【Javaweb】四（关于接口类的作用）

这里我们还是以房产信息管理系统的题目举例：

发现在DAO层和service层都有接口类（注：impl是实现类）

为什么要用接口，不直接写实现类：

1、简单、规范性：这些接口不仅告诉开发人员你需要实现那些业务，而且也将命名规范限制住了（防止一些开发人员随便命名导致别的程序员无法看明白）

2、便于维护、拓展：在不久将来，你突然发现这个类满足不了你了，然后你又要重新设计这个类，更糟糕是你可能要放弃这个类，那么其他地方可能有引用他，这样修改起来很麻烦，如果你一开始定义一个接口，把函数功能放在接口里，然后定义类时实现这个接口，然后你只要用这个接口去引用实现它的类就行了，以后要换的话只不过是引用另一个类而已，这样就达到维护、拓展的方便性。

3、安全、严密性：它描述了系统对外的所有服务，而不涉及任何具体的实现细节。这样比较安全、严密一些（一般软件服务商考虑的比较多）

DAO层接口类

package com.yan.web.dao;

import com.yan.web.entity.AdminEntity;
import com.yan.web.entity.Customer;

import java.util.List;

public interface AdminDao {
    AdminEntity getAdminByUserName(String userName);

    //注册
    int addUser(AdminEntity adminEntity);

    List<Customer> adminList(String userName, Integer id);
    List<Customer> adminList();

    int deleteAdminById(Integer id);

    int updateAdmin(AdminEntity admin);
}

service层接口

package com.yan.web.service;

import com.yan.web.entity.AdminEntity;

/**
 * 管理服务
 *
 * @author galax
 * @date 2022/10/19
 */
public interface AdminService {
    /**
     * 被用户名admin
     *
     * @param userName 用户名
     * @return {@link AdminEntity}
     */
    AdminEntity getAdminByUserName(String userName);

    /**
     * 添加用户
     *
     * @param adminEntity 管理实体
     * @return boolean
     */// 注册
    boolean addUser(AdminEntity adminEntity);
}

DAO层实现类

AdminDaoImpl.java(其他dao类同理)【完整代码】

package com.yan.web.dao.Impl;

import com.yan.web.dao.AdminDao;
import com.yan.web.entity.AdminEntity;
import com.yan.web.entity.Customer;
import com.yan.web.util.jdbcUtil;

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

/**
 * @author chenshy
 * @date 2022/10/19
 */
public class AdminDaoImpl implements AdminDao {
    /**
     * 被用户名admin
     *
     * @param userName 用户名
     * @return {@code AdminEntity}
     */
    @Override
/*通过姓名获取输入的信息*/
    public AdminEntity getAdminByUserName(String userName) {
        Connection connection = jdbcUtil.getConnection();
        PreparedStatement ps = null;
        ResultSet rs = null;
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append("select * from admin where user_name=?");
        try {
            ps = connection.prepareStatement(stringBuilder.toString());
            // 第一个?的参数
            ps.setString(1, userName);
            rs = ps.executeQuery();
            if (rs.next()) {
                int aid = rs.getInt("id");
                String name = rs.getString("user_name");
                String password = rs.getString("pwd");
                int state = rs.getInt("state");
                AdminEntity adminEntity = new AdminEntity();
                adminEntity.setId(aid);
                adminEntity.setUserName(name);
                adminEntity.setPwd(password);
                adminEntity.setState(state);
                return adminEntity;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            jdbcUtil.ReleaseResource(connection, ps, rs);
        }
        return null;
    }

    /**
     * 添加用户
     *
     * @param adminEntity 管理实体
     * @return int
     */
    @Override
    /*将获取的信息添加到数据库中*/
    public int addUser(AdminEntity adminEntity) {
        Connection connection = jdbcUtil.getConnection();
        PreparedStatement ps = null;
        ResultSet rs = null;
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append("insert into admin(user_name,pwd,state) VALUES(?,?,?)");
        try {
            ps = connection.prepareStatement(stringBuilder.toString());
            ps.setString(1, adminEntity.getUserName());
            ps.setString(2, adminEntity.getPwd());
            ps.setInt(3, adminEntity.getState());
            return ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            jdbcUtil.ReleaseResource(connection, ps, rs);
        }
        return 0;
    }

    @Override
    public List<Customer> adminList(String userName, Integer id) {
        Connection connection = jdbcUtil.getConnection();
        PreparedStatement ps = null;
        ResultSet rs = null;
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append("select * from customer");
        try {
            ps = connection.prepareStatement(stringBuilder.toString());
            // ps.setObject(1, "%" + userName + "%");
            // ps.setObject(2, id);
            rs = ps.executeQuery();
            List<Customer> list = new ArrayList<>();
            while (rs.next()) {
                long ids = rs.getInt("UserID");
                String userName1 = rs.getString("UserName");
                String sex = rs.getString("sex");
                String IdNumber = rs.getString("IdNumber");
                String Phone = rs.getString("Phone");
                String User = rs.getString("User");
                int audit = rs.getInt("audit");
                String password = rs.getString("password");
                Customer customer = new Customer();
                customer.setUserid(ids);
                customer.setUsername(userName1);
                customer.setSex(sex);
                customer.setIdnumber(IdNumber);
                customer.setPhone(Phone);
                customer.setUser(User);
                customer.setAudit(audit);
                customer.setPassword(password);
                list.add(customer);
            }
            return list;
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            jdbcUtil.ReleaseResource(connection, ps, rs);
        }
        return null;
    }

    public List<Customer> adminList() {
        Connection connection = jdbcUtil.getConnection();
        PreparedStatement ps = null;
        ResultSet rs = null;
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append("select * from customer");
        try {
            ps = connection.prepareStatement(stringBuilder.toString());
            // ps.setObject(1, "%" + userName + "%");
            // ps.setObject(2, id);
            rs = ps.executeQuery();
            List<Customer> list = new ArrayList<>();
            while (rs.next()) {
                long ids = rs.getInt("UserID");
                String userName1 = rs.getString("UserName");
                String sex = rs.getString("sex");
                String IdNumber = rs.getString("IdNumber");
                String Phone = rs.getString("Phone");
                String User = rs.getString("User");
                int audit = rs.getInt("audit");
                String password = rs.getString("password");
                Customer customer = new Customer();
                customer.setUserid(ids);
                customer.setUsername(userName1);
                customer.setSex(sex);
                customer.setIdnumber(IdNumber);
                customer.setPhone(Phone);
                customer.setUser(User);
                customer.setAudit(audit);
                customer.setPassword(password);
                list.add(customer);
            }
            return list;
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            jdbcUtil.ReleaseResource(connection, ps, rs);
        }
        return null;
    }

    @Override
    public int deleteAdminById(Integer id) {
        Connection connection = jdbcUtil.getConnection();
        PreparedStatement ps = null;
        ResultSet rs = null;
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append("delete from admin where id=?");
        try {
            ps = connection.prepareStatement(stringBuilder.toString());
            ps.setObject(1, id);
            return ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            jdbcUtil.ReleaseResource(connection, ps, rs);
        }
        return 0;
    }

    @Override
    public int updateAdmin(AdminEntity admin) {
        Connection connection = jdbcUtil.getConnection();
        PreparedStatement ps = null;
        ResultSet rs = null;
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append("update admin set user_name=?,pwd=?,state=? where id =?");
        try {
            ps = connection.prepareStatement(stringBuilder.toString());
            ps.setObject(1, admin.getUserName());
            ps.setObject(2, admin.getPwd());
            ps.setObject(3, admin.getState());
            ps.setObject(4, admin.getId());
            return ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            jdbcUtil.ReleaseResource(connection, ps, rs);
        }
        return 0;
    }
}

下面我们来解读一下（下一篇）