Mybatis_02_JDBC回顾

JDBC回顾

• 将数据库中的user表中的数据，封装在User对象中

• 代码：

       

        import javax.servlet.ServletException;
        import javax.servlet.http.HttpServlet;
        import javax.servlet.http.HttpServletRequest;
        import javax.servlet.http.HttpServletResponse;
        import java.io.IOException;
        import java.sql.*;
        import java.util.ArrayList;
        import java.util.Iterator;
        import java.util.List;

        public class StudentServlet extends HttpServlet {
            @Override
            protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

                //建立用户集合
                ListuserList=new ArrayList();

                //建立用户对象
                User user=new User();

                 //建立JDBC链接对象
                Connection connection=null;
                PreparedStatement preparedStatement=null;
                ResultSet resultSet=null;

                try {
                    //注册驱动
                    Class.forName("com.mysql.cj.jdbc.Driver");

                    //获取链接
                    connection= DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/mydb?useUnicode=true&characterEncoding=utf8&serverTimezone=Asia/Shanghai",
                            "root","123456");

                    //获取预编译数据库操做对象
                    String sql="select username,email,userpwd from t_userinfo";
                    preparedStatement=connection.prepareStatement(sql);

                    //执行Sql语句
                    resultSet=preparedStatement.executeQuery();

                    //处理查询结果集
                    while(resultSet.next()){
                     //将在数据库中查询到的信息，封装在实例类中
                      user=new User();
                      user.setUserName(resultSet.getString("username"));
                      user.setUserEmail(resultSet.getString("email"));
                      user.setUserPwd(resultSet.getString("userpwd"));

                     //将每个用户对象添加到集合中
                       userList.add(user);
                    }
                } catch (ClassNotFoundException | SQLException e) {
                    e.printStackTrace();
                }finally {
                    if(resultSet!=null){
                        try {
                            resultSet.close();
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }

                    if(preparedStatement!=null){
                        try {
                            preparedStatement.close();
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }

                    if(connection!=null){
                        try {
                            connection.close();
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }
                     //遍历集合，输出用户信息
                    if(userList!=null){
                        Iterator iterator=userList.iterator();
                        while(iterator.hasNext()){
                            System.out.println(iterator.next());
                        }
                    }
                }
            }
        }