Use parameterized XPath query

Klausuren/Sda1/2016Summer/Solve/src/main/java/de/hdm_stuttgart/mi/sda1/exam/movie_by_actor/Moviedb2MovieByActor.java

 package de.hdm_stuttgart.mi.sda1.exam.movie_by_actor;
 
 
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
-import org.apache.logging.log4j.LogManager;
-import org.apache.logging.log4j.Logger;
 import org.jdom2.Document;
 import org.jdom2.Element;
 import org.jdom2.filter.Filters;
@@ -14,57 +14,61 @@ import org.jdom2.xpath.XPathFactory;
 import de.hdm_stuttgart.mi.unitmarking.jdom.DomFilter;
 
 public class Moviedb2MovieByActor implements DomFilter {
-	
-	final Logger log = LogManager.getLogger(Moviedb2MovieByActor.class);
-	
-	Element movieDb;
-	
+
+	static private final String SEARCH_BY_ID_KEY = "searchById";
+
+	static { // Initialize static parameterized Xpath query object,
+		     // see https://freedocs.mi.hdm-stuttgart.de/__slidedom.html#/sda1_dom_fig_domXpathVariables.
+
+		final Map<String, Object> xpathVarsNamespacePrefix = new HashMap<>();
+
+		xpathVarsNamespacePrefix.put(SEARCH_BY_ID_KEY, null /* default namespace */);
+
+		searchMovieByActorId = XPathFactory.instance().compile(
+				"/movieDb/movies/movie[cast/actor[@ref=$" + SEARCH_BY_ID_KEY + "]]",
+				Filters.element(),
+				xpathVarsNamespacePrefix);
+	}
+
+	static private final XPathExpression<Element> searchMovieByActorId;
+
 	@Override
 	public Document process(final Document input) {
-		
+
 		final Element html = new Element("html");
 		final Document htmlDoc = new Document(html);
-		
+
 		final Element body = new Element("body");
 		html.addContent(body);
-		
+
 		final Element dl = new Element("dl");
 		body.addContent(new Element("h1")
 				.addContent("List of actors among with their corresponding films"))
 				.addContent(dl);
-		
-		movieDb = input.getRootElement();
-		
-		movieDb.getChild("persons").getChildren().stream().forEach(
+
+		input.getRootElement().getChild("persons").getChildren().forEach(
 				p -> addFilmsToActor(dl, p)
-				);
-		
+		);
+
 		return htmlDoc;
 	}
-	
-	void addFilmsToActor(final Element dl, final Element person) {
-		
-		final String movies2actorId = "movie[cast/actor[@ref='" 
-		+ person.getAttributeValue("id") +"']]";
-
-		final XPathExpression<Element> xpath =
-			    XPathFactory.instance().compile(movies2actorId, Filters.element());
-		
-		final List<Element> titles = xpath.evaluate(movieDb.getChild("movies"));
-		
-		if (0 < titles.size()) {
+
+	private void addFilmsToActor(final Element dl, final Element person) {
+
+		searchMovieByActorId.setVariable(SEARCH_BY_ID_KEY, person.getAttributeValue("id"));
+
+		final List<Element> movies = searchMovieByActorId.evaluate(person);
+
+		if (0 < movies.size()) {
 			final Element dt = new Element("dt"),
 					dd = new Element("dd");
-			
+
 			dl.addContent(dt).addContent(dd);
 			dt.addContent(person.getChild("name").getText());
-			
-			titles.stream()
-			.map(t -> t.getChild("title").getText())
-			.forEach(s -> {
-				dd.addContent(new Element("p").addContent(s));
-			});
+
+			movies.stream()
+					.map(t -> t.getChild("title").getText())
+					.forEach(s -> dd.addContent(new Element("p").addContent(s)));
 		}
 	}
-
-}
+}
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