MVC初识

MVC,即Model,View,Controller。
MVC可以理解为一种代码组织方式,它可以为代码的编写降低一些成本。
下面通过一个项目的代码来体验一下MVC:

项目简介:在数据库中有一张表account,存放着用户的账号、密码、用户名、余额。本项目要实现对account表的增删查改。

account表的定义:

create table account(
    id int primary key auto_increment,
    account_name varchar(30),
    account_pwd varchar(30),
    account_no varchar(30),
    account_balance int
);

entity层Account类定义:

/**
 * 
 * @TableName account
 */
@Data
public class Account implements Serializable {
    //
    private Integer id;
    
    private String accountName;

    //
    private String accountPwd;

    //
    private String accountNo;

    //
    private Integer accountBalance;

    private static final long serialVersionUID = 1L;

    @Override
    public boolean equals(Object that) {
        if (this == that) {
            return true;
        }
        if (that == null) {
            return false;
        }
        if (getClass() != that.getClass()) {
            return false;
        }
        Account other = (Account) that;
        return (this.getId() == null ? other.getId() == null : this.getId().equals(other.getId()))
            && (this.getAccountName() == null ? other.getAccountName() == null : this.getAccountName().equals(other.getAccountName()))
            && (this.getAccountPwd() == null ? other.getAccountPwd() == null : this.getAccountPwd().equals(other.getAccountPwd()))
            && (this.getAccountNo() == null ? other.getAccountNo() == null : this.getAccountNo().equals(other.getAccountNo()))
            && (this.getAccountBalance() == null ? other.getAccountBalance() == null : this.getAccountBalance().equals(other.getAccountBalance()));
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((getId() == null) ? 0 : getId().hashCode());
        result = prime * result + ((getAccountName() == null) ? 0 : getAccountName().hashCode());
        result = prime * result + ((getAccountPwd() == null) ? 0 : getAccountPwd().hashCode());
        result = prime * result + ((getAccountNo() == null) ? 0 : getAccountNo().hashCode());
        result = prime * result + ((getAccountBalance() == null) ? 0 : getAccountBalance().hashCode());
        return result;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append(getClass().getSimpleName());
        sb.append(" [");
        sb.append("Hash = ").append(hashCode());
        sb.append(", id=").append(id);
        sb.append(", accountName=").append(accountName);
        sb.append(", accountPwd=").append(accountPwd);
        sb.append(", accountNo=").append(accountNo);
        sb.append(", accountBalance=").append(accountBalance);
        sb.append(", serialVersionUID=").append(serialVersionUID);
        sb.append("]");
        return sb.toString();
    }
}

mapper层的AccountMapper接口定义:

/**
* @author Administrator
* @description 针对表【account】的数据库操作Mapper
* @createDate 2022-08-12 16:19:39
* @Entity com.wn.ssm080812.entity.Account
*/
public interface AccountMapper {

    int deleteByPrimaryKey(Long id);

    int insert(Account record);

    int insertSelective(Account record);

    Account selectByPrimaryKey(Long id);

    Account login(String accountName,String accountPwd);

    List<Account> queryAll();

    int updateByPrimaryKeySelective(Account record);

    int updateByPrimaryKey(Account record);

}

service层的AccountService接口定义:

public interface AccountService {
    int deleteByPrimaryKey(Long id);

    int insert(Account record);

    int insertSelective(Account record);

    Account selectByPrimaryKey(Long id);

    Account login(String accountName,String accountPwd);

    List<Account> queryAll();

    int updateByPrimaryKeySelective(Account record);

    int updateByPrimaryKey(Account record);
}

service层的AccountServiceImpl类定义:

@Service
public class AccountServiceImpl implements AccountService {
    @Autowired
    private AccountMapper accountMapper;

    @Override
    public int deleteByPrimaryKey(Long id) {
        return accountMapper.deleteByPrimaryKey(id);
    }

    @Override
    public int insert(Account record) {

        return accountMapper.insert(record);
    }

    @Override
    public int insertSelective(Account record) {
        return 0;
    }

    @Override
    public Account selectByPrimaryKey(Long id) {

        return accountMapper.selectByPrimaryKey(id);
    }

    @Override
    public Account login(String accountName, String accountPwd) {

        return accountMapper.login(accountName,accountPwd);
    }

    @Override
    public List<Account> queryAll() {
        return accountMapper.queryAll();
    }

    @Override
    public int updateByPrimaryKeySelective(Account record) {
        return 0;
    }

    @Override
    public int updateByPrimaryKey(Account record) {

        return accountMapper.updateByPrimaryKey(record);
    }
}

Controller层的AccountController定义:

@RestController
@RequestMapping("account")
public class AccountController {
    @Autowired
    private AccountService accountService;

    @GetMapping(value = "loginDo")
    @ResponseBody
    public Result login(String accountName, String accountPwd, HttpSession session){

        Account account = accountService.login(accountName, accountPwd);
        if(account!=null){
            session.setAttribute("account",account);
            return Result.ok();
        }else {
            return Result.error("用户名或密码错误");
        }


    }

    @GetMapping(value = "queryAll")
    @ResponseBody
    public Result queryAll(){

        List<Account> list = accountService.queryAll();
        return Result.ok().data("list",list);
    }

    @GetMapping(value = "queryById")
    @ResponseBody
    public Result queryById(Long id){
        Account account = accountService.selectByPrimaryKey(id);
        return Result.ok().data("account",account);

    }

    @PostMapping(value = "/addDo")
    @ResponseBody
    public Object add(Account account){

        int result = accountService.insert(account);
        HashMap<String, Integer> map = new HashMap<>();
        map.put("code",result>0 ? 200 : 500);
        return map;
    }

    @GetMapping(value = "delete")
    @ResponseBody
    public Object delete(Long id){

        int result = accountService.deleteByPrimaryKey(id);
        HashMap<String, Integer> map = new HashMap<>();
        map.put("code",result>0 ? 200 : 500);
        return map;
    }

    @PostMapping(value = "update")
    @ResponseBody
    public void update(Account account){

        int result = accountService.updateByPrimaryKey(account);
        HashMap<String, Integer> map = new HashMap<>();
        map.put("code",result>0 ? 200 : 500);
    }

}

Controller层的IndexController定义:

@Controller
public class IndexController {
    @RequestMapping("account")
    public String toAccount(){

        return "account/account";
    }

    @RequestMapping("login")
    public String toLogin(){

        return "/WEB-INF/static/login.html";
    }

    @RequestMapping("admin")
    public String toAdmin(){

        return "/WEB-INF/static/admin.html";
    }
}

MVC中的M对应项目的service层、mapper层,V对应项目的webapp.WEB-INF.templates(存放页面),C对应项目的controller层。

1.页面用于展示数据。
2.controller层用于接收不同的HTTP请求并将数据返回给网页。
3.service层用于接收controller层的调用，实现具体业务，并将数据返回给controller层。
4.mapper层用于接收service层的调用,实现对数据库中account表的增删查改，并将数据返回给service层。

MVC使用面向接口编程的风格，这样使得各层实现类的替换比较简单，使用实现类的上层类中几乎无需变更，特别是在使用了IOC(Inversion Of Control)容器的时候。
因为采用了分层管理代码,在开发时，如果应用报错，可以将问题锁定在某一层。