JDBC由来与描述

• 没有JDBC前

开发者想操作数据库，必须需要了解每个数据库对应的数据库驱动程序API，由于每个数据库驱动程序的API都不同，所以当需要迁移数据库时，根本不平滑，需要大量修改与重写

• 有了JDBC后

Sum公司也知道问题之后，就提出一种约束 —— JDBC规范，让所有数据库厂商都按照这个JDBC规范来开发数据库驱动程序，以便于Java程序能用统一方式操作不同的数据库，数据库迁移变成可行

• JDBC描述

JDBC是一种Java web的规范，需要具体开发者（数据库厂商）来实现

JDBC常用四大API

• DriverManager

作用：
1、注册驱动
Class.forName("com.jdbc.mysql.Driver");2、获取连接
Connection conn = DriverManager.getConnection();

• Connection

作用：
1、创建执行SQL语句的对象（3种）
Statement createStatement()    // 执行SQL语句
PreparedStatement prepareStatement()   // 预编译SQL并执行
CallableStatement prepareCall()    // 执行SQL存储过程2、进行事务管理
setAutoCommit(boolean b)
commit()
rollback()

• Statement

作用：
1、执行SQL语句
boolean execute(String sql)   // 执行SQL语句，执行select就返回true,否则返回false
ResultSet executeQuery(String sql)     // 执行SQL中的select语句
int executeUpdate(String sql)          // 执行SQL中的insert/update/delete语句2、执行批量SQL语句
addBatch(String sql)    // 添加到批量处理
executeBatch()          // 执行批量处理
clearBatch()            // 清空批量处理

• ResultSet

（select语句）查询结果的集合
作用：获取到查询的结果
next()           //判断是否有下一条数据
getXXX()         //根据数据类型获取查询记录的数据
getObject()      //通用获取数据方法

JDBC资源释放

释放原则：晚创建，早释放；资源稀有，不释放很快会阻塞

Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb","root","root");
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("select * from user");rs.close();
stmt.close();
conn.close();

JDBC CURD操作

• 增加

Connection conn = null;
Statement stmt = null;try{// 注册驱动Class.forName("com.mysql.jdbc.Driver");// 获得连接conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/myDB","root","root");// 获取执行SQL语句对象stmt = conn.createStatement();// 编写SQLString sql = "insert into user values ("xiaomin","女人",12)";// 执行SQL语句int i = stmt.executeUpdate(sql);if(i > 0){System.out.println("插入成功！");}
}catch(Exception e){e.printStackTrace();
}finally{if(stmt != null){try{stmt .close();}catch(SQLException e){e.printStackTrace();}finally{stmt = null;}}if(conn != null){try{conn.close();}catch(SQLException e){e.printStackTrace();}finally{conn = null;}}
}

• 更新

Connection conn = null;
Statement stmt = null;try{// 注册驱动Class.forName("com.mysql.jdbc.Driver");// 获得连接conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/myDB","root","root");// 获取执行SQL语句对象stmt = conn.createStatement();// 编写SQLString sql = "update user set name = 'wt'";// 执行SQL语句int i = stmt.executeUpdate(sql);if(i > 0){System.out.println("更新成功！");}
}catch(Exception e){e.printStackTrace();
}finally{if(stmt != null){try{stmt .close();}catch(SQLException e){e.printStackTrace();}finally{stmt = null;}}if(conn != null){try{conn.close();}catch(SQLException e){e.printStackTrace();}finally{conn = null;}}
}

• 删除

Connection conn = null;
Statement stmt = null;try{// 注册驱动Class.forName("com.mysql.jdbc.Driver");// 获得连接conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/myDB","root","root");// 获取执行SQL语句对象stmt = conn.createStatement();// 编写SQLString sql = "delete from user where id = 3";// 执行SQL语句int i = stmt.executeUpdate(sql);if(i > 0){System.out.println("删除成功！");}
}catch(Exception e){e.printStackTrace();
}finally{if(stmt != null){try{stmt .close();}catch(SQLException e){e.printStackTrace();}finally{stmt = null;}}if(conn != null){try{conn.close();}catch(SQLException e){e.printStackTrace();}finally{conn = null;}}
}

• 查询

Connection conn = null;
Statement stmt = null;
ResultSet rs = null;try{// 注册驱动Class.forName("com.mysql.jdbc.Driver");// 获得连接conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/myDB","root","root");// 获取执行SQL语句对象stmt = conn.createStatement();// 编写SQLString sql = "select * from user";// 执行SQL语句rs = stmt.executeQuery(sql);if(rs.next()){System.out.print(rs.getString("name"));}
}catch(Exception e){e.printStackTrace();
}finally{if(rs != null){try{rs .close();}catch(SQLException e){e.printStackTrace();}finally{rs = null;}}if(stmt != null){try{stmt .close();}catch(SQLException e){e.printStackTrace();}finally{stmt = null;}}if(conn != null){try{conn.close();}catch(SQLException e){e.printStackTrace();}finally{conn = null;}}
}

JDBC SQL注入解决方案

开发时，使用 PreparedStatement对象 取代 Statement对象 来执行SQL，有效避免SQL注入

• 增加

Connection conn = null;
PreparedStatement pstmt = null;try{// 注册驱动Class.forName("com.mysql.jdbc.Driver");// 获得连接conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/myDB","root","root");// 编写SQLString sql = "insert into user values (?,?,?)";// 获取执行SQL语句对象pstmt = conn.preparedStatement(sql);// 设置参数pstmt.setString(1, "qqq");pstmt.setString(2, "bbb");pstmt.setString(3, "ccc");// 执行SQL语句int i = pstmt.executeUpdate();if(i > 0){System.out.println("插入成功！");}
}catch(Exception e){e.printStackTrace();
}finally{if(pstmt != null){try{pstmt.close();}catch(SQLException e){e.printStackTrace();}finally{pstmt = null;}}if(conn != null){try{conn.close();}catch(SQLException e){e.printStackTrace();}finally{conn = null;}}
}

• 更新

Connection conn = null;
PreparedStatement pstmt = null;try{// 注册驱动Class.forName("com.mysql.jdbc.Driver");// 获得连接conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/myDB","root","root");// 编写SQLString sql = "update user set name = ?, age = ?, pwd = ? where id = ?";// 获取执行SQL语句对象pstmt = conn.preparedStatement(sql);// 设置参数pstmt.setString(1, "wt");pstmt.setString(2, 15);pstmt.setString(3, "basdcx");pstmt.setString(4, 10);// 执行SQL语句int i = pstmt.executeUpdate();if(i > 0){System.out.println("更新成功！");}
}catch(Exception e){e.printStackTrace();
}finally{if(pstmt != null){try{pstmt.close();}catch(SQLException e){e.printStackTrace();}finally{pstmt = null;}}if(conn != null){try{conn.close();}catch(SQLException e){e.printStackTrace();}finally{conn = null;}}
}

• 删除

Connection conn = null;
PreparedStatement pstmt = null;try{// 注册驱动Class.forName("com.mysql.jdbc.Driver");// 获得连接conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/myDB","root","root");// 编写SQLString sql = "delete from user where id = ?";// 获取执行SQL语句对象pstmt = conn.preparedStatement(sql);// 设置参数pstmt.setString(1, 16);// 执行SQL语句int i = pstmt.executeUpdate();if(i > 0){System.out.println("删除成功！");}
}catch(Exception e){e.printStackTrace();
}finally{if(pstmt != null){try{pstmt.close();}catch(SQLException e){e.printStackTrace();}finally{pstmt = null;}}if(conn != null){try{conn.close();}catch(SQLException e){e.printStackTrace();}finally{conn = null;}}
}

• 查询

Connection conn = null;
PreparedStatement pstmt = null;
ResultSet rs = null;try{// 注册驱动Class.forName("com.mysql.jdbc.Driver");// 获得连接conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/myDB","root","root");// 编写SQLString sql = "select * from user where sex = ？";// 获取执行SQL语句对象pstmt = conn.preparedStatement(sql);// 设置参数pstmt.setString(1, '男');// 执行SQL语句rs = pstmt.executeQuery();while(rs.next()){System.out.println(rs.getString("name"));}
}catch(Exception e){e.printStackTrace();
}finally{if(rs != null){try{rs.close();}catch(SQLException e){e.printStackTrace();}finally{rs = null;}}if(pstmt != null){try{pstmt.close();}catch(SQLException e){e.printStackTrace();}finally{pstmt = null;}}if(conn != null){try{conn.close();}catch(SQLException e){e.printStackTrace();}finally{conn = null;}}
}

连接池（数据源）JDBC优化技术

数据库连接频繁创建与消耗，在资源使用上是一种浪费

• 常用连接池

C3P0、HikariCP、Druid、Tomcat、Dbcp

• 用法（以C3P0为例）

ComboPooledDataSource dataSource = new ComboPooledDataSource();   // 只需一个对象
// 获取连接
Connection conn = dataSource.getConnection();