public void setFileSystemId(String fileSystemId) {
        this.fileSystemId = fileSystemId;
    }
<p>
(Optional) ID of the file system whose description you want to retrieve (String).
</p>

@param fileSystemId
       (Optional) ID of the file system whose description you want to retrieve (String).
aws-java-sdk-efs/src/main/java/com/amazonaws/services/elasticfilesystem/model/DescribeFileSystemsRequest.java