OSGi系列 第一个OSGi Bundle

安装好了Apache Felix，下面要做的是开发我的第一个Bundle。整个过程是参考Apache Felix Tutorial Example 1 - Service Event Listener Bundle实现的。

打开一个DOS窗口，切换到要存放Bundle的目录，这里以D:\develop\eclipse-jee-indigo-SR2-win32\workspace\felix-analysis为例。然后使用Maven创建一个空的项目。

mvn archetype:create -DgroupId=felix.tutorial -DartifactId=example1 -DpackageName=felix.tutorial.example1 -Dversion=1.0.0

执行完成后会出现下面的目录结构：

切换到目录src\main\java\felix\tutorial\example1，删除Maven创建的App.java文件，新建文件Activator.java，文件内容如下：

package felix.tutorial.example1;

import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceListener;
import org.osgi.framework.ServiceEvent;

/**
 * This class implements a simple bundle that utilizes the OSGi
 * framework's event mechanism to listen for service events. Upon
 * receiving a service event, it prints out the event's details.
**/
public class Activator implements BundleActivator, ServiceListener
{
    /**
     * Implements BundleActivator.start(). Prints
     * a message and adds itself to the bundle context as a service
     * listener.
     * @param context the framework context for the bundle.
    **/
    public void start(BundleContext context)
    {
        System.out.println("Starting to listen for service events.");
        context.addServiceListener(this);
    }

    /**
     * Implements BundleActivator.stop(). Prints
     * a message and removes itself from the bundle context as a
     * service listener.
     * @param context the framework context for the bundle.
    **/
    public void stop(BundleContext context)
    {
        context.removeServiceListener(this);
        System.out.println("Stopped listening for service events.");

        // Note: It is not required that we remove the listener here,
        // since the framework will do it automatically anyway.
    }

    /**
     * Implements ServiceListener.serviceChanged().
     * Prints the details of any service event from the framework.
     * @param event the fired service event.
    **/
    public void serviceChanged(ServiceEvent event)
    {
        String[] objectClass = (String[])
            event.getServiceReference().getProperty("objectClass");

        if (event.getType() == ServiceEvent.REGISTERED)
        {
            System.out.println(
                "Ex1: Service of type " + objectClass[0] + " registered.");
        }
        else if (event.getType() == ServiceEvent.UNREGISTERING)
        {
            System.out.println(
                "Ex1: Service of type " + objectClass[0] + " unregistered.");
        }
        else if (event.getType() == ServiceEvent.MODIFIED)
        {
            System.out.println(
                "Ex1: Service of type " + objectClass[0] + " modified.");
        }
    }
}

用文字编辑软件打开pom.xml文件，修改成如下内容（注意这里的packaging变成了bundle）：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>felix.tutorial</groupId>
  <artifactId>example1</artifactId>
  <version>1.0.0</version>
  <packaging>bundle</packaging>

  <name>Service listener example</name>
  <description>A bundle that displays messages at startup and when service events occur</description>
  <organization>
    <name>Apache Felix</name>
  </organization>
  
  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>
  
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.felix</groupId>
        <artifactId>maven-bundle-plugin</artifactId>
        <extensions>true</extensions>
        <configuration>
          <instructions>
            <Bundle-Activator>felix.tutorial.example1.Activator</Bundle-Activator>
            <Import-Package>org.osgi.framework</Import-Package>
          </instructions>
        </configuration>
      </plugin>
    </plugins>
  </build>

  <dependencies>
    <dependency>
      <groupId>org.apache.felix</groupId>
      <artifactId>org.osgi.core</artifactId>
      <version>1.0.0</version>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>

打包bundle，在DOS窗口下执行mvn package。执行完成后target目录下有一个example1-1.0.0.jar文件，这就是最终需要发布的bundle文件。使用WinRar打开example1-1.0.0.jar，找到META-INFI/MANIFEST.MF，查看其内容，会发现maven-bundle-plugin产生了很多的条目，这些内容对OSGi容器非常的重要。

启动Felix，使用start file:/D:/develop/eclipse-jee-indigo-SR2-win32/workspace/felix-analysis/example1/target/example1-1.0.0.jar命令启动bundle。

为了测试我们的bundle，可以对它进行停止和启动，相应的会输出对应的信息提示。注意：这里启动和停止命令后面的5，是特定于当前Felix实例的example bundle序号，需要根据情况相应进行改变。

到这一步，我们的第一个bundle也就大功告成了。

使用Maven开发Bundle的文章：

Bundle Plugin for Maven