在调用javaScript前要先引入刚才在dwr.xml中定义的javaScript
  <script type='text/javascript' src='dwr/interface/MyTest.js'></script>
  <script type='text/javascript' src='dwr/interface/showData.js'></script>
  <script type='text/javascript' src='dwr/engine.js'></script>
  <script type='text/javascript' src='dwr/util.js'></script>
  前面两行是我们刚才定义的javaScript的引入，后面两行是dwr中的本身定义的javaScript