Why a file always missing after build in Intellij with maven?

Why a file always missing after build in Intellij with maven?

I have been stuck in the problem for quite a while.I use Intellij and
maven not very long. the problem like this:
the version of my Intellij is 12.1.4,I am making a project of Spring MVC
with maven.So the output directory is 'target' in the project workspace.I
have a mybatis xml file in my path.
once I found that the xml file did not change autoautomaticly in the
target directory.so I delete it in the target directory.after I have done
this,I rebuild the project,but the file never appear any more.
why?how should I do?