This Server Object Extension calculates lengths of all street (polyline) features in the associated map service and can be accessed by a client application through DCOM. 

这个服务器对象扩展SOE可以计算在指定的地图服务中的所有街道(折线)的长度,并且可以通过客户端应用程序使用DCOM来访问。

此SOE没有实现rest和soap接口，所以在启用此SOE后，在地图服务的rest网页无法看到这个功能。他只能通过客户端使用DCOM来访问。其功能是 计算Streets地图图层de要素类的长度。默认在portLand地图有此地图图层，其他的地图服务如果没有这个要素类是会报错的。当然也可以更改源码改为其他的地图图层。

下面就是主要的源码：

MapServer mapServer = null;        mapServer = (MapServer) soHelper.getServerObject();    /****************************************************************************************************************************     * ICalculateLength method: This is a custom interface. It exposes 1 method:     * calculateLength()     ****************************************************************************************************************************/    /**     * Calculates length of all polylines     */    public double calculateLength() throws Exception {                // Get index of layer containing all locations        Map map = (Map) this.mapServer.getMap("Layers");        FeatureClass streetsFC = new FeatureClass(this.mapServer.getDataSource(this.mapServer.getDefaultMapName(), getLayerIndex(map, "Streets")));        // count num of features        int numFeatures = streetsFC.featureCount(null);        IFeatureCursor featureCursor = streetsFC.search(null, true);        // calculate length of each feature and add up        double totalLength = 0.0;        for (int i = 0; i < numFeatures; i++) {            IFeature feature = featureCursor.nextFeature();            Polyline polyline = (Polyline) feature.getShape();            totalLength += polyline.getLength();        }        return totalLength;    }    /************************************************************************     * Util methods     ************************************************************************/    /**     * Retrieves ID of a layer in MapEJB based on its name     *      * @param mapServer     * @param layerName     * @return     */    private int getLayerIndex(Map map, String layerName) throws IOException, AutomationException {        int layerID = -1;        for (int i = 0; i < map.getLayerCount(); i++) {            String name = map.getLayer(i).getName();            if (layerName.equalsIgnoreCase(name)) {                layerID = i;                break;            }        }        if (layerID < 0) {            serverLog.addMessage(4, 8000, "Could not find layer " + layerName + " in " + map.getName());            throw new RuntimeException("Could not find layer " + layerName + " in " + map.getName());        }        return layerID;    }

通过 soHelper.getServerObject();获得mapserver对象，在通过mapserver的getMap("Layers")获得Map对象，通过Mapserver的getDataSource方法获得一个FeatureClass对象，再根据FeatureClass的一个游标获得feature对象，因而获得polyline feature的length，遍历累计相加，返回结果。

我更感兴趣的是：客户端如何通过DCOM来调用这个Length Calculator Server Object Extension

/* Copyright 2010 ESRI* * All rights reserved under the copyright laws of the United States* and applicable international laws, treaties, and conventions.* * You may freely redistribute and use this sample code, with or* without modification, provided you include the original copyright* notice and use restrictions.* * See the use restrictions at <your ArcGIS install location>/DeveloperKit10.0/userestrictions.txt.* */package arcgissamples.soe.client;import arcgissamples.soe.ICalculateLength;import com.esri.arcgis.carto.MapServer;import com.esri.arcgis.server.IServerObjectExtension;import com.esri.arcgis.server.IServerObjectExtensionManager;import com.esri.arcgis.server.ServerConnection;import com.esri.arcgis.server.ServerContext;import com.esri.arcgis.server.ServerObjectManager;import com.esri.arcgis.system.ServerInitializer;public class LengthCalculatorClient {    private static String serverName, domainName, userName, password, serviceName;    private static ServerConnection connection;    public static void main(String[] args) {        try {            if (args.length != 5) {                System.out.println("Wrong Usage. For correct usage, see following: \n"                        + "\nUsage: LengthCalculatorClient [server name] [domain name] [user name] [password] [map service name]\n\n"                    + "[server name]\tSpecifies name of ArcGIS Server\n" + "[domain name]\tSpecifies domain name of user\n"                    + "[user name]\tSpecifies user name\n" + "[password]\tSpecifies user password\n"                     + "[map service name]\tSpecifies name of map service\n");                                System.exit(1);            } else {                // connect to Server                serverName = args[0];                domainName = args[1];                userName = args[2];                password = args[3];                serviceName = args[4];                ServerInitializer serverInit = new ServerInitializer();                serverInit.initializeServer(domainName, userName, password);                System.out.print("Connecting to ArcGIS Server " + serverName + "...");                connection = new ServerConnection();                connection.connect(serverName);                System.out.println("Done.");                // Retrieve the SOM to get ServerContext and the Map Server Object                System.out.print("Retrieving Server Object Manager.");                ServerObjectManager som = new ServerObjectManager(connection.getServerObjectManager());                System.out.println("Done.");                System.out.print("Creating Server Context...");                String soeName = "LengthCalculatorSOE";                ServerContext serverContext = new ServerContext(som.createServerContext(serviceName, "MapServer"));                MapServer mapServer = (MapServer) serverContext.getServerObject();                System.out.println("Done.");                // Access the soe through the IServerObjectExtensionManager                System.out.println("Creating instance of SOE..");                IServerObjectExtensionManager extnMgr = (IServerObjectExtensionManager) mapServer;                IServerObjectExtension calculatorSOE = extnMgr.findExtensionByTypeName(soeName);                System.out.println("Done.");                // Consume the SOE                System.out.println("\nInvoking SOE's calculateLength() method...");                ICalculateLength mySOE = (ICalculateLength) calculatorSOE;                System.out.println("Total Length returned by SOE: " + mySOE.calculateLength());                // releasing connection                System.out.print("\nDisconnecting " + serverName + "...");                connection.release();                System.out.println("Done.");            }        } catch (Exception e) {            try {                connection.release();            } catch (Exception e1) {                e1.printStackTrace();            }            e.printStackTrace();        }    }}

这个java 程序 居然可以不用engine的许可，就调用ao的类。。

传递几个参数：serverName:localhost domainName：127.0.0.1 userName：arcgismanager password：arcgismanager serviceName：portland。username和password貌似没啥必要。不清楚。

通过 new ServerConnection();然后一步一步的获得了Mapserver对象，继而获得SOE对象，最后强制转换为ICalculateLength的SOE对象，直接调用calculatgeLength方法直接得到结果了，貌似跟本地程序一样，这就是 传说中的 DCOM 远程调用。。。看不出任何 内部细节。只能作罢。