Java tutorial
/* * $Header: /home/cvs/jakarta-struts/contrib/struts-legacy/src/java/org/apache/struts/legacy/GenericDataSource.java,v 1.1 2003/05/09 10:15:38 husted Exp $ * $Revision: 1.1 $ * $Date: 2003/05/09 10:15:38 $ * ==================================================================== * * The Apache Software License, Version 1.1 * * Copyright (c) 1999-2001 The Apache Software Foundation. All rights * reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 2. 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. * * 3. 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For more * information on the Apache Software Foundation, please see * <http://www.apache.org/>. * */ package org.apache.struts.legacy; import java.io.PrintWriter; import java.sql.Connection; import java.sql.Driver; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import java.util.LinkedList; import java.util.Properties; import javax.sql.DataSource; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /** * <p>Generic data source implementation of the <code>DataSource</code> * interface. <b>WARNING</b> - This implementation does not know how to * provide connections with different username/password combinations. * Calling this version of the implementation using the * getConnection(username,password) signature will throw an exception.</p> * * <p>The following properties are supported by the standard * <code>GenericDataSource</code> implementation:</p> * <table> * <tr> * <th width="15%">Property</th> * <th width="85%">Description</th> * </tr> * <tr> * <td align="center">autoCommit</td> * <td>Set to <code>true</code> if you want the connections returned to you * by calling <code>getConnection()</code> to be configured in * "auto-commit after every statement" mode. The default value is * <code>true</code>, to conform to JDBC standard conventions.</td> * </tr> * <tr> * <td align="center">description</td> * <td>A short textual description of this data source. This property is * required by the <code>javax.sql.DataSource</code> interface, but is * not used within this implementation.</td> * </tr> * <tr> * <td align="center">driverClass</td> * <td>The fully qualified class name of the JDBC driver to be utilized for * the connections created by this data source. Consult the * documentation for your JDBC driver to identify the value to be * configured for this property.</td> * </tr> * <tr> * <td align="center">maxCount</td> * <td>The maximum number of JDBC connections that will be created by this * data source. This value must be greater than or equal to the value * specified for the <code>minCount</count> property.</td> * </tr> * <tr> * <td align="center">minCount</td> * <td>The minimum number of JDBC connections to establish when this data * source is first opened. This value must be less than or equal to the * value specified for the <code>maxCount</code> property.</td> * </tr> * <tr> * <td align="center">password</td> * <td>The database password used to establish the connections created by * this connection pool, in conjunction with the username specified in * the <code>user</code> property.</td> * </tr> * <tr> * <td align="center">pingCommand</td> * <td>A non-query SQL command that, if specified, will be executed before * a connection is returned by a call to <code>getConnection()</code>. * If any SQLException is thrown by the execution of this statement, * it is assumed that this connection is stale and it will be discarded. * Because this happens on every connection allocation, you should ensure * that the statement executes very quickly.</td> * </tr> * <tr> * <td align="center">pingQuery</td> * <td>A query SQL command (i.e. a SELECT) that, if specified, will be * executed before a connection is returned by a call to * <code>getConnection()</code>. If any SQLException is thrown by the * execution of this query (or by the subsequent processing of the * entire returned <code>ResultSet</code>), it is assumed that this * connection is stale and it will be discarded. Because this happens * on every connection allocation, you should ensure that the * statement executes very quickly.</td> * </tr> * <tr> * <td align="center">readOnly</td> * <td>Set to <code>true</code> if you want the connections returned to you * by calling <code>getConnection()</code> to be configured for read only * operations. This can result in more efficient database access, * because the database will know it does not need to retain undo logs * for rolling back the transaction. The default value is * <code>false</code>.</td> * </tr> * <tr> * <td align="center">url</td> * <td>The connection URL to be passed to our JDBC driver when establishing * a new connection. The value specified typically starts with * <code>jdbc:</code>, and includes a reference to the host (and, * optionally, the port number) at which the database server is listening * for connections, plus the name of the database to be opened. Consult * the documentation for your JDBC driver to identify the value to be * configured for this property.</td> * </tr> * <tr> * <td align="center">user</td> * <td>The database username used to establish the connections created by * this connection pool, in conjunction with the password specified in * the <code>password</code> property.</td> * </tr> * </table> * * <p>In addition, you can add to the set of <code>Properties</code> passed to * the JDBC driver by calling <code>addProperty()</code>.</p> * <p> * This class was originally maintained in the core Struts util package [revision 1.11]. * </p> * * @author Craig R. McClanahan * @author Ted Husted * @version $Revision: 1.1 $ $Date: 2003/05/09 10:15:38 $ */ public class GenericDataSource implements DataSource { // ----------------------------------------------------------- Util Methods /** * Return the <code>Class</code> object for the specified fully qualified * class name, from this web application's class loader. * <p> * See util.RequestUtils.applicationClass for maintained original. * * @param className Fully qualified class name to be loaded * @return Class object * @exception ClassNotFoundException if the class cannot be found */ private static Class applicationClass(String className) throws ClassNotFoundException { // Look up the class loader to be used ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); if (classLoader == null) { classLoader = GenericDataSource.class.getClassLoader(); } // Attempt to load the specified class return (classLoader.loadClass(className)); } /** * Return a new instance of the specified fully qualified class name, * after loading the class from this web application's class loader. * The specified class <strong>MUST</strong> have a public zero-arguments * constructor. * <p> * See util.RequestUtils.applicationClass for maintained original. * * @param className Fully qualified class name to use * @return new instance of class * @exception ClassNotFoundException if the class cannot be found * @exception IllegalAccessException if the class or its constructor * is not accessible * @exception InstantiationException if this class represents an * abstract class, an interface, an array class, a primitive type, * or void * @exception InstantiationException if this class has no * zero-arguments constructor */ private static Object applicationInstance(String className) throws ClassNotFoundException, IllegalAccessException, InstantiationException { return (applicationClass(className).newInstance()); } // ----------------------------------------------------- Instance Constants private static final String SQLEXCEPTION_GETCONNECTION = "getConnection(String username, String password) Method not supported. Use getConnection() instead."; // ----------------------------------------------------- Instance Variables /** * Has this data source been closed? */ protected boolean closed = false; /** * The list of Connections (wrapped in our associated wrapper class) that * have been created but are not currently in use. */ protected LinkedList connections = new LinkedList(); /** * The JDBC driver that we use as a connection factory. */ protected Driver driver = null; /** * Commons Logging instance. */ protected Log log = LogFactory.getLog(this.getClass()); /** * The login timeout for this data source. */ protected int loginTimeout = 0; /** * The log writer for this data source. */ protected PrintWriter logWriter = null; // ------------------------------------------------------------- Properties /** * Add a generic property to the list of connection properties to be used. * * @param name Name of the generic property * @param value Corresponding generic property value */ public void addProperty(String name, String value) { properties.put(name, value); } /** * The number of connections that have been created by this data source. */ protected int activeCount = 0; public int getActiveCount() { return (this.activeCount); } /** * The default auto-commit state for newly created connections. */ protected boolean autoCommit = true; public boolean getAutoCommit() { return (this.autoCommit); } public void setAutoCommit(boolean autoCommit) { this.autoCommit = autoCommit; } /** * The debugging detail level for this data source. */ protected int debug = 0; public int getDebug() { return (this.debug); } public void setDebug(int debug) { this.debug = debug; } /** * The description of this data source. */ protected String description = null; public String getDescription() { return (this.description); } public void setDescription(String description) { this.description = description; } /** * The Java class name of the JDBC driver to use. */ protected String driverClass = null; public String getDriverClass() { return (this.driverClass); } public void setDriverClass(String driverClass) { this.driverClass = driverClass; } /** * The maximum number of connections to be created. */ protected int maxCount = 2; public int getMaxCount() { return (this.maxCount); } public void setMaxCount(int maxCount) { this.maxCount = maxCount; } /** * The minimum number of connections to be created. */ protected int minCount = 1; public int getMinCount() { return (this.minCount); } public void setMinCount(int minCount) { this.minCount = minCount; } /** * The database password for use in establishing a connection. */ protected String password = null; public String getPassword() { return (this.password); } public void setPassword(String password) { this.password = password; addProperty("password", this.password); } /** * The non-query SQL command used to ping an allocated connection. */ protected String pingCommand = null; public String getPingCommand() { return (this.pingCommand); } public void setPingCommand(String pingCommand) { this.pingCommand = pingCommand; } /** * The query SQL command used to ping an allocated connection. */ protected String pingQuery = null; public String getPingQuery() { return (this.pingQuery); } public void setPingQuery(String pingQuery) { this.pingQuery = pingQuery; } /** * The connection properties for use in establishing connections. */ protected Properties properties = new Properties(); /** * The default read-only state for newly created connections. */ protected boolean readOnly = false; public boolean getReadOnly() { return (this.readOnly); } public void setReadOnly(boolean readOnly) { this.readOnly = readOnly; } /** * The JDBC URL for the database connection to be opened. */ protected String url = null; public String getUrl() { return (this.url); } public void setUrl(String url) { this.url = url; } /** * The number of connections created by this data source that are * currently in use. */ protected int useCount = 0; public int getUseCount() { return (this.useCount); } /** * The database username for use in establishing a connection. */ protected String user = null; public String getUser() { return (this.user); } public void setUser(String user) { this.user = user; addProperty("user", this.user); } // ----------------------------------------------------- DataSource Methods /** * Attempt to establish a database connection. * * @exception SQLException if a database access error occurs */ public Connection getConnection() throws SQLException { int seconds = 0; if (log.isInfoEnabled()) { log.info(" getConnection()"); } // Validate the opened status of this data source if (closed) { throw new SQLException("getConnection: Data source is closed"); } if (driver == null) { open(); } while (true) { // Have we timed out yet? if (log.isInfoEnabled()) { log.info(" Check for timeout, activeCount=" + activeCount + ", useCount=" + useCount); } if ((loginTimeout > 0) && (seconds >= loginTimeout)) { break; } // Return an existing connection from the pool if there is one synchronized (connections) { if (!connections.isEmpty()) { // Allocate the first available connection GenericConnection connection = (GenericConnection) connections.removeFirst(); if (log.isInfoEnabled()) { log.info(" Found available connection"); } // Make sure this connection is not stale connection.setClosed(false); try { ping(connection); } catch (SQLException e) { log.warn(" Connection stale, releasing"); try { connection.getConnection().close(); } catch (SQLException f) { ; } activeCount--; continue; } // unclose the connection's wrapper and return it useCount++; if (log.isInfoEnabled()) { log.info(" Return allocated connection, activeCount=" + activeCount + ", useCount=" + useCount); } return (connection); } } // Create a new connection if we are not yet at the maximum if (activeCount < maxCount) { Connection connection = createConnection(); if (connection != null) { try { ping(connection); } catch (SQLException e) { throw e; } useCount++; if (log.isInfoEnabled()) { log.info(" Return new connection, activeCount=" + activeCount + ", useCount=" + useCount); } return (connection); } } // Wait for an existing connection to be returned if (log.isInfoEnabled()) { log.info(" Sleep until next test"); } try { Thread.sleep(1000); seconds++; } catch (InterruptedException e) { ; } } // We have timed out awaiting an available connection if (log.isInfoEnabled()) { log.info(" Timeout awaiting connection"); } throw new SQLException("getConnection: Timeout awaiting connection"); } /** * Attempt to establish a database connection. <b>WARNING</b> - The * specified username and password are not supported by this * implementation. * * @param username Database username for this connection * @param password Database password for this connection * * @exception SQLException if a database access error occurs */ public Connection getConnection(String username, String password) throws SQLException { throw new SQLException(SQLEXCEPTION_GETCONNECTION); // Not implemented } /** * Return the login timeout for this data source. * * @exception SQLException if a database access error occurs */ public int getLoginTimeout() throws SQLException { return (this.loginTimeout); } /** * Return the log writer for this data source. * * @exception SQLException if a database access error occurs */ public PrintWriter getLogWriter() throws SQLException { return (this.logWriter); } /** * Set the login timeout for this data source. * * @param loginTimeout The new login timeout * * @exception SQLException if a database access error occurs */ public void setLoginTimeout(int loginTimeout) throws SQLException { this.loginTimeout = loginTimeout; } /** * Set the log writer for this data source. * * @param logWriter The new log writer * * @exception SQLException if a database access error occurs */ public void setLogWriter(PrintWriter logWriter) throws SQLException { this.logWriter = logWriter; } // --------------------------------------------------------- Public Methods /** * Close all connections that have been created by this data source. * * @exception SQLException if a database access error occurs */ public void close() throws SQLException { if (closed) throw new SQLException("close: Data Source already closed"); if (log.isDebugEnabled()) { log.debug(" close()"); } // Shut down all active connections while (activeCount > 0) { GenericConnection conn = (GenericConnection) getConnection(); conn.getConnection().close(); activeCount--; } // Mark this data source as having been closed and release our driver closed = true; driver = null; } /** * Open the initial connections that are appropriate for this data source. * * @exception SQLException if a database access error occurs */ public void open() throws SQLException { // Have we already been opened? if (driver != null) return; if (log.isDebugEnabled()) { log.debug(" open()"); } // Instantiate our database driver try { driver = (Driver) applicationInstance(driverClass); } catch (Throwable t) { throw new SQLException("open: " + t); } // Create the initial minimum number of required connections synchronized (connections) { for (int i = 0; i < minCount; i++) { connections.addLast(createConnection()); } } closed = false; } /** * Return a string representation of this component. */ public String toString() { StringBuffer sb = new StringBuffer("GenericDataSource["); sb.append("activeCount="); sb.append(activeCount); sb.append(", autoCommit="); sb.append(autoCommit); sb.append(", closed="); sb.append(closed); if (description != null) { sb.append(", description="); sb.append(description); } sb.append(", driverClass="); sb.append(driverClass); sb.append(", loginTimeout="); sb.append(loginTimeout); sb.append(", maxCount="); sb.append(maxCount); sb.append(", minCount="); sb.append(minCount); sb.append(", password="); sb.append(password); sb.append(", readOnly="); sb.append(readOnly); sb.append(", url="); sb.append(url); sb.append(", useCount="); sb.append(useCount); sb.append(", user="); sb.append(user); sb.append("]"); return (sb.toString()); } // ------------------------------------------------------ Protected Methods /** * Create, configure, and return a new JDBC Connection that has been * wrapped in our corresponding wrapper. * * @exception SQLException if a database access error occurs */ protected synchronized Connection createConnection() throws SQLException { if (activeCount < maxCount) { if (log.isInfoEnabled()) { log.info(" createConnection()"); } Connection conn = driver.connect(url, properties); activeCount++; return (new GenericConnection(this, conn, autoCommit, readOnly)); } log.error(" createConnection() returning null"); return (null); } /** * Log the specified message to our log writer, if we have one. * * @param message The message to be logged */ protected void log(String message) { if (logWriter != null) { logWriter.print("GenericDataSource["); logWriter.print(description); logWriter.print("]: "); logWriter.println(message); } } /** * Log the specified message and exception to our log writer, if we * have one. * * @param message The message to be logged * @param throwable The exception to be logged */ protected void log(String message, Throwable throwable) { if (logWriter != null) { logWriter.print("GenericDataSource["); logWriter.print(description); logWriter.print("]: "); logWriter.println(message); throwable.printStackTrace(logWriter); } } /** * Perform any configured <code>pingCommand</code> and/or * <code>pingQuery</code> on the specified connection, returning any * SQLException that is encountered along the way. * * @param conn The connection to be pinged */ protected void ping(Connection conn) throws SQLException { if (pingCommand != null) { if (log.isDebugEnabled()) { log.debug(" ping(" + pingCommand + ")"); } Statement stmt = conn.createStatement(); try { stmt.execute(pingCommand); stmt.close(); } catch (SQLException e) { log.warn("ping failed: " + e.getMessage(), e); try { if (stmt != null) { stmt.close(); } } catch (SQLException f) { ; } throw e; } } if (pingQuery != null) { if (log.isDebugEnabled()) { log.debug(" ping(" + pingQuery + ")"); } ResultSet rs = null; Statement stmt = conn.createStatement(); try { rs = stmt.executeQuery(pingQuery); while (rs.next()) { ; } rs.close(); stmt.close(); } catch (SQLException e) { log.warn("ping failed: " + e.getMessage(), e); try { if (rs != null) rs.close(); } catch (SQLException f) { ; } try { if (stmt != null) stmt.close(); } catch (SQLException f) { ; } throw e; } } } // -------------------------------------------------------- Package Methods /** * Return this connection to the available connection pool. * * @param conn The connection being returned */ void returnConnection(GenericConnection conn) { if (log.isInfoEnabled()) { log.info(" releaseConnection(), activeCount=" + activeCount + ", useCount=" + (useCount - 1)); } synchronized (connections) { connections.addLast(conn); useCount--; } } }