三层架构：界面层、业务逻辑层、数据访问层_用户界面层业务逻辑层数据访问层-优快云博客

本文探讨了三层架构，包括界面层、业务逻辑层和数据访问层，并详细说明了Spring如何接管这些层的对象创建。非Spring接管的情况下，分别介绍了实体类、数据访问层、业务逻辑层和服务接口的构建过程。

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1.spring会接管三层架构中的那些对象的创建

2.非spring接管下的三层项目构建：从下往上

1）实体类

com.bjpowernode.pojo Users

package com.bjpowernode.pojo;

public class Users {
    //定义字段
    private int uid;
    private String uname;
    private int uage;

    //构造、get、set、toString方法

    public Users() {  //无参
    }

    public Users(int uid, String uname, int uage) {
        this.uid = uid;  //有参
        this.uname = uname;
        this.uage = uage;
    }

    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 int getUage() {
        return uage;
    }

    public void setUage(int uage) {
        this.uage = uage;
    }

    @Override
    public String toString() {
        return "Users{" +
                "uid=" + uid +
                ", uname='" + uname + '\'' +
                ", uage=" + uage +
                '}';
    }
}

2)数据访问层

com.bjpowernode.dao UsersMapper.java（接口） UsersMapperImpl.java（实现类）

package com.bjpowernode.dao;

import com.bjpowernode.pojo.Users;

public interface UsersMapper {
    //增加用户
    int insert(Users u);
}

package com.bjpowernode.dao;

import com.bjpowernode.pojo.Users;
//数据访问层的实现类
public class UsersMapperImpl implements UsersMapper{
    @Override
    public int insert(Users u) {
        System.out.println(u.getUname()+"用户增加成功");
        return 1;
    }

}

3）业务逻辑层

com.bjpowernode.service.java（接口） UsersServiceImpl.java（实现类）

package com.bjpowernode.service;

import com.bjpowernode.pojo.Users;

public interface UsersService {
    int insert(Users users);

}

package com.bjpowernode.service.impl;
//业务逻辑层的实现类
import com.bjpowernode.dao.UsersMapper;
import com.bjpowernode.dao.UsersMapperImpl;
import com.bjpowernode.pojo.Users;
import com.bjpowernode.service.UsersService;

public class UsersServiceImpl implements UsersService {
    //在所有的业务逻辑层都必定有数据访问层的对象
    //接口指向实现类
    private UsersMapper usersMapper=new UsersMapperImpl();
    @Override
    public int insert(Users users) {
        return usersMapper.insert(users);
    }
}

4）界面层

com.bjpowernode.controller UsersController.java

package com.bjpowernode.controller;

import com.bjpowernode.pojo.Users;
import com.bjpowernode.service.UsersService;
import com.bjpowernode.service.impl.UsersServiceImpl;

//界面层
public class UsersController {
    //如何去访问业务逻辑层，就是创建对象
    //所有的界面层都会有业务逻辑层
    //java宗旨：面向接口编程
    public UsersService usersService=new UsersServiceImpl();
    //界面层的功能实现，对外提供访问的功能
    public int insert(Users users){
        return usersService.insert(users);
    }
}