title: Mongodb saves list of object
body: <p>I know how to save a list of String</p>
  
  <p>Now, e.g. I create my own Animal class</p>
  
  <p>But when I try to save list in mongodb, it gives </p>
  
  <blockquote>
    <p>java.lang.IllegalArgumentException: can't serialize class Project</p>
  </blockquote>
  
  <p>I do create a new mongo collection Animal， but it is still not working.</p>