package tmall.filter;

import java.io.IOException;
import java.util.List;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.lang.StringUtils;

import tmall.bean.Category;
import tmall.bean.OrderItem;
import tmall.bean.User;
import tmall.dao.CategoryDAO;
import tmall.dao.OrderItemDAO;

public class ForeServletFilter implements Filter{
	
	@Override
	public void destroy() {
		
	}

	@Override
	public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
			throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) res;
		String contextPath=request.getServletContext().getContextPath();
		request.getServletContext().setAttribute("contextPath", contextPath);
		
		User user =(User) request.getSession().getAttribute("user");
		int cartTotalItemNumber= 0;
		if(null!=user){
			List<OrderItem> ois = new OrderItemDAO().listByUser(user.getId());
			for (OrderItem oi : ois) {
				cartTotalItemNumber+=oi.getNumber();
			}
		}
		request.setAttribute("cartTotalItemNumber", cartTotalItemNumber);
		
		List<Category> cs=(List<Category>) request.getAttribute("cs");
		if(null==cs){
			cs=new CategoryDAO().list();
			request.setAttribute("cs", cs);			
		}
		
		String uri = request.getRequestURI();
		uri =StringUtils.remove(uri, contextPath);
		if(uri.startsWith("/fore")&&!uri.startsWith("/foreServlet")){
			String method = StringUtils.substringAfterLast(uri,"/fore" );
			request.setAttribute("method", method);
			req.getRequestDispatcher("/foreServlet").forward(request, response);
			return;
		}
		
		chain.doFilter(request, response);
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		
	}
	
}

package tmall.servlet;

import java.util.List;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import tmall.bean.Category;
import tmall.dao.CategoryDAO;
import tmall.dao.ProductDAO;
import tmall.util.Page;

public class ForeServlet extends BaseForeServlet {
	public String home(HttpServletRequest request, HttpServletResponse response, Page page) {
		List<Category> cs= new CategoryDAO().list();
		new ProductDAO().fill(cs);
		new ProductDAO().fillByRow(cs);
		request.setAttribute("cs", cs);
		return "home.jsp";
	}
}

package tmall.servlet;

import java.lang.reflect.Method;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import tmall.dao.CategoryDAO;
import tmall.dao.OrderDAO;
import tmall.dao.OrderItemDAO;
import tmall.dao.ProductDAO;
import tmall.dao.ProductImageDAO;
import tmall.dao.PropertyDAO;
import tmall.dao.PropertyValueDAO;
import tmall.dao.ReviewDAO;
import tmall.dao.UserDAO;
import tmall.util.Page;

public class BaseForeServlet extends HttpServlet{

	protected CategoryDAO categoryDAO = new CategoryDAO();
	protected OrderDAO orderDAO = new OrderDAO();
	protected OrderItemDAO orderItemDAO = new OrderItemDAO();
	protected ProductDAO productDAO = new ProductDAO();
	protected ProductImageDAO productImageDAO = new ProductImageDAO();
	protected PropertyDAO propertyDAO = new PropertyDAO();
	protected PropertyValueDAO propertyValueDAO = new PropertyValueDAO();
	protected ReviewDAO reviewDAO = new ReviewDAO();
	protected UserDAO userDAO = new UserDAO();
	
	public void service(HttpServletRequest request, HttpServletResponse response) {
		try {
			
			int start= 0;
			int count = 10;
			try {
				start = Integer.parseInt(request.getParameter("page.start"));
			} catch (Exception e) {
				
			}
			
			try {
				count = Integer.parseInt(request.getParameter("page.count"));
			} catch (Exception e) {
			}
			
			Page page = new Page(start,count);
			
			String method = (String) request.getAttribute("method");

			Method m = this.getClass().getMethod(method, javax.servlet.http.HttpServletRequest.class,
					javax.servlet.http.HttpServletResponse.class,Page.class);
			
			String redirect = m.invoke(this,request, response,page).toString();
			
			if(redirect.startsWith("@"))
				response.sendRedirect(redirect.substring(1));
			else if(redirect.startsWith("%"))
				response.getWriter().print(redirect.substring(1));
			else
				request.getRequestDispatcher(redirect).forward(request, response);
			
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			throw new RuntimeException(e);
		}
	}
}

    <servlet>
        <servlet-name>ForeServlet</servlet-name>
        <servlet-class>tmall.servlet.ForeServlet</servlet-class>
    </servlet>
 
    <servlet-mapping>
        <servlet-name>ForeServlet</servlet-name>
        <url-pattern>/foreServlet</url-pattern>
    </servlet-mapping>