ResourceResolver.java

#set( $symbol_pound = '#' )
#set( $symbol_dollar = '$' )
#set( $symbol_escape = '\' )
package ${package};

import java.security.AccessController;
import java.security.Permission;
import java.security.PrivilegedAction;
import java.util.Collections;
import java.util.Date;
import javax.ws.rs.GET;
import javax.ws.rs.HeaderParam;
import javax.ws.rs.Path;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.UriInfo;
import org.apache.clerezza.jaxrs.utils.TrailingSlash;
import org.apache.clerezza.commons.rdf.BlankNode;
import org.apache.clerezza.commons.rdf.Graph;
import org.apache.clerezza.commons.rdf.IRI;
import org.apache.clerezza.rdf.core.access.EntityAlreadyExistsException;
import org.apache.clerezza.rdf.core.access.TcManager;
import org.apache.clerezza.rdf.core.access.security.TcAccessController;
import org.apache.clerezza.rdf.core.access.security.TcPermission;
import org.apache.clerezza.commons.rdf.impl.utils.PlainLiteralImpl;
import org.apache.clerezza.rdf.ontologies.DC;
import org.apache.clerezza.rdf.ontologies.RDF;
import org.apache.clerezza.rdf.ontologies.RDFS;
import org.apache.clerezza.rdf.utils.GraphNode;
import org.apache.clerezza.rdf.utils.UnionGraph;
import org.apache.felix.scr.annotations.Activate;
import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Deactivate;
import org.apache.felix.scr.annotations.Property;
import org.apache.felix.scr.annotations.Reference;
import org.apache.felix.scr.annotations.Service;
import org.apache.stanbol.commons.indexedgraph.IndexedGraph;
import org.apache.stanbol.commons.web.viewable.RdfViewable;
import org.apache.stanbol.entityhub.model.clerezza.RdfValueFactory;
import org.apache.stanbol.entityhub.servicesapi.model.Entity;
import org.apache.stanbol.entityhub.servicesapi.model.Representation;
import org.apache.stanbol.entityhub.servicesapi.site.SiteManager;
import org.osgi.service.component.ComponentContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Uses the SiteManager to resolve entities. Every requested is recorded to
 * a graph. The client gets information and meta-information about the resource
 * and sees all previous requests for that resource.
 */
@Component
@Service(Object.class)
@Property(name="javax.ws.rs", boolValue=true)
@Path("${artifactId}")
public class ResourceResolver {
    
    /**
     * Using slf4j for normal logging
     */
    private static final Logger log = LoggerFactory.getLogger(ResourceResolver.class);
    
    /**
     * This service allows to get entities from configures sites
     */
    @Reference
    private SiteManager siteManager;
    
    /**
     * This service allows accessing and creating persistent triple collections
     */
    @Reference
    private TcManager tcManager;
    
    /**
     * This is the name of the graph in which we "log" the requests
     */
    private IRI REQUEST_LOG_GRAPH_NAME = new IRI("http://example.org/resource-resolver-log.graph");
    
    @Activate
    protected void activate(ComponentContext context) {
        log.info("The example service is being activated");
        try {
            tcManager.createGraph(REQUEST_LOG_GRAPH_NAME);
            //now make sure everybody can read from the graph
            //or more precisly, anybody who can read the content-graph
            TcAccessController tca = tcManager.getTcAccessController();
            tca.setRequiredReadPermissions(REQUEST_LOG_GRAPH_NAME, 
                    Collections.singleton((Permission)new TcPermission(
                    "urn:x-localinstance:/content.graph", "read")));
        } catch (EntityAlreadyExistsException ex) {
            log.debug("The graph for the request log already exists");
        }
        
    }
    
    @Deactivate
    protected void deactivate(ComponentContext context) {
        log.info("The example service is being deactivated");
    }
    
    /**
     * This method return an RdfViewable, this is an RDF serviceUri with associated
     * presentational information.
     */
    @GET
    public RdfViewable serviceEntry(@Context final UriInfo uriInfo, 
            @QueryParam("iri") final IRI iri, 
            @HeaderParam("user-agent") String userAgent) throws Exception {
        //this maks sure we are nt invoked with a trailing slash which would affect
        //relative resolution of links (e.g. css)
        TrailingSlash.enforcePresent(uriInfo);
        final String resourcePath = uriInfo.getAbsolutePath().toString();
        //The URI at which this service was accessed accessed, this will be the 
        //central serviceUri in the response
        final IRI serviceUri = new IRI(resourcePath);
        //the in memory graph to which the triples for the response are added
        final Graph responseGraph = new IndexedGraph();
        //A union graph containing both the response specif triples as well 
        //as the log-graph
        final UnionGraph resultGraph = new UnionGraph(responseGraph, getRequestLogGraph());
        //This GraphNode represents the service within our result graph
        final GraphNode node = new GraphNode(serviceUri, resultGraph);
        //The triples will be added to the first graph of the union
        //i.e. to the in-memory responseGraph
        node.addProperty(RDF.type, Ontology.ResourceResolver);
        node.addProperty(RDFS.comment, new PlainLiteralImpl("A RDFTerm Resolver"));
        if (iri != null) {
            node.addProperty(Ontology.describes, iri);
            addResourceDescription(iri, responseGraph);
            logRequest(iri, userAgent);
        }
        //What we return is the GraphNode we created with a template path
        return new RdfViewable("ResourceResolver", node, ResourceResolver.class);
    }
    

    /**
     * Add the description of a serviceUri to the specified Graph using SiteManager.
     * The description includes the metadata provided by the SiteManager.
     * 
     */
    private void addResourceDescription(IRI iri, Graph mGraph) {
        final Entity entity = siteManager.getEntity(iri.getUnicodeString());
        if (entity != null) {
            final RdfValueFactory valueFactory = new RdfValueFactory(mGraph);
            final Representation representation = entity.getRepresentation();
            if (representation != null) {
                valueFactory.toRdfRepresentation(representation);
            }
            final Representation metadata = entity.getMetadata();
            if (metadata != null) {
                valueFactory.toRdfRepresentation(metadata);
            }
        }
    }

    /**
     * Logs a request to the log-graph
     */
    private void logRequest(final IRI iri, final String userAgent) {
        //writing to a persistent graph requires some special permission
        //by executing the code in a do-priviledged section
        //the user doesn't need this permissions, anonymous users are thus not
        //asked to log in
        AccessController.doPrivileged(new PrivilegedAction<Object>() {
            public Object run() {
                final Graph logGraph = getRequestLogGraph();
                GraphNode loggedRequest = new GraphNode(new BlankNode(), logGraph);
                loggedRequest.addProperty(RDF.type, Ontology.LoggedRequest);
                loggedRequest.addPropertyValue(DC.date, new Date());
                loggedRequest.addPropertyValue(Ontology.userAgent, userAgent);
                loggedRequest.addProperty(Ontology.requestedEntity, iri);
                return null;
            }
        });
        
    }

    /**
     * This returns the existing Graph for the log .
     * 
     * @return the Graph to which the requests are logged
     */
    private Graph getRequestLogGraph() {
        return tcManager.getGraph(REQUEST_LOG_GRAPH_NAME);
    }
    
}