Mysql -- 配置C3P0

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1. 需要导入的包

• c3p0-0.9.5.2.jar
• mchange-commons-0.2.15.jar
• mysql-connector.jar

2. 配置xml

创建c3p0-config.xml文件，名字不能改动，并且放到src下，c3p0包会自动到src下查找c3p0-config.xml，名字错了，地方不对都不能配置成功

配置

<c3p0-config>
    <!-- 默认配置，如果没有指定使用则使用这个配置 -->
    <default-config>
        <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"></property>
        <property name="checkoutTimeout">30000</property>
        <property name="acquireIncrement">5</property>
        <property name="initialPoolSize">40</property>
        <property name="minPoolSize">30</property>
        <property name="maxPoolSize">50</property>
        <property name="maxStatements">200</property>
        <property name="maxStatementsPerConnection">20</property>
    </default-config>
    
    <!-- 自定义配置  -->
    <named-config name="Howl">
    	<property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/zero_demo</property>
        <property name="user">root</property>
        <property name="password"></property>
        <property name="checkoutTimeout">30000</property>
        <property name="acquireIncrement">5</property>
        <property name="initialPoolSize">40</property>
        <property name="minPoolSize">30</property>
        <property name="maxPoolSize">50</property>
        <property name="maxStatements">200</property>
        <property name="maxStatementsPerConnection">20</property>
    </named-config>
</c3p0-config>

或者到官网查看标准配置 C3P0

3. C3P0Util工具类

public class C3P0Util {
	
	// num = 1 使用默认的
	private static ComboPooledDataSource comboPooledDataSourceDefault = new ComboPooledDataSource();
	// num = 2 使用自定义的
	private static ComboPooledDataSource comboPooledDataSourceMydefine = new ComboPooledDataSource("Howl");
	
	public static Connection getConnection(int num){
		try {
			if(num == 1){
				return comboPooledDataSourceDefault.getConnection();
			}else if(num == 2){
				return comboPooledDataSourceMydefine.getConnection();
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return null;
	}
}

4. 测试

public class Test {
	
	public static void main(String[] args) throws SQLException {

		// 分别在两个不同的库设计了一张表，数据不同
		String sql = "SELECT * FROM user";
		
		// 使用默认数据源
		Connection connOne = C3P0Util.getConnection(1);
		PreparedStatement psOne = connOne.prepareStatement(sql);
		ResultSet rsOne = psOne.executeQuery();
		while(rsOne.next()){
			System.out.println(rsOne.getString("username"));
		}
		connOne.close();

		System.out.println("-------人工分割线-------");
		
		// 使用自定义的数据源
		Connection connTwo = C3P0Util.getConnection(2);
		PreparedStatement psTwo = connTwo.prepareStatement(sql);
		ResultSet rsTwo = psTwo.executeQuery();
		while(rsTwo.next()){
			System.out.println(rsTwo.getString("username"));
		}
        connTwo.close();
	}
}

输出结果

Howl
-------人工分割线-------
123123

5. 验证

验证Close方法在连接池中是归还给池，而不是关闭

public static void main(String[] args) throws SQLException {
	
	// 循环获取40个连接，输出其地址，然后关闭连接
	// 若关闭之后，再获取的连接地址有重复，则说明该连接没有被真正关闭，而是归还到连接池
	// 这里的关闭函数被c3p0动态代理了，被改写为放入连接池
	for(int i = 0; i < 40;i++) {
		 Connection conn = C3P0Util.getConnection(1);
		 System.out.println(conn);
		 conn.close();
	}
}

// 列出部分，可以看到地址重复，验证正确
com.mchange.v2.c3p0.impl.NewProxyConnection@6aaa5eb0 [wrapping: com.mysql.jdbc.JDBC4Connection@50cafc0a]
com.mchange.v2.c3p0.impl.NewProxyConnection@1a407d53 [wrapping: com.mysql.jdbc.JDBC4Connection@68c80b21]
com.mchange.v2.c3p0.impl.NewProxyConnection@5ebec15 [wrapping: com.mysql.jdbc.JDBC4Connection@50cafc0a]