maven settings.xml profiles中配置的repository不起作用

maven settings.xml profiles中配置的repository不起作用， 下载包的时候还是去maven中央库而不是阿里云maven库，求解。

 <profiles>
            <profile>
                <id>prod</id>
                <repositories>
                    <repository>
                        <id>aliyun</id>

                        <url>http://maven.aliyun.com/nexus/content/groups/public/</url>
                        <layout>default</layout>
                    </repository>
                </repositories>
            </profile>
        </profiles>

        <activeProfiles>
            <activeProfile>prod</activeProfile>
        </activeProfiles>

 <profiles> 
        <profile> 
            <id>nexus</id> 
            <repositories> 
                <repository> 
                    <id>nexus</id> 
                    <name>nexus repository</name> 
                    <url>http://192.168.3.253:8081/nexus/content/groups/public/</url> 
                    <releases> 
                        <enabled>true</enabled> 
                    </releases> 
                    <snapshots> 
                        <enabled>true</enabled> 
                    </snapshots> 
                </repository> 
            </repositories> 
            <pluginRepositories> 
                <pluginRepository> 
                    <id>nexus</id> 
                    <name>nexus repository</name> 
                    <url>http://192.168.3.253:8081/nexus/content/groups/public/</url> 
                    <releases> 
                        <enabled>true</enabled> 
                    </releases> 
                    <snapshots> 
                        <enabled>true</enabled> 
                    </snapshots> 
                </pluginRepository> 
            </pluginRepositories> 
        </profile>
        <profile>   
            <id>jdk1.7</id>    
            <activation>   
                <activeByDefault>true</activeByDefault>    
                <jdk>1.7</jdk>   
            </activation>    
            <properties>   
                <maven.compiler.source>1.7</maven.compiler.source>    
                <maven.compiler.target>1.7</maven.compiler.target>    
                <maven.compiler.compilerVersion>1.7</maven.compiler.compilerVersion>   
            </properties>   
        </profile>
    </profiles> 

http://192.168.3.253:8081/nexus/content/groups/public/改成http://maven.aliyun.com/nexus/content/groups/public/试试看！

我的解决方法是把repository的id改成central，这样我理解所有本来去central下载的包会去阿里的仓库下载。但我不确定这样子是不是最佳方案。

<repository>
                    <id>central</id>
                    <url>http://maven.aliyun.com/nexus/content/groups/public/</url>

为啥不直接该setting,xml里的mirror啊？