我按照第9章的过滤器案例做的，为什么eclipse上显示出错啊?
package c2;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
/**
 * 统计过滤器
 * @author Li YongQiang
 */
public class CountFilter implements Filter {
// 来访数量
private int count;

@Override
public void init(FilterConfig filterConfig) throws ServletException {
// 获取初始化参数
String param = filterConfig.getInitParameter("count");
// 将字符串转换为int
count = Integer.valueOf(param);
}

@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
// 访问数量自增
count ++;
// 将ServletRequest转换成HttpServletRequest
HttpServletRequest req = (HttpServletRequest) request;
// 获取ServletContext
ServletContext context = req.getSession().getServletContext();
// 将来访数量值放入到ServletContext中
context.setAttribute("count", count);
// 向下传递过滤器
chain.doFilter(request, response);
}

@Override
public void destroy() {

}
}