c3p0简介及简单案例

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        <p>c3p0应该说是十分常用的连接池了，很常用的dao层框架hibernate都是用c3p0的</p>

他的用法相当简便，当然，要懂一点连接数据库的知识作为前提，直接上代码了。

至于jar包，可以直接百度，也可以到这里下载：Java连接数据库的工具类

下面是基本用法

package cn.bl.v4_DataSource.c3p0;
 
import java.sql.SQLException;
 
import org.junit.Test;
 
import com.mchange.v2.c3p0.ComboPooledDataSource;
 
public class Demo1 {
	
	/**
	 * 方式1：使用纯Java方式
	 * @throws Exception
	 */
	@Test
	public void test1() throws Exception {
		ComboPooledDataSource source = new ComboPooledDataSource();
		source.setDriverClass("com.mysql.jdbc.Driver");
		source.setJdbcUrl("jdbc:mysql://127.0.0.1:3306/aa?useUnicode=true&characterEncoding=utf-8");
		source.setUser("root");
		source.setPassword("000");
		
		//获取链接
		System.out.println(source.getConnection());
		
		/*输出如下信息（除了最后一行，前面的其实都是自动输出的基本信息）：
			九月 23, 2018 11:40:45 上午 com.mchange.v2.log.MLog <clinit>
			信息: MLog clients using java 1.4+ standard logging.
			九月 23, 2018 11:40:45 上午 com.mchange.v2.c3p0.C3P0Registry banner
			信息: Initializing c3p0-0.9.1.2 [built 21-May-2007 15:04:56; debug? true; trace: 10]
			九月 23, 2018 11:40:45 上午 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 -> 1hgf2td9y193nu61qxzvdh|160847b, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.jdbc.Driver, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1hgf2td9y193nu61qxzvdh|160847b, idleConnectionTestPeriod -> 0, initialPoolSize -> 2, jdbcUrl -> jdbc:mysql://127.0.0.1:3306/aa?useUnicode=true&characterEncoding=utf-8, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 30, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 10, maxStatements -> 50, maxStatementsPerConnection -> 0, minPoolSize -> 2, numHelperThreads -> 3, numThreadsAwaitingCheckoutDefaultUser -> 0, preferredTestQuery -> null, properties -> {user=******, password=******}, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false ]
			com.mchange.v2.c3p0.impl.NewProxyConnection@d64342
		 */
	}
	
	@Test
	public void test2() throws SQLException {
		//1.空参--默认配置
		ComboPooledDataSource ds = new ComboPooledDataSource();
		
		//2.带参--指定名称的配置
		//ComboPooledDataSource ds = new ComboPooledDataSource("BarryLee");
		
		System.out.println(ds.getConnection());
		//输出的信息类似test1
	}
	
	/*
	 * 测试c3p0工具类
	 */
	@Test
	public void testUtil() {
		System.err.println(C3P0Utils.getConnection());
	}
}

下面是配置文件，配置文件一定到放置到src下，命名为：c3p0-config.xml

<c3p0-config>
	<!-- 默认配置，如果没有指定则使用这个配置 -->
	<default-config>
		<property name="driverClass">com.mysql.jdbc.Driver</property>
		<property name="jdbcUrl">
			<![CDATA[jdbc:mysql://127.0.0.1:3306/aa?useUnicode=true&characterEncoding=UTF-8]]>
		</property>
		<property name="user">root</property>
		<property name="password">000</property>
		<!-- 初始化池大小 -->
		<property name="initialPoolSize">2</property>
		<!-- 最大空闲时间 -->
		<property name="maxIdleTime">30</property>
		<!-- 最多有多少个连接 -->
		<property name="maxPoolSize">10</property>
		<!-- 最少几个连接 -->
		<property name="minPoolSize">2</property>
		<!-- 每次最多可以执行多少个批处理语句 -->
		<property name="maxStatements">50</property>
	</default-config> 
	<!-- 命名的配置 -->
	<named-config name="BarryLee">
		<property name="driverClass">com.mysql.jdbc.Driver</property>
		<property name="jdbcUrl">jdbc:mysql://127.0.0.1:3306/aa</property>
		<property name="user">root</property>
		<property name="password">000</property>
		<property name="acquireIncrement">5</property><!-- 如果池中数据连接不够时一次增长多少个 -->
		<property name="initialPoolSize">100</property>
		<property name="minPoolSize">50</property>
		<property name="maxPoolSize">1000</property>
		<property name="maxStatements">0</property>
		<property name="maxStatementsPerConnection">5</property> <!-- he's important, but there's only one of him -->
	</named-config>
</c3p0-config> 

下面是一个工具类

package cn.bl.v4_DataSource.c3p0;
 
import java.sql.Connection;
import java.sql.SQLException;
 
import javax.sql.DataSource;
 
import com.mchange.v2.c3p0.ComboPooledDataSource;
 
public class C3P0Utils {
	private C3P0Utils() {}
	private static ComboPooledDataSource ds = null;
	private static ThreadLocal<Connection>tLocal = new ThreadLocal<>();
	static {
		ds = new ComboPooledDataSource();//读取默认配置文件
	}
	public static DataSource getDataSource() {
		return ds;
	}
	public static Connection getConnection() {
		Connection con = tLocal.get();
		if(con==null) {
			try {
				con = ds.getConnection();
				tLocal.set(con);
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
		return con;
	}
}