JDBC exercise - query data encapsulated into object return & simple login demo

Catalog

1、 Package data return

1.1、 Write entity class Person

1.2、 To write jdbc Code

2、 Simple login logic

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After learning jdbc, Use jdbc Little exercises to do

1、 Query... In the database person surface Encapsulate the queried data into Person Object returns

2、 Simple login logic judgment

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1、 Package data return

Define a method , Inquire about person The table's data encapsulates it as an object , Then load the collection , return .
     1. Definition Person class
     2. Define methods public List<Person> findAll(){}
     3. Implementation method select * from emp;

1.1、 Write entity class Person

package com.zhou.exercise;


public class Person {
    private int id;
    private String name;
    private String email;
    private String addr;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getAddr() {
        return addr;
    }

    public void setAddr(String addr) {
        this.addr = addr;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", email='" + email + '\'' +
                ", addr='" + addr + '\'' +
                '}';
    }
}

1.2、 To write jdbc Code

package com.zhou.exercise;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;


public class JDBC_queryForObj {
    public static void main(String[] args) {
        //  Calling method 
        List<Person> personList = findAll();

        //  Ergodic set 
        for (Person person : personList) {
            System.out.println(person);
        }

    }

    //  Define a method to query data 
    public static List<Person> findAll() {
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        //  Define loading Person Set 
        List<Person> list = new ArrayList<Person>();

        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql:///day10", "root", "123456");
            String sql = "select * from person";
            pstmt = conn.prepareStatement(sql);
            rs = pstmt.executeQuery();

            while (rs.next()) {
                Person person = new Person(); //  take person Mention the outside 
                int id = rs.getInt(1);
                String name = rs.getString(2);
                String email = rs.getString(3);
                String addr = rs.getString(4);
                person.setId(id);
                person.setName(name);
                person.setEmail(email);
                person.setAddr(addr);
                list.add(person);

            }

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

        }
        //  return list
        return list;
    }
}

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2、 Simple login logic

1. Enter the user name and password through the keyboard
 2. Determine whether the user has successfully logged in

package com.zhou.exercise;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class JDBC_login {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println(" Please enter a user name ：");
        String username = scanner.next();
        System.out.println(" Please input a password ：");
        String password = scanner.next();

        //  Calling method   Judge 
        boolean login = login(username, password);
        if (login){
            System.out.println(" Login successful ！");
        }else {
            System.out.println(" Login failed ！");
        }


    }

    //  Define a method to query data 
    public static boolean login(String username, String password) {
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        //  Define loading Person Set 
        List<Person> list = new ArrayList<Person>();

        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql:///day10", "root", "123456");
            String sql = "select * from user where username = ? and password = ?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, username);
            pstmt.setString(2, password);
            rs = pstmt.executeQuery();

            // rs.next The return value of is a Boolean value   Just what we need  true: Indicates that the current line is not the last line   There's data  false  Indicates that the current line is the last line   There's no data 
            //  Indicates that the data queried is not empty   Proof basis username and password Relevant records can be found 
            return rs.next();

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

        }
       return false; //  If try The inside is back   Then changing the code will not execute 
    }
}

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1、 Of course, here we find that many codes are highly repetitive Local laws that are almost used in addition, deletion, modification and inspection

Then we can extract the code into a tool class

2、 Our database connection information is in java In the code Caused and java Code coupling is dead

Then we can extract the connection information of the database into a configuration file