Query the database table and return the object of the data if there is a data whose username is lisi in the user table sw_user

Using the original method, the operation is as follows:

1. Write a tool class first. There are ways to realize MySQL database connection, and methods to close database connection, ResultSet result set and PreparedStatement. The code is as follows:

package com.swift;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class DBUtil {
        //Connect MySQL Database Tools
        public static Connection getConn() {
            Connection conn=null;
            try {
                Class.forName("com.mysql.jdbc.Driver");
                try {
                    conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/sw_database?user=root&password=root");
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
            return conn;
        }
        //Close the database connection, sql Connection, result set
        public static void closeAll(Connection conn,PreparedStatement ps,ResultSet rs) {
            if(conn!=null)
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            if(ps!=null) {
                try {
                    ps.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if(rs!=null) {
                try {
                    rs.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
}

Use this DBUtil to query whether there is a data named lisi in the database table and return this data as a User object

package com.swift;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class QueryOneObject {

    public static User queryOneObject() {
        
        Connection conn=DBUtil.getConn();
        PreparedStatement ps=null;
        ResultSet rs=null;
        User user=null;
        try {
            ps=conn.prepareStatement("select * from sw_user where username=? and password=?");
            ps.setString(1, "lisi");
            ps.setString(2, "abcdef");
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            rs=ps.executeQuery();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            while(rs.next()) {
                String username=rs.getString("username");
                String password=rs.getString("password");
                user=new User(username,password);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return user;
    }
    
    
}

Test class SeverletDemo

package com.swift;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/demo")
public class ServletDemo extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    public ServletDemo() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.getWriter().append("Served at: ").append(request.getContextPath());
        User user=QueryOneObject.queryOneObject();
        response.getWriter().append(user.toString());
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

Result:

Next, we will complete the above process with JdbcTemplate method: JdbcTemplate, JdbcTemplate, JdbcTemplate, JdbcTemplate, JdbcTemplate, JdbcTemplate, JdbcTemplate, JdbcTemplate