因为maven下载依赖jar包时，特别慢，所以取消了下载过程，再次打开eclipse时，maven的pom.xml文件报错如下：
ArtifactTransferException: Failure to transfer xom:xom:jar:1.2.5
from http://repo.maven.apache.org/maven2 was cached in the local repository,
resolution will not be reattempted until the update interval of central has elapsed or updates are forced.
Original error: Could not transfer artifact xom:xom:jar:1.2.5
from/to central (http://repo.maven.apache.org/maven2): The operation was cancelled.
解决办法，上面也提到了：updates are forced，强制刷新maven的依赖。
如下图所示：
右键点击项目，然后
然后勾上 Forse update ....，然后maven就会重新自动下载依赖jar包了。