OSGi服务发布与引用工具-SAT

     OSGi的服务层（Service Layer）为bundle之间的解耦合及服务引用提供的强大而又灵活的实现机制。通过BundleActivator控制组件的生命周期，通过BundleContext 与其他组件和服务交互。但是，OSGi服务层在提供强大的功能的同时，也给使用者造成了很大的困惑，比如，组件的启动顺序，服务的查找策略等等。OSGi通过Declarative Service给出了一种通过XML配置文件发布和绑定服务的功能，用户只需要定义XML文件即可向OSGi环境中发布服务对象和获取其他bundle组件发布的服务。

     在OSGi编程过程中，获取其他Bundle提供的服务是比较复杂的，尤其是获取多个服务时需要做很多重复性的工作。有没有更为简单的方式实现服务的发布和绑定呢？最近在Equinox邮件列表中看到Patrick的向equinox开发组的一项提议，建议将Service Activator Toolkit（SAT）组件添加到Equinox项目中，SAT目前位于Eclipse 技术项目OHF中。

     SAT大大简化了OSGi Service Bundle开发的复杂性。用户可以通过SAT插件引用服务，发布服务，自定义Bundle Activator。下面是SAT插件的功能略图：

上图展示了如何引用和发布服务

上图展示了如何定制BundleActivator。

     下面通过几行简单的代码展示SAT如何简化服务的发布和引用。

//服务的发布

public class Activator extends BaseBundleActivator { protected void activate() {  LogUtility.logInfo("The Hotdog Vendor bundle has been activated");  //$NON-NLS-1$  addExportedVendorService(); }

//将HotdogVendor服务发布到OSGi环境中

 private void addExportedVendorService() {  VendorService service = new HotdogVendor();  Dictionary properties = new Hashtable(11);  properties.put(VendorService.SPICINESS_PROPERTY, new Integer(10));  addExportedService(VendorService.SERVICE_NAME, service, properties); }

 protected void deactivate() {  LogUtility.logInfo("The Hotdog Vendor bundle has been deactivated");  //$NON-NLS-1$ }}

//服务的引用

public class Activator extends BaseBundleActivator { private Customer customer;

//组件启动激活

 protected void activate() {  LogUtility.logInfo("The Customer bundle has been activated");  //$NON-NLS-1$  VendorService vendor = getVendorService();  Customer customer = getCustomer();  customer.setVendor(vendor);  customer.eat(); }

//组件停止注销

 protected void deactivate() {  Customer customer = getCustomer();  customer.setVendor(null);  LogUtility.logInfo("The Customer bundle has been deactivated");  //$NON-NLS-1$ }

 private Customer getCustomer() {  return customer; }

//声明需要引用的服务的名称

 protected String[] getImportedServiceNames() {  return new String[] {   VendorService.SERVICE_NAME  }; }

//设定服务过滤条件

 private String getVendorFilter() {  StringBuffer buffer = new StringBuffer(50);  buffer.append('(');  buffer.append(VendorService.SPICINESS_PROPERTY);  buffer.append("<=");  //$NON-NLS-1$  buffer.append(8);  buffer.append(')');  String filter = buffer.toString();  return filter; }

//获取HotdogVender服务

 private VendorService getVendorService() {  return (VendorService) getImportedService(VendorService.SERVICE_NAME); }

 private void setCustomer(Customer customer) {  this.customer = customer; }

 protected void start() throws Exception {  LogUtility.logInfo("The Customer bundle has been started");  //$NON-NLS-1$  Customer customer = new Customer();  setCustomer(customer);  String filter = getVendorFilter();  addImportedServiceFilter(VendorService.SERVICE_NAME, filter); }

 protected void stop() throws Exception {  setCustomer(null);  LogUtility.logInfo("The Customer bundle has been stopped");  //$NON-NLS-1$ }}

    SAT目前从Eclipse CVS上可以获取到。CVS的访问地址为：

    :pserver:dev.eclipse.org:/cvsroot/technology      org.eclipse.ohf/plugins/org.eclipse.soda.sat