DBUtils工具类

import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;

public class DBUtils {
    private static String driverName;
    private static String url;
    private static String username;
    private static String password;

    static{
        try {
            //读取配置文件的信息
            Properties properties = new Properties();
            //从资源路径中去获取配置属性
            InputStream is = DBUtils.class.getClassLoader().getResourceAsStream("dbconfig.properties");
            try {
                properties.load(is);
                driverName = properties.getProperty("driverName");
                url = properties.getProperty("url");
                username = properties.getProperty("username");
                password = properties.getProperty("password");
            } catch (IOException e) {
                e.printStackTrace();
            }
            //1. 加载驱动
            Class.forName(driverName);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    public static Connection getConnection(){
        //获取连接对象
        Connection connection = null;
        try {
            connection = DriverManager.getConnection(url, username, password);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return connection;
    }

    public static void closeAll(AutoCloseable...cs){
        if(cs != null){  //如果只传了一个null过来，则不用进行遍历
            for(AutoCloseable c: cs){
                if(c != null){  //如果多个参数中有一个为null，则不用关闭
                    try {
                        c.close();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
}

//CommonUtils 公共的数据库操作工具类

import java.io.IOException;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

//公共的数据库操作工具类--增删改
public class CommonUtils <T> {
    //公共类--增删改
    public static int updateCommon(String sql,Object...objs){
            //获取连接对象，再获取执行对象，操作添加
            Connection conn = null;
            PreparedStatement prst = null;
            try {
                conn = DBUtils.getConnection();
                prst = conn.prepareStatement(sql);
                //遍历传入的对象的多个字段
                for(int i=0;i<objs.length;i++){
                    prst.setObject(i+1, objs[i]);
                }
                return prst.executeUpdate();
            } catch (SQLException e) {
                e.printStackTrace();
            }finally{
                DBUtils.closeAll(prst,conn);
            }
            return 0;
    }

    //公共类---查询---注意：要传一个反射对象进来
    public List<T> queryCommon(String sql,Class<T> clazz,Object...objs){
        Connection conn = null;
        PreparedStatement prst = null;
        ResultSet resultSet = null;
        List<T> list = new ArrayList<>();
        try {
            conn = DBUtils.getConnection();  //获取连接对象
            prst = conn.prepareStatement(sql);
            //遍历传入的对象的多个字段
            for(int i=0;i<objs.length;i++){
                prst.setObject(i+1, objs[i]);
            }

            resultSet = prst.executeQuery();  //获取到结果集
            //---最终将结果集的信息存储到List集合中---
            while(resultSet.next()){  //循环一次，就是一条记录（一个对象）
                //clazz.getFields();  //私有的属性获取不到
                Field[] fields = clazz.getDeclaredFields();
                T t = clazz.newInstance();  //通过反射对象获取到实体类对象
                for(Field f: fields){
                    String fieldName = f.getName();  //得到属性名

                    //获取字段对应值
                    Object value = null;
                    try {
                         value = resultSet.getObject(fieldName);  //如何确定获取的字段---对应上属性名
                    } catch (SQLException e) {
                        //获取映射属性中的字段名（is_admin）
                        Properties properties = new Properties();
                        try {
                            properties.load(CommonUtils.class.getClassLoader().getResourceAsStream("mapping.properties"));
                        } catch (IOException e1) {
                            e1.printStackTrace();
                        }
                        fieldName = properties.getProperty("isAdmin");
                        value = resultSet.getObject(fieldName);
                    }

                    f.setAccessible(true);  //设置权限
                    f.set(t, value);    //把值设置的对象的属性中
                }
                list.add(t);  //将对象存储到集合中
            }

        } catch (SQLException | InstantiationException | IllegalAccessException e) {
            e.printStackTrace();
        }finally {
            DBUtils.closeAll(resultSet,prst,conn);
        }
        return list;
    }

    //-------分页获取总条数-------
    public static int getTotalCount(String sql){
        //获取连接对象，再获取执行对象，操作添加
        Connection conn = null;
        PreparedStatement prst = null;
        ResultSet   resultSet = null;
        try {
            conn = DBUtils.getConnection();
            prst = conn.prepareStatement(sql);
            resultSet = prst.executeQuery();
            if(resultSet.next()){
                return resultSet.getInt(1);  //获取第一个字段
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally{
            DBUtils.closeAll(resultSet,prst,conn);
        }
        return -1;
    }
}

//Dao层示例

import java.util.List;
import com.qf.dao.IUserDao;
import com.qf.entity.User;
import com.qf.utils.CommonUtils;

public class UserDaoImpl extends CommonUtils<User> implements IUserDao {

    @Override
    public int addUser(User user) {
        String sql = "insert into t_user(name,password,sex,phone,email,is_admin) values(?,?,?,?,?,?)";
        int result = CommonUtils.updateCommon(sql, user.getName(),user.getPassword(),user.getSex()
                ,user.getPhone(),user.getEmail(),user.getIsAdmin());
        return result;
    }

    @Override
    public int updateUser(User user) {
        String sql="update t_user set name=?,password=?,sex=?,phone=?,email=?,is_admin=? where id=?";
        int result = CommonUtils.updateCommon(sql, user.getName(),user.getPassword(),user.getSex()
                ,user.getPhone(),user.getEmail(),user.getIsAdmin(),user.getId());
        return result;
    }

    @Override
    public int delUserById(Integer id) {
        String sql="delete from t_user where id=?";
        return CommonUtils.updateCommon(sql, id);
    }

    @Override
    public List<User> getUserList() {
        String sql="SELECT id, NAME, PASSWORD, CASE WHEN sex = 1 THEN '男' WHEN sex = 0 THEN '女' END AS sex, email, phone, CASE WHEN is_admin = 1 THEN '是' WHEN is_admin = 0 THEN '否' END AS is_admin FROM t_user";
        return super.queryCommon(sql, User.class);
    }

    @Override
    public User getUserById(Integer id) {
        String sql="select * from t_user where id = ?";
        List<User> list = super.queryCommon(sql, User.class,id);
        if(list.size()>0){  //如果取到数据，则返回该对象
            return list.get(0);
        }
        return null;  //取不到数据，则返回null
    }

    @Override
    public int getTotalCount() {
        String sql="select count(1) from t_user";
        return CommonUtils.getTotalCount(sql);
    }

    @Override
    public List<User> getUserListPage(Integer startIndex, Integer pageSize) {
        String sql="SELECT id, NAME, PASSWORD, CASE WHEN sex = 1 THEN '男' WHEN sex = 0 THEN '女' END AS sex, email, phone, CASE WHEN is_admin = 1 THEN '是' WHEN is_admin = 0 THEN '否' END AS is_admin FROM t_user limit ?,?";
        return super.queryCommon(sql, User.class,startIndex,pageSize);
    }

    @Override  //批量删除
    public int batchDelIds(String[] ids) {
        StringBuilder builder = new StringBuilder("delete from t_user where id in (");
        for(int i=0;i<ids.length;i++){
            if(i==ids.length-1){  //最后一个则不用+“，”；要加“）”
                builder.append(ids[i]+")");
            }else{
                builder.append(ids[i]+",");
            }
        }
        String sql = builder.toString();
        return CommonUtils.updateCommon(sql);
    }

    @Override   //验证用户名和密码是否正确
    public User getUserByBackLogin(String name, String password) {

        String sql="select * from t_user where name=? and password=?";
        List<User> list = super.queryCommon(sql, User.class, name,password);
        if(list.size()>0){
            return list.get(0);
        }
        return null;
    }
}