Mysql -- 配置C3P0

<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>

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;
    }
}

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();
    }
}

Howl
-------人工分割线-------
123123

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]