JDBC

题目一：

编写一个应用程序，输入用户名和密码，访问test数据库中t_login表（字段包括id、username、password），验证登录是否成功。

代码：

Test.java

package cn.edu.ccut;
import java.sql.*;
import java.util.Scanner;

public class Trest {

    public static void main(String[] args) {
        Scanner r = new Scanner(System.in);
        String username = r.next();
        String password = r.next();
        Connection con = null;
        Statement st = null;
        ResultSet rs =null;
        try {
            Class.forName("com.mysql.jdbc.Driver"); //加载JDBC驱动器;
            con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root",""); //创建数据库连接;
            st = con.createStatement(); //创建执行SQL语句的对象;
            rs = st.executeQuery("select * from t_login where username='"+username+"' and password='"+password+"'"); //执行SQL语句(拼串);
            if(rs.next()){
                System.out.println("登陆成功");
            }
            else{
                System.out.println("登录失败");
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }finally{
                try {
                    rs.close();//关闭数据库连接;
                    st.close();
                    con.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
    }
        
}

运行结果：

题目二：

在上一题基础上，当登录成功后，将t_user表（id、name、sex、birthday）的信息进行显示（要求使用DB.java完成登录和获取t_user表中数据的操作），最后再对t_user表进行一条记录的添加操作。

 代码：

1、Test.java

package cn.edu.ccut2;

import java.sql.SQLException;
import java.util.Scanner;

public class Test {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String username = in.next();
        String password = in.next();
        Object []a = {username, password};
        String sql = "select * from t_login where username=? and password=?";
        DB db = DB.getInstance();
        db.excuteSelect(sql, a);
        try {
            if(db.rs.next()){
                System.out.println("登陆成功!");
                Object []b = new Object[0];
                sql = "select * from t_user ";
                db.excuteSelect(sql, b);
                String mname = null;
                String msex = null;
                String mbirthday = null;
                while(db.rs.next()){//输出显示t_user表内容;
                    mname = db.rs.getString(2);
                    msex = db.rs.getString(3);
                    mbirthday = db.rs.getString(4);
                    System.out.println("name:"+mname+" sex:"+msex+" birthday:"+mbirthday+"");
                }
                System.out.println("请输入想要添加的一条记录:");
                String newname = in.next();
                String newsex = in.next();
                String newbirthday = in.next();
                Object []c = {newname, newsex , newbirthday};
                sql = "insert into t_user (name,sex,birthday) values(?,?,?)";
                int count = db.executModify(sql, c); //添加记录;
                if(count == 0){
                    System.out.println("插入失败!");
                }else{
                    System.out.println("插入成功!");
                }
            }else{
                System.out.println("登录失败!");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

}

2、DB.java

package cn.edu.ccut2;

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

public class DB {
    private static DB db;
    Connection con = null;
    PreparedStatement pre = null;
    ResultSet rs = null;
    public static DB getInstance(){
        if(db == null){
            db = new DB();
        }
        return db;
    }
    private DB(){//构造方法创建数据库连接;
        try {
             con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","");
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    static{//静态代码块,提高程序执行效率;
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    public ResultSet excuteSelect(String sql , Object []args){//数据库查询操作;
        try {
            pre = con.prepareStatement(sql);
            if(args.length > 0){
                for(int i = 0; i < args.length; i++){
                    pre.setObject(i+1, args[i]);
                }
            }
            rs = pre.executeQuery();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return rs;
    }
    public int executModify(String sql, Object []args){//数据库增/删/改操作;
        int n = 0;
        try {
            pre = con.prepareStatement(sql);
            if(args.length > 0){
                for(int i = 0; i < args.length; i++){
                    pre.setObject(i+1, args[i]);
                }
            }
            n = pre.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return n;
    }
    public void close(){
            try {
                if(rs != null){//关闭链接;
                rs.close();
                }
                con.close();
                pre.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
    }
}

运行结果：