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Optional components of Mahout which generally support interaction with third party systems,
formats, APIs, etc.
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/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.mahout.cf.taste.web;
import org.apache.mahout.cf.taste.common.TasteException;
import org.apache.mahout.cf.taste.model.DataModel;
import org.apache.mahout.cf.taste.model.Preference;
import org.apache.mahout.cf.taste.model.PreferenceArray;
import org.apache.mahout.cf.taste.recommender.RecommendedItem;
import org.apache.mahout.cf.taste.recommender.Recommender;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
/**
* A servlet which returns recommendations, as its name implies. The servlet accepts GET and POST
* HTTP requests, and looks for two parameters:
*
*
* - userID: the user ID for which to produce recommendations
* - howMany: the number of recommendations to produce
* - debug: (optional) output a lot of information that is useful in debugging.
* Defaults to false, of course.
*
*
* The response is text, and contains a list of the IDs of recommended items, in descending
* order of relevance, one per line.
*
* For example, you can get 10 recommendations for user 123 from the following URL (assuming
* you are running taste in a web application running locally on port 8080):
* {@code http://localhost:8080/taste/RecommenderServlet?userID=123&howMany=10}
*
* This servlet requires one {@code init-param} in {@code web.xml}: it must find
* a parameter named "recommender-class" which is the name of a class that implements
* {@link Recommender} and has a no-arg constructor. The servlet will instantiate and use
* this {@link Recommender} to produce recommendations.
*/
public final class RecommenderServlet extends HttpServlet {
private static final int NUM_TOP_PREFERENCES = 20;
private static final int DEFAULT_HOW_MANY = 20;
private Recommender recommender;
@Override
public void init(ServletConfig config) throws ServletException {
super.init(config);
String recommenderClassName = config.getInitParameter("recommender-class");
if (recommenderClassName == null) {
throw new ServletException("Servlet init-param \"recommender-class\" is not defined");
}
RecommenderSingleton.initializeIfNeeded(recommenderClassName);
recommender = RecommenderSingleton.getInstance().getRecommender();
}
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException {
String userIDString = request.getParameter("userID");
if (userIDString == null) {
throw new ServletException("userID was not specified");
}
long userID = Long.parseLong(userIDString);
String howManyString = request.getParameter("howMany");
int howMany = howManyString == null ? DEFAULT_HOW_MANY : Integer.parseInt(howManyString);
boolean debug = Boolean.parseBoolean(request.getParameter("debug"));
String format = request.getParameter("format");
if (format == null) {
format = "text";
}
try {
List items = recommender.recommend(userID, howMany);
if ("text".equals(format)) {
writePlainText(response, userID, debug, items);
} else if ("xml".equals(format)) {
writeXML(response, items);
} else if ("json".equals(format)) {
writeJSON(response, items);
} else {
throw new ServletException("Bad format parameter: " + format);
}
} catch (TasteException | IOException te) {
throw new ServletException(te);
}
}
private static void writeXML(HttpServletResponse response, Iterable items) throws IOException {
response.setContentType("application/xml");
response.setCharacterEncoding("UTF-8");
response.setHeader("Cache-Control", "no-cache");
PrintWriter writer = response.getWriter();
writer.print("");
for (RecommendedItem recommendedItem : items) {
writer.print("");
writer.print(recommendedItem.getValue());
writer.print(" ");
writer.print(recommendedItem.getItemID());
writer.print(" ");
}
private static void writeJSON(HttpServletResponse response, Iterable items) throws IOException {
response.setContentType("application/json");
response.setCharacterEncoding("UTF-8");
response.setHeader("Cache-Control", "no-cache");
PrintWriter writer = response.getWriter();
writer.print("{\"recommendedItems\":{\"item\":[");
boolean first = true;
for (RecommendedItem recommendedItem : items) {
if (first) {
first = false;
} else {
writer.print(',');
}
writer.print("{\"value\":\"");
writer.print(recommendedItem.getValue());
writer.print("\",\"id\":\"");
writer.print(recommendedItem.getItemID());
writer.print("\"}");
}
writer.println("]}}");
}
private void writePlainText(HttpServletResponse response,
long userID,
boolean debug,
Iterable items) throws IOException, TasteException {
response.setContentType("text/plain");
response.setCharacterEncoding("UTF-8");
response.setHeader("Cache-Control", "no-cache");
PrintWriter writer = response.getWriter();
if (debug) {
writeDebugRecommendations(userID, items, writer);
} else {
writeRecommendations(items, writer);
}
}
private static void writeRecommendations(Iterable items, PrintWriter writer) {
for (RecommendedItem recommendedItem : items) {
writer.print(recommendedItem.getValue());
writer.print('\t');
writer.println(recommendedItem.getItemID());
}
}
private void writeDebugRecommendations(long userID, Iterable items, PrintWriter writer)
throws TasteException {
DataModel dataModel = recommender.getDataModel();
writer.print("User:");
writer.println(userID);
writer.print("Recommender: ");
writer.println(recommender);
writer.println();
writer.print("Top ");
writer.print(NUM_TOP_PREFERENCES);
writer.println(" Preferences:");
PreferenceArray rawPrefs = dataModel.getPreferencesFromUser(userID);
int length = rawPrefs.length();
PreferenceArray sortedPrefs = rawPrefs.clone();
sortedPrefs.sortByValueReversed();
// Cap this at NUM_TOP_PREFERENCES just to be brief
int max = Math.min(NUM_TOP_PREFERENCES, length);
for (int i = 0; i < max; i++) {
Preference pref = sortedPrefs.get(i);
writer.print(pref.getValue());
writer.print('\t');
writer.println(pref.getItemID());
}
writer.println();
writer.println("Recommendations:");
for (RecommendedItem recommendedItem : items) {
writer.print(recommendedItem.getValue());
writer.print('\t');
writer.println(recommendedItem.getItemID());
}
}
@Override
public void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException {
doGet(request, response);
}
@Override
public String toString() {
return "RecommenderServlet[recommender:" + recommender + ']';
}
}