DatabaseCache.java

/*
 * Copyright (c) 2011, the Last.fm Java Project and Committers
 * All rights reserved.
 *
 * Redistribution and use of this software in source and binary forms, with or without modification, are
 * permitted provided that the following conditions are met:
 *
 * - Redistributions of source code must retain the above
 *   copyright notice, this list of conditions and the
 *   following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the
 *   following disclaimer in the documentation and/or other
 *   materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
 * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package de.umass.lastfm.cache;

import java.io.*;
import java.sql.*;

/**
 * Generic class for caching into a database. Its constructor takes a {@link Connection} instance, which must be opened and closed by the
 * client. SQL code used in this class should work with all common databases (which support varchar, timestamp and longvarchar
 * datatypes).<br/> For more specialized versions of this class for different databases one may extend this class and override methods as
 * needed.
 *
 * @author Janni Kovacs
 */
public class DatabaseCache extends Cache {

	protected static final String DEFAULT_TABLE_NAME = "LASTFM_CACHE";
	protected String tableName = DEFAULT_TABLE_NAME;

	protected Connection conn;

	public DatabaseCache(Connection connection) throws SQLException {
		this.conn = connection;
		ResultSet tables = conn.getMetaData().getTables(null, null, tableName, null);
		if (!tables.next()) {
			createTable();
		}
	}

	protected void createTable() throws SQLException {
		PreparedStatement stmt = conn.prepareStatement("CREATE TABLE " + tableName + " (key varchar, expiration_date timestamp, response longvarchar);");
		stmt.execute();
		stmt.close();
	}

	public boolean contains(String cacheEntryName) {
		try {
			PreparedStatement stmt = conn.prepareStatement("SELECT key FROM " + tableName + " WHERE key = ?;");
			stmt.setString(1, cacheEntryName);
			ResultSet result = stmt.executeQuery();
			boolean b = result.next();
			stmt.close();
			return b;
		} catch (SQLException e) {
			return false;
		}
	}

	public InputStream load(String cacheEntryName) {
		try {
			PreparedStatement stmt = conn.prepareStatement("SELECT response FROM " + tableName + " WHERE key = ?;");
			stmt.setString(1, cacheEntryName);
			ResultSet result = stmt.executeQuery();
			if (result.next()) {
				String s = result.getString("response");
				stmt.close();
				return new ByteArrayInputStream(s.getBytes("UTF-8"));
			}
			stmt.close();
		} catch (SQLException e) {
			// ignore
		} catch (UnsupportedEncodingException e) {
			// won't happen
		}
		return null;
	}

	public void remove(String cacheEntryName) {
		try {
			PreparedStatement stmt = conn.prepareStatement("DELETE FROM " + tableName + " WHERE key = ?;");
			stmt.setString(1, cacheEntryName);
			stmt.execute();
			stmt.close();
		} catch (SQLException e) {
			// ignore
		}
	}

	public void store(String cacheEntryName, InputStream inputStream, long expirationDate) {
		try {
			InputStreamReader reader = new InputStreamReader(inputStream);
			StringBuilder sb = new StringBuilder(inputStream.available());
			char[] buf = new char[2048];
			int read;
			while ((read = reader.read(buf, 0, buf.length)) != -1) {
				sb.append(buf, 0, read);
			}
			PreparedStatement stmt = conn.prepareStatement("INSERT INTO " + tableName + " (key, expiration_date, response) VALUES(?, ?, ?);");
			stmt.setString(1, cacheEntryName);
			stmt.setTimestamp(2, new Timestamp(expirationDate));
			stmt.setString(3, sb.toString());
			stmt.execute();
			stmt.close();
		} catch (SQLException e) {
			e.printStackTrace();
			// ignore
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
			// won't happen
		} catch (IOException e) {
			e.printStackTrace();
			// better won't happen
		}
	}

	public boolean isExpired(String cacheEntryName) {
		try {
			PreparedStatement stmt = conn.prepareStatement("SELECT expiration_date FROM " + tableName + " WHERE key = ?;");
			stmt.setString(1, cacheEntryName);
			ResultSet result = stmt.executeQuery();
			if (result.next()) {
				Timestamp timestamp = result.getTimestamp("expiration_date");
				long expirationDate = timestamp.getTime();
				stmt.close();
				return expirationDate < System.currentTimeMillis();
			}
		} catch (SQLException e) {
			// ignore
		}
		return false;
	}

	public void clear() {
		try {
			PreparedStatement stmt = conn.prepareStatement("DELETE FROM " + tableName + ";");
			stmt.execute();
			stmt.close();
		} catch (SQLException e) {
			// ignore
		}
	}
}