How to write GML with Geotools?

Question

I'd like to write GML using Geotools. Unfortunately, I can't find documentation on a GML Writer (except for this one from 2006: http://docs.codehaus.org/display/GEOTOOLS/WFS+++GML+DataStore).

Could you point me at documentation/examples?

Answer 1

I will be trying to migrate the geotools documentation to a different technology (other than wiki) so that the code examples do not go out of date.

Update this is now done (I gathered things up so all the geometry examples are together):

• http://docs.geotools.org/latest/userguide/library/xml/geometry.html
• http://docs.geotools.org/latest/userguide/library/xml/faq.html

Here is a complete example from that page:

SimpleFeatureType TYPE = DataUtilities.createType("location", "geom:Point,name:String");

File locationFile = new File("location.xsd");
locationFile = locationFile.getCanonicalFile();
locationFile.createNewFile();

URL locationURL = locationFile.toURI().toURL();
URL baseURL = locationFile.getParentFile().toURI().toURL();

FileOutputStream xsd = new FileOutputStream(locationFile);

GML encode = new GML(Version.GML2);
encode.setBaseURL(baseURL);
encode.setNamespace("location", locationURL.toExternalForm());
encode.encode(xsd, TYPE);

xsd.close();

SimpleFeatureCollection collection = FeatureCollections.newCollection("internal");
WKTReader2 wkt = new WKTReader2();

collection.add(SimpleFeatureBuilder.build(TYPE, new Object[] { wkt.read("POINT (1 2)"),"name1" }, null));
collection.add(SimpleFeatureBuilder.build(TYPE, new Object[] { wkt.read("POINT (4 4)"),"name2" }, null));

ByteArrayOutputStream xml = new ByteArrayOutputStream();

GML encode2 = new GML(Version.GML2);
encode2.setBaseURL(baseURL);
encode2.setNamespace("location", "location.xsd");
encode2.encode(out2, collection);

xml.close();

String gml = xml.toString();

Additional examples of how to use the 4 different GML parsing technologies is the test cases included with the source code.

1. SAX
2. DOM
3. GTXML version 1.x (used for GML2 in WFSDataStore VERSION=1.0)
4. GTXML version 4.x (used for everything else now )

The two GTXML technologies are basically a combination of the best part of the SAX parser with the ability to figure out which fragment of code (called a binding) to use to parse each element as it comes in (based on looking the element up in the schema).

Answer 2

You can also look at http://svn.osgeo.org/geotools/trunk/modules/library/xml/src/test/java/org/geotools/GMLTest.java to see how the tests do it. The key section seems to be:

GML encode2 = new GML(Version.GML2);
    encode2.setBaseURL(baseURL);
    encode2.setNamespace("location", "location.xsd");
    encode2.encode(out2, collection);

    out.close();

Where collection is a featureCollection.

Answer 3

Try:

//create the encoder with the gml 2.0 configuration
org.geotools.xml.Configuration configuration = new org.geotools.gml2.GMLConfiguration();
org.geotools.xml.Encoder encoder = new org.geotools.xml.Encoder( configuration );

//output stream to serialize to
OutputStream xml = ...

//encode
encoder.encode( featureCollection, new QName( "http://www.geotools.org/test", "featureType1"));

Documentation:

• http://docs.geotools.org/latest/userguide/library/xml/geometry.html