OSGi一小步

网上有很多介绍osgi概念的文章,有兴趣的同学可以去google一下.这里写一个简单的例子,记录自己的学习历程,也希望对初学osgi的同学有所帮助.

osgi强调模块化与服务化,我们可以在不重启Java虚拟机的情况下切换一个服务的实现,达到动态更新目的.与spring不同的是,osgi可 以动态绑定服务的实现,而Spring容器一旦启动就无法更改服务的实现,要想改变服务的实现,只有重新配置spring-bean文件,再重启 spring容器

下面例子就说明了这一点,我们要做的事情如下

• 我们有一个HelloService,用户需要实现sayHello方法
• 实现1,实现sayHello方法,输出HelloService1
• 实现2,实现sayHello方法,输出HelloService2
• 在运行时,将实现1切换到实现2,相当于模拟一种更新
•  卸载实现2,将实现还原为实现1,相当于模拟一种回滚

创建以下几个maven工程

• hello 为主工程
• hello.service 该工程包含HelloService接口
• hello.service.impl1 该工程包含HelloService的实现
• hello.service.impl2 该工程包含HelloService的实现
• hello.service.consumer 该工程会使用HelloService
• 以上四个工程皆为hello工程的module

hello.service工程

该工程为一个接口bundle,不包含BundleActivator

其用处是为其他几个bundle提供HelloService接口,隔离hello.service.impl与hello.service.consumer

package org.lazyman.osgi.hello.service;

public interface HelloService {

       public void sayHello();

}

由于其他几个bundle需要使用到HelloService接口,该bundle需要导出HelloService接口,其MANIFEST.MF文件如下

Manifest-Version: 1.0

Created-By: Freewind

Bundle-Version: 1.0.0

Bundle-Name: Hello Service Bundle

Bundle-Vendor: Freewind

Bundle-ManifestVersion: 2

Bundle-SymbolicName: hello.service

Export-Package: org.lazyman.osgi.hello.service

hello.service.impl1 工程

该工程为HelloService的一个实现bundle,包含一个BundleActivator向osgi容器注册HelloService的实现,hello.service.consumer可以从osgi容器获取该实现,调用相关服务

//HelloService 实现1

package org.lazyman.osgi.hello.service.impl1;

import org.lazyman.osgi.hello.service.HelloService;

public class HelloServiceImpl1 implements HelloService {

       @Override

       public void sayHello() {

              System.out .println(“HelloService1″);//实现1

       }

}

//实现1的BundleActivator

package org.lazyman.osgi.hello.service.impl1;

import org.lazyman.osgi.hello.service.HelloService;

import org.osgi.framework.BundleActivator;

import org.osgi.framework.BundleContext;

import org.osgi.framework.ServiceRegistration;

public class HelloServiceActivator implements BundleActivator {

       private ServiceRegistration sr;

       @Override

       public void start(BundleContext context) throws Exception {

              System.out .println(“HelloServiceActivator1.start”);

              //向osgi容器注册HelloService的实现1

              sr = context.registerService(HelloService.class.getName(),new HelloServiceImpl1(), null);

       }

       @Override

       public void stop(BundleContext context) throws Exception {

              sr.unregister();

       }

}

由于该bundle需要使用到HelloService接口及osgi的相关接口,该bundle需要导入相关的接口类,其MANIFEST.MF文件如下

Manifest-Version: 1.0

Created-By: Freewind

Bundle-Version: 1.0.0

Bundle-Name: Hello Service Impl1

Bundle-Vendor: Freewind

Bundle-ManifestVersion: 2

Bundle-SymbolicName: hello.service.impl1

Import-Package: org.lazyman.osgi.hello.service,org.osgi.framework

Bundle-Activator: org.lazyman.osgi.hello.service.impl1.HelloServiceActivator

hello.service.impl2 工程

该bundle与hello.service.impl1类似,改变的是如下代码

       public void sayHello() {

              System.out .println(“HelloService2″);//实现2

       }

篇幅所限,该工程其他的代码就不贴出了,有兴趣可参看下附件

hello.service.consumer 工程

该工程向osgi容器注册HelloService的服务监听器,当有HelloService服务注册时,服务监听器会取得该服务,并添加到 hello.service.consumer中,当HelloService卸载时,服务监听器会从hello.service.consumer去除 该服务,具体如下

//hello.service.consumer BundleActivator

package org.lazyman.osgi.hello.service.consumer;

import java.util.ArrayList;

import java.util.List;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.TimeUnit;

import org.lazyman.osgi.hello.service.HelloService;

import org.osgi.framework.BundleActivator;

import org.osgi.framework.BundleContext;

import org.osgi.framework.ServiceEvent;

import org.osgi.framework.ServiceListener;

public class HelloServiceConsumer implements BundleActivator {

      //HelloService列表,有可能存在多个HelloService实现

     //但我们优先使用最后注册的,达到服务更新的目的

       private List<HelloService> helloServices = new ArrayList<HelloService>();

       private ExecutorService executor;

       @Override

       public void start(BundleContext context) throws Exception {

              System.out .println(“HelloServiceConsumer.start”);

             //添加服务监听器,监听HelloService的状态

              context.addServiceListener(new HelloServiceListener(context));

              executor = Executors.newFixedThreadPool (1);

              //线程里循环调用HelloService

              executor.execute(new HelloServiceVisitorThread());

       }

       @Override

       public void stop(BundleContext context) throws Exception {

              System.out .println(“HelloServiceConsumer stop”);

       }

       public void setHelloService(HelloService helloService) {

              if (this.helloServices.isEmpty()) {// 如果列表为空,直接加入

                     this.helloServices.add(helloService);

              } else {// 将后启动的服务插入到列表之前,优先使用后加入的服务

                     this.helloServices.add(0, helloService);

              }

       }

       public void unsetHelloService(HelloService helloService) {

              //当HelloService卸载时,从服务列表删除

              this.helloServices.remove(helloService);

       }

       class HelloServiceListener implements ServiceListener {

              private BundleContext context;

              public HelloServiceListener(BundleContext context) {

                     this.context = context;

              }

              @Override

              public void serviceChanged(ServiceEvent evt) {

                     HelloService hs = (HelloService) context.getService(evt.getServiceReference());

                     if (evt.getType() == ServiceEvent.REGISTERED ) {

                            setHelloService(hs);//添加服务

                     } else if (evt.getType() == ServiceEvent.UNREGISTERING ) {

                            System.out .println(“service unregistered”);

                            unsetHelloService(hs);//卸载服务

                     }

              }

       }

       class HelloServiceVisitorThread implements Runnable {

              public void run() {

                     while (true) {

                            try {

                                   synchronized (helloServices) {

                                          if (helloServices.size() > 0) {//判断是否有HelloService服务

                                                 helloServices.get(0).sayHello();

                                          } else {

                                                 System.out .println(“NO HelloService”);

                                          }

                                   }

                                   TimeUnit.SECONDS .sleep(20);

                            } catch (InterruptedException e) {

                                   // ignore

                            }

                     }

              }

       }

}

其MANIFEST.MF文件如下

Manifest-Version: 1.0

Created-By: Freewind

Bundle-Version: 1.0.0

Bundle-Name: Hello Service Consumer

Bundle-Vendor: Freewind

Bundle-ManifestVersion: 2

Bundle-SymbolicName: hello.service.consumer

Import-Package: org.osgi.framework,org.lazyman.osgi.hello.service

Bundle-Activator: org.lazyman.osgi.hello.service.consumer.HelloServiceConsumer

以上各工程的MANIFEST.MF文件放置布局如下:

我们需要在打包时,将自定义的MANIFEST.MF打入jar包,只需要在主pom配置maven-jar-plugin即可

                     <plugin>

                            <groupId>org.apache.maven.plugins</groupId>

                            <artifactId>maven-jar-plugin</artifactId>

                            <configuration>

                                   <archive>

                                          <manifestFile>META-INF/MANIFEST.MF</manifestFile>

                                   </archive>

                            </configuration>

                     </plugin>

打包各工程

命令行进入主工程目录

mvn clean package

拷出各工程target下的jar到你喜欢的地方,比如c:/lib

此处给个脚本,以方便拷出jar包—cp.bat

copy /Y hello.service\target\hello.service.jar c:\lib

copy /Y hello.service.consumer\target\hello.service.consumer.jar c:\lib

copy /Y hello.service.impl1\target\hello.service.impl1.jar c:\lib

copy /Y hello.service.impl2\target\hello.service.impl2.jar c:\lib

启动osgi容器,此处使用equinox

 java -jar org.eclipse.osgi.jar –console                     

 此时只有一个bundle,也就是容器本身

安装刚刚打包好的各个bundle

install file:///c:/lib/hello.service.jar

install file:///c:/lib/hello.service.impl1.jar

install file:///c:/lib/hello.service.impl2.jar

install file:///c:/lib/hello.service.consumer.jar

安装的顺序可以随意,稍后启动的顺序必须先启动hello.service,因为后面三个对hello.service有依赖

目前的状态如下

可以看到有四个bundle处于已安装状态

启动已安装的bundle

上面提过,必须先启动hello.service,你也可以尝试下先启动其他bundle,看会有什么情况出现

从上图可以看到,hello.service的id为2,此处的id相当于pid,我们可以用以下方式启动hello.service bundle

start 2

可以看到hello.service已经处于活动状态

再启动hello.service.consumer,看看什么情况

start 1     

有NO HelloService输出,因为此时还没有注册HelloService的实现

启动实现1

 start 4

此后将一直输出HelloService1

更新HelloService的实现,此时只需要启动实现2即可

start 3

此后HelloService将会切换到实现2上

回滚到实现1上,只需要停止实现2即可

 stop 3

 

此后HelloService将会回滚到实现1上

你也可以编写实现3,并动态加载到osgi容器,替换实现1或实现2,为hello.service.consumer提供不一样的服务~~~

equinox的osgi实现还有很多令人振奋的功能,比如声明式服务(ds),通过它以配置的方式注册或获取服务,可以省下很多繁琐的注册代码, 并且无需耦合osgi api,也不需要再写BundleActivator了,该功能在下篇文章会介绍到,尽请期待o(∩_∩)o