使用c3p0开源的JDBC连接池小实例

C3P0是一个开源的JDBC连接池，它实现了数据源和JNDI绑定，支持JDBC3规范和JDBC2的标准扩展。目前使用它的开源项目有Hibernate，Spring等。

C3P0 properties配置文件：

c3p0.DriverClass=com.microsoft.sqlserver.jdbc.SQLServerDriver
c3p0.JdbcUrl=jdbc:sqlserver://200.10.10.172:1433;DatabaseName=Test;selectMethod=cursor
c3p0.user=sa
#c3p0.user=root
c3p0.password=123
#c3p0.password=RHqlO9D2wCM=
#Number of Connections a pool will try to acquire upon startup.
c3p0.initialPoolSize=30
#Maximum number of Connections a pool will maintain at any given time.
c3p0.maxPoolSize=50
#Minimum number of Connections a pool will maintain at any given time.
c3p0.minPoolSize=20
#Determines how many connections at a time c3p0 will try to acquire when the pool is exhausted.
c3p0.acquireIncrement=3
#If this is a number greater than 0, c3p0 will test all idle, pooled but unchecked-out connections, every this number of seconds.
c3p0.idleConnectionTestPeriod=60
#
c3p0.maxIdleTime=60
#Defines how many times c3p0 will try to acquire a new Connection from the database before giving up.
c3p0.acquireRetryAttempts=10
#Milliseconds, time c3p0 will wait between acquire attempts.
c3p0.acquireRetryDelay=1000

C3P0管理类，实现配置文件的读取，获取连接和关闭连接等功能：

package com.hodmct.db;

import java.beans.PropertyVetoException;
import java.io.FileInputStream;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.Properties;

import org.apache.log4j.Logger;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class ConnectionManager {
    private static Logger log = Logger.getLogger(ConnectionManager.class);
    private static String CONFIG_FILE_LOCATION = System.getProperty("user.dir") + "/config/db.properties";
    private final ThreadLocal<Connection> threadLocal = new ThreadLocal<Connection>();
    private String configFile = CONFIG_FILE_LOCATION;
    private ComboPooledDataSource ds;
    private static ConnectionManager instance;
    
    public static ConnectionManager getInstance(String path)
    {
        if (instance == null)
        {
            if (path == null)
            {
                path = CONFIG_FILE_LOCATION; 
            }
            instance = new ConnectionManager(path);
        }
        
        return instance;
    }
    
    public static ConnectionManager getInstance()
    {
        return getInstance(CONFIG_FILE_LOCATION);
    }
    
    private void init() {
        Properties dbProps = new Properties();
        try {
            InputStream is = new FileInputStream(configFile);
            dbProps.load(is);
            log.info("db config load success!");
        } catch (Exception e) {
            e.printStackTrace();
            log.error("DB config load failed.");
            throw new RuntimeException("DB config load failed.");
        }
        ds = new ComboPooledDataSource();
        try {
            ds.setDriverClass(dbProps.getProperty("c3p0.DriverClass").trim());
        } catch (PropertyVetoException e1) {
            throw new RuntimeException("com.sqlserver.jdbc.Driver加载失败");
        }
        // ds.setJdbcUrl("jdbc:mysql://127.0.0.1/mysession");
        // ds.setUser("sessadmin");
        // ds.setPassword("8877007");
        log.error(dbProps.toString());
        ds.setJdbcUrl(dbProps.getProperty("c3p0.JdbcUrl").trim());
        ds.setUser(dbProps.getProperty("c3p0.user").trim());
        String password = dbProps.getProperty("c3p0.password").trim();
        //password = UtilCommon.dec(password);
        ds.setPassword(password);
        //ds.setPassword(UtilCommon.dec(dbProps.getProperty("c3p0.password").trim()));
        // 连接关闭时默认将所有未提交的操作回滚。Default: false autoCommitOnClose
        ds.setAutoCommitOnClose(true);

        // 定义所有连接测试都执行的测试语句。在使用连接测试的情况下这个一显著提高测试速度。注意：
        // 测试的表必须在初始数据源的时候就存在。Default: null preferredTestQuery
        ds.setPreferredTestQuery("select 1");
        // 因性能消耗大请只在需要的时候使用它。如果设为true那么在每个connection提交的
        // 时候都将校验其有效性。建议使用idleConnectionTestPeriod或automaticTestTable
        // 等方法来提升连接测试的性能。Default: false testConnectionOnCheckout
        ds.setTestConnectionOnCheckout(false);
        // 如果设为true那么在取得连接的同时将校验连接的有效性。Default: false testConnectionOnCheckin
        ds.setTestConnectionOnCheckin(false);
        // 获取连接失败将会引起所有等待连接池来获取连接的线程抛出异常。但是数据源仍有效
        // 保留，并在下次调用getConnection()的时候继续尝试获取连接。如果设为true，那么在尝试
        // 获取连接失败后该数据源将申明已断开并永久关闭。Default: false breakAfterAcquireFailure
        ds.setBreakAfterAcquireFailure(false);

        try {
            // 初始化时获取三个连接，取值应在minPoolSize与maxPoolSize之间。Default: 3
            // initialPoolSize
            ds.setInitialPoolSize(Integer.parseInt(dbProps.getProperty("c3p0.initialPoolSize").trim()));
            // ds.setInitialPoolSize(3);
            // 连接池中保留的最大连接数。Default: 15 maxPoolSize
            ds.setMaxPoolSize(Integer.parseInt(dbProps.getProperty("c3p0.maxPoolSize").trim()));
            // ds.setMaxPoolSize(10);
            // 连接池中保留的最小连接数。
            ds.setMinPoolSize(Integer.parseInt(dbProps.getProperty("c3p0.maxPoolSize").trim()));
            // ds.setMinPoolSize(1);
            // 当连接池中的连接耗尽的时候c3p0一次同时获取的连接数。Default: 3 acquireIncrement
            ds.setAcquireIncrement(Integer.parseInt(dbProps.getProperty("c3p0.acquireIncrement").trim()));
            // ds.setAcquireIncrement(1);
            // 每60秒检查所有连接池中的空闲连接。Default: 0 idleConnectionTestPeriod
            ds.setIdleConnectionTestPeriod(Integer.parseInt(dbProps.getProperty("c3p0.idleConnectionTestPeriod").trim()));
            // ds.setIdleConnectionTestPeriod(60);
            // 最大空闲时间,25000秒内未使用则连接被丢弃。若为0则永不丢弃。Default: 0 maxIdleTime
            ds.setMaxIdleTime(Integer.parseInt(dbProps.getProperty("c3p0.maxIdleTime").trim()));
            // ds.setMaxIdleTime(25000);
            // 定义在从数据库获取新连接失败后重复尝试的次数。Default: 30 acquireRetryAttempts
            ds.setAcquireRetryAttempts(Integer.parseInt(dbProps.getProperty("c3p0.acquireRetryAttempts").trim()));
            // ds.setAcquireRetryAttempts(30);
            // 两次连接中间隔时间，单位毫秒。Default: 1000 acquireRetryDelay
            ds.setAcquireRetryDelay(Integer.parseInt(dbProps.getProperty("c3p0.acquireRetryDelay").trim()));
            // ds.setAcquireRetryDelay(1000);
            log.info("db set config success!");
        } catch (Exception e) {
            log.error("oh, db set config failed!");
            e.printStackTrace();
        }

    }

    private ConnectionManager() {
        init();
        log.info(threadLocal);
    }

    private ConnectionManager(String dbFilePath) {
        configFile = dbFilePath;
        log.info(threadLocal);
        init();
    }

    public Connection getConnection() {
        Connection connection = threadLocal.get();
        if (connection == null) {
            try {
                connection = ds.getConnection();
            } catch (SQLException e) {
                log.error(e.getMessage(), e);
            }
            threadLocal.set(connection);
        }
        return connection;
    }

    public void closeConnection() {
        Connection connection = threadLocal.get();
        try {
            if (connection != null && !connection.isClosed()) {
                connection.close();
                threadLocal.set(null);
            }
        } catch (SQLException e) {
            log.error(e.getMessage(), e);
        }
    }
}

测试效果：

import java.sql.Connection;

import org.junit.Test;

public class ConnectionManagerTest {

    @Test
    public void testGetConnection() throws Exception{
        
        Connection con = ConnectionManager.getInstance().getConnection();
        if(!con.isClosed() && con != null){
            System.out.println("success....");
        }
    }

}