title: android can not find a class 'javax.activation.MimetypesFileTypeMap', but that class is in the jre libs locates at rt.jar
body: <p>In my android project, I use a external jar which will use the class</p>
  
  <p>Here is the error information:</p>
  
  <p>06-13 02:45:18.586: ERROR/dalvikvm(228): Could not find class <code>'javax.activation.MimetypesFileTypeMap', referenced from method weibo4j.http.HttpClient.multPartURL</code></p>
  
  <p>Who can tell me why this happened?</p>