JDBC:

概念：Java DataBase Connectivity Java 数据库连接，Java语言操作数据库

本质：其实是官方(sun公司)定义的一套操作所有关系型数据库的规则，即接口，各个数据库厂商去实现这套接口，提供数据库驱动jar包。我们可以使用这套接口编程，真正执行的代码是驱动jar包中的实现类(多态调用 Fu f = new Zi();)

package cn.itcast.jdbc;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;public class JdbcDemo1 {public static void main(String[] args) throws Exception{//导入驱动jar包//加载Driver类进内存，执行Driver类的静态代码块，就可以注册驱动Class.forName("com.mysql.jdbc.Driver");//获取数据库连接对象// DriverManager驱动管理对象，//DriverManager是一个类// DriverManager类中的方法getConnection ,会返回一个Connection对象//Connection叫做数据库连接对象//Connection是一个接口Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db3","root","12345");//定义一条sql语句String sql = "update emp set salary = 10000 where id = 1001";//DriverManager.getConnection返回的是一个Connection对象，所以可以使用该对象conn调用需要的方法//该createStatement方法将会获得一个可以执行sql语句的对象//获取执行sql对象 StatementStatement stmt = conn.createStatement();//执行sql语句，返回值Int代表着有多少行执行成功，受到影响int count = stmt.executeUpdate(sql);System.out.println(count);stmt.close();conn.close();}
}

JDBC练习

package cn.itcast.jdbc;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;// 通过JDBC添加一条记录
public class JdbcDemo2 {public static void main(String[] args){Statement stmt = null;Connection conn = null;try{//1.注册驱动Class.forName("com.mysql.jdbc.Driver");//定义sql语句String sql = "insert into emp values(null,'张飞','男',5000,'2014-05-20',3)";//获取执行Connection对象conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db2","root","12345");//获取执行sql的对象stmt = conn.createStatement();//执行sqlstmt.executeUpdate(sql);}catch(Exception e){e.printStackTrace();}finally{//避免空指针异常if(stmt !=null){try{stmt.close();}catch(Exception e){e.printStackTrace();}}else{System.out.println("发生null指针异常");}if(conn !=null){try {conn.close();}catch(Exception e){e.printStackTrace();}}else{System.out.println("null指针异常");}}}
}

ResultSet:结果集对象，封装查询结果

常用方法有两个：

boolean next():游标向下移动一行，判断当前行是否是最后一行末尾

getxxx(参数) xxx代表数据类型，参数代表编号，编号从1开始，也可以代表列的名称

package cn.itcast.jdbc;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;import static javax.swing.text.html.parser.DTDConstants.NAME;// 通过JDBC添加一条记录
public class JdbcDemo2 {public static void main(String[] args){Statement stmt = null;Connection conn = null;ResultSet rs = null;try{//1.注册驱动Class.forName("com.mysql.jdbc.Driver");//定义sql语句String sql = "select * from emp";//获取执行Connection对象conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db2","root","12345");//获取执行sql的对象stmt = conn.createStatement();//执行sqlrs = stmt.executeQuery(sql);//re.next的返回值是boolean类型while(rs.next()){//若为真，则获取数据int i= rs.getInt(1);//这个参数是编号参数String s = rs.getString("name"); //这个参数是一个列名称参数String s1 = rs.getString("gender");System.out.println(i+" "+s1+" "+s);}}catch(Exception e){e.printStackTrace();}finally{//避免空指针异常if(rs!=null){try{stmt.close();}catch(Exception e){e.printStackTrace();}}else{System.out.println("发生null指针异常");}}}
}

//定义一个方法，查询emp表的数据将其封装为对象，然后装载集合，返回
import java.util.Date;/*** 封装Emp表数据的JavaBean*/
public class Emp {private int id;private String ename;private int job_id;private int mgr;private Date joindate;private double salary;private double bonus;private int dept_id;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getEname() {return ename;}public void setEname(String ename) {this.ename = ename;}public int getJob_id() {return job_id;}public void setJob_id(int job_id) {this.job_id = job_id;}public int getMgr() {return mgr;}public void setMgr(int mgr) {this.mgr = mgr;}public Date getJoindate() {return joindate;}public void setJoindate(Date joindate) {this.joindate = joindate;}public double getSalary() {return salary;}public void setSalary(double salary) {this.salary = salary;}public int getDept_id() {return dept_id;}public void setDept_id(int dept_id) {this.dept_id = dept_id;}public double getBonus() {return bonus;}public void setBonus(double bonus) {this.bonus = bonus;}@Overridepublic String toString() {return "Emp{" +"id=" + id +", ename='" + ename + '\'' +", job_id=" + job_id +", mgr=" + mgr +", joindate=" + joindate +", salary=" + salary +", bonus=" + bonus +", dept_id=" + dept_id +'}';}
}

import java.sql.*;
import java.util.ArrayList;
import java.util.List;public class JDBCDemo3 {public static void main(String[] args){List<Emp> list = new JDBCDemo3().findALL();System.out.println(list);}public List<Emp> findALL() {Connection conn = null;Statement stat = null;ResultSet rs = null;List<Emp> list = null;try {Class.forName("com.mysql.jdbc.Driver");//获取到Connection对象conn = DriverManager.getConnection("jdbc:mysql:///db3", "root", "12345");//有了Connecttion对象才会有Statement执行sql语句的对象stat = conn.createStatement();//定义sql语句String sql = "SELECT * FROM emp";//执行sql语句,返回的是结果集对象ResultSet()rs = stat.executeQuery(sql);//通过结果集对象的方法，可以获取到每一行的数据Emp emp = null;list = new ArrayList<Emp>();while (rs.next()) {int id = rs.getInt("id");String ename = rs.getString("ename");int job_id = rs.getInt("job_id");int mgr = rs.getInt("mgr");Date joindate = rs.getDate("joindate");double salary = rs.getDouble("salary");double bonus = rs.getDouble("bonus");int dept_id = rs.getInt("dept_id");emp  = new Emp();emp.setId(id);emp.setEname(ename);emp.setJob_id(job_id);emp.setMgr(mgr);emp.setJoindate(joindate);emp.setSalary(salary);emp.setBonus(bonus);emp.setDept_id(dept_id);list.add(emp);}} catch (Exception e) {e.printStackTrace();} finally {if (rs != null) {try {rs.close();} catch (SQLException e) {e.printStackTrace();}}if (stat != null) {try {rs.close();} catch (SQLException e) {e.printStackTrace();}}if (conn != null) {try {rs.close();} catch (SQLException e) {e.printStackTrace();}}}return list;}
}

通过JDBCutils工具类改进代码

package cn.itcast.jdbc;import java.io.FileReader;
import java.io.IOException;
import java.net.URL;
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;static {try{Properties pro = new Properties();//可以通过字节码来获取类加载器ClassLoader classLoader = JDBCUtils.class.getClassLoader();//getResource方法可以找到sre文件夹下的配置文件URL res = classLoader.getResource("jdbc.properties");String path = res.getPath();pro.load(new FileReader(path));url = pro.getProperty("url");user = pro.getProperty("user");password = pro.getProperty("password");driver = pro.getProperty("driver");Class.forName(driver);}catch(IOException e){e.printStackTrace();}catch(ClassNotFoundException e){e.printStackTrace();}}//调用方法，返回Connection对象public static Connection getConnection() throws SQLException{return DriverManager.getConnection(url,user,password);}//执行增删改需要释放Statement和Connection对象public static void close(Statement stmt, Connection conn){if(stmt != null){try {stmt.close();} catch (SQLException e) {e.printStackTrace();}}if(conn != null){try {conn.close();} catch (SQLException e) {e.printStackTrace();}}}//执行查询需要释放resultset，Statement和Connection对象public static void close(ResultSet rs, Statement stmt, Connection conn){if(rs != null){try {rs.close();} catch (SQLException e) {e.printStackTrace();}}if(stmt != null){try {stmt.close();} catch (SQLException e) {e.printStackTrace();}}if(conn != null){try {conn.close();} catch (SQLException e) {e.printStackTrace();}}}
}

package cn.itcast.jdbc;import java.sql.*;
import java.util.ArrayList;
import java.util.List;public class JDBCDemo3 {public static void main(String[] args){List<Emp> list = new JDBCDemo3().findALL();System.out.println(list);}public List<Emp> findALL() {Connection conn = null;Statement stat = null;ResultSet rs = null;List<Emp> list = null;try {conn = JDBCUtils.getConnection();//有了Connecttion对象才会有Statement执行sql语句的对象stat = conn.createStatement();//定义sql语句String sql = "SELECT * FROM emp";//执行sql语句,返回的是结果集对象ResultSet()rs = stat.executeQuery(sql);//通过结果集对象的方法，可以获取到每一行的数据Emp emp = null;list = new ArrayList<Emp>();while (rs.next()) {int id = rs.getInt("id");String ename = rs.getString("ename");int job_id = rs.getInt("job_id");int mgr = rs.getInt("mgr");Date joindate = rs.getDate("joindate");double salary = rs.getDouble("salary");double bonus = rs.getDouble("bonus");int dept_id = rs.getInt("dept_id");emp  = new Emp();emp.setId(id);emp.setEname(ename);emp.setJob_id(job_id);emp.setMgr(mgr);emp.setJoindate(joindate);emp.setSalary(salary);emp.setBonus(bonus);emp.setDept_id(dept_id);list.add(emp);}} catch (Exception e) {e.printStackTrace();} finally {JDBCUtils.close(rs,stat,conn);}return list;}
}

JDBC练习_登录案例

需求：通过键盘录入用户名和密码，查看数据库，判断是否登录成功

CREATE TABLE USER(id INT PRIMARY KEY AUTO_INCREMENT,username VARCHAR(32),PASSWORD VARCHAR(32)
);
INSERT INTO USER VALUES
(NULL,'zhangsan','123'),
(NULL,'lisi','234');

package cn.itcast.newjdbc;import javax.xml.transform.Result;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;public class JDBCDemo5 {public static void main(String[] args) {Scanner sc = new Scanner(System.in);System.out.println("请输入用户名: ");String username = sc.nextLine();System.out.println("请输入密码: ");String password  = sc.nextLine();boolean flag = new JDBCDemo5().login(username,password);if(flag){System.out.println("登录成功");}else{System.out.println("用户名或密码错误");}}public boolean login(String username,String password){//若传入参数为null，自接返回falseif(username == null|| password == null){return  false;}Connection conn = null;Statement stme = null;ResultSet rs = null;try{//获得数据库连接Connectionconn=  JDBCUtils.getConnection();//写sql语句String sql = "select * from user where username = '"+username+"'and password='"+password+"'";//获得执行sql语句对象Statement stmt = conn.createStatement();rs = stmt.executeQuery(sql);return rs.next();}catch (SQLException e){e.printStackTrace();}return  false;}
}

JDBC管理事务：

事务：一个包含多个步骤的业务操作，如果这个业务被操作被事务管理，则这多个步骤要么同时成功，要么同时失败

使用Connection对象来管理事务操作：

1.开启事务：在执行sql语句之前开启事务

2.提交事务，当所有sql都执行完提交事务

3，回滚事务，在catch中回滚事务

使用Connection对象来管理事务

数据库连接池

概念：其实就是一个容器，存放数据库连接的容器

数据库连接池c3p0的使用

步骤：

1. 导入jar包,jar包要单独一个目录
2. 定义配置文件
3. 创建核心对象
4. 获取连接

package cn.itcast.datasourcejdbc;import com.mchange.v2.c3p0.ComboPooledDataSource;import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;public class C3P0Demo1 {public static void main(String[] args) {//DataSource是一个接口//创建数据库连接池对象//使用父类引用指向子类对象，多态DataSource ds = new ComboPooledDataSource();//获取连接对象try {Connection conn = ds.getConnection();System.out.println(conn);} catch (SQLException e) {e.printStackTrace();}}
}