public class JDBCUtils {
    static String driverClass = null;
    static String url = null;
    static String user = null;
    static String password = null;

    static {
        // 需求： 通过properties对象读取 外部配置的内容
        Properties prop = new Properties();

        try {
            FileInputStream in = new FileInputStream("files/jdbc.properties");
            // 加载外部的配置文件
            prop.load(in);
            // 读取外部配置文件的内容
            driverClass = prop.getProperty("driverClass");
            url = prop.getProperty("url");
            user = prop.getProperty("user");
            password = prop.getProperty("password");
            // 注册驱动
            Class.forName(driverClass);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    // 获得连接
    public static Connection getConnection() {
        Connection con = null;
        try {
            con = DriverManager.getConnection(url, user, password);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return con;
    }

    public static void release(Connection connection, Statement statement, ResultSet resultSet) {
        // 释放资源
        try {
            if (resultSet != null) {
                resultSet.close();
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        try {
            if (statement != null) {
                statement.close();
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        try {
            if (connection != null) {
                connection.close();
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

<?xml version="1.0" encoding="UTF-8" ?>
<c3p0-config>
    <default-config>
        <property name="driverClacc">com.mysql.cj.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/how2sql?serverTimezone=Asia/Shanghai</property>
        <property name="user">user</property>
        <property name="password">passwd</property>
    </default-config>

    <named-config name="intergalactoApp">
    </named-config>

    <named-config name="day04">
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/day_04db</property>
        <property name="user">root</property>
        <property name="password">123</property>
    </named-config>
</c3p0-config>

ComboPooledDataSource cpds = new ComboPooledDataSource();//可以在这填入参数选择不同的参数
Connection conn = null;
PreparedStatement stmt = null;
ResultSet rs = null;
try {
    conn = cpds.getConnection();
    String sql = "select * from user";
    stmt = conn.prepareStatement(sql);
    rs = stmt.executeQuery();
    while (rs.next()) {
        System.out.println(rs.getInt("id") + " "
                + rs.getString("username") + " "
                + rs.getString("password"));
    }
} catch (SQLException e) {
    e.printStackTrace();
} finally {
    JDBCUtils.release(conn, stmt, rs);
}

driverClassName=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/how2sql?serverTimezone=Asia/Shanghai
username=user
password=passwd

@Test
public void druid() throws Exception {
    //加载properties文件的内容到Properties对象中
    Properties info = new Properties();
    //加载项目下的属性文件
    FileInputStream fis = new FileInputStream("files/druid.properties");
    //从输入流中加载属性
    info.load(fis);
    System.out.println(info);
    //创建DRUID连接池，使用配置文件中的参数
    DataSource dataSource = DruidDataSourceFactory.createDataSource(info);
    //从DRUID连接池中取出连接
    //Connection conn = dataSource.getConnection();
    //System.out.println("conn = " + conn);
// 需求: 根据用户名和密码 查询用户信息
    Connection conn = null;
    PreparedStatement pstmt = null;
    ResultSet rs = null;
    try {
        // 获得连接
        conn = dataSource.getConnection();
        // 获得发送sql的对象
        String sql = "select * from user where id = ?";
        pstmt = conn.prepareStatement(sql);
        // 如果有问号,需要 设置参数,注意:下标从1开始
        pstmt.setInt(1, 1);
        // 执行sql 获得结果
        rs = pstmt.executeQuery();
        // 处理结果
        if (rs.next()) {
            int id = rs.getInt("id");
            String username = rs.getString("username");
            String pwd = rs.getString("password");
            System.out.println(id + ":::" + username + "===" + pwd);
        } else {
            System.out.println("没有查到对应的用户信息!");
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        JDBCUtils.release(conn, pstmt, rs);
    }
}

public static Connection getDruidConnection()
{
    try {
        //创建Properties集合对象
        Properties p = new Properties();
        //调用方法加载配置文件中的数据
        p.load(new FileInputStream("files/druid.properties"));
        //使用德鲁伊核心类调用静态方法获取配置文件中的数据
        DataSource ds = DruidDataSourceFactory.createDataSource(p);
        //从德鲁伊数据库连接池中获取连接
        Connection conn = ds.getConnection();
        //返回连接
        return conn;
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

private static JdbcTemplate jdbcTemplate = new JdbcTemplate(JDBCUtils.getDataSource());

@Test
public void delete2() {
    int row = jdbcTemplate.update("delete from student where id=?", 6);
    System.out.println("删除" + row + "行记录");
}

@Test
public void update() {
    int row = jdbcTemplate.update("update student set name=?, birthday=? where id=?",
            "克林", "1994-12-10", 5);
    System.out.println("更新了" + row + "行记录");
}

@Test
public void insert() {
    jdbcTemplate.update("insert into student values (null, ?,?)", "孙悟空", "1999-12-10");
    jdbcTemplate.update("insert into student values (null, ?,?)", "孙悟天", "1999-12-10");
    jdbcTemplate.update("insert into student values (null, ?,?)", "孙悟饭", "1999-12-10");
    jdbcTemplate.update("insert into student values (null, ?,?)", "龟仙人", "1999-12-10");
    jdbcTemplate.update("insert into student values (null, ?,?)", "牛魔王", "1999-12-10");
    jdbcTemplate.update("insert into student values (null, ?,?)", "18号", "1997-12-10");
}