【数据库连接池】

1.数据连接池概念

目的：数据库连接池的目的，为了减少频繁开关链接的时间，提高整个系统的响应能力
应具备的属性值：

• 初始大小
• 每次扩容大小
• 连接池最大个数
• 空闲连接的死亡时间

2.常见的数据库连接池：

• DBCP
• C3P0
• Druid
• hikariCP

DBCP练习

public class DBCPTest {
    public static void main(String[] args) {
        //数据库的连接池资源，在之后操作的时候只需要从池中获取即可
        BasicDataSource dataSource = new BasicDataSource();
        dataSource.setDriverClassName("com.mysql.jdbc.Driver");
        dataSource.setUrl("jdbc:mysql://localhost:3306/demo");
        dataSource.setUsername("root");
        dataSource.setPassword("123456");

        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;

        try {
            connection = dataSource.getConnection();
            String sql = "select * from emp";
            preparedStatement = connection.prepareStatement(sql);
            resultSet = preparedStatement.executeQuery();

            while(resultSet.next()){
                System.out.println(resultSet.getString("ename"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

C3P0练习

public class C3P0Test {

    public static Connection connection;
    public static ComboPooledDataSource dataSource;

    public static void getConnection(){
        dataSource = new ComboPooledDataSource();

    }

    public static void queryData(){
        try {
            connection = dataSource.getConnection();
            String sql = "select * from emp";
            PreparedStatement ps = connection.prepareStatement(sql);
            ResultSet rs = ps.executeQuery();
            while (rs.next()){
                System.out.println(rs.getString("ename"));

            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

    }

public class C3p0Test2 {
    public static void main(String[] args) throws SQLException {
        DataSource ds_unpooled = DataSources.unpooledDataSource("jdbc:mysql://localhost:3306/demo",
                "root",
                "123456");
//        DataSource ds_pooled = DataSources.pooledDataSource( ds_unpooled );
        Map overrides = new HashMap();
        overrides.put("maxStatements", "200");         //Stringified property values work
        overrides.put("maxPoolSize", new Integer(50)); //"boxed primitives" also work
        DataSource ds_pooled = DataSources.pooledDataSource( ds_unpooled ,overrides);
        Connection connection = ds_pooled.getConnection();
        System.out.println(connection);
        connection.close();
    }
}
public class C3p0Test3 {
    public static void main(String[] args) throws Exception {
        // fetch a JNDI-bound DataSource
        InitialContext ictx = new InitialContext();
        DataSource ds = (DataSource) ictx.lookup( "java:comp/env/jdbc/myDataSource" );

// make sure it's a c3p0 PooledDataSource
        if ( ds instanceof PooledDataSource)
        {
            PooledDataSource pds = (PooledDataSource) ds;
            System.err.println("num_connections: "      + pds.getNumConnectionsDefaultUser());
            System.err.println("num_busy_connections: " + pds.getNumBusyConnectionsDefaultUser());
            System.err.println("num_idle_connections: " + pds.getNumIdleConnectionsDefaultUser());
            System.err.println();
        }
        else
            System.err.println("Not a c3p0 PooledDataSource!");
    }
}

druid练习

public class DruidTest {
    public static void main(String[] args) throws Exception {
        Properties properties = new Properties();
        FileInputStream fileInputStream = new FileInputStream("src/pool/druid/druid.properties");
        properties.load(fileInputStream);

        DataSource dataSource = DruidDataSourceFactory.createDataSource(properties);
        Connection connection = dataSource.getConnection();
        System.out.println(connection);
        connection.close();
    }
}

HikariCP练习

public class HikariCPTest {
    public static void main(String[] args) throws SQLException {
//        HikariConfig config = new HikariConfig();
//        config.setJdbcUrl("jdbc:mysql://localhost:3306/demo");
//        config.setUsername("root");
//        config.setPassword("123456");
//
//        HikariDataSource ds = new HikariDataSource(config);
//        Connection connection = ds.getConnection();
//        System.out.println(connection);
//        connection.close();

//        HikariDataSource hikariDataSource = new HikariDataSource();
//        hikariDataSource.setJdbcUrl("jdbc:mysql://localhost:3306/demo");
//        hikariDataSource.setUsername("root");
//        hikariDataSource.setPassword("123456");

        HikariConfig config = new HikariConfig("src/pool/hikariCP/hikariCP.properties");
        HikariDataSource dataSource = new HikariDataSource(config);

        Connection connection = dataSource.getConnection();
        System.out.println(connection);
        connection.close();
    }
}