Java tutorial
/* * Copyright (c) 2011 Enrico Franchi, Michele Tomaiuolo and University of Parma. * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN * THE SOFTWARE. */ package net.blogracy.controller; import java.io.File; import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; import java.security.KeyPair; import java.security.PublicKey; import java.util.HashMap; import java.util.Iterator; import javax.jms.Connection; import javax.jms.ConnectionFactory; import javax.jms.DeliveryMode; import javax.jms.Destination; import javax.jms.Message; import javax.jms.MessageConsumer; import javax.jms.MessageListener; import javax.jms.MessageProducer; import javax.jms.Session; import javax.jms.TextMessage; import net.blogracy.config.Configurations; import net.blogracy.util.JsonWebSignature; import org.apache.activemq.ActiveMQConnection; import org.apache.activemq.ActiveMQConnectionFactory; import org.json.JSONArray; import org.json.JSONException; import org.json.JSONObject; import org.json.JSONTokener; /** * Generic functions to manipulate feeds are defined in this class. */ public class DistributedHashTable { private ConnectionFactory connectionFactory; private Connection connection; private Session session; private Destination lookupQueue; private Destination storeQueue; private Destination downloadQueue; private MessageProducer producer; private MessageConsumer consumer; static final String CACHE_FOLDER = Configurations.getPathConfig().getCachedFilesDirectoryPath(); private HashMap<String, JSONObject> records = new HashMap<String, JSONObject>(); private static final DistributedHashTable THE_INSTANCE = new DistributedHashTable(); public static DistributedHashTable getSingleton() { return THE_INSTANCE; } public DistributedHashTable() { try { File recordsFile = new File(CACHE_FOLDER + File.separator + "records.json"); if (recordsFile.exists()) { JSONArray recordList = new JSONArray(new JSONTokener(new FileReader(recordsFile))); for (int i = 0; i < recordList.length(); ++i) { JSONObject record = recordList.getJSONObject(i); records.put(record.getString("id"), record); } } connectionFactory = new ActiveMQConnectionFactory(ActiveMQConnection.DEFAULT_BROKER_URL); connection = connectionFactory.createConnection(); connection.start(); session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE); producer = session.createProducer(null); producer.setDeliveryMode(DeliveryMode.NON_PERSISTENT); lookupQueue = session.createQueue("lookup"); storeQueue = session.createQueue("store"); } catch (Exception e) { e.printStackTrace(); } } public void lookup(final String id) { try { Destination tempDest = session.createTemporaryQueue(); MessageConsumer responseConsumer = session.createConsumer(tempDest); responseConsumer.setMessageListener(new MessageListener() { @Override public void onMessage(Message response) { try { String msgText = ((TextMessage) response).getText(); JSONObject keyValue = new JSONObject(msgText); String value = keyValue.getString("value"); PublicKey signerKey = JsonWebSignature.getSignerKey(value); JSONObject record = new JSONObject(JsonWebSignature.verify(value, signerKey)); JSONObject currentRecord = getRecord(id); if (currentRecord == null || currentRecord.getString("version").compareTo(record.getString("version")) < 0) { putRecord(record); String uri = record.getString("uri"); FileSharing.getSingleton().download(uri); } } catch (Exception e) { e.printStackTrace(); } } }); JSONObject record = new JSONObject(); record.put("id", id); TextMessage message = session.createTextMessage(); message.setText(record.toString()); message.setJMSReplyTo(tempDest); producer.send(lookupQueue, message); } catch (Exception e) { e.printStackTrace(); } } public void store(final String id, final String uri, final String version) { try { JSONObject record = new JSONObject(); record.put("id", id); record.put("uri", uri); record.put("version", version); // put "magic" public-key; e.g. // RSA.modulus(n).exponent(e) // record.put("signature", user); // TODO KeyPair keyPair = Configurations.getUserConfig().getUserKeyPair(); String value = JsonWebSignature.sign(record.toString(), keyPair); JSONObject keyValue = new JSONObject(); keyValue.put("key", id); keyValue.put("value", value); TextMessage message = session.createTextMessage(); message.setText(keyValue.toString()); producer.send(storeQueue, message); putRecord(record); } catch (Exception e) { e.printStackTrace(); } } public JSONObject getRecord(String user) { return records.get(user); } public void putRecord(JSONObject record) { try { records.put(record.getString("id"), record); } catch (JSONException e1) { e1.printStackTrace(); } JSONArray recordList = new JSONArray(); Iterator<JSONObject> entries = records.values().iterator(); while (entries.hasNext()) { JSONObject entry = entries.next(); recordList.put(entry); } File recordsFile = new File(CACHE_FOLDER + File.separator + "records.json"); try { FileWriter writer = new FileWriter(recordsFile); recordList.write(writer); writer.close(); } catch (IOException e) { e.printStackTrace(); } catch (JSONException e) { e.printStackTrace(); } } }