从 WMS 请求地图并将其作为 PNG 图像保存到磁盘

Question

我必须使用 java 和 GeoTools 编写代码来执行 WMS 请求，获取图像并将其保存到我计算机上的特定位置。我已经按照 GeoTools WMS 教程进行了代码编译，没有错误，但我不知道如何检查它是否有效或如何保存请求的图像？

这是带有所有必要参数的 GetMap 请求：http://ows.mundialis.de/services/service?request=GetMap&service=WMS&version=1.3.0&layers=OSM-Overlay-WMS&styles=default&crs=EPSG%3A4326&bbox=47.75,12.98,47.86,13.12&&width=2000&height=2000&format=image/png&transparent=true

代码如下：

public class WmsConnectorMaven {

    public static void main(String[] args) {

        URL url = null;
        try {
          url = new URL("http://ows.mundialis.de/services/service?service=wms&version=1.3.0&request=GetCapabilities");
        } catch (MalformedURLException e) {
          //will not happen
        }

        WebMapServer wms = null;
        try {
          wms = new WebMapServer(url);
          GetMapRequest request = wms.createGetMapRequest();
          request.addLayer("OSM-Overlay-WMS", "defualt");
          request.setFormat("image/png");
          request.setDimensions("800", "800"); //sets the dimensions of the image to be returned from the server
          request.setTransparent(true);
          request.setSRS("EPSG:4326");
          request.setBBox("47.75,12.98,47.86,13.12");

          GetMapResponse response = (GetMapResponse) wms.issueRequest(request);
          BufferedImage image = ImageIO.read(response.getInputStream());

         /* File outputfile = new File("saved.png");
            ImageIO.write(image, "png", outputfile); */

         // FileOutputStream img = new FileOutputStream("C:\\Users\\Edhem\\Desktop\\WMSimage.png");
        } catch (IOException e) {
          //There was an error communicating with the server
          //For example, the server is down
        } catch (ServiceException e) {
          //The server returned a ServiceException (unusual in this case)
        } 



    }
}

Answer 1

您需要检查返回的response 的contentType 并根据该值做出决定。比如：

try {
  GetMapResponse response = wms.issueRequest(getMapRequest);
  if (response.getContentType().equalsIgnoreCase(format)) {
    BufferedImage image = ImageIO.read(response.getInputStream());
    return image;
  } else {
    StringWriter writer = new StringWriter();
    IOUtils.copy(response.getInputStream(), writer);
    String error = writer.toString();
    System.out.println(error);
    return null;
  }
} catch (ServiceException | IOException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
  return null;
} 

更新

我刚刚跑了your code with my checks，我得到了：

<?xml version="1.0"?>
<ServiceExceptionReport version="1.3.0"
  xmlns="http://www.opengis.net/ogc"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.opengis.net/ogc
http://schemas.opengis.net/wms/1.3.0/exceptions_1_3_0.xsd">
    <ServiceException code="StyleNotDefined">unsupported styles: defualt</ServiceException>
</ServiceExceptionReport>

删除（拼错的）“defualt”给出（我猜是正确的）：