Allow configuration of data sources and prefixes.

Author: RubenVerborgh

.gitignore

@@ -1,2 +1,3 @@
 .settings
 build
+WebContent/WEB-INF/config.json

WebContent/WEB-INF/config-example.json

@@ -0,0 +1,25 @@
+{
+  "datasources": {
+    "dbpedia": {
+      "path": "/path/to/dataset.hdt",
+    },
+  },
+
+  "prefixes": {
+    "rdf":         "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
+    "rdfs":        "http://www.w3.org/2000/01/rdf-schema#",
+    "owl":         "http://www.w3.org/2002/07/owl#",
+    "skos":        "http://www.w3.org/2004/02/skos/core#",
+    "xsd":         "http://www.w3.org/2001/XMLSchema#",
+    "dc":          "http://purl.org/dc/terms/",
+    "dcterms":     "http://purl.org/dc/terms/",
+    "dc11":        "http://purl.org/dc/elements/1.1/",
+    "foaf":        "http://xmlns.com/foaf/0.1/",
+    "geo":         "http://www.w3.org/2003/01/geo/wgs84_pos#",
+    "dbpedia":     "http://dbpedia.org/resource/",
+    "dbpedia-owl": "http://dbpedia.org/ontology/",
+    "dbpprop":     "http://dbpedia.org/property/",
+    "hydra":       "http://www.w3.org/ns/hydra/core#",
+    "void":        "http://rdfs.org/ns/void#"
+  }
+}

src/org/linkeddatafragments/config/ConfigReader.java

@@ -0,0 +1,59 @@
+package org.linkeddatafragments.config;
+
+import java.io.File;
+import java.io.FileReader;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Map.Entry;
+
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParser;
+
+/**
+ * Reads the configuration of a Linked Data Fragments server.
+ * @author Ruben Verborgh
+ */
+public class ConfigReader {
+	private final Map<String, String> dataSources = new HashMap<String, String>();
+	private final Map<String, String> prefixes = new HashMap<String, String>();
+	
+	/**
+	 * Creates a new configuration reader.
+	 * @param configFile the name of the configuration file
+	 * @throws Exception if the configuration cannot be loaded
+	 */
+	public ConfigReader(String configFile) throws Exception {
+		// check the configuration file
+		if (configFile == null || configFile.length() == 0)
+			throw new Exception("No configuration file name specified.");
+		final File config = new File(configFile);
+		if (!config.exists())
+			throw new Exception("Configuration file " + configFile + " does not exist.");
+		
+		// read the configuration file
+        final JsonObject root = new JsonParser().parse(new FileReader(config)).getAsJsonObject();
+        for (final Entry<String, JsonElement> entry : root.getAsJsonObject("datasources").entrySet()) {
+        	final JsonObject dataSource = entry.getValue().getAsJsonObject();
+        	this.dataSources.put(entry.getKey(), dataSource.getAsJsonPrimitive("path").getAsString());
+        }
+        for (final Entry<String, JsonElement> entry : root.getAsJsonObject("prefixes").entrySet())
+        	this.prefixes.put(entry.getKey(), entry.getValue().getAsString());
+	}
+	
+	/**
+	 * Gets the data sources.
+	 * @return the data sources
+	 */
+	public Map<String, String> getDataSources() {
+		return dataSources;
+	}
+	
+	/**
+	 * Gets the prefixes.
+	 * @return the prefixes
+	 */
+	public Map<String, String> getPrefixes() {
+		return prefixes;
+	}
+}

src/org/linkeddatafragments/servlets/BasicLdfServlet.java

@@ -1,5 +1,7 @@
 package org.linkeddatafragments.servlets;
 
+import java.util.HashMap;
+import java.util.Map.Entry;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -9,6 +11,7 @@
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
+import org.linkeddatafragments.config.ConfigReader;
 import org.rdfhdt.hdt.hdt.HDT;
 import org.rdfhdt.hdt.hdt.HDTManager;
 import org.rdfhdt.hdtjena.HDTGraph;
@@ -29,15 +32,18 @@ public class BasicLdfServlet extends HttpServlet {
 	private final static int TRIPLES_PER_PAGE = 100;
 	private final static Pattern STRINGPATTERN = Pattern.compile("^\"(.*)\"(?:\\^\\^<(.*)>|@(.*))?$");
 
-	private Model model;
+	private ConfigReader config;
+	private HashMap<String, Model> dataSources = new HashMap<String, Model>();
 
 	@Override
-	public void init(ServletConfig config) throws ServletException {
+	public void init(ServletConfig servletConfig) throws ServletException {
 		try {
-			final String dataFile = config.getInitParameter("dataFile");
-			final HDT hdt = HDTManager.mapIndexedHDT(dataFile, null);
-			final HDTGraph graph = new HDTGraph(hdt);
-			model = ModelFactory.createModelForGraph(graph);
+			config = new ConfigReader(servletConfig.getInitParameter("configFile"));
+			for (Entry<String, String> dataSource : config.getDataSources().entrySet()) {
+				final HDT hdt = HDTManager.mapIndexedHDT(dataSource.getValue(), null);
+				final Model model = ModelFactory.createModelForGraph(new HDTGraph(hdt));
+				dataSources.put(dataSource.getKey(), model);
+			}
 		}
 		catch (Exception e) {
 			throw new ServletException(e);
@@ -47,16 +53,24 @@ public void init(ServletConfig config) throws ServletException {
 	@Override
 	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException {
 		try {
+			// find the data source
 			final String path = request.getRequestURI().substring(request.getContextPath().length());
+			final String dataSourceName = path.substring(1);
+			final Model dataSource = dataSources.get(dataSourceName);
+			if (dataSource == null)
+				throw new Exception("data source not found");
 
-			// parse the subject, predicate, and object parameters
+			// create the output model
 			final Model output = ModelFactory.createDefaultModel();
+			output.setNsPrefixes(config.getPrefixes());
+			
+			// parse the subject, predicate, and object parameters
 			final Resource subject = parseAsResource(request.getParameter("subject"), output);
 			final Property predicate = parseAsProperty(request.getParameter("predicate"), output);
 			final RDFNode object = parseAsNode(request.getParameter("object"), output);
 
 			// add all statements with the given parameters to the output model
-			final StmtIterator statements = model.listStatements(subject, predicate, object);
+			final StmtIterator statements = dataSource.listStatements(subject, predicate, object);
 			for (int i = 0; i < TRIPLES_PER_PAGE && statements.hasNext(); i++)
 				output.add(statements.next());