# OSGI DS 註解(annotation) 使用

###### tags: `OSGI` `Declarative Services` `Annotation`

參考文獻：
https://liferay.dev/blogs/-/blogs/liferay-osgi%25E6%25B3%25A8%25E8%25A7%25A3%25EF%25BC%2588annotation%25EF%25BC%2589-%25E4%25BD%25BF%25E7%2594%25A8%25E6%2589%258B%25E5%2586%258C-%25E8%25AF%2591%25E6%2596%2587-

## Declarative Services環境：
felix 環境要有三個

org.apache.felix.scr 2.1.16
org.osgi.util.promise	1.1.1.201810101357	
org.osgi.util.function	1.1.0.201802012106	

eclipse 環境

<dependency>
    <groupId>org.osgi</groupId>
    <artifactId>org.osgi.service.component.annotations</artifactId>
    <version>1.4.0</version>
    <scope>provided</scope>
</dependency>

## Declarative Service(DS)

http://blog.vogella.com/2016/06/21/getting-started-with-osgi-declarative-services/

http://blog.vogella.com/2016/09/26/configuring-osgi-declarative-services/

使用DS，就不需要register 與 get Service的冗余動作，而且服務的相關步驟會一切都處理好

### @Component

需要再osgi發佈任何組件時用

immediate：立即start
properties：配置組件，或是過濾
service：定義組件的服務，可以是接口 也可以是實例

範例

@Component(service = hello.class, immediate = true)
public class hello {
	@Override
	public void sayhello() {
		System.out.println("hello");
	}
}

@Component(service = Servlet.class, property = { "alias=/api" })
public class HttpApi extends HttpServlet {

}

### @Reference

需要把其他組件加入到自己組件的時候

target: 過濾
service:
policy:

cardinality: 組件啟動前 引入是否必須或是其他機制
1. MANDITORY：
1. OPTIONAL：
1. MULTIPLE：
1. AT_LEAST_ONE：

範例

@Component()
public class StaticConfiguredComponent {

    @Reference(service = hello.class)
    public void setHello(hello hoo){
        hoo.sayhello();
    }
    
    @Reference(service = DBtools.class, policy = ReferencePolicy.STATIC, cardinality = ReferenceCardinality.AT_LEAST_ONE)
    public void setHello(hello hoo){
        hoo.sayhello();
    }

}

### @Activate @Deactivate 啟動，停止調用的方法

@Activate
public void start() {
    System.out.println("test~");
}

@Deactivate
public void stop() {
    System.out.println("bye test~");
}

### @Compose 註冊http api

需配合 felix whiteborad使用

@Component(service = Servlet.class, property = { "alias=/api" })
public class HttpApi extends HttpServlet {
    
}

## Component 使用 inline properties

@Component(
    property = {
        "message=Welcome to the inline configured service",
        "iteration:Integer=3"
    }
)
public class StaticConfiguredComponent {
 
    @Activate
    void activate(Map<String, Object> properties) {
        String msg = (String) properties.get("message");
        Integer iter = (Integer) properties.get("iteration");
 
        for (int i = 1; i <= iter; i++) {
            System.out.println(i + ": " + msg);
        }
        System.out.println();
    }
}

## 使用 resource files

這邊是用的是bndtools的方式

@Component(
    properties="OSGI-INF/config.properties"
)
public class FileConfiguredComponent {
 
    @Activate
    void activate(Map<String, String> properties) {
        String msg = (String) properties.get("message");
        String iter = (String) properties.get("iteration");
 
        if (msg != null && iter != null) {
            Integer count = Integer.valueOf(iter);
            for (int i = 1; i <= count; i++) {
                System.out.println(i + ": " + msg);
            }
            System.out.println();
        }
    }
}

## 不使用DS，註冊及使用服務的方式

import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import org.osgi.service.http.HttpService;

public class Activator implements BundleActivator {

//	private HttpService service;

	public void start(BundleContext context) throws Exception {
//		System.out.println("123123");
//		
//		ServiceReference ref2 = context.getServiceReference(ConnectionPool.class.getName());
//		ConnectionPool pool = (ConnectionPool) context.getService(ref2);
//		
//		ServiceReference serviceReference = context.getServiceReference(HttpService.class.getName());
//		service = (HttpService) context.getService(serviceReference);
//		
//		
//		service.registerServlet("/api", new HttpApi(pool), null, null);
//		System.out.println("register /api");
	}

	public void stop(BundleContext context) throws Exception {
		// stop tracking all HTTP services...
//		System.out.println("345345");
//		service.unregister("/api");
//		System.out.println("byebye /api");
//		context = null;
	}

}