怎样解决这个错误呢？？？？？？

再你的CLASSPATH中指明servlet.jar的路径
我的是：D:\TOMCAT\lib\servlet.jar
javax.servlet包包含的类主要有:
F:\java>jar -ft servlet.jar
META-INF/
META-INF/MANIFEST.MF
javax/
javax/servlet/
javax/servlet/http/
javax/servlet/jsp/
javax/servlet/jsp/tagext/
javax/servlet/http/Cookie.class
javax/servlet/http/HttpServlet.class
javax/servlet/http/NoBodyResponse.class
javax/servlet/http/NoBodyOutputStream.class
javax/servlet/http/HttpServletRequest.class
javax/servlet/http/HttpServletResponse.class
javax/servlet/http/HttpSession.class
javax/servlet/http/HttpSessionBindingEvent.class
javax/servlet/http/HttpSessionBindingListener.class
javax/servlet/http/HttpSessionContext.class
javax/servlet/http/HttpUtils.class
javax/servlet/http/LocalStrings.properties
javax/servlet/http/LocalStrings_es.properties
javax/servlet/jsp/tagext/BodyContent.class
javax/servlet/jsp/tagext/BodyTag.class
javax/servlet/jsp/tagext/BodyTagSupport.class
javax/servlet/jsp/tagext/Tag.class
javax/servlet/jsp/tagext/TagAttributeInfo.class
javax/servlet/jsp/tagext/TagData.class
javax/servlet/jsp/tagext/TagExtraInfo.class
javax/servlet/jsp/tagext/TagInfo.class
javax/servlet/jsp/tagext/TagLibraryInfo.class
javax/servlet/jsp/tagext/TagSupport.class
javax/servlet/jsp/tagext/VariableInfo.class
javax/servlet/jsp/HttpJspPage.class
javax/servlet/jsp/JspEngineInfo.class
javax/servlet/jsp/JspException.class
javax/servlet/jsp/JspFactory.class
javax/servlet/jsp/JspPage.class
javax/servlet/jsp/JspTagException.class
javax/servlet/jsp/JspWriter.class
javax/servlet/jsp/PageContext.class
javax/servlet/GenericServlet.class
javax/servlet/RequestDispatcher.class
javax/servlet/Servlet.class
javax/servlet/ServletConfig.class
javax/servlet/ServletContext.class
javax/servlet/ServletException.class
javax/servlet/ServletInputStream.class
javax/servlet/ServletOutputStream.class
javax/servlet/ServletRequest.class
javax/servlet/ServletResponse.class
javax/servlet/SingleThreadModel.class
javax/servlet/UnavailableException.class
javax/servlet/LocalStrings.properties