Java tutorial
/** * The contents of this file are subject to the license and copyright * detailed in the LICENSE and NOTICE files at the root of the source * tree and available online at * * http://www.dspace.org/license/ */ package org.dspace.rdf.providing; import com.hp.hpl.jena.rdf.model.Model; import java.io.IOException; import java.io.PrintWriter; import java.sql.SQLException; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.commons.lang.StringUtils; import org.apache.log4j.Logger; import org.dspace.content.DSpaceObject; import org.dspace.core.Context; import org.dspace.handle.factory.HandleServiceFactory; import org.dspace.handle.service.HandleService; import org.dspace.rdf.RDFUtil; import org.dspace.services.factory.DSpaceServicesFactory; /** * * @author Pascal-Nicolas Becker (dspace -at- pascal -hyphen- becker -dot- de) */ public class DataProviderServlet extends HttpServlet { protected static final String DEFAULT_LANG = "TURTLE"; private static final Logger log = Logger.getLogger(DataProviderServlet.class); protected final transient HandleService handleService = HandleServiceFactory.getInstance().getHandleService(); /** * Processes requests for both HTTP * <code>GET</code> and * <code>POST</code> methods. * * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // set all incoming encoding to UTF-8 request.setCharacterEncoding("UTF-8"); // we expect either a path containing only the language information // or a path in the form /handle/<prefix>/<suffix>[/language]. String lang = this.detectLanguage(request); String cType = this.detectContentType(request, lang); String pathInfo = request.getPathInfo(); log.debug("lang = " + lang + ", cType = " + cType + " and pathInfo: " + pathInfo); if (StringUtils.isEmpty(pathInfo) || StringUtils.countMatches(pathInfo, "/") < 2) { String dspaceURI = DSpaceServicesFactory.getInstance().getConfigurationService() .getProperty("dspace.url"); this.serveNamedGraph(dspaceURI, lang, cType, response); return; } // remove trailing slash of the path info and split it. String[] path = request.getPathInfo().substring(1).split("/"); // if we have 2 slashes or less, we sent repository information (see above) assert path.length >= 2; String handle = path[0] + "/" + path[1]; log.debug("Handle: " + handle + "."); // As we offer a public sparql endpoint, all information that we stored // in the triplestore is public. It is important to check whether a // DSpaceObject is readable for a anonym user before storing it in the // triplestore. It is important to remove DSpaceObjects from the // triplestore, that gets revoked or become restricted. As this is done // by RDFizer and RDFUtil we do not have to take care for permissions here! Context context = null; DSpaceObject dso = null; try { context = new Context(Context.Mode.READ_ONLY); dso = handleService.resolveToObject(context, handle); } catch (SQLException ex) { log.error("SQLException: " + ex.getMessage(), ex); context.abort(); // probably a problem with the db connection => send Service Unavailable response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE); return; } catch (IllegalStateException ex) { log.error("Cannot resolve handle " + handle + ". IllegalStateException:" + ex.getMessage(), ex); context.abort(); response.sendError(HttpServletResponse.SC_BAD_REQUEST); return; } if (dso == null) { log.info("Cannot resolve handle '" + handle + "' to dso. => 404"); context.abort(); response.sendError(HttpServletResponse.SC_NOT_FOUND); return; } String identifier = null; try { identifier = RDFUtil.generateIdentifier(context, dso); } catch (SQLException ex) { log.error("SQLException: " + ex.getMessage(), ex); context.abort(); // probably a problem with the db connection => send Service Unavailable response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE); return; } if (identifier == null) { // cannot generate identifier for dso?! log.error("Cannot generate identifier for UUID " + dso.getID().toString() + "!"); context.abort(); response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR); return; } log.debug("Loading and sending named graph " + identifier + "."); context.abort(); this.serveNamedGraph(identifier, lang, cType, response); } protected void serveNamedGraph(String uri, String lang, String contentType, HttpServletResponse response) throws ServletException, IOException { Model result = null; result = RDFUtil.loadModel(uri); if (result == null || result.isEmpty()) { response.sendError(HttpServletResponse.SC_NOT_FOUND); if (result != null) result.close(); log.info("Sent 404 Not Found, as the loaded model was null or " + "empty (URI: " + uri + ")."); return; } response.setContentType(contentType); PrintWriter out = response.getWriter(); log.debug("Set content-type to " + contentType + "."); try { result.write(out, lang); } finally { result.close(); out.close(); } } protected String detectContentType(HttpServletRequest request, String lang) { // It is usefull to be able to overwrite the content type, to see the // request result directly in the browser. If a parameter "text" is part // of the request, we send the result with the content type "text/plain". if (request.getParameter("text") != null) return "text/plain;charset=UTF-8"; if (lang.equalsIgnoreCase("TURTLE")) return "text/turtle;charset=UTF-8"; if (lang.equalsIgnoreCase("n3")) return "text/n3;charset=UTF-8"; if (lang.equalsIgnoreCase("RDF/XML")) return "application/rdf+xml;charset=UTF-8"; if (lang.equalsIgnoreCase("N-TRIPLE")) return "application/n-triples;charset=UTF-8"; throw new IllegalStateException("Cannot set content type for unknown language."); } protected String detectLanguage(HttpServletRequest request) { String pathInfo = request.getPathInfo(); if (StringUtils.isEmpty(pathInfo)) return DEFAULT_LANG; String[] path = request.getPathInfo().split("/"); String lang = path[(path.length - 1)]; if (StringUtils.endsWithIgnoreCase(lang, "ttl")) return "TURTLE"; if (StringUtils.equalsIgnoreCase(lang, "n3")) return "N3"; if (StringUtils.equalsIgnoreCase(lang, "rdf") || StringUtils.equalsIgnoreCase(lang, "xml")) { return "RDF/XML"; } if (StringUtils.endsWithIgnoreCase(lang, "nt")) return "N-TRIPLE"; return DEFAULT_LANG; } /** * Handles the HTTP * <code>GET</code> method. * * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); } /** * Handles the HTTP * <code>POST</code> method. * * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); } /** * Returns a short description of the servlet. * * @return a String containing servlet description */ public String getServletInfo() { return "Serves repository content as rdf serialization (RDF/XML, Turtle, N-Triples and N3)."; } }