PrefixDeclProcessor.java

/*
 * Copyright Aduna (http://www.aduna-software.com/) (c) 1997-2006.
 *
 * Licensed under the Aduna BSD-style license.
 */
package org.openrdf.query.parser.sparql;

import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import org.openrdf.query.MalformedQueryException;
import org.openrdf.query.parser.sparql.ast.ASTIRI;
import org.openrdf.query.parser.sparql.ast.ASTPrefixDecl;
import org.openrdf.query.parser.sparql.ast.ASTQName;
import org.openrdf.query.parser.sparql.ast.ASTQueryContainer;
import org.openrdf.query.parser.sparql.ast.SyntaxTreeBuilderTreeConstants;
import org.openrdf.query.parser.sparql.ast.VisitorException;

/**
 * Processes the prefix declarations in a SPARQL query model.
 *
 * @author Arjohn Kampman 
 */
class PrefixDeclProcessor {

	/**
	 * Processes prefix declarations in queries. This method collects all
	 * prefixes that are declared in the supplied query, verifies that prefixes
	 * are not redefined and replaces any {@link ASTQName} nodes in the query
	 * with equivalent {@link ASTIRI} nodes.
	 * 
	 * @param qc
	 *        The query that needs to be processed.
	 * @return A map containing the prefixes that are declared in the query (key)
	 *         and the namespace they map to (value).
	 * @throws MalformedQueryException
	 *         If the query contains redefined prefixes or qnames that use
	 *         undefined prefixes.
	 */
	public static Map<String, String> process(ASTQueryContainer qc)
		throws MalformedQueryException
	{
		List<ASTPrefixDecl> prefixDeclList = qc.getPrefixDeclList();

		// Build a prefix --> IRI map
		Map<String, String> prefixMap = new LinkedHashMap<String, String>();
		for (ASTPrefixDecl prefixDecl : prefixDeclList) {
			String prefix = prefixDecl.getPrefix();
			String iri = prefixDecl.getIRI().getValue();

			if (prefixMap.containsKey(prefix)) {
				throw new MalformedQueryException("Multiple prefix declarations for prefix '" + prefix + "'");
			}

			prefixMap.put(prefix, iri);
		}

		QNameProcessor visitor = new QNameProcessor(prefixMap);
		try {
			qc.jjtAccept(visitor, null);
		}
		catch (VisitorException e) {
			throw new MalformedQueryException(e);
		}

		return prefixMap;
	}

	private static class QNameProcessor extends ASTVisitorBase {

		private Map<String, String> prefixMap;

		public QNameProcessor(Map<String, String> prefixMap) {
			this.prefixMap = prefixMap;
		}

		@Override
		public Object visit(ASTQName qnameNode, Object data)
			throws VisitorException
		{
			String qname = qnameNode.getValue();

			int colonIdx = qname.indexOf(':');
			assert colonIdx >= 0 : "colonIdx should be >= 0: " + colonIdx;

			String prefix = qname.substring(0, colonIdx);
			String localName = qname.substring(colonIdx + 1);

			String namespace = prefixMap.get(prefix);
			if (namespace == null) {
				throw new VisitorException("QName '" + qname + "' uses an undefined prefix");
			}

			// Replace the qname node with a new IRI node in the parent node
			ASTIRI iriNode = new ASTIRI(SyntaxTreeBuilderTreeConstants.JJTIRI);
			iriNode.setValue(namespace + localName);
			qnameNode.jjtReplaceWith(iriNode);

			return null;
		}
	}
}