GeoTools WebMapServer GetMapRequest issue

Question

I'm using GeoTools 12.2 for developing java class library project.

Firstly, I'm working on GeoTools WMS module with this guide. The point that I was failed is doing get map request so that I could get capabilities document and layers etc.

My wms url http://sampleserver1.arcgisonline.com/ArcGIS/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/WMSServer

It contains 3 layers (States,Rivers,Cities)

I'm using structure to get map operation like below.

GetMapRequest getMapRequest = wms.createGetMapRequest();//wms is my WebMapServer object

getMapRequest.addLayer(tempLayer);//tempLayer contains states layer

GetMapResponse response = (GetMapResponse) wms.issueRequest(getMapRequest);

BufferedImage image = ImageIO.read(response.getInputStream());

I also tried other methods in guide to do GetMapRequest but I can't succeed, always getting NullPointerException to BufferedImage object.

What is your suggestions? Thanks in advance.

Answer 1

You need to set some more parameters for your request, the WMS getMapResponse doesn't provide any defaults for several of them (as they are unique to your request/map). So you need at least the following:

private BufferedImage getLayer(Layer l) {
    GetMapRequest getMapRequest = wms.createGetMapRequest();
    getMapRequest.addLayer(l);
    getMapRequest.setBBox(l.getEnvelope(DefaultGeographicCRS.WGS84));
    getMapRequest.setDimensions(200, 400);
    getMapRequest.setFormat("image/png");
    getMapRequest.setSRS("CRS:84");
    System.out.println(getMapRequest.getFinalURL());
    try {
        GetMapResponse response = wms.issueRequest(getMapRequest);
        BufferedImage image = ImageIO.read(response.getInputStream());
        return image;
    } catch (ServiceException | IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        return null;
    }

}

In general to avoid getting an empty image you can do some error checking on the response:

     if (response.getContentType().equalsIgnoreCase("image/png")) {
            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;
        }

which will give you an XML encoded error to tell you what went wrong:

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<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="InvalidFormat">
Parameter 'bbox' can not be empty.
  </ServiceException>
</ServiceExceptionReport>