轉載自：https://blog.csdn.net/AinUser/article/details/81533858

第一種情況:

在application.properties/或者application.yml檔案中沒有新增資料庫配置資訊

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/read_data?useUnicode=true&characterEncoding=UTF-8&useSSL=false
    username: root
    password: 123456
    driver-class-name: com.mysql.jdbc.Driver
 

第二種情況

yml或者properties檔案沒有被掃描到

需要在pom檔案中<build></build>新增如下

<!-- 如果不新增此節點mybatis的mapper.xml檔案都會被漏掉。 -->
<resources>
    <resource>
        <directory>src/main/java</directory>
        <includes>
            <include>**/*.yml</include>
            <include>**/*.properties</include>
            <include>**/*.xml</include>
        </includes>
        <filtering>false</filtering>
    </resource>
    <resource>
        <directory>src/main/resources</directory>
        <includes>
            <include>**/*.yml</include>
            <include>**/*.properties</include>
            <include>**/*.xml</include>
        </includes>
        <filtering>false</filtering>
    </resource>
</resources>