c3p0的几种使用方式(原文地址: https://my.oschina.net/liangtee/blog/101047)

package com.c3p0.test;

import java.sql.Connection;
import java.sql.SQLException;
import java.beans.PropertyVetoException;
import com.mchange.v2.c3p0.ComboPooledDataSource;

public class DBPool {
    private static DBPool dbPool;
    private ComboPooledDataSource dataSource;

    static {
        dbPool = new DBPool();
    }

    public DBPool() {
        try {
            dataSource = new ComboPooledDataSource();
            dataSource.setUser("id");
            dataSource.setPassword("pw");
            dataSource.setJdbcUrl(
                    "jdbc:mysql://127.0.0.1:3306/test?autoReconnect=true&useUnicode=true&characterEncoding=GB2312");
            dataSource.setDriverClass("com.mysql.jdbc.Driver");
            dataSource.setInitialPoolSize(2);
            dataSource.setMinPoolSize(1);
            dataSource.setMaxPoolSize(10);
            dataSource.setMaxStatements(50);
            dataSource.setMaxIdleTime(60);
        } catch (PropertyVetoException e) {
            throw new RuntimeException(e);
        }
    }

    public final static DBPool getInstance() {
        return dbPool;
    }

    public final Connection getConnection() {
        try {
            return dataSource.getConnection();
        } catch (SQLException e) {
            throw new RuntimeException("无法从数据源获取连接", e);
        }
    }

    public static void main(String[] args) throws SQLException {
        Connection con = null;
        try {
            con = DBPool.getInstance().getConnection();
        } catch (Exception e) {
        } finally {
            if (con != null)
                con.close();
        }
    }

}

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
    <default-config>
        <property name="user">test</property>
        <property name="password">test</property>
        <property name="jdbcUrl">jdbc:oracle:thin:@localhost:1521:orcl</property>
        <property name="driverClass">oracle.jdbc.OracleDriver</property>
        <property name="automaticTestTable">con_test</property>
        <property name="checkoutTimeout">30000</property>
        <property name="idleConnectionTestPeriod">30</property>
        <property name="initialPoolSize">10</property>
        <property name="maxIdleTime">30</property>
        <property name="maxPoolSize">100</property>
        <property name="minPoolSize">10</property>
        <property name="maxStatements">200</property>

        <user-overrides user="test-user">
            <property name="maxPoolSize">10</property>
            <property name="minPoolSize">1</property>
            <property name="maxStatements">0</property>
        </user-overrides>
    </default-config>

    <!-- This app is massive! -->
    <named-config name="intergalactoApp">
        <property name="acquireIncrement">50</property>
        <property name="initialPoolSize">100</property>
        <property name="minPoolSize">50</property>
        <property name="maxPoolSize">1000</property>

        <!-- intergalactoApp adopts a different approach to configuring statement 
            caching -->
        <property name="maxStatements">0</property>
        <property name="maxStatementsPerConnection">5</property>

        <!-- he‘s important, but there‘s only one of him -->
        <user-overrides user="master-of-the-universe">
            <property name="acquireIncrement">1</property>
            <property name="initialPoolSize">1</property>
            <property name="minPoolSize">1</property>
            <property name="maxPoolSize">5</property>
            <property name="maxStatementsPerConnection">50</property>
        </user-overrides>
    </named-config>
    
    <named-config name="userApp">
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/test</property>
        <property name="user">root</property>
        <property name="password">123456</property>
        <property name="acquireIncrement">5</property>
        <property name="initialPoolSize">10</property>
        <property name="minPoolSize">10</property>
        <property name="maxPoolSize">20</property>
        <property name="maxStatements">0</property>
        <property name="maxStatementsPerConnection">5</property>
        <!-- he‘s important, but there‘s only one of him -->
        <user-overrides user="master-of-the-universe">
            <property name="acquireIncrement">1</property>
            <property name="initialPoolSize">1</property>
            <property name="minPoolSize">1</property>
            <property name="maxPoolSize">5</property>
            <property name="maxStatementsPerConnection">50</property>
        </user-overrides>
    </named-config>
</c3p0-config>

package com.c3p0.test;

import java.sql.Connection;
import java.sql.SQLException;
import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;


public class DbConnection {
    private static DataSource dataSource;
    static {
        dataSource = new ComboPooledDataSource("userApp");
    }

    public static Connection getConnectioon() throws SQLException {
        return dataSource.getConnection();
    }
}

package com.c3p0.test;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.Properties;

import com.mchange.v2.c3p0.ComboPooledDataSource;
import com.mchange.v2.c3p0.DataSources;

public final class ConnectionManager {
    private static ConnectionManager instance;

    public ComboPooledDataSource ds;
    private static String c3p0Properties = "c3p0.properties";

    private ConnectionManager() throws Exception {
        Properties p = new Properties();
        p.load(this.getClass().getResourceAsStream(c3p0Properties));
        ds = new ComboPooledDataSource();
        ds.setUser(p.getProperty("user"));
        ds.setPassword(p.getProperty("password"));
        ds.setJdbcUrl(p.getProperty("jdbcUrl"));
        ds.setDriverClass(p.getProperty("driverClass"));
        ds.setInitialPoolSize(Integer.parseInt(p.getProperty("initialPoolSize")));
        ds.setMinPoolSize(Integer.parseInt(p.getProperty("minPoolSize")));
        ds.setMaxPoolSize(Integer.parseInt(p.getProperty("maxPoolSize")));
        ds.setMaxStatements(Integer.parseInt(p.getProperty("maxStatements")));
        ds.setMaxIdleTime(Integer.parseInt(p.getProperty("maxIdleTime")));
    }

    public static final ConnectionManager getInstance() {
        if (instance == null) {
            try {
                instance = new ConnectionManager();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return instance;
    }

    public synchronized final Connection getConnection() {
        try {
            return ds.getConnection();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    protected void finalize() throws Throwable {
        DataSources.destroy(ds); // 关闭datasource
        super.finalize();
    }
}