Encoder in GeoTools does not work for SLD

Question

I'm trying to use GeoTools to write SLDs on the fly for an application I am developing. But try as I might, I can't get the SLDs to be output.

Starting with an SLD that looks like this:

<StyledLayerDescriptor xmlns="http://www.opengis.net/sld" version="1.0.0"
xsi:schemaLocation="http://www.opengis.net/sld http://schemas.opengis.net/sld/1.0.0/StyledLayerDescriptor.xsd"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <NamedLayer>
        <Name>named_layer</Name>
        <UserStyle>
            <Name>style</Name>
            <IsDefault>true</IsDefault>
            <FeatureTypeStyle>
                <Rule>
                    <PointSymbolizer>
                        <Graphic>
                            <Mark>
                                <WellKnownName>circle</WellKnownName>
                                <Fill>
                                    <CssParameter name="fill">#00aa00</CssParameter>
                                </Fill>
                                <Stroke>
                                    <CssParameter name="stroke">#000000</CssParameter>
                                    <CssParameter name="stroke-width">0.15</CssParameter>
                                </Stroke>
                            </Mark>
                            <Size>8</Size>
                        </Graphic>
                    </PointSymbolizer>
                </Rule>
            </FeatureTypeStyle>
        </UserStyle>
    </NamedLayer>
</StyledLayerDescriptor>

I use the following code:

package com.example.sld;

import org.geotools.sld.SLDConfiguration;
import org.geotools.sld.bindings.SLD;
import org.geotools.styling.StyledLayerDescriptor;
import org.geotools.xml.Configuration;
import org.geotools.xml.Encoder;
import org.geotools.xml.Parser;
import org.xml.sax.SAXException;

import javax.xml.parsers.ParserConfigurationException;
import java.io.IOException;
import java.io.InputStream;

public class TestStyle {

    private String style;

    public TestStyle() {

        Configuration config = new SLDConfiguration();
        Parser parser = new Parser(config);

        InputStream is = getClass().getResourceAsStream("test-sld.xml");

        StyledLayerDescriptor sld = null;
        try {
            sld = (StyledLayerDescriptor) parser.parse(is);
        } catch (SAXException e) {
            e.printStackTrace();
        } catch (ParserConfigurationException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        Configuration configuration = new SLDConfiguration();
        Encoder encoder = new Encoder(configuration);
        encoder.setOmitXMLDeclaration(true);
        try {
            this.style = encoder.encodeAsString(sld, SLD.STYLEDLAYERDESCRIPTOR);
        } catch (IOException e) {
            e.printStackTrace();
        }

        this.style = new String();

    }
}

The SLD parses OK. I can inspect its structure in my debugger and it is read correctly. But on encoding, the resultant SLD is empty:

<sld:StyledLayerDescriptor xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:ogc="http://www.opengis.net/ogc" xmlns:sld="http://www.opengis.net/sld" xmlns:xlink="http://www.w3.org/1999/xlink"/>

What am I doing wrong?

(Version of GeoTools is 20.1, following the guide here: http://docs.geotools.org/latest/userguide/library/xml/style.html#encoder)

Thanks in advance

Answer 1

Your approach would work if you had a version 1.1.0 SLD (or more properly an SE) document, and if you used a import org.geotools.sld.v1_1.SLD object to pass to the encoder. However you have a version 1.0.0 SLD document so you need to use a SLDTransformer class to output your style objects. So something like:

ByteArrayOutputStream bos = new ByteArrayOutputStream();
SLDTransformer transformer = new SLDTransformer();
transformer.setIndentation(2);
transformer.transform(sld, bos);
String style = bos.toString();
System.out.println(style);