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1.创建一个springboot的maven项目（完成图中勾选处后，一路next继续）

设置项目的元数据，第一个是包结构（Group），第二个是项目标识（Artifact）：

添加项目所需要的依赖，Web的依赖和数据库的依赖：

第一次建立项目，需要下载许多包，请耐心等待一下。最后pom.xml如下：

   
       
    
     4.0.0
        
            
     
      org.springframework.boot
             
     
      spring-boot-starter-parent
             
     
      2.1.4.RELEASE
             
      
         
        
    
     com.ljy.project
        
    
     springdemo
        
    
     0.0.1-SNAPSHOT
        
    
     springdemo
        
    
     Demo project for Spring Boot
        
            
     
      1.8
         
        
            
                 
      
       org.springframework.boot
                  
      
       spring-boot-starter-jdbc
              
             
                 
      
       org.springframework.boot
                  
      
       spring-boot-starter-web
              
             
                 
      
       org.mybatis.spring.boot
                  
      
       mybatis-spring-boot-starter
                  
      
       2.0.1
              
             
                 
      
       mysql
                  
      
       mysql-connector-java
                  
      
       runtime
              
             
                 
      
       org.springframework.boot
                  
      
       spring-boot-starter-test
                  
      
       test
              
         
        
            
                 
                      
       
        org.springframework.boot
                       
       
        spring-boot-maven-plugin
                   
              
         
    
   

手动添加的dependency需要 右键pom.xml->Maven->Reimport导入依赖。

2.在启动类同级目录下创建domain,dao,service,controller四个目录

在domain文件夹下创建User类：

package com.ljy.project.springdemo.domain;public class User {    private String username;    private String password;    private String patternLock;    public String getUsername() {        return username;    }    public void setUsername(String username) {        this.username = username;    }    public String getPassword() {        return password;    }    public void setPassword(String password) {        this.password = password;    }    public String getPatternLock() {        return patternLock;    }    public void setPatternLock(String patternLock) {        this.patternLock = patternLock;    }}

然后在dao文件夹下创建UserDao接口：

package com.ljy.project.springdemo.dao;import com.ljy.project.springdemo.domain.User;import org.apache.ibatis.annotations.Mapper;import org.apache.ibatis.annotations.Select;import java.util.List;@Mapperpublic interface UserDao {//    List
   
     selectUsers();    @Select("select * from user")    public List
    
      getAllUsers();}
    
   

在service文件夹下创建UserService接口：

package com.ljy.project.springdemo.service;import com.ljy.project.springdemo.dao.UserDao;import com.ljy.project.springdemo.vo.ResultVo;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;@Servicepublic interface UserService {    public ResultVo getAllUsers();    }

该结果返回值类型为ResultVo，在启动类同级目录下创建vo视图文件夹，在vo文件夹下创建ResultVo视图：

package com.ljy.project.springdemo.vo;/*http请求返回的最外层对象*/public class ResultVo
   
     {    private Integer code;    private String msg;    private T data;    private ResultVo(T data){        this.code = 0;        this.msg = "success";        this.data = data;    }    private ResultVo(CodeMsg cm){        if(cm==null){            return;        }else {            this.code = cm.getCode();            this.msg = cm.getMsg();            this.data = null;        }    }    public static 
    
      ResultVo
     
       success(T data){        return new ResultVo
      
       (data);    }    public static 
       
         ResultVo
        
          error(CodeMsg cm){ return new ResultVo
         
          (cm); } public Integer getCode() { return code; } public void setCode(Integer code) { this.code = code; } public String getMsg() { return msg; } public void setMsg(String msg) { this.msg = msg; } public T getData() { return data; } public void setData(T data) { this.data = data; }}
         
        
       
      
     
    
   

在vo文件夹下创建CodeMsg错误码视图：

package com.ljy.project.springdemo.vo;public class CodeMsg {    private int code;    private String msg;    //错误码    public static CodeMsg SUCCESS = new CodeMsg(0,"success");    public static CodeMsg INSERT_ERROR = new CodeMsg(100001,"插入失败");    public static CodeMsg SELECT_ERROR = new CodeMsg(100002,"查询失败");    public static CodeMsg UPDATE_ERROR = new CodeMsg(100003,"更新失败");    public CodeMsg(int code, String msg) {        this.code = code;        this.msg = msg;    }    public int getCode() {        return code;    }    public void setCode(int code) {        this.code = code;    }    public String getMsg() {        return msg;    }    public void setMsg(String msg) {        this.msg = msg;    }}

在service文件夹下创建Impl文件夹，在Impl文件夹下创建UserServiceImpl实现类：

package com.ljy.project.springdemo.service.Impl;import com.ljy.project.springdemo.dao.UserDao;import com.ljy.project.springdemo.domain.User;import com.ljy.project.springdemo.service.UserService;import com.ljy.project.springdemo.vo.CodeMsg;import com.ljy.project.springdemo.vo.ResultVo;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;import java.util.List;@Servicepublic class UserServiceImpl implements UserService {    @Autowired    UserDao userDao;    @Override    public ResultVo getAllUsers() {        List
   
     allUsers = userDao.getAllUsers();        if(allUsers.size()==0){            return ResultVo.error(CodeMsg.SELECT_ERROR);        }else{            return ResultVo.success(allUsers);        }    }}
   

此处别忘了加@Service注解，我忘加了，运行时报如下错误：

Description:Field userService in com.ljy.project.springdemo.controller.UserController required a bean of type 'com.ljy.project.springdemo.service.UserService' that could not be found.The injection point has the following annotations:	- @org.springframework.beans.factory.annotation.Autowired(required=true)Action:Consider defining a bean of type 'com.ljy.project.springdemo.service.UserService' in your configuration.Disconnected from the target VM, address: '127.0.0.1:54425', transport: 'socket'Process finished with exit code 1

在controller文件夹下创建UserController类：

package com.ljy.project.springdemo.controller;import com.ljy.project.springdemo.dao.UserDao;import com.ljy.project.springdemo.domain.User;import com.ljy.project.springdemo.service.UserService;import com.ljy.project.springdemo.vo.ResultVo;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.boot.autoconfigure.EnableAutoConfiguration;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;import javax.xml.ws.RequestWrapper;import java.util.List;@RestController@RequestMapping(value = "/try")@EnableAutoConfigurationpublic class UserController {//    @Autowired//    private UserDao userDao;    @Autowired    private UserService userService;//    @RequestMapping(value = "/user")//    public List
   
     getUsers(){//        return userDao.selectUsers();//    }    @RequestMapping(value = "/getAll")    public ResultVo getAllUsers(){        return userService.getAllUsers();    }}
   

3.创建数据库（与domain中的实体类对应）

create table User(  id          int auto_increment    primary key,  username    varchar(20)  null,  password    varchar(500) null,  patternlock varchar(30)  null);

向数据库中插入测试数据：

insert into User(username, password, patternlock) values ('zhangsan','123456','123456');insert into User(username, password, patternlock) values ('lisi','123456','123456');insert into User(username, password, patternlock) values ('wangwu','123456','123456');

4.在application.properties里面进行配置

spring.datasource.url=jdbc:mysql://127.0.0.1:3306/你的数据库名?useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMTspring.datasource.username=你的用户名spring.datasource.password=你的密码spring.datasource.driver-class-name=com.mysql.jdbc.Driver mybatis.typeAliasesPackage=你的实体类包名 （例子项目的包名是com.ljy.project.springdemo.domain）mybatis.mapperLocations=classpath:mapper/*.xmllogging.level.com.shizhao.project.springdemo:DEBUGserver.port=你的服务端口号，要保证与其他服务不冲突，如8080

我的配置如下：

spring.datasource.url=jdbc:mysql://127.0.0.1:3306/dbgirl?useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMTspring.datasource.username=rootspring.datasource.password=newpassspring.datasource.driver-class-name=com.mysql.cj.jdbc.Drivermybatis.typeAliasesPackage=com.ljy.project.springdemo.domainmybatis.mapperLocations=classpath:mapper/*.xmllogging.level.com.shizhao.project.springdemo:DEBUGserver.port=8080

5.启动程序，在浏览器地址栏输入，得到结果：

此处能看到返回值为json格式，是因为我使用了插件：

到此，创建springboot+mybatis且返回值带错误码的项目创建成功。

补充：

sql语句除了能通过注解写在UserDao中外，还能写在mapper.xml中。在resources文件夹下创建mapper文件夹，在mapper文件夹下创建UserMapper.xml文件：

   
       
            
             
             
         
        
            SELECT * FROM User    
   

在UserDao中使用：

在UserController中直接调用：

在浏览器地址栏中输入,结果如下：

 完整版项目连接：

本来只是想分享，但是CSDN上传资源下载积分不能自己设定了，所以下面提供了百度网盘下载连接：

链接：https://pan.baidu.com/s/1v5CdCY-QOet5lG6Q0cGCHA 

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