实际上，问题在于在Tomcat 6下，我已经覆盖了默认servlet的定义.

In fact the problem was that under Tomcat 6, I had overrided the definition of the default servlet.

搜索了很长时间之后，我尝试注释默认的servlet定义...并且一切正常.

After having searched long times and long times, I tried commenting the default servlet definition... and everything worked.

因此，在web.xml中，注释以下几行以使它们相同:

So in web.xml, comment the following lines to have the same :

  <!-- 
  <servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>*.png</url-pattern>
    <url-pattern>*.js</url-pattern>
    <url-pattern>*.css</url-pattern>
    <url-pattern>*.gif</url-pattern>
  </servlet-mapping> -->

它修复了所有问题.