Failed to configure a DataSource: ‘url‘ attribute is not specified and no Reaso（附解决思路）

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APPLICATION FAILED TO START
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Description:

Failed to configure a DataSource: 'url' attribute is not specified and no embedded datasource could be configured.

Reason: Failed to determine a suitable driver class


Action:

Consider the following:
 If you want an embedded database (H2, HSQL or Derby), please put it on the classpath.
 If you have database settings to be loaded from a particular profile you may need to activate it (no profiles are currently active).

@MapperScan("com.wsc.core.mapper")//映射mapper地址
@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})　　//启动类 SpringBoot
public class Start {
    public static void main(String[] args) {
        SpringApplication.run(Start.class,args);
    }
}

# sharding-jdbc 水平分表策略
# 配置数据源，给数据源起别名  m1 起的名字随意单要和下面的一致
spring.shardingsphere.datasource.names=m1

# 一个实体类对应两张表，覆盖
spring.main.allow-bean-definition-overriding=true

# 配置数据源的具体内容，包含连接池，驱动，地址，用户名，密码  druid单独配置
spring.shardingsphere.datasource.m1.type=com.alibaba.druid.pool.DruidDataSource
#com.mysql.cj.jdbc.Driver 8版本      我本地数据版本低 5.7
spring.shardingsphere.datasource.m1.driver-class-name=com.mysql.cj.jdbc.Driver
#高版本加入了时区  jdbc:mysql://localhost:3306/course_db?serverTimezone=GMT%2B8
spring.shardingsphere.datasource.m1.url=jdbc:mysql://127.0.0.1:3306/course_db?serverTimezone=GMT%2B8
spring.shardingsphere.datasource.m1.username=root
spring.shardingsphere.datasource.m1.password=root
# 指定course表分布的情况，配置表在哪个数据库里，表的名称都是什么  course 表规则（暂时这么理解）  m1.course_$->{1..2}=m1.course_1,m1.course_2
spring.shardingsphere.sharding.tables.course.actual-data-nodes=m1.course_$->{1..2}

# 指定 course 表里面主键 cid 的生成策略| SNOWFLAKE 雪花算法生成一个唯一的字符串
spring.shardingsphere.sharding.tables.course.key-generator.column=cid
spring.shardingsphere.sharding.tables.course.key-generator.type=SNOWFLAKE

# 配置分表策略    约定 cid 值偶数添加到 course_1 表，如果 cid 是奇数添加到 course_2 表
spring.shardingsphere.sharding.tables.course.table-strategy.inline.sharding-column=cid
#这部分理解起来比较复杂我这边就啰嗦下:course_$->{cid % 2 + 1}    course_也是相当于对应表空间m1.course_1
#cid 是他的主键的iD cid % 2 + 1  举例说明下： 当cid =(偶数)4/2余0 0+1=1 那么他的数据就在  course_1 中，上面指定了2个 1.course_$->{1..2}
#其余的结果就都匹配上面的 2 我理解的就是 不满足条件1 就都是条件2的东西
spring.shardingsphere.sharding.tables.course.table-strategy.inline.algorithm-expression=course_$->{cid % 2 + 1}
# 打开 sql 输出日志
spring.shardingsphere.props.sql.show=true

   <dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>druid-spring-boot-starter</artifactId>
                <version>1.1.14</version>
            </dependency>

   <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
        <!--新增加入的 -->


        <resources>



            <resource>

                <!--指定根目录 到源文件夹 一般如下-->

                <directory>src/main/java</directory>

                <includes>

                    <include>**/*.yml</include>

                    <include>**/*.yaml</include>

                    <include>**/*.xml</include>

                    <include>**/*.properties</include>

                </includes>

                <filtering>false</filtering>

            </resource>

            <resource> <!--指定根目录 到源文件夹 一般如下-->

                <directory>src/main/resources</directory>

                <includes>

                    <include>**/*.yml</include>

                    <include>**/*.yaml</include>

                    <include>**/*.xml</include>

                    <include>**/*.properties</include>

                </includes>
                <filtering>false</filtering>
            </resource>
        </resources>
   <!--新增加入的 -->
    </build>

 <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

<dependency>
            <groupId>org.apache.shardingsphere</groupId>
            <artifactId>sharding-jdbc-spring-boot-starter</artifactId>
            <version>4.0.0-RC1</version>
        </dependency>