title: Map implementation with duplicate keys
body: <p>I want to have a map with duplicate keys.</p>
  
  <p>I know there are many map implementations (Eclipse shows me about 50), so I bet there must be one that allows this. I know it's easy to write your own map that does this, but I would rather use some existing solution.</p>
  
  <p>Maybe something in commons-collections or google-collections?</p>