Mybatis入门:
目录
2.9 应用启动层StudentmybatisspringApplication
一、spring boot 应用mybatis 核心
spring boot 应用mybatis 核心，就是把mybatis 的mapper 通过spring注入实例。
二、举例：
2.1 背景
实现一个查询的接口，返回结果为多个实例的集合。
select * from MyStudent where name = #{name}
2.2 项目结构：
相对于单纯的mybatis 使用，spring boot 应用mybatis 缺少了mybatis 的总配置文件。
2.3 依赖包 pom
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation=
"http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0
</modelVersion>
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<parent>
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<groupId>org.springframework.boot
</groupId>
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<artifactId>spring-boot-starter-parent
</artifactId>
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<version>2.4.4
</version>
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<relativePath/>
<!-- lookup parent from repository -->
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</parent>
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<groupId>com.example
</groupId>
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<artifactId>studentmybatisspring
</artifactId>
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<version>0.0.1-SNAPSHOT
</version>
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<name>studentmybatisspring
</name>
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<description>Demo project for Spring Boot
</description>
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<properties>
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<java.version>1.8
</java.version>
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</properties>
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<dependencies>
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<dependency>
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<groupId>org.springframework.boot
</groupId>
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<artifactId>spring-boot-starter-web
</artifactId>
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</dependency>
-
-
<dependency>
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<groupId>org.springframework.boot
</groupId>
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<artifactId>spring-boot-starter-test
</artifactId>
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<scope>test
</scope>
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</dependency>
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<dependency>
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<groupId>org.projectlombok
</groupId>
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<artifactId>lombok
</artifactId>
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</dependency>
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<dependency>
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<groupId>mysql
</groupId>
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<artifactId>mysql-connector-java
</artifactId>
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<version>8.0.20
</version>
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</dependency>
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<dependency>
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<groupId>org.mybatis.spring.boot
</groupId>
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<artifactId>mybatis-spring-boot-starter
</artifactId>
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<version>2.1.4
</version>
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</dependency>
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</dependencies>
-
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<build>
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<plugins>
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<plugin>
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<groupId>org.springframework.boot
</groupId>
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<artifactId>spring-boot-maven-plugin
</artifactId>
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</plugin>
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</plugins>
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</build>
-
-
</project>
2.4 项目配置文件application.yml
application.yml
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server:
-
port:
8080
-
-
spring:
-
datasource:
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url:
jdbc:
mysql:/
/124.70.87.136:3306/chen?useUnicode=
true&characterEncoding=UTF-
8
-
username: root
-
password:
123456
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driver-
class-name: com.mysql.cj.jdbc.Driver
-
-
logging:
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level:
-
com.example.studentmybatisspring.
mapper: debug
里面包含项目端口信息
数据库连接信息
以及开启查看执行sql的日志。
这里设置查看日志，我们一般只设置查看对应包的日志。这里是想要查看的包名。
这个mapper就是我们mabits里面的mapper。
当我们启动项目，触发相应的sql时，就会显示对应的sql日志。
2.5 实例层entity
存放的是我们需要的实例。
ResultMsg，我们用来封装接口的返回结果。
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package com.example.studentmybatisspring.entity;
-
-
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import lombok.AllArgsConstructor;
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import lombok.Data;
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import lombok.NoArgsConstructor;
-
-
@Data
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@NoArgsConstructor
-
@AllArgsConstructor
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public
class
ResultMsg<T> {
-
public
static
final
String
SUCCESS_NO
=
"200";
-
public
static
final
String
SUCCESS_SUCCESS
=
"success";
-
-
private String no;
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private String msg;
-
private T data;
-
-
public
ResultMsg
(String no, String msg) {
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this.no = no;
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this.msg = msg;
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}
-
-
public
static <T> ResultMsg<T>
success
(T data){
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return
new
ResultMsg(SUCCESS_NO,SUCCESS_SUCCESS,data);
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}
-
-
public
static <T> ResultMsg<T>
error
(String no,String msg){
-
return
new
ResultMsg(no,msg);
-
}
-
}
MyStudent，是数据库里MyStudent表对应的实例。
数据库的表：
对应表的实例MyStudent
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package com.example.studentmybatisspring.entity;
-
-
import lombok.AllArgsConstructor;
-
import lombok.Data;
-
import lombok.NoArgsConstructor;
-
-
@Data
-
@NoArgsConstructor
-
@AllArgsConstructor
-
public
class
MyStudent {
-
private
long id;
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private String name;
-
private
int age;
-
-
public
MyStudent
(String name, int age) {
-
this.name = name;
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this.age = age;
-
}
-
-
public
MyStudent
(String name) {
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this.name = name;
-
}
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}
2.6 mybatis的mapper层
接口：MyStudentMapper
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package com.example.studentmybatisspring.mapper;
-
-
import com.example.studentmybatisspring.entity.MyStudent;
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import org.apache.ibatis.annotations.Select;
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import org.springframework.stereotype.Repository;
-
-
import java.util.List;
-
-
@Repository
-
public
interface
MyStudentMapper {
-
-
@Select("select * from MyStudent where name = #{name}")
-
List<MyStudent>
findByName
(String name);
-
}
接口：MyStudentMapper中，包含sql语句，以及sql语句对应的方法。
2.7 spring boot service 层
service接口
-
package com.example.studentmybatisspring.service;
-
-
import com.example.studentmybatisspring.entity.MyStudent;
-
-
import java.util.List;
-
-
public
interface
MyStudentService {
-
List<MyStudent>
findByName
(String name);
-
-
}
service实现类
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package com.example.studentmybatisspring.service.impl;
-
-
import com.example.studentmybatisspring.entity.MyStudent;
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import com.example.studentmybatisspring.mapper.MyStudentMapper;
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import com.example.studentmybatisspring.service.MyStudentService;
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import org.springframework.beans.factory.annotation.Autowired;
-
import org.springframework.stereotype.Service;
-
-
import java.util.List;
-
-
@Service
-
public
class
MyStudentServiceImpl
implements
MyStudentService {
-
-
@Autowired
-
private MyStudentMapper myStudentMapper;
-
-
@Override
-
public List<MyStudent>
findByName
(String name) {
-
return myStudentMapper.findByName(name);
-
}
-
-
-
}
我们在spring boot service 实现类中，注入了mybatis 的 mapper接口。
2.8 controller层
MyStudentController
-
package com.example.studentmybatisspring.controller;
-
-
import com.example.studentmybatisspring.entity.MyStudent;
-
import com.example.studentmybatisspring.entity.ResultMsg;
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import com.example.studentmybatisspring.service.MyStudentService;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.web.bind.annotation.RequestMapping;
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import org.springframework.web.bind.annotation.RestController;
-
-
import java.util.List;
-
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@RestController
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@RequestMapping("/chen")
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public
class
MyStudentController {
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@Autowired
-
private MyStudentService myStudentService;
-
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@RequestMapping("/findByName")
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public ResultMsg<List<MyStudent>>
findByName
(String name){
-
List<MyStudent> byName = myStudentService.findByName(name);
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return ResultMsg.success(byName);
-
}
-
}
2.9 应用启动层StudentmybatisspringApplication
我们需要在项目启动层，增加mapper的扫描。
相对于单纯的mybatis 使用，spring boot 应用mybatis 缺少了mybatis 的总配置文件。
这里填写包名。@MapperScan(basePackages =
-
package com.example.studentmybatisspring;
-
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import org.mybatis.spring.annotation.MapperScan;
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import org.springframework.boot.SpringApplication;
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import org.springframework.boot.autoconfigure.SpringBootApplication;
-
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@SpringBootApplication
-
@MapperScan(basePackages = "com.example.studentmybatisspring.mapper")
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public
class
StudentmybatisspringApplication {
-
-
public
static
void
main
(String[] args) {
-
SpringApplication.run(StudentmybatisspringApplication.class, args);
-
}
-
-
}
在浏览器里访问：
在控制台显示sql日志
三、数据库字段名称与java实体类字段名称不一致
同一个表，数据库的字段名称，与java实体类字段名称不一致。
如数据库中，字段名称为user_id
但是在java项目中，实体类的名称为驼峰格式，userId。
我们需要在application.yml，开启驼峰命名的映射。
转载：https://blog.csdn.net/qq_39208536/article/details/128167464
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