之前ssm框架没有遇到啥问题，但是学习springboot之后各种问题

1.springboot 版本2.1.6.RELEASE
2.mysql 8.0
3.JDK 1.8
4IDEA 2019版

pom文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.6.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>demo_mapper</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>demo_mapper</name>
<description>Demo project for Spring Boot</description>

<properties>
<java.version>1.8</java.version>
</properties>

<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>

<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.11</version>
</dependency>

<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid-spring-boot-starter</artifactId>
</dependency>

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>

<dependency>
<groupId>org.webjars</groupId>
<artifactId>jquery</artifactId>
<version>3.3.1</version>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis-spring</artifactId>
<version>2.0.0</version>
</dependency>

</dependencies>

<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
<resources>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.xml</include>
</includes>
</resource>
<resource>
<directory>src/main/resources</directory>
</resource>
</resources>
</build>

</project>

项目架构

pojo对象

public class Student {
private Integer id;
private String name;
private Integer age;

public int getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(Integer age) {
this.age = age;
}
}

Mapper

@Repository
public interface StudentMapper {
Student getStudents();
}

mapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.example.springbootsql.mapper.StudentMapper" >

<select id="getStudents" resultType="com.example.springbootsql.pojo.Student">
select * FROM student where id = 1;
</select>
</mapper>

service

public interface StudentService {
Student getStudent();
}

service实现类

@Service
public class StudentServiceImpl implements StudentService {

@Autowired
public StudentMapper mapper;

public Student getStudent(){
return mapper.getStudents();
}
}

Controller

@Controller
public class StudentController {

@Autowired
private StudentService studentService;

@RequestMapping("/getStu")
@ResponseBody
public String getStu(){
Student student = studentService.getStudent();
System.out.println(student.getName());
return "sucess";
}

}

启动类

@MapperScan("com.example.springbootsql.mapper")
@SpringBootApplication
public class SpringbootSqlApplication {

public static void main(String[] args) {
SpringApplication.run(SpringbootSqlApplication.class, args);
}

}

application.yml

spring:
profiles:
active: dev

application-dev.yml

server:
port: 8080

spring:
datasource:
username: root
password: Changeme_123
url: jdbc:mysql://localhost:3306/taotao?serverTimezone=UTC&useSSL=false
driver-class-name: com.mysql.cj.jdbc.Driver

mybatis:
<!--Mapper.xml-->
mapper-locations: classpath:mapping/*.xml
<!--映射别名包-->
type-aliases-package: com.example.springbootsql.pojo

注意事项

1.因为我用的mysql8.0 所以driver-class-name：com.mysql.cj.jdbc.Driver

2.mapper-locations 后面值classpath:mapping/*.xml（写在mapper文件下不行，不知道为什么）

3.datasource在yml文件中不能用提示的date-username date-password不然会抛一个异常java.sql.SQLException: Access denied for user ‘’@‘localhost’ (using password: NO)

4.启动类一定要加上@MapperScan

5.mapper类用@Repository