一个连接池的例子（来自JIVE）（1）

//文件：DbConnectionDefaultPool.java的第一部分

//请注意看里面注明的一处需要修改连接参数的地方
package com.qingtuo.db.pool;

import java.sql.*;
import java.util.*;
import java.io.*;
import java.text.*;
import java.util.Date;


/**
* Default Jive connection provider. It uses the excellent connection pool
* available from http://www.javaexchange.com. This connection provider is a
* a good choice unless you can use a container-managed one.
*/
public class DbConnectionDefaultPool extends DbConnectionProvider {

    private static final String NAME = "Default Connection Pool";
    private static final String DESCRIPTION = "The default connection provider "
        + "that uses the connection pool from javaexchange.com. It works with "
        + "almost any database setup, is customizable, and offers good performance. "
        + "Use this connection provider unless you have your own or can use a "
        + "container managed connection pool.";
    private static final String AUTHOR = "CoolServlets.com";
    private static final int MAJOR_VERSION = 1;
    private static final int MINOR_VERSION = 0;
    private static final boolean POOLED = true;

    private ConnectionPool connectionPool = null;
    private Properties props;
    private Properties propDescriptions;

    private Object initLock = new Object();

    public DbConnectionDefaultPool() {
        //this.manager = manager;
        props = new Properties();
        propDescriptions = new Properties();
        //Initialize all property values
        initializeProperties();
        //Load any existing property values
        loadProperties();
    }

    /**
     * Returns a database connection.
     */
    public Connection getConnection() {
        if (connectionPool == null) {
            //block until the init has been done
            synchronized(initLock) {
                //if still null, something has gone wrong
                if (connectionPool == null) {
                    System.err.println("Warning: DbConnectionDefaultPool.getConnection() was " +
                    "called when the internal pool has not been initialized.");
                    return null;
                }
            }
        }
        return new ConnectionWrapper(connectionPool.getConnection(), connectionPool);
    }

    /**
     * Starts the pool.
     */
    protected void start() {
        //acquire lock so that no connections can be returned.
        synchronized (initLock) {
            //Get properties
            String driver = props.getProperty("driver");
            String server = props.getProperty("server");
            String username = props.getProperty("username");
            String password = props.getProperty("password");
            int minConnections = 0, maxConnections = 0;
            double connectionTimeout = 0.0;
            try {
                minConnections = Integer.parseInt(props.getProperty("minConnections"));
                maxConnections = Integer.parseInt(props.getProperty("maxConnections"));
                connectionTimeout = Double.parseDouble(props.getProperty("connectionTimeout"));
            }
            catch (Exception e) {
                System.err.println("Error: could not parse default pool properties. " +
                    "Make sure the values exist and are correct.");
                e.printStackTrace();
                return;
            }
            String logPath = props.getProperty("logPath");

            try {
                connectionPool = new ConnectionPool(driver, server, username, password,
                    minConnections, maxConnections, logPath, connectionTimeout);
            }
            catch (IOException ioe) {
                System.err.println("Error starting DbConnectionDefaultPool: " + ioe);
                ioe.printStackTrace();
            }
        }
    }

    /**
     * Restarts the pool to take into account any property changes.
     */
    protected void restart() {
        //Kill off pool.
        destroy();
        //Reload properties.
        loadProperties();
        //Start a new pool.
        start();
    }

    /**
     * Destroys the connection pool.
     */
    protected void destroy() {
        if (connectionPool != null) {
            try {
                connectionPool.destroy(1);
            }
            catch (Exception e) {
                e.printStackTrace();
            }
        }
        //Release reference to connectionPool
        connectionPool = null;
    }

    /**
     * Returns the value of a property of the connection provider.
     *
     * @param name the name of the property.
     * @returns the value of the property.
     */
    public String getProperty(String name) {
        return (String)props.get(name);
    }

    /**
     * Returns the description of a property of the connection provider.
     *
     * @param name the name of the property.
     * @return the description of the property.
     */
    public String getPropertyDescription(String name) {
        return (String)propDescriptions.get(name);
    }

    /**
     * Returns an enumeration of the property names for the connection provider.
     */
    public Enumeration propertyNames() {
        return props.propertyNames();
    }

    /**
     * Sets a property of the connection provider. Each provider has a set number
     * of properties that are determined by the author. Trying to set a non-
     * existant property will result in an IllegalArgumentException.
     *
     * @param name the name of the property to set.
     * @param value the new value for the property.
     *
     */
    public void setProperty(String name, String value) {
        props.put(name, value);
        saveProperties();
    }

    /**
     * Give default values to all the properties and descriptions.
     */
    private void initializeProperties() {
        props.put("driver","");
        props.put("server","");
        props.put("username","");
        props.put("password","");
        props.put("minConnections","");
        props.put("maxConnections","");
        props.put("logPath","");
        props.put("connectionTimeout","");

        propDescriptions.put("driver","JDBC driver. e.g. @#oracle.jdbc.driver.OracleDriver@#");
        propDescriptions.put("server","JDBC connect string. e.g. @#jdbc:oracle:thin:@203.92.21.109:1526:orcl@#");
        propDescriptions.put("username","Database username. e.g. @#Scott@#");
        propDescriptions.put("password","Database password. e.g. @#Tiger@#");
        propDescriptions.put("minConnections","Minimum # of connections to start with in pool. Three is the recommended minimum");
        propDescriptions.put("maxConnections","Maximum # of connections in dynamic pool. Fifteen should give good performance for an average load.");
        propDescriptions.put("logPath","Absolute path name for log file. e.g. @#c:\\logs\\jiveDbLog.log@#");
        propDescriptions.put("connectionTimeout","Time in days between connection resets. e.g. @#.5@#");
    }

    /**
     * Load whatever properties that already exist.
     */
    private void loadProperties() {
        //在这里修改一些连接参数
        //in 2000
        /*
        String driver="org.gjt.mm.mysql.Driver";
        String server="jdbc:mysql://192.100.100.11/pcc";
        String username="pcc";
        String password="pcc123";
        String minConnections="3";
        String maxConnections="10";
        String logPath="c:\\temp\\qingtuoDbLog.log";
        String connectionTimeout="0.5";
        */
        //in Linux
        
        String driver="org.gjt.mm.mysql.Driver";
        String server="jdbc:mysql://192.100.100.1/qingtuo";
        //String server="jdbc:mysql://192.168.0.1/qingtuo";
        String username="qingtuo";
        String password="qingtuo";
        String minConnections="3";
        String maxConnections="20";
        String logPath="c:\\temp\\qingtuoDbLog.log";
//        String logPath="/tmp/qingtuoDbLog.log";
        String connectionTimeout="0.5";
        
        
        if (driver != null) {  props.setProperty("driver", driver);  }
        if (server != null) {  props.setProperty("server", server);  }
        if (username != null) {  props.setProperty("username", username);  }
        if (password != null) {  props.setProperty("password", password);  }
        //if (database != null) {  props.setProperty("database", database);  }
        if (minConnections != null) {  props.setProperty("minConnections", minConnections);  }
        if (maxConnections != null) {  props.setProperty("maxConnections", maxConnections);  }
        if (logPath != null) {  props.setProperty("logPath", logPath);  }
        if (connectionTimeout != null) {  props.setProperty("connectionTimeout", connectionTimeout);  }
    }

    private void saveProperties() {
        PropertyManager.setProperty("DbConnectionDefaultPool.driver", props.getProperty("driver"));
        PropertyManager.setProperty("DbConnectionDefaultPool.server", props.getProperty("server"));
        PropertyManager.setProperty("DbConnectionDefaultPool.username", props.getProperty("username"));
        PropertyManager.setProperty("DbConnectionDefaultPool.password", props.getProperty("password"));
        PropertyManager.setProperty("DbConnectionDefaultPool.minConnections", props.getProperty("minConnections"));
        PropertyManager.setProperty("DbConnectionDefaultPool.maxConnections", props.getProperty("maxConnections"));
        PropertyManager.setProperty("DbConnectionDefaultPool.logPath", props.getProperty("logPath"));
        PropertyManager.setProperty("DbConnectionDefaultPool.connectionTimeout", props.getProperty("connectionTimeout"));
    }

    private class ConnectionPool implements Runnable {
        private Thread runner;
    
        private Connection[] connPool;
        private int[] connStatus;

        private long[] connLockTime, connCreateDate;
        private String[] connID;
        private String dbDriver, dbServer, dbLogin, dbPassword, logFileString;
        private int currConnections, connLast, minConns, maxConns, maxConnMSec;

        //available: set to false on destroy, checked by getConnection()
        private boolean available=true;

        private PrintWriter log;
        private SQLWarning currSQLWarning;
        private String pid;

        /**
         * Creates a new Connection Broker<br>
         * dbDriver:        JDBC driver. e.g. @#oracle.jdbc.driver.OracleDriver@#<br>
         * dbServer:        JDBC connect string. e.g. @#jdbc:oracle:thin:@203.92.21.109:1526:orcl@#<br>
         * dbLogin:         Database login name.  e.g. @#Scott@#<br>
         * dbPassword:      Database password.    e.g. @#Tiger@#<br>
         * minConns:        Minimum number of connections to start with.<br>
         * maxConns:        Maximum number of connections in dynamic pool.<br>
         * logFileString:   Absolute path name for log file. e.g. @#c:\temp\mylog.log@# <br>
         * maxConnTime:     Time in days between connection resets. (Reset does a basic cleanup)<br>
         */
        public ConnectionPool (String dbDriver, String dbServer, String dbLogin,
                String dbPassword, int minConns, int maxConns,
                    String logFileString, double maxConnTime) throws IOException
        {
            connPool = new Connection[maxConns];
            connStatus = new int[maxConns];
            connLockTime = new long[maxConns];
            connCreateDate = new long[maxConns];
            connID = new String[maxConns];
            currConnections = minConns;
            this.maxConns = maxConns;
            this.dbDriver = dbDriver;
            this.dbServer = dbServer;
            this.dbLogin = dbLogin;
            this.dbPassword = dbPassword;
            this.logFileString = logFileString;
            maxConnMSec = (int)(maxConnTime * 86400000.0);  //86400 sec/day
            if(maxConnMSec < 30000) {  // Recycle no less than 30 seconds.
                maxConnMSec = 30000;
            }

            try {
                log = new PrintWriter(new FileOutputStream(logFileString),true);

                // Can@#t open the requested file. Open the default file.
            }
            catch (IOException e1) {
                System.err.println("Warning: DbConnectionDefaultPool could not open \""
                    + logFileString + "\" to write log to. Make sure that your Java " +
                    "process has permission to write to the file and that the directory exists."
                );
                try {
                    log = new PrintWriter(new FileOutputStream("DCB_" +
                        System.currentTimeMillis() + ".log"), true
                    );
                }
                catch (IOException e2) {
                    throw new IOException("Can@#t open any log file");
                }
            }

            // Write the pid file (used to clean up dead/broken connection)
            SimpleDateFormat formatter
                = new SimpleDateFormat ("yyyy.MM.dd G @#at@# hh:mm:ss a zzz");
            java.util.Date nowc = new java.util.Date();
            pid = formatter.format(nowc);

            BufferedWriter pidout = new BufferedWriter(new
                                    FileWriter(logFileString + "pid"));
            pidout.write(pid);
            pidout.close();

            log.println("Starting ConnectionPool:");
            log.println("dbDriver = " + dbDriver);
            log.println("dbServer = " + dbServer);
            log.println("dbLogin = " + dbLogin);
            log.println("log file = " + logFileString);
            log.println("minconnections = " + minConns);
            log.println("maxconnections = " + maxConns);
            log.println("Total refresh interval = " + maxConnTime + " days");
            log.println("-----------------------------------------");

        
            // Initialize the pool of connections with the mininum connections:
            // Problems creating connections may be caused during reboot when the
            //    servlet is started before the database is ready.  Handle this
            //    by waiting and trying again.  The loop allows 5 minutes for
            //    db reboot.
            boolean connectionsSucceeded=false;
            int dbLoop=20;
        
            try {
                for(int i=1; i < dbLoop; i++) {
                    try {
                        for(int j=0; j < currConnections; j++) {
                            log.println("Create Conn "+j);
                            createConn(j);
                        }
                        connectionsSucceeded=true;
                        break;
                    }
                    catch (SQLException e){
                        log.println("--->Attempt (" + String.valueOf(i) +
                                " of " + String.valueOf(dbLoop) +
                                ") failed to create new connections set at startup: ");
                        log.println("    " + e);
                        log.println("    Will try again in 15 seconds...");
                        try { Thread.sleep(15000); }
                        catch(InterruptedException e1) {}
                    }
                }
                if(!connectionsSucceeded) { // All attempts at connecting to db exhausted
                    log.println("\r\nAll attempts at connecting to Database exhausted");
                    throw new IOException();
                }
            }
            catch (Exception e) {
                throw new IOException();
            }
        
            // Fire up the background housekeeping thread

            runner = new Thread(this);
            runner.start();

        } //End ConnectionPool()

原文转自：http://www.ltesting.net