異常：The build could not read 1 project -> [Help 1]   
The project com.atguigu.gulimail:gulimail-coupon:0.0.1-SNAPSHOT (D:\gulimail\gulimail-coupon\pom.xml) has 1 error  
Non-resolvable import POM: Failure to find org.springframework.cloud:spring-cloud-dependencies:pom:2020.0.0-M5 in http://maven.aliyun.com/nexus/content/groups/public was cached in the local repository, resolution will not be reattempted until the update interval of nexus-aliyun has elapsed or updates are forced @ line 42, column 25 -> 
[Help 2] To see the full stack trace of the errors, re-run Maven with the -e switch. Re-run Maven using the -X switch to enable full debug logging. For more information about the errors and possible solutions, please read the following articles: [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/ProjectBuildingException 
[Help 2] http://cwiki.apache.org/confluence/display/MAVEN/UnresolvableModelException
解決：
<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>${spring-cloud.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>
改為

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-alibaba-dependencies</artifactId>
            <version>2.1.0.RELEASE</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>