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