Equinox初體驗(上)－Jemmy Walker

　　連兩天打麻將，晚上就研究Equinox在Eclipse的官網上的QuickStart兩個Sample飯粒。昨天小輸，研究也遇瓶頸，今天小贏，終於也了解這兩個Sample在搞什麼把戲。

　　在http://www.eclipse.org/equinox/server/http_in_container.php，可以下載sample.http和sample.http.registry兩顆飯粒。這兩個差別是前者透過程式碼去定義Servlet或html去對映URL，後者則是透過設定檔去對映，而後者要import的Jar比前者多些。先講前者：

在Equinox上Run Jetty要import的Jar的檔清單

id    State       Bundle
0    ACTIVE      org.eclipse.osgi_3.5.1.R35x_v20090827
1    ACTIVE      org.eclipse.osgi.util_3.2.0.v20090520-1800
2    ACTIVE      org.apache.commons.logging_1.0.4.v200904062259
3    ACTIVE      javax.servlet.jsp_2.0.0.v200806031607
4    ACTIVE      org.mortbay.jetty.util_6.1.15.v200905182336
5    ACTIVE      javax.servlet_2.5.0.v200806031605
6    ACTIVE      org.eclipse.equinox.http.jetty_2.0.0.v20090520-1800
7    ACTIVE      org.mortbay.jetty.server_6.1.15.v200905151201
8    ACTIVE      org.eclipse.osgi.services_3.2.0.v20090520-1800
9    ACTIVE      org.eclipse.equinox.http.servlet_1.0.200.v20090520-1800

在MENIFEST.MF的設定：Import以下的設定，均是用程式碼對映Servlet所需。

Import-Package: javax.servlet,
javax.servlet.http,
org.osgi.framework;version="1.3.0",
org.osgi.service.http;version="1.2.0",
org.osgi.util.tracker;version="1.3.1"

程式碼(sample.http.Activator.java)

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

public class Activator implements BundleActivator {

    private ServiceTracker httpServiceTracker;
    public void start(BundleContext context) throws Exception {
        httpServiceTracker = new HttpServiceTracker(context); // 呼叫內部類別 Step 0
        httpServiceTracker.open();
    }

    public void stop(BundleContext context) throws Exception {
        httpServiceTracker.close();
        httpServiceTracker = null;
    }

private class HttpServiceTracker extends ServiceTracker { // 寫個內部類別繼承ServiceTracer Step 1

        public HttpServiceTracker(BundleContext context) {
            super(context, HttpService.class.getName(), null);
        }

        public Object addingService(ServiceReference reference) {　// 對映Servlet與URL主程式
            HttpService httpService = (HttpService) context.getService(reference);　　// Step 2
            try {
                httpService.registerResources("/helloworld.html", "/helloworld.html", null);     // Step3
                httpService.registerServlet("/helloworld", new HelloWorldServlet(), null, null); // Step3
            } catch (Exception e) {
                e.printStackTrace();
            }
            return httpService;
        }
        public void removedService(ServiceReference reference, Object service) { // 無作用時記得取消對映。
            HttpService httpService = (HttpService) service;
            httpService.unregister("/helloworld.html");
            httpService.unregister("/helloworld");
            super.removedService(reference, service);
        }
    }
}

　　上例中，HelloWorldServlet是一個標準的Servlet Class，沒有任何和OSGi有關的置入性code。因果關係可以上面標出的Step看出，而Step 3的HttpService的兩個method：registerResources與registerServlet，第一個參數是URL，第二個參數是對映的實體，new HelloServlet()沒問題，而/helloworld.html是指向與META-INF目錄同層。

　　像HttpService一個個設定URL與實體資源的對映很麻煩，而sample.http.registry飯粒就提供像web.xml設定的功能(如果能做到把WAR當作一個OSGi Jar更好，但Equinox平台目前還看不出，而別的平台如Spring的dm Server似乎可以)。

在Equinox上Run Jetty的清單以外，還得加以下的Jar：

3     ACTIVE      org.eclipse.equinox.http.registry_1.0.200.v20090520-1800
14    ACTIVE      org.eclipse.equinox.common_3.5.1.R35x_v20090807-1100
15    ACTIVE      org.eclipse.equinox.registry_3.4.100.v20090520-1800

在MENIFEST.MF的設定：只需import javax.servlet和javax.servlet.http，另外需要加上：

Require-Bundle: org.eclipse.equinox.http.registry

在plugin.xml設定，plugin.xml需與META-INF目錄同層。

<?xml version="1.0" encoding="UTF-8"?>
<?eclipse version="3.0"?>
<plugin>
   <extension-point id="servlets" name="HttpService servlets" schema="schema/servlets.exsd"/>
   <extension-point id="resources" name="HttpService resources" schema="schema/resources.exsd"/>
   <extension-point id="httpcontexts" name="HttpService httpcontexts" schema="schema/httpcontexts.exsd"/>
     <extension
           id="helloServlet"
           point="org.eclipse.equinox.http.registry.servlets">
        <servlet
              alias="/ext1/helloworld"
              class="sample.http.registry.HelloWorldServlet">
           <init-param
                 name="servlet-name"
                 value="Test Servlet">
           </init-param>
           <init-param
                 name="testParam"
                 value="test param value">
           </init-param>
        </servlet>
     </extension>
     <extension
           id="helloResource"
           point="org.eclipse.equinox.http.registry.resources">
        <resource
              alias="/ext1/helloworld.html"
              base-name="/helloworld.html"
              />
     </extension>
</plugin>