看源碼的小伙伴，記得加上相關(guān)的 maven 依賴項(xiàng)，不然會(huì)出現(xiàn)老師有某個(gè)實(shí)現(xiàn)類而你沒有的情況

<!-- 查看源碼需要使用到的依賴 -->
<dependency>
    <groupId>org.apache.hadoop</groupId>
    <artifactId>hadoop-hdfs-client</artifactId>
    <version>3.1.3</version>
</dependency>

<!-- Yarn 源碼 -->
<dependency>
    <groupId>org.apache.hadoop</groupId>
    <artifactId>hadoop-yarn-server-resourcemanager</artifactId>
    <version>3.1.3</version>
</dependency>

<dependency>
    <groupId>org.apache.hadoop</groupId>
    <artifactId>hadoop-mapreduce-client-app</artifactId>
    <version>3.1.3</version>
</dependency>