Java tutorial
/* * NOTE: This copyright does *not* cover user programs that use HQ * program services by normal system calls through the application * program interfaces provided as part of the Hyperic Plug-in Development * Kit or the Hyperic Client Development Kit - this is merely considered * normal use of the program, and does *not* fall under the heading of * "derived work". * * Copyright (C) [2004-2008], Hyperic, Inc. * This file is part of HQ. * * HQ is free software; you can redistribute it and/or modify * it under the terms version 2 of the GNU General Public License as * published by the Free Software Foundation. This program is distributed * in the hope that it will be useful, but WITHOUT ANY WARRANTY; without * even the implied warranty of MERCHANTABILITY or FITNESS FOR A * PARTICULAR PURPOSE. See the GNU General Public License for more * details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 * USA. */ package org.hyperic.hq.product; import java.sql.Connection; import java.sql.ResultSet; import java.sql.ResultSetMetaData; import java.sql.SQLException; import java.sql.Statement; import java.util.ArrayList; import java.util.HashMap; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.Set; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.hyperic.util.jdbc.DBUtil; /** * JDBCQueryCache is a simple caching mechanism to be used with * JDBCMeasurementPlugins. * * example: * * mysql> select Value, Default from sys_table; * +-----------------------------------+----------+---------+ * | Variable_name | Value | Default | * +-----------------------------------+----------+---------+ * | DB_Max_Memory | 8192 | 1024 | * | DB_Max_Connections | 400 | 10 | * ... * ... * * <code> * String query = "select Value, Default from sys_table"; * JDBCQueryCache cache = new JDBCQueryCache(query, "Variable_name", 5000); * Double val = Double.valueOf(cache.get("DB_Max_Memory", "Value").toString()); * val = Double.valueOf(cache.get("DB_Max_Connections", "Default").toString()); * </code> */ public class JDBCQueryCache { private static final String _logCtx = JDBCQueryCache.class.getName(); private final Log _log = LogFactory.getLog(_logCtx); private final Map _cache = new HashMap(); private final String _query, _queryKey; private long _last = -1l; private final long _cacheTimeout; public JDBCQueryCache(String query, String queryKey, long cacheTimeout) { _query = query; _queryKey = queryKey; _cacheTimeout = cacheTimeout; } /** * Explicitly clears any cached value */ public void clearCache() { _cache.clear(); } /** * Explicitly sets the expire time of the cache to expireTime. Cache will * not repopulate until System.currentTimeMillis() <= expireTime. */ public void setExpireTime(long expireTime) { _last = expireTime - _cacheTimeout; } /** * @return Object representation of the *only* row and column value * or null if it does not exist * @throws JDBCQueryCacheException if there are 0 or > 1 rows in the cache. */ public Object getOnlyRow(Connection conn, String column) throws SQLException, JDBCQueryCacheException { final long now = System.currentTimeMillis(); if (_cache.isEmpty() || (now - _cacheTimeout) > _last) { repopulateCache(conn); } final Set keys = _cache.keySet(); if (keys.size() > 1) { throw new JDBCQueryCacheException("cache contains more than one row"); } else if (keys.size() <= 0) { throw new JDBCQueryCacheException("cache does not contain any results"); } List list = null; for (final Iterator it = _cache.entrySet().iterator(); it.hasNext();) { final Map.Entry entry = (Map.Entry) it.next(); list = (List) entry.getValue(); break; } if (list == null) { return null; } for (final Iterator it = list.iterator(); it.hasNext();) { final NameValuePair pair = (NameValuePair) it.next(); if (pair.getName().equals(column)) { return pair.getValue(); } } throw new JDBCQueryCacheException("column " + column + " not found."); } /** * @return Object representation of the row key/column value or null if it * does not exist */ public Object get(Connection conn, String key, String column) throws JDBCQueryCacheException, SQLException { long now = System.currentTimeMillis(); if (_cache.isEmpty() || (now - _cacheTimeout) > _last) { repopulateCache(conn); } List list = (List) _cache.get(key); if (list == null) { return null; } for (Iterator it = list.iterator(); it.hasNext();) { NameValuePair pair = (NameValuePair) it.next(); if (pair.getName().equalsIgnoreCase(column)) { return pair.getValue(); } } throw new JDBCQueryCacheException("key " + key + ", column " + column + " not found."); } private void repopulateCache(Connection conn) throws SQLException, JDBCQueryCacheException { Statement stmt = null; ResultSet rs = null; if (_log.isDebugEnabled()) { final String msg = "re-populating JDBCQueryCache for " + _query + " with queryKey of " + _queryKey; _log.debug(msg); } try { _cache.clear(); stmt = conn.createStatement(); rs = stmt.executeQuery(_query); final List columns = getQueryColumns(rs); final boolean debug = _log.isDebugEnabled(); while (rs.next()) { int i = 1; final List vals = new ArrayList(); String key = null; for (final Iterator it = columns.iterator(); it.hasNext(); i++) { final String column = (String) it.next(); if (column.equalsIgnoreCase(_queryKey)) { key = rs.getString(i); } else { String tmp = rs.getString(i); tmp = (rs.wasNull()) ? null : tmp; if (debug) { _log.debug("adding nameValuePair=" + column + "/" + tmp); } vals.add(new NameValuePair(column, tmp)); } } if (key == null) { throw new JDBCQueryCacheException( "queryKey, " + _queryKey + " was not represented in the query"); } if (debug) _log.debug("adding key=" + key); _cache.put(key, vals); } } catch (SQLException e) { throw e; } finally { DBUtil.closeJDBCObjects(_logCtx, null, stmt, rs); // even if a failure occurs we want to set the _last update time. // this will alleviate the situation where there are a bunch // of subsequent failures. These failures could potentially hold // up the ScheduleThread _last = System.currentTimeMillis(); } } private List getQueryColumns(ResultSet rs) throws SQLException { ResultSetMetaData rsmd = rs.getMetaData(); int size = rsmd.getColumnCount(); List rtn = new ArrayList(size); for (int i = 1; i <= size; i++) { rtn.add(rsmd.getColumnLabel(i)); } return rtn; } private class NameValuePair { private final String _name; private final Object _value; public NameValuePair(String name, Object value) { _name = name; _value = value; } public String getName() { return _name; } public Object getValue() { return _value; } } }