1、JDBC概述

（1）概念

• JDBC：Java DataBase Connectivity
• JDBC是官方定义的一套操作所有关系型数据库的规则，各个数据库厂商去实现这套接口，并提供数据驱动jar包。我们可以使用JDBC编程，真正执行的代码是驱动jar包的实现类

（2）第一个JDBC

• 下载JDBC架包，https://dev.mysql.com/downloads/connector/j/，选择Platform Independent
  ``` import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.Statement;

public class Main {

private static final String URL = "jdbc:mysql://localhost:3306/test";
private static final String USERNAME = "root";
private static final String PASSWORD = "root";
public static void main(String[] args) throws Exception {
    //加载驱动程序
    Class.forName("com.mysql.cj.jdbc.Driver");
    //获得数据库连接
    Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
    //获取sql执行对象
    Statement statement = connection.createStatement();
    // 进行增删改查操作
    ResultSet resultSet = statement.executeQuery("select * from card");
    while (resultSet.next()){
        int money = resultSet.getInt("money");
        String username = resultSet.getString("name");
        System.out.println(username+" , "+money);
    }
    // 关闭数据库资源
    resultSet.close();
    statement.close();
    connection.close();
}

}

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### （3）流程分析
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#### 注册驱动

- Class.forName加载类到内存，类中有个静态代码块，执行了DriverManager.registerDriver(new Driver());
- Class.forName()这行代码可以不写，后续版本后加了自动引入

public class Driver extends NonRegisteringDriver implements java.sql.Driver { public Driver() throws SQLException { }

static {
    try {
        DriverManager.registerDriver(new Driver());
    } catch (SQLException var1) {
        throw new RuntimeException("Can't register driver!");
    }
}

}
```

Connection

• 数据库连接对象
• 获取执行sql的对象
  • Statement createStatement() throws SQLException;
  • PreparedStatement prepareStatement(String sql) throws SQLException;
• 管理事务
  • 开启事务：void setAutoCommit(boolean autoCommit)
  • 提交事务：void commit();
  • 回滚事务：void rollback();

Statement

• boolean execute(string sql)
• int executeUpdate(string sql)
  • 返回影响的行数：执行DML（insert update delete）语句，DDL(create alter drop)语句
• ResultSet executeQuery(string sql)
  • DQL语句

中文乱码

url=jdbc:mysql://localhost:3306/test?characterEncoding=utf8