UserDAO

package com.svse.dao;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

import com.svse.entity.UserEntity;

public class UserDAO {

    // 全查询
    public List<UserEntity> getAll() {

        List<UserEntity> ar = new ArrayList<UserEntity>();
        /************* 第一步：得到数据库的连接 *****************/
        String driver = "com.mysql.jdbc.Driver";
        String url = "jdbc:mysql://localhost:3306/test";
        String user = "root";
        String password = "root";
        Connection conn = null;
        try {
            Class.forName(driver);
            conn = DriverManager.getConnection(url, user, password);
        } catch (Exception e) {
            e.printStackTrace();
        }
        /***************** 第二步：开始查询 **************************/
        try {
            // 第一小步：写查询的SQL语句
            String sql = "select * from userinfo";
            // 第二小步：写预处理语句
            PreparedStatement pre = conn.prepareStatement(sql);
            // 第三小步：发送到数据库中去执行，并得到返回结果
            ResultSet rs = pre.executeQuery();
            // 第四小步：循环取出每一条
            while (rs.next()) {
                int uid = rs.getInt("uid");
                String uname = rs.getString("uname");
                String upsw = rs.getString("upsw");
                // 第五小步：一 一封装到实体----ar
                UserEntity u = new UserEntity();
                u.setUid(uid);
                u.setUname(uname);
                u.setUpsw(upsw);
                ar.add(u);
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
        return ar;
    }
}

UserEntity

package com.svse.entity;

public class UserEntity {
    
    //编号 
    private int uid;
    //姓名 
    private String uname;
    //密码
    private String upsw;
    
    
    public int getUid() {
        return uid;
    }
    public void setUid(int uid) {
        this.uid = uid;
    }
    public String getUname() {
        return uname;
    }
    public void setUname(String uname) {
        this.uname = uname;
    }
    public String getUpsw() {
        return upsw;
    }
    public void setUpsw(String upsw) {
        this.upsw = upsw;
    }
    
    

}

Test

package com.svse.test;

import java.util.List;

import com.svse.dao.UserDAO;
import com.svse.entity.UserEntity;

public class Test {

    public static void main(String[] args) {
        System.out.println("编号\t姓名\t密码");
        //调用全查询
        UserDAO dao=new UserDAO();
        List<UserEntity> ar=dao.getAll();
        for (int i = 0; i < ar.size(); i++) {
            System.out.println(ar.get(i).getUid()+"\t"+ar.get(i).getUname()+"\t"+ar.get(i).getUpsw());
        }
    }
}