="com.edu.osgi.event.publish.EventPublish" init-method="publish">
        <property name="eventAdmin" ref="eventAdmin" />
    </bean>
</blueprint>

2.4 接收事件(osgi-event-subscribe)

import org.osgi.service.event.Event;
import org.osgi.service.event.EventHandler;

public class SendEventHandler implements EventHandler {

    public void handleEvent(Event event) {
        System.out.println("=======handleEvent=======");
        System.out.println(event.getTopic());

        for(String key : event.getPropertyNames()) {
            System.out.println(key + "=" + event.getProperty(key));
        }
    }
}

blueprint.xml 配制

<?xml version="1.0" encoding="UTF-8"?>
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://www.osgi.org/xmlns/blueprint/v1.0.0 http://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">

    <service interface="org.osgi.service.event.EventHandler">
        <service-properties>
            <entry key="event.topics" value="send/*"/>
        </service-properties>
        <bean class="com.edu.osgi.event.subscribe.SendEventHandler" />
    </service>
</blueprint>

2.5 karaf 测试

# 查看 EventAdmin 服务是否发布
ls EventAdmin
# 安装 eventadmin
feature:list | grep eventadmin
feature:install eventadmin

注意： osgi-event-subscribe 只能处理启动后发布的事件，不能处理启动前的事件。

3. 事件过滤

3.1 基于主题的过滤

<service interface="org.osgi.service.event.EventHandler">
    <service-properties>
        <entry key="event.topics" value="send/*"/>
    </service-properties>
    <bean class="com.edu.osgi.event.subscribe.SendEventHandler" />
</service>

3.2 基于内容的过滤

<service interface="org.osgi.service.event.EventHandler">
    <service-properties>
        <entry key="event.topics" value="send/*"/>
        <entry key="event.filter" value="(phone=10010)"/>
    </service-properties>
    <bean class="com.edu.osgi.event.subscribe.SendEventHandler" />
</service>