数据库连接池

介绍

概念

• 一个容器（集合），存放数据库连接
• 在系统初始化时创建
• 按需请求连接，用完返回

好处：
避免频繁创建和销毁连接对象，提供用户访问速度

标准接口：
javax.sql包下的DataSource类：

• getConection：获取连接对象
• Connection.close()：归还连接

数据库厂商：c3p0和druid（阿里巴巴）

注意：在使用这两者的时候都需要导入驱动jar包

c3p0

1)引入jar包（两个）

<dependency>
  <groupId>com.mchange</groupId>
  <artifactId>mchange-commons-java</artifactId>
  <version>0.2.12</version>
</dependency>
<dependency>
  <groupId>com.mchange</groupId>
  <artifactId>c3p0</artifactId>
  <version>0.9.5.2</version>
</dependency>

2）定义配置文件：c3p0.properties或者c3p0-config.xml
c3p0-config.xml

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
    <default-config>
        <property name="user">root</property>
        <property name="password">3145tj</property>
        <property name="driverClass">com.mysql.cj.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/study?useSSL=false&amp;serverTimezone=UTC&amp;characterEncoding=utf8</property>
    </default-config>
</c3p0-config>

3）创建核心对象ComboPooledDataSource
4）获取连接

DataSource dataSource = new ComboPooledDataSource();
Connection connection = dataSource.getConnection();
String sql = "select * from tb_user";
PreparedStatement ps = connection.prepareStatement(sql);
ResultSet resultSet = ps.executeQuery();
while(resultSet.next()){
  System.out.println(resultSet.getInt(1)+",账号："+resultSet.getString(2)+"，密码："+resultSet.getString(3));
}
resultSet.close();
ps.close();
connection.close();
((ComboPooledDataSource) dataSource).close();

druid

1）引入jar包

<dependency>
  <groupId>com.alibaba</groupId>
  <artifactId>druid</artifactId>
  <version>1.0.9</version>
</dependency>

2）定义配置文件：properties格式

username=root
password=3145tj
driverClassName=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/study?useSSL=false&serverTimezone=UTC&characterEncoding=utf8

3）加载配置文件
4）获取数据库连接池对象
5）获取连接

        Properties properties = new Properties();
        InputStream inputStream = DruidTest.class.getClassLoader().getResourceAsStream("db.properties");
        properties.load(inputStream);
        DataSource dataSource = DruidDataSourceFactory.createDataSource(properties);
        Connection connection = dataSource.getConnection();
        String sql = "select * from tb_user";
        PreparedStatement ps = connection.prepareStatement(sql);
        ResultSet resultSet = ps.executeQuery();
        while(resultSet.next()){
            System.out.println(resultSet.getInt(1)+",账号："+resultSet.getString(2)+"，密码："+resultSet.getString(3));
        }
        resultSet.close();
        ps.close();
        connection.close();