[初学]过滤器的使用

import java.io.IOException;

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 javax.servlet.http.HttpSession;

//二.过滤器的使用：
public class LoginFilter implements Filter {

	public void destroy() {
	}

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		HttpServletRequest httpRequest = (HttpServletRequest) request;
		HttpServletResponse httpResponse = (HttpServletResponse) response;
		HttpSession session = httpRequest.getSession();
		User userBean = (User) session.getAttribute("user");
		if (userBean == null) {
			// 当没有Session时 跳转到登陆页面
			httpResponse.sendRedirect(httpRequest.getContextPath() + "/index.jsp");
		} else {
			chain.doFilter(request, response);
		}
	}

	public void init(FilterConfig arg0) throws ServletException {
	}
	/*
	 * web.xml中配置(过滤WebRoot目录下的back文件夹下的所有jsp文件)： 
	 * <filter>
	 * <filter-name>loginFilter</filter-name>
	 * <filter-class>com.jungle.filter.LoginFilter</filter-class>
	 * </filter>
	 * 
	 * <filter-mapping>
	 * <filter-name>loginFilter</filter-name>
	 * <url-pattern>/back/*</url-pattern>
	 * </filter-mapping>
	 */

}

class User {
}