linebreak in url with Bibtex and hyperref package

Why is this item not shown properly in my bibliography?

@misc{ann,
    abstract = {ANN is an implbmentation of nearest neighbor search.},
    author = {David M. Mount and Sunil Arya},
    howpublished = {\url{http://www.cs.umd.edu/~mount/ANN/}},
    keywords = {knn},
    posted-at = {2010-04-08 00:05:04},
    priority = {2},
    title = {ANN.},
    url = "http://www.cs.umd.edu/~mount/ANN/",
    year = {2008}
}

@misc{Nilsson96introductionto,  
    author = {Nilsson, Nils J.},  
    citeulike-article-id = {6995464},  
    howpublished = {\url{http://robotics.stanford.edu/people/nilsson/mlbook.html}},  
    keywords = {*file-import-10-04-11},  
    posted-at = {2010-04-11 06:52:28},  
    priority = {2},  
    title = {Introduction to Machine Learning: An Early Draft of a Proposed Textbook.},  
    year = {1996}  
}  

---

EDIT:

I am using

\usepackage{hyperref}

not

\usepackage{url}

. It produces error when using url package together with it. So can the two not work together?

I would like to use hyper links inside pdf file, so I want to use hyperref package instead of url package. I googled a bit, and try

\usepackage[hyperindex,breaklinks]{hyperref}

but there is still no line break just as before. How can I do it?

---

EDIT:

When using url and hyperref together, if it is just

\usepackage{hyperref}  
\usepackage{url}

the compilation by latex is fine, but the link is still hyperlink and has still no linebreak. If I do not use hyperref package, the link has linebreak, but I lose hyper links. Since \url can be used in both hyperref and url packages, how can I specify which package's \url is being used?

If it is

\usepackage{hyperref}  
\usepackage[hyphens]{url}

the compilation by latex command will report clash with url:

! LaTex Error: Option clash for package url.

So I wonder how I should do?

If you mean the too-wide spacing, that's because the URLs seems to not allow line-breaks. Why this happens is another question, and the answer depends on your preamble (the packages you use etc.). In principle, if properly used, the url package should allow line breaks.

EDIT This problem (and its solution) is described here (sending you to a Google cache since the site is offline at the moment). Bottom line: either use the breakurl package, or PDFLaTeX, or both.