JDBC与数据库连接

JDBC

1、概述:

1.1概念:

java数据库连接

1.2作用:

提供了通用访问关系型数据库的接口规范.

2、入门案例

2.1导入驱动jar包

1.复制mysql-connector-java-5.1.37-bin.jar到项目的libs目录下
2.右键–>Add As Library

2.2注册驱动

Class.forName(“com.mysql.jdbc.Driver”)

2.3获取连接

Connection conn =DriverManager.getConnection(“jdbc:mysql://localhost:3306/db2”,“root”,“1234”)

2.4编写SQL

2.5获取语句执行对象 Statement

Statement st = conn.createStatement();

2.6执行SQL

int executeUpdate(sql) 执行DML语句
Result executeQuery(sql) 执行DQL语句

2.7处理结果集(查询操作)

2.8释放资源

package com.itfenghua01;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;public class JdbcDemo01 {public static void main(String[] args) throws ClassNotFoundException, SQLException {//注册驱动Class.forName("com.mysql.jdbc.Driver");//获取连接Connection con = DriverManager.getConnection("jdbc:mysql:///demo01", "root", "root");//sql语句String sql = "update stu set math=100 where name ='陈墨瞳' ";//获取执行对象Statement sta = con.createStatement();//执行语句int update = sta.executeUpdate(sql);System.out.println(update);//释放资源sta.close();con.close();}
}

3、相关的Api

3.1DriverManager ★

3.1.1注册驱动 registerDriver(Driver driver) -

3.1.2获取连接 getConnection(url,user,pwd)

1.参数url:
标准写法: jdbc:mysql://localhost:3306/数据库名称
简单写法: jdbc:mysql:///数据库名称
2.参数user: 数据库用户
3.参数pwd: 数据库密码

3.2Connection连接 ★

3.2.1获取语句执行对象

Statement st = conn.createStatement();
PreparedStatement pst = conn.preparedStatement(String sql);

3.区别:

1）PreparedStatement 防止SQL注入问题

2）执行效率更高

3）编写起来更加简单

3.2.2管理事务
开启事务 setAutoCommit(false);
1. 提交事务 commit();
2. 回滚事务 rollback();
3.3 Statement语句执行

1.int executeUpdate(String sql) 用于执行增删改的SQL语句,返回影响的行数

2.ResultSet executeQuery(String sql); 用于执行查询语句,返回结果集对象

3.4 ResultSet 结果集 ★

3.4.1作用:

封装了查询的数据

3.4.2操作

1.boolean next(); 游标向下移动一行, 若有下一行返回true,反之为false
2.getXxx(int 编号);
3.getXxx(“列名”) ★
Xxx 必须和列类型一样
int getInt(…)
varchar getString(…)
Date getDate(…)
double getDouble(…)

package com.itfenghua01;import java.sql.*;public class jdbcDemo03 {public static void main(String[] args)  {Connection con =null;Statement sta =null;ResultSet resultSet =null;try {con = DriverManager.getConnection("jdbc:mysql:///demo01", "root", "root");String sql ="select  * from  stu ";sta = con.createStatement();resultSet = sta.executeQuery(sql);while (resultSet.next()){String name = resultSet.getString("name");int age = resultSet.getInt("age");Date date = resultSet.getDate("time");int math = resultSet.getInt("math");String sex = resultSet.getString("sex");System.out.println(name+","+age+","+date+","+math+","+sex);}} catch (SQLException e) {e.printStackTrace();}finally {if (sta!=null)try {resultSet.close();sta.close();con.close();} catch (SQLException e) {e.printStackTrace();}}}}

4、PreparedStatement预处理对象 ★

4.1SQL注入问题

用户输入一些特殊字符,导致整个SQL的结构发生了改变

4.2开发步骤

1.导入jar包

2.注册驱动

获取连接
编写SQL
SELECT * FROM USER WHERE username = ? AND PASSWORD = ? ;
获取语句执行对象 PreparedStatement
conn.preparedStatement(String sql);
给?占位符赋值
preparedStatement.setXxx(int 问号的编号,值)
注意: ? 从 1开始的
Xxx 必须和数据库列类型一样
7 执行SQL

8.处理结果集(查询操作)

9.释放资源

4.3操作

1.int executeUpdate() 用于执行增删改的SQL语句,返回影响的行数

2.ResultSet executeQuery(); 用于执行查询语句,返回结果集对象

package com.itfenghua02;import com.JDBCUtils.JDBCUtils;
import org.junit.Test;import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;public class JDBCDemo01 {@Testpublic void add() throws SQLException {Connection conn = JDBCUtils.getConnection();String sql = "insert into ss VALUE(?,?)";PreparedStatement pst = conn.prepareStatement(sql);pst.setInt(1,8);pst.setInt(2,119);pst.executeUpdate();JDBCUtils.close(null,pst,conn);}@Testpublic void delect() throws SQLException {//获取连接Connection conn = JDBCUtils.getConnection();//sql语句String sql = "delete from ss where id=? ";//获取预处理对象PreparedStatement pst = conn.prepareStatement(sql);//给占位符赋值pst.setInt(1,1);//执行操作pst.executeUpdate();//释放资源JDBCUtils.close(null,pst,conn);}@Testpublic void update() throws SQLException {Connection conn = JDBCUtils.getConnection();String sql ="update ss set num=? where id=? ";PreparedStatement pst = conn.prepareStatement(sql);pst.setInt(1,10000);pst.setInt(2,2);pst.executeUpdate();JDBCUtils.close(null,pst,conn);}@Testpublic void query() throws SQLException {Connection conn = JDBCUtils.getConnection();String sql = "select * from ss";PreparedStatement pst = conn.prepareStatement(sql);//结果集ResultSet res = pst.executeQuery();//遍历结果集,结果集对象,封装查询结果while (res.next()){int id = res.getInt("id");int num = res.getInt("num");System.out.println(id+","+num);}JDBCUtils.close(res,pst,conn);}
}

5、事务管理

1.开启事务 setAutoCommit(false);

提交事务 commit();
回滚事务 rollback();
事务模版

6、JDBC工具类提取

package com.JDBCUtils;import java.io.InputStream;
import java.sql.*;
import java.util.Properties;public class JDBCUtils {private static String url;private static String user;private static String password;private static String driver;//静态代码块//只执行一次static {try {//获取集合对象Properties prop = new Properties();//读取配置文件：jdbc.propertiesInputStream in = JDBCUtils.class.getClassLoader().getResourceAsStream("jdbc.properties");//加载文件prop.load(in);//获取文件中的关键字值url = prop.getProperty("url");user = prop.getProperty("user");password = prop.getProperty("password");driver = prop.getProperty("driver");//1.注册驱动Class.forName(driver);} catch (Exception e) {e.printStackTrace();}}/*** //2.获取连接* @return* @throws SQLException*/public static Connection getConnection() throws SQLException {return DriverManager.getConnection(url,user,password);}/*** //释放资源* @param res* @param sta* @param con*/public static void close(ResultSet res, Statement sta,Connection con){if (res!=null){try {res.close();} catch (SQLException e) {e.printStackTrace();}}  if (sta!=null){try {sta.close();} catch (SQLException e) {e.printStackTrace();}}  if (con!=null){try {con.close();} catch (SQLException e) {e.printStackTrace();}}}
}