openlayers wfs获取要素

var wfsProtocol = new OpenLayers.Protocol.WFS.v1_1_0({
 url: mapServerUrl + "/wfs",
 featureType: layerConfig.layerName,
 featureNS: nameSpace,//正式环境代码：nameSpace
 maxFeatures: 2000,
 outputFormat: 'JSON',
 callback: function (req) {
 var features = req.features;
 //根据attributeName代表的值的大小排序，从小到大排序
 features = features.sort(
 function (a, b) {
 return a.attributes[attributeName] - b.attributes[attributeName];
 }
 );
 queryResultCache[layerConfig.layerName] = features;
 }
});
//propertyNames中可配置关心的属性名，而不是查询所有属性，这样能加快查询速度，其中the_geom查询的是空间数据，其他是属性数据
wfsProtocol.read({
 propertyNames: ["ROADBM", "ROADPOS","the_geom"]
});