ベースJDBC API使用

import com.mysql.jdbc.Driver;
import org.junit.Test;

import java.sql.*;

public class Demo1 {
    @Test
    public void demo1() {
        //               ,   try  
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        //1.    
        try {
            //DriverManager.registerDriver(new Driver());
            //         
            //   Class.forName()  
            Class.forName("com.mysql.cj.jdbc.Driver");
            //2.    
            conn = DriverManager.getConnection("jdbc:mysql:///jdbctest", "root", "root");
            //      DriverManager
            //Connection       sql     
            //Statement createStatement/                     ===>   sql  (    sql    )
            //PreparedStatement prepareStatement(String sql) ===>    sql  
            //CallableStatement prepareCall(String sql)      ===>   sql     

            //    
            //setAutoCommit(boolean autoCommit) ===>         
            //commit()                          ===>     
            //rollback()                        ===>     
            //3.    
            String sql = "select * from user";
            stmt = conn.createStatement();
            //Statement
            //boolean execute(String sql)            ===>  sql(  select    true/  false)
            //ResultSet executeQuery(String sql)     ===>sql select  
            //int executeUpdate(String sql)          ===>sql insert/update/delete  

            //   
            //addBatch(String sql)        ===>      
            //executeBatch()              ===>     
            //clearBatch()                ===>     
            rs = stmt.executeQuery(sql);
            //   (        )
            //next()         
            //              getString...
            //    getObject   
            while (rs.next()) {
                int uid = rs.getInt("uid");
                String username = rs.getString("username");
                String password = rs.getString("password");
                String name = rs.getString("name");
                System.out.println(uid + "" + username + " " + password + " " + name);
            }
            //4.    
            //rs.close();
            //stmt.close();
            //conn.close();
            //connection      ,       
            //             final 

        } catch (SQLException | ClassNotFoundException e) {
            e.printStackTrace();
        } finally {
            //      
            if (rs != null) {
                try {
                    rs.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                rs = null;
                //       
            }
            if (stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                stmt = null;
            }
            if (conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                conn = null;
            }
        }

    }

public class Demo2 {
    @Test
    public void demo1() {
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;

        try {
            Class.forName("com.mysql.cj.jdbc.Driver");

            conn = DriverManager.getConnection("jdbc:mysql:///jdbctest","root","root");

            stmt = conn.createStatement();

            String sql = "insert into user values(null,'eee','123','  ')";

            int i = stmt.executeUpdate(sql);

            if(i>0){
                System.out.println("success");
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                stmt = null;
            }
            if (conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                conn = null;
            }
        }
    }
}

String sql = "update user set username = 'qqq',password = '423', name ='  ' where uid = 4";

String sql = "delete from user where uid = 4";