JDBC01-----JDBC的基本使用

一. 什么是JDBC

1. JDBC(Java DataBase Connectivity, java数据库连接）就是用我们的java程序去连接数据库，它是一个执行SQL语句的JAVA API。（不管是什么数据库，只要提供了JDBC驱动就行）。

  note: 上面的jar包就是连接驱动包。

2. JDBC就是JAVA连接数据库的中间桥梁

3. JDBC的API

二. JDBC连接MySql

1. 新建立一个maven项目jdbctest

2. 在pom.xml中添加jdbc驱动依赖

<dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>6.0.6</version>
        </dependency>

3. 在com.test.jdbctest包下新建立一个class: ConnectionClass

public class ConnectionClass {
    public static void main(String args[]) throws ClassNotFoundException, SQLException {
        //1.加载驱动（静态代码块中会创建一个驱动，来帮助我们连接JAVA到驱动之间的关联，但是驱动到数据库的连接还没有连上）
        Class.forName("com.mysql.jdbc.Driver");
        //2.获取连接对象，URL是数据库地址
        String url="jdbc:mysql://localhost:3306/test";
        String user="Hermioner";
        String password="1234";
        Connection connection=DriverManager.getConnection(url, user, password);
        System.out.println(connection);//测试连接是否成功
    }

}

com.mysql.cj.jdbc.ConnectionImpl@17d99928

说明：

（1）加载驱动: 把com.mysql.jdbc.Driver这份字节码加载进JVM，当一份字节码被加载到JVM时，就会自动执行该字节码中的静态代码块。

（2）Driver的源码

package com.mysql.jdbc;

import java.sql.SQLException;

/**
 * Backwards compatibility to support apps that call <code>Class.forName("com.mysql.jdbc.Driver");</code>.
 */
public class Driver extends com.mysql.cj.jdbc.Driver {
    public Driver() throws SQLException {
        super();
    }

    static {
        System.err.println("Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. "
                + "The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.");
    }
}

/*
  Copyright (c) 2002, 2015, Oracle and/or its affiliates. All rights reserved.

  The MySQL Connector/J is licensed under the terms of the GPLv2
  <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most MySQL Connectors.
  There are special exceptions to the terms and conditions of the GPLv2 as it is applied to
  this software, see the FOSS License Exception
  <http://www.mysql.com/about/legal/licensing/foss-exception.html>.

  This program is free software; you can redistribute it and/or modify it under the terms
  of the GNU General Public License as published by the Free Software Foundation; version 2
  of the License.

  This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
  without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  See the GNU General Public License for more details.

  You should have received a copy of the GNU General Public License along with this
  program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth
  Floor, Boston, MA 02110-1301  USA

 */

package com.mysql.cj.jdbc;

import java.sql.SQLException;

/**
 * The Java SQL framework allows for multiple database drivers. Each driver should supply a class that implements the Driver interface
 * 
 * <p>
 * The DriverManager will try to load as many drivers as it can find and then for any given connection request, it will ask each driver in turn to try to
 * connect to the target URL.
 * 
 * <p>
 * It is strongly recommended that each Driver class should be small and standalone so that the Driver class can be loaded and queried without bringing in vast
 * quantities of supporting code.
 * 
 * <p>
 * When a Driver class is loaded, it should create an instance of itself and register it with the DriverManager. This means that a user can load and register a
 * driver by doing Class.forName("foo.bah.Driver")
 */
public class Driver extends NonRegisteringDriver implements java.sql.Driver {
    //
    // Register ourselves with the DriverManager
    //
    static {
        try {
            java.sql.DriverManager.registerDriver(new Driver());
        } catch (SQLException E) {
            throw new RuntimeException("Can't register driver!");
        }
    }

    /**
     * Construct a new driver and register it with DriverManager
     * 
     * @throws SQLException
     *             if a database error occurs.
     */
    public Driver() throws SQLException {
        // Required for Class.forName().newInstance()
    }
}

当类加载时，会执行如下静态代码块：

 static {
        try {
            java.sql.DriverManager.registerDriver(new Driver()); //在这个静态代码块里面会创建一个驱动，来帮助我们连接JAVA到驱动之间的关联，但是驱动到数据库的连接还没有连上
        } catch (SQLException E) {
            throw new RuntimeException("Can't register driver!");
        }
    }

 （3）测试连接

        除了上面的打印对象，也可以通过mysql中的命令来查看是否连接成功：show processlist；

 参考文献：

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