Unless you are specifically looking to write a Java program to do this, the simplest way is to use the MS Word 'Save As' option and select HTML as the format.
If you dont already own Word, the free Open Office editor can save in a variety of formats. There is supposed to be a way to automate processing multiple files automatically with Open Office but I have not used it.
Unfortunately, both Word and OO save ghastly HTML that is incredibly bulky with needless repeated formatting that could be replaced with CSS.