DatabaseCache.java :  » Music » harmonium » net » roarsoftware » lastfm » cache » Java Open Source

package net.roarsoftware.lastfm.cache;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Timestamp;

/**
 * Generic class for caching into a database. It's 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 TABLE_NAME = "LASTFM_CACHE";

  protected Connection conn;

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

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

  public boolean contains(String cacheEntryName) {
    try {
      PreparedStatement stmt = conn.prepareStatement("SELECT key FROM " + TABLE_NAME + " 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 " + TABLE_NAME + " 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 " + TABLE_NAME + " 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 " + TABLE_NAME + " (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 " + TABLE_NAME + " 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 " + TABLE_NAME + ";");
      stmt.execute();
      stmt.close();
    } catch (SQLException e) {
      // ignore
    }
  }
}