/**
* Writes the opening RDF tag (with namespaces) to the print Writer.
*
* @param out PrintWriter
* @throws IOException
*/
protected void writeRDFHeader(PrintWriter out) throws IOException {
// validate
if (out != null) {
// print opening RDF tag (including namespaces)
out.print("<rdf:RDF ");
// print namespaces
Set<String> keys = namespaces.keySet();
if (keys != null) {
for (String currentKey : keys) {
String currentValue = namespaces.get(currentKey);
if ((currentKey != null) && (currentValue != null)) {
// use entities: xmlns:ns="&ns;"
out.print(NEWLINE + " xmlns:" + currentKey + "=\"&" + currentKey + ";\"");
}
}
}
// close the opening tag (add a space for readability)
out.print(">" + NEWLINE + NEWLINE);
} else {
throw new IllegalArgumentException("Cannot write to null Writer.");
}
}
/**
* If the URI contains the URI of a known namespace, it is replaced.
*
* @param original original URI.
* @return new URI with namespace references.
*/
protected String replaceNamespace(String original) throws GraphException {
// value to be returned
String uri = original;
// validate URI (only replace uri's with fragments)
if (original != null) {
// replace any URI occurances with namespace prefixes
for (String currentKey : namespaces.keySet()) {
String currentValue = namespaces.get(currentKey);
// validate the Objects
if ((currentKey != null) && (currentValue != null)) {
// if the entire namespace is used, replace it with an entity
if (original.equals(currentValue)) {
uri = "&" + currentKey + ";";
} else if (original.startsWith(currentValue.toString())) {
// replace with namespace
uri = original.replaceAll(currentValue.toString(), currentKey + ":");
}
}
}
}
// return the URI with any collection/container items renamed
return replaceCollection(uri);
}
/**
* Writes the XML Entities (used for namespaces) to the print Writer.
*
* @param out PrintWriter
* @throws IOException
*/
protected void writeXMLEntities(PrintWriter out) throws IOException {
// validate
if (out != null) {
// print opening DOCTYPE DECLARATION tag
out.print(NEWLINE + "<!DOCTYPE rdf:RDF [");
// print namespaces
Set<String> keys = namespaces.keySet();
if (keys != null) {
for (String currentKey : keys) {
String currentValue = namespaces.get(currentKey);
if ((currentKey != null) && (currentValue != null)) {
// write as: <!ENTITY ns 'http://example.org/abc#'>
out.print(NEWLINE + " <!ENTITY " + currentKey + " '" + currentValue + "'>");
}
}
}
// close the opening tag (add a space for readability)
out.print("]>" + NEWLINE + NEWLINE);
} else {
throw new IllegalArgumentException("Cannot write to null Writer.");
}
}
/**
* Populates the namespaces map with default namespaces and namespaces used by the graph.
*
* @param graph Graph
* @throws GraphException
*/
protected void populateNamespaces(Graph graph) throws GraphException {
// default namespaces
namespaces = new HashMap<String, String>();
namespaces.put(RDF_PREFIX, RDF.BASE_URI.toString());
namespaces.put(RDFS_PREFIX, RDFS.BASE_URI.toString());
namespaces.put("owl", "http://www.w3.org/2002/07/owl#");
namespaces.put("dc", "http://purl.org/dc/elements/1.1/");
// validate graph before reading
if (graph == null) {
throw new IllegalArgumentException("Graph argument is null.");
}
// get all statements
ClosableIterator<Triple> tripleIter = graph.find(null, null, null);
if (tripleIter != null) {
while (tripleIter.hasNext()) {
// get the next triple
Triple triple = tripleIter.next();
if (triple != null) {
// evaluate subject
SubjectNode subject = triple.getSubject();
if (subject instanceof URIReference) {
addNamespaceURI(((URIReference) subject).getURI());
}
// evaluate predicate (must be URIReference)
PredicateNode predicate = triple.getPredicate();
addNamespaceURI(((URIReference) predicate).getURI());
// evaluate object
ObjectNode object = triple.getObject();
if (object instanceof URIReference) {
addNamespaceURI(((URIReference) object).getURI());
}
}
}
// close the Iterator
tripleIter.close();
}
}
/**
* Evaluates a URI and adds it to the namespace map as a namespace.
*
* @param uri URI
*/
protected void addNamespaceURI(URI uri) {
if (uri == null) {
throw new IllegalArgumentException("URI argument is null.");
}
// extract URI without fragment
String uriString = uri.toString();
String newURI = null;
if (uriString != null) {
// determine what comes last a '#' or '/'
int hashindex = uriString.lastIndexOf('#');
int slashindex = uriString.lastIndexOf('/');
// validate (URI must contain a forward slash)
if (slashindex == -1) {
// namespace may have been evaluated already
return;
}
// is there a '/' after the '#'?
if (slashindex > hashindex) {
// remove everything after the last '/'
int index = uriString.lastIndexOf('/');
newURI = uriString.substring(0, index) + "/";
} else {
// '#' comes after last '/' (remove entire fragment)
newURI = uriString.replaceAll(uri.getFragment(), "");
}
// only add namespace if it is new
if ((newURI != null) && (!namespaces.containsValue(newURI))) {
// add to namespaces
namespaces.put("ns" + namespaces.size(), newURI);
}
}
}