也是初级开发的错误:

     在web.xml中设置了
         
   <servlet-mapping>
  <servlet-name>dispatcherServlet</servlet-name>
<!--
<url-pattern>*.do</url-pattern>
<url-pattern>*.screen</url-pattern> -->
<url-pattern>/</url-pattern>
  </servlet-mapping>

     改成了:   <url-pattern>*.do</url-pattern>   就好了

                但不是根本的解决办法.....

在这个网页中找到了原因 :::::: http://love-love-l.blog.163.com/blog/static/21078304201111895950748/
应用springMVC时 JS等文件找不到错误

应用springMVC时如果配置URL映射时如下配置
<servlet>
        <servlet-name>appServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/spring/appServlet/servlet-context.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>appServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

会导致页面引用的JS CSS发生找不到的错误
此时应在web.xml中添加
<servlet-mapping>
        <servlet-name>default</servlet-name>
        <url-pattern>*.css</url-pattern>
    </servlet-mapping>

    <servlet-mapping>
        <servlet-name>default</servlet-name>
        <url-pattern>*.gif</url-pattern>
    </servlet-mapping>

    <servlet-mapping>
        <servlet-name>default</servlet-name>
        <url-pattern>*.jpg</url-pattern>
    </servlet-mapping>

    <servlet-mapping>
        <servlet-name>default</servlet-name>
        <url-pattern>*.js</url-pattern>
    </servlet-mapping>