springBoot2整合pagehelper的爬坑经历

<parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.heke</groupId>
    <artifactId>ssm</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>ssm</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.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>1.3.2</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper-spring-boot-starter</artifactId>
            <version>1.2.12</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.10</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

##helperDialect: mysql
##reasonable: true
##supportMethodsArguments: true
##parames: count=countSql
server.port=8081

#mysql
spring.datasource.driver-class-name = com.mysql.jdbc.Driver
spring.datasource.url= jdbc:mysql://localhost:3306/hake?serverTimezone=Asia/Shanghai&characterEncoding=utf8
spring.datasource.username = root
spring.datasource.password = longfor

mybatis.mapper-locations = classpath*:mapper/*.xml
mybatis.type-aliases-package=heke.ssm

/**
 * @Author: Liu Yue
 * @Descripition:
 * @Date; Create in 2020/2/15 16:00
 **/
@Mapper
public interface UserMapper {
    List<User> findAll();
}

<mapper namespace="com.heke.ssm.UserMapper">
    <select id="findAll" parameterType="java.lang.String" resultType="com.heke.ssm.User" >
        select * from user
    </select>
</mapper>

import lombok.Data;

@Data
public class User {
    // 主键id
    private Integer id;
    private String name;
    private Integer age;
}

@Slf4j
@RestController
@RequestMapping("/user")
public class UserController {

    @Autowired
    private UserMapper userMapper;


    @GetMapping("/findAll")
    public List<User> findAll(@RequestParam(defaultValue = "1") Integer pageNum, @RequestParam(defaultValue = "20") Integer pageSize) {
        PageHelper.startPage(pageNum, pageSize);
        List<User> countries = userMapper.findAll();

        PageInfo<User> page = PageInfo.of(countries);
        System.out.println("每页展示条数：" + page.getPageSize());
        System.out.println("总条数：" + page.getTotal());
        System.out.println("当前页：" + page.getPageNum());
        System.out.println("总页数：" + page.getPages());

        return countries;
    }
}

@SpringBootApplication
@MapperScan("heke.ssm")
public class SsmApplication {

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

}

错误的启动类
 @SpringBootApplication(exclude = {
         DataSourceAutoConfiguration.class
 })
 @MapperScan("heke.ssm")
 @EnableScheduling
 @ComponentScan(value = {"com"})
 public class SsmApplication {
    public static void main(String[] args) {
         SpringApplication.run(SsmApplication.class, args);
     }
}
 DataSourceAutoConfiguration的类解读可以参考这位师兄的博客
 https://blog.csdn.net/kangsa998/article/details/90231518

CREATE TABLE `user` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `name` varchar(20) COLLATE utf8mb4_unicode_ci DEFAULT NULL COMMENT '姓名',
  `age` int(3) DEFAULT NULL COMMENT '年龄',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci