Nico Verwer wrote:
I am looking at the same problem at the moment, and triied several
things (like the IncludeTransformer). My next attempt will be to build
a SPARQLTransformer. When it is ready, I'll let you know.
I think the following code works. Please try it, and let me know if it
works.
The Java code follows:
---------------------
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.cocoon.transformation;
import java.io.IOException;
import java.util.Map;
import org.apache.avalon.framework.parameters.Parameters;
import org.apache.cocoon.ProcessingException;
import org.apache.cocoon.components.source.SourceUtil;
import org.apache.cocoon.environment.SourceResolver;
import org.apache.excalibur.source.Source;
import org.apache.excalibur.source.SourceParameters;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
/**
* * @cocoon.sitemap.component.documentation
* This transformer triggers for the element <code>query</code> in the
namespace "http://apache.org/cocoon/sparql/1.0";.
* These elements must not be nested.
* The <code>src</code> attribute contains the url which points to a
SPARQL endpoint.
* The optional <code>method</code> attribute contains the HTTP method
for the request (default is GET).
* Attributes in the "http://apache.org/cocoon/sparql/1.0"; namespace are
used as request parameters (using the local name).
* This allows for parameters such as 'format' or 'maxrows'.
* The text of the content of the <code>query</code> element is passed
as the value of the 'query' parameter.
*
* The XML input to this transformer would look like:
* <pre>
* <sparql:query xmlns:sparql="http://apache.org/cocoon/sparql/1.0";
* method="POST" src="http://dbpedia.org/sparql";
* sparql:maxrows="25" sparql:format="XML"
* >
* <![CDATA[
* PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
* SELECT *
* FROM <http://dbpedia.org>
* WHERE {
* ?person rdf:type <http://dbpedia.org/class/yago/Person100007846> .
* }
* ]]>
* </sparql:query>
* </pre>
*
* @author Nico Verwer
*
*/
public class SparqlTransformer extends AbstractSAXTransformer {
public static final String SPARQL_NAMESPACE_URI =
"http://apache.org/cocoon/sparql/1.0";;
public static final String QUERY_ELEMENT = "query";
public static final String METHOD_ATTR = "method";
public static final String SRC_ATTR = "src";
public static final String QUERY_PARAM = "query";
private boolean inQuery;
private String src;
private String method;
private SourceParameters requestParameters;
public SparqlTransformer() {
this.defaultNamespaceURI = SPARQL_NAMESPACE_URI;
}
public void setup(SourceResolver resolver, Map objectModel, String src,
Parameters params) throws ProcessingException, SAXException,
IOException {
super.setup(resolver, objectModel, src, params);
inQuery = false;
}
public void startTransformingElement(String uri, String name, String
raw, Attributes attr)
throws ProcessingException, IOException, SAXException {
if (name.equals(QUERY_ELEMENT)) {
if (inQuery) {
throw new ProcessingException("Nested SPARQL queries are not
allowed.");
}
inQuery = true;
src = attr.getValue(SRC_ATTR);
method = attr.getValue(METHOD_ATTR);
method = (method == null ? "GET" : method.toUpperCase());
requestParameters = new SourceParameters();
for (int i = 0; i < attr.getLength(); ++i) {
if (attr.getURI(i).equals(SPARQL_NAMESPACE_URI)) {
requestParameters.setParameter(attr.getLocalName(i),
attr.getValue(i));
}
}
startTextRecording();
}
}
public void endTransformingElement(String uri, String name, String raw)
throws ProcessingException, IOException, SAXException {
if (name.equals(QUERY_ELEMENT)) {
inQuery = false;
String query = endTextRecording();
requestParameters.setParameter(QUERY_PARAM, query);
Parameters typeParameters = new Parameters();
typeParameters.setParameter("method", method);
Source source = SourceUtil.getSource(src, typeParameters,
requestParameters, resolver);
SourceUtil.toSAX(source, this.xmlConsumer);
}
}
}
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