JAVA开源数据库连接池C3P0简介

先看官方对C3P0的介绍：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，目前在Hibernate和Spring中，均有使用。

工欲善其事必先利其器，先下相关的jar包吧，CSDN上一搜一大把，我的资源中也有。

C3P0就是一个数据库连接池，我们先看一个巨简单的使用C3P0的例子吧，访问本机Oracle的一张表：

package cn.test;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class C3P0Test {

	public static void main(String[] args) {

		try {
			// 创建一个数据源
			ComboPooledDataSource cpds = new ComboPooledDataSource();
			// 设置数据库的相关信息
			cpds.setDriverClass("oracle.jdbc.driver.OracleDriver");
			cpds.setJdbcUrl("jdbc:oracle:thin:@localhost:1521:ORCL");
			cpds.setUser("testdb");
			cpds.setPassword("testdb");
			cpds.setMaxStatements(180);
			cpds.setMaxPoolSize(100);

			Connection con = null;
			Statement stmt = null;
			ResultSet rs = null;
			con = cpds.getConnection();
			stmt = con.createStatement();
			rs = stmt.executeQuery("select id, name ,age, job, address from test_user ");
			while (rs.next()) {
				System.out.println("ID : " + rs.getString("id") + " , NAME : " + rs.getString("name")
						+" , AGE : " + rs.getInt("age") + " , JOB : " + rs.getString("job")
						+ " , ADDRESS : " + rs.getString("address"));
			}

		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}

最后的输出结果为：

2012-8-16 15:44:09 com.mchange.v2.log.MLog <clinit>
信息: MLog clients using java 1.4+ standard logging.
2012-8-16 15:44:10 com.mchange.v2.c3p0.C3P0Registry banner
信息: Initializing c3p0-0.9.1 [built 16-January-2007 14:46:42; debug? true; trace: 10]
2012-8-16 15:44:11 com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource getPoolManager
信息: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 3, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, dataSourceName -> 2rxpor8pcvddxxgwjcsb|e4f972, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> oracle.jdbc.driver.OracleDriver, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 2rxpor8pcvddxxgwjcsb|e4f972, idleConnectionTestPeriod -> 0, initialPoolSize -> 3, jdbcUrl -> jdbc:oracle:thin:@localhost:1521:ORCL, lastAcquisitionFailureDefaultUser -> null, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 0, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 100, maxStatements -> 180, maxStatementsPerConnection -> 0, minPoolSize -> 3, numHelperThreads -> 3, numThreadsAwaitingCheckoutDefaultUser -> 0, preferredTestQuery -> null, properties -> {user=******, password=******}, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false ]
ID : 00000000000000000001 , NAME : tom , AGE : 40 , JOB : manager , ADDRESS : ny
ID : 00000000000000000002 , NAME : jimmy , AGE : 35 , JOB : ceo , ADDRESS : huston
ID : 00000000000000000003 , NAME : tim , AGE : 33 , JOB : cfo , ADDRESS : canada

输出前部分是C3P0自己往控制台输出的一些信息。最后3行是，该表在数据库中的3条记录。

在实际应用中，C3P0可以结合应用服务器提供的JNDI服务为业务应用提供数据库连接池对象，业务中可以通过这个对象获取数据库连接。如Tomcat本身内置了一个数据库连接池，我们可以通过C3P0进行替换！