Dynamic Styling and Filtering of a Geoserver WMS Using OpenLayers.Layer.WMS.Post

There is a new layer class in OpenLayers API: OpenLayers.Layer.WMS.Post [1]. – Great work!

While the “normal” OpenLayers.Layer.WMS class requests maps via HTTP GET, this new class sends the request via HTTP POST. This way, we can now send big client-side created SLD files in our GetMap requests that used to exceed size limits of GET.

This code snippet shows the basic use of OpenLayers.Layer.WMS.Post with a client-side created SLD. You’ll need at least OpenLayers 2.9 to test this on your server. (A full example can be found at http://www.openlayers.org/dev/examples/wms-long-url.html)

var sld = 'define your SLD here';

wms = new OpenLayers.Layer.WMS.Post(
  "name",
  "http://localhost:8080/geoserver/wms",
  {
    'layers': 'myNs:layername',
    format: 'image/jpeg',
    sld_body: sld
  },
  {
    unsupportedBrowsers: []
  }
);

Setting unsupportedBrowsers to an empty list is important! This list by default contains [“mozilla”, “firefox”, “opera”]. These browsers support long GET requests so the developers argued that these browsers wouldn’t need to use POST. Well, turns out that they do ;)

I performed a small stress test using an SLD with approximately 1,000 rules being applied on a big city road network. While my browser would willingly send a GET request of that size, Apache doesn’t want to accept it. So, I tried the POST way and it turns out that it really works! (But it’s slow, very slow …)

Thanks to the developers for yet another great feature!

[1] http://trac.openlayers.org/ticket/2224