jdbc基础

JDBC概念

java连接数据库的一系列接口，接口的实现类交给第三方数据库厂商去实现

四大参数

驱动 com.mysql.jdbc.Driver

DriverManager

Class.forname("com.mysql.jdbc.Driver");

Connection

String url="jdbc:mysql://localhost:3306/数据库名称?useUnicode=true&characterEncoding=utf-8";
String user="root";
String password ="";
Connection con = DriverManager.getConnection(url,user,password);

Statement

        Statement statement=con.createStatement();
        String sql="update employee set username='YYT'where id=1 ";
        int i = statement.executeUpdate(sql);
        System.out.println(i);
        con.close();

ResultSet

//得到一条记录
String sql="select * from employee ";
 ResultSet  rs =statement.executeQuery(sql);
 if(rs.next()){
     rs.getInt("字段名");
     String empno = rs.getString("empno");
 }

//得到所有记录
        while(rs.next()){
                int id = rs.getInt("id");
                String empno = rs.getString("empno");
        }

事务

1.完整性
2.一致性
3.原子性
4.隔离性

       try{
            con.setAutoCommit(false);
           String sql="delete from employee where id=1";
           String sql1="delete from employee where id=2";
           statement.executeUpdate(sql);
            statement.executeUpdate(sql1);
            con.commit();
        }catch(Exception e){
        System.out.println("操作失败");
            con.rollback();
        }

简单的封装登录方法

static String url="jdbc:mysql://localhost:3306/employee?useUnicode=true&characterEncoding=utf-8";
    static String us="root";
    static String psw="";
    public void driver(){
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {

            e.printStackTrace();
        }
    }
   public static Connection connect(){
       try {
          Connection con=DriverManager.getConnection(url,us,psw);
          return con;
    } catch (SQLException e) {
        
        e.printStackTrace();
    }
           return null;
   }
 
   public User  login(String usn,String psw){
       Statement statement=null;
       Connection con=null;
       try {
         con = connect();
         statement = con.createStatement();
        String sql="select * from user where username='"+usn+"'and password="+psw;
        ResultSet qs = statement.executeQuery(sql);
        if(qs.next()){
            String username = qs.getString("username");
            String password = qs.getString("password");
            User user=new User(username,password);
            return user;
        }
    } catch (SQLException e) {
        e.printStackTrace();
        
    }   
     finally{
         try {
            if(statement!=null){
                statement.close();
            }
            if(con!=null){
            con.close();
            }
        } catch (SQLException e) {
    
            e.printStackTrace();
        }
        
     }
        return null; 
       
   }