1、GeometryService的缓冲区（Buffer）功能实现

1、创建地图，并创建load的响应函数initToolbar

            map = new Map("map", {
                basemap: "streets",
                center: [-111.5, 39.541],
                zoom: 7
            });
            map.on("load", initToolbar);        

2、initToolbar函数，启用Draw对象，draw-end事件触发时响应doBuffer函数

             function initToolbar(evtObj) {
                app.tb = new Draw(evtObj.map);
                app.tb.on("draw-end", doBuffer);
            }    

3、dobuffer

   function doBuffer(evtObj) {
                var geometry = evtObj.geometry,
                map = app.map,
                gsvc = app.gsvc;
                switch (geometry.type) {
                    case "point":
                        var symbol = new SimpleMarkerSymbol(SimpleMarkerSymbol.STYLE_SQUARE, 10, new SimpleLineSymbol(SimpleLineSymbol.STYLE_SOLID, new Color([255, 0, 0]), 1), new Color([0, 255, 0, 0.25]));
                        break;
                    case "polyline":
                        var symbol = new SimpleLineSymbol(SimpleLineSymbol.STYLE_DASH, new Color([255, 0, 0]), 1);
                        break;
                    case "polygon":
                        var symbol = new SimpleFillSymbol(SimpleFillSymbol.STYLE_NONE, new SimpleLineSymbol(SimpleLineSymbol.STYLE_DASHDOT, new Color([255, 0, 0]), 2), new Color([255, 255, 0, 0.25]));
                        break;
                }

                var graphic = new Graphic(geometry, symbol);
                map.graphics.add(graphic);

                //setup the buffer parameters
                var params = new BufferParameters();
                params.distances = [dom.byId("distance").value];
                params.bufferSpatialReference = new esri.SpatialReference({ wkid: dom.byId("bufferSpatialReference").value });
                params.outSpatialReference = map.spatialReference;
                params.unit = GeometryService[dom.byId("unit").value];

                if (geometry.type === "polygon") {
                    //if geometry is a polygon then simplify polygon.  This will make the user drawn polygon topologically correct.
                    gsvc.simplify([geometry], function (geometries) {
                        params.geometries = geometries;
                        gsvc.buffer(params, showBuffer);
                    });
                } else {
                    params.geometries = [geometry];
                    gsvc.buffer(params, showBuffer);
                }
            }

            function showBuffer(bufferedGeometries) {
                var symbol = new SimpleFillSymbol(
                  SimpleFillSymbol.STYLE_SOLID,
                  new SimpleLineSymbol(
                    SimpleLineSymbol.STYLE_SOLID,
                    new Color([255, 0, 0, 0.65]), 2
                  ),
                  new Color([255, 0, 0, 0.35])
                );

                array.forEach(bufferedGeometries, function (geometry) {
                    var graphic = new Graphic(geometry, symbol);
                    app.map.graphics.add(graphic);
                });
                app.tb.deactivate();
                app.map.showZoomSlider();
            }