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Java与数据库的连接方案，数据库编程
Java DataBase Contectivity
分为两个部分:
?JDK:配置完成
?SDK:是由数据库厂商提供的api,可以帮助我们连接java
??根据数据库版本下载jar包
1.加载驱动
2.创建连接
3.准备语句对象
4.执行SQL指令
5.处理结果
6.关闭资源
我们需要预先准备数据库厂商提供的SDK(jar文件)
?jar文件:其实就是一个压缩包,内部存放的是.class文件(第三方为我们编辑好的,可以直接使用的)
??例如:mysql-connector-java-8.0.17.jar
?mysql主流有两个版本:5.x 和 8.x 都有对应的jar文件提供
将驱动的jar文件,添加到java项目(工程)中
?1.在java项目下创建lib文件夹
?2.将下载好的jar文件,复制粘贴到lib中
?3.选择jar文件,右键"Build Path"
package com.qf.jdbc;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class Demo01 {
public static void main(String[] args) throws Exception {
// 1.加载驱动(之前已经"biu"成功)
// 将SDK中提供的驱动类,可以帮助我们进行JDBC连接的一个类,添加到JVM中
Class.forName("com.mysql.cj.jdbc.Driver");
// 2.创建连接
// 通过JDK提供的,DriverManager类获取数据库连接
// url:数据库统一的资源定位器(为了连接到指定的数据库资源使用的)
String url = "jdbc:mysql://localhost:3306/mysql?serverTimezone=UTC&useUnicode=true&characterEncoding=utf8&useSSL=true";
// username:连接数据库的用户
String username = "root";
// password:连接数据库的用户对应的密码
String password = "root";
Connection connection = DriverManager.getConnection(url, username, password);
// 3.准备语句对象
Statement createStatement = connection.createStatement();
// 4.执行SQL指令
String sql = "select u_id,u_name,u_balance from t_user";
// 语句执行成功后,结果被封装到结果集中
ResultSet resultSet = createStatement.executeQuery(sql);
// 5.处理结果
while(resultSet.next()) {
int uid = resultSet.getInt(1);
String uname = resultSet.getString(2);
double balance = resultSet.getDouble(3);
System.out.println(uid+", "+uname+", "+balance);
// 得到的数据可以做判断
if(uname.equals("大佑")) {
System.out.println("登录成功");
}else {
System.out.println("登录失败");
}
}
// 6.关闭资源
resultSet.close();
createStatement.close();
connection.close();
}
}
sql语句一定是在工具中执行成功后,拿到jdbc中使用的
DML:使用excuteUpdate进行sql语句的执行
DQL:使用excuteQuery进行sql语句的执行
public class Demo02 {
public static void main(String[] args) throws Exception {
Class.forName("com.mysql.cj.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/mysql?serverTimezone=UTC&useUnicode=true&characterEncoding=utf8&useSSL=true";
String username = "root";
String password = "root";
Connection connection = DriverManager.getConnection(url, username, password);
Statement createStatement = connection.createStatement();
// 编写正确的sql语句
String sql = "insert into t_user (u_name,u_balance) values ('jack',20)";
// DQL使用executeQuery(返回结果为ResultSet) DML使用executeUpdate(int类型,受影响的行数)
int result = createStatement.executeUpdate(sql);
System.out.println("添加的行数为:"+result);
createStatement.close();
connection.close();
}
}
public class Demo03 {
public static void main(String[] args) throws Exception {
Class.forName("com.mysql.cj.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/mysql?serverTimezone=UTC&useUnicode=true&characterEncoding=utf8&useSSL=true";
String username = "root";
String password = "root";
Connection connection = DriverManager.getConnection(url, username, password);
Statement createStatement = connection.createStatement();
// 编写正确的sql语句
String sql = "delete from t_user where u_id = 13";
// DQL使用executeQuery(返回结果为ResultSet) DML使用executeUpdate(int类型,受影响的行数)
int result = createStatement.executeUpdate(sql);
System.out.println("删除的行数为:"+result);
createStatement.close();
connection.close();
}
}
public class Demo04 {
public static void main(String[] args) throws Exception {
Class.forName("com.mysql.cj.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/mysql?serverTimezone=UTC&useUnicode=true&characterEncoding=utf8&useSSL=true";
String username = "root";
String password = "root";
Connection connection = DriverManager.getConnection(url, username, password);
Statement createStatement = connection.createStatement();
// 编写正确的sql语句
String sql = "update t_user set u_name = 'zs' where u_id = 17";
// DQL使用executeQuery(返回结果为ResultSet) DML使用executeUpdate(int类型,受影响的行数)
int result = createStatement.executeUpdate(sql);
System.out.println("修改的行数为:"+result);
createStatement.close();
connection.close();
}
}
public class Demo05 {
public static void main(String[] args) throws Exception {
Class.forName("com.mysql.cj.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/mysql?serverTimezone=UTC&useUnicode=true&characterEncoding=utf8&useSSL=true";
String username = "root";
String password = "root";
Connection connection = DriverManager.getConnection(url, username, password);
Statement createStatement = connection.createStatement();
// CRUD的每次SQL都不相同
String sql = "select u_id,u_name,u_balance from t_user where u_id = 17";
// 查询有结果集,使用executeQuery方法
ResultSet resultSet = createStatement.executeQuery(sql);
if(resultSet.next()) {
int uid = resultSet.getInt(1);
String uname = resultSet.getString(2);
double balance = resultSet.getDouble(3);
System.out.println(uid+", "+uname+", "+balance);
}
// 6.关闭资源
resultSet.close();
createStatement.close();
connection.close();
}
}
public class Demo06 {
public static void main(String[] args) throws Exception {
Class.forName("com.mysql.cj.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/mysql?serverTimezone=UTC&useUnicode=true&characterEncoding=utf8&useSSL=true";
String username = "root";
String password = "root";
Connection connection = DriverManager.getConnection(url, username, password);
Statement createStatement = connection.createStatement();
// CRUD的每次SQL都不相同
String sql = "select u_id,u_name,u_balance from t_user";
// 查询有结果集,使用executeQuery方法
ResultSet resultSet = createStatement.executeQuery(sql);
while(resultSet.next()) {
int uid = resultSet.getInt(1);
String uname = resultSet.getString(2);
double balance = resultSet.getDouble(3);
System.out.println(uid+", "+uname+", "+balance);
}
// 6.关闭资源
resultSet.close();
createStatement.close();
connection.close();
}
}
封装:保护代码,提高代码的利用率,减少重复的代码
/**
*
* @author y1538
* JDBC工具类:
* 1.帮助我们获取数据库连接对象
* 2.关闭资源
*/
public class DBUtil {
// 写成参数的作用是为了之后换库方便
private static final String DRIVER = "com.mysql.cj.jdbc.Driver";
private static final String URL = "jdbc:mysql://localhost:3306/mysql?serverTimezone=UTC&useUnicode=true&characterEncoding=utf8&useSSL=true";
private static final String USERNAME = "root";
private static final String PASSWORD = "root";
static {
try {
Class.forName(DRIVER);
} catch (ClassNotFoundException e) {
System.out.println("加载驱动类失败...");
}
}
/**
* 获取连接方法,返回值为数据库连接对象
*/
public static Connection getConnetion() {
Connection connection = null;
try {
connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return connection;
}
/**
* 关闭资源
* DQL的关闭
* */
public static void close(Connection conn,Statement stmt,ResultSet rs) {
try {
if(rs != null && !rs.isClosed() /*开启状态时*/) {
rs.close();
}
if(stmt != null && !stmt.isClosed() /*开启状态时*/) {
stmt.close();
}
if(conn != null && !conn.isClosed() /*开启状态时*/) {
conn.close();
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* 关闭资源
* DML的关闭
* */
public static void close(Connection conn,Statement stmt) {
close(conn,stmt,null);
}
}
Data Transfer Object
?数据传输对象,就是java实体类
DTO是实体类的封装规则
?规则:私有属性,get/set,构造方法(有参,无参),toString,hashCode,equals等
DTO是为数据表封装java实例类
?规则:类名和表名对应,属性和字段对应,对象和记录(元组)对应
DTO包的命名:
?pojo,vo,entry,dto…
DTO作用:
?1.为DML操作作为参数
?2.为DQL封装查询结果
public class Emp {
// 表中字段对应的属性
private int empno;
private String ename;
private String job;
private Date hiredate;
private double sal;
private double comm;
private int deptno;
...
public class Demo07 {
public static void main(String[] args) throws Exception {
Demo07 demo07 = new Demo07();
/*List<Emp> queryAll = demo07.queryAll();
System.out.println(queryAll);*/
Emp emp = demo07.queryByNo(3);
System.out.println(emp);
}
// 封装了一个查询所有数据的方法
public List<Emp> queryAll() throws Exception{
List<Emp> list = new ArrayList<>();
Connection connetion = DBUtil.getConnetion();
Statement createStatement = connetion.createStatement();
String sql = "select empno,ename,hiredate,sal,comm,deptno,job from emp";
ResultSet rs = createStatement.executeQuery(sql);
while(rs.next()) {
int empno = rs.getInt(1);
String ename = rs.getString(2);
Date hiredate = rs.getDate(3);//jdbc中可以直接获取日期
double sal = rs.getDouble(4);
double comm = rs.getDouble(5);
int deptno = rs.getInt(6);
String job = rs.getString(7);
// 通过构造创建Emp对象
Emp emp = new Emp(empno, ename, job, hiredate, sal, comm, deptno);
list.add(emp);
}
DBUtil.close(connetion, createStatement, rs);
return list;
}
// 通过id查询
public Emp queryByNo(int id) throws Exception {
Connection connetion = DBUtil.getConnetion();
Statement createStatement = connetion.createStatement();
String sql = "select empno,ename,hiredate,sal,comm,deptno,job from emp where empno = " + id;
ResultSet rs = createStatement.executeQuery(sql);
while(rs.next()) {
int empno = rs.getInt(1);
String ename = rs.getString(2);
Date hiredate = rs.getDate(3);//jdbc中可以直接获取日期
double sal = rs.getDouble(4);
double comm = rs.getDouble(5);
int deptno = rs.getInt(6);
String job = rs.getString(7);
return new Emp(empno, ename, job, hiredate, sal, comm, deptno);
}
DBUtil.close(connetion, createStatement, rs);
return null;
}
}
public class Demo08 {
public static void main(String[] args) throws Exception {
Demo08 demo08 = new Demo08();
// demo08.add("bmh",new Date(System.currentTimeMillis()),1200,6000,40);
/*Emp emp = new Emp(0, "wxy", "", new Date(2024,10,3), 12000, -300, 40);
demo08.add(emp);*/
// demo08.update("sxc",10000,2);
Emp emp = new Emp();
emp.setEmpno(3);
emp.setEname("lz");
emp.setSal(8000);
demo08.update(emp);
}
// 定义一个添加方法,使用JDBC将数据作为参数传到数据库中
public void add(String name,Date hiredate,double sal,double comm,int deptno) throws Exception {
Connection connection = DBUtil.getConnection();
Statement createStatement = connection.createStatement();
String sql = "insert into emp (ename,hiredate,sal,comm,deptno) values ('"+name+"','"+hiredate+"',"+sal+","+comm+","+deptno+")";
System.out.println("SQL:"+sql);
createStatement.executeUpdate(sql);
DBUtil.close(connection, createStatement);
}
// 使用DTO对上述的方法进行改造
public void add(Emp emp) throws Exception {
Connection connection = DBUtil.getConnection();
Statement createStatement = connection.createStatement();
String sql = "insert into emp (ename,hiredate,sal,comm,deptno) "
+ "values ('"+emp.getEname()+"','"+emp.getHiredate()+"',"+emp.getSal()+","+emp.getComm()+","+emp.getDeptno()+")";
System.out.println("SQL:"+sql);
createStatement.executeUpdate(sql);
DBUtil.close(connection, createStatement);
}
// 修改操作
public void update(String name,double sal/*涨薪的值*/,int empno) throws Exception {
Connection connection = DBUtil.getConnection();
Statement createStatement = connection.createStatement();
String sql = "update emp set ename = '"+name+"',sal = sal + "+sal+" where empno = " + empno;
System.out.println("SQL:"+sql);
createStatement.executeUpdate(sql);
DBUtil.close(connection, createStatement);
}
// 使用DTO进行改造上述功能
public void update(Emp emp) throws Exception {
Connection connection = DBUtil.getConnection();
Statement createStatement = connection.createStatement();
String sql = "update emp set ename = '"+emp.getEname()+"',sal = sal + "+emp.getSal()+" where empno = " + emp.getEmpno();
System.out.println("SQL:"+sql);
createStatement.executeUpdate(sql);
DBUtil.close(connection, createStatement);
}
}