Filter简单过滤器的实现

package cn.buaa.core.filter;

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 cn.buaa.core.constant.Constant;

public class LoginFilter implements Filter {

@Override
public void destroy() {

}

@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) servletRequest;
HttpServletResponse response = (HttpServletResponse)servletResponse;
String uri = request.getRequestURI();
//判断当前请求地址是否是登录的请求地址
if(!uri.contains("sys/login_")){
//非登录请求
if(request.getSession().getAttribute(Constant.USER) != null){
//说明已经登陆过，放行
chain.doFilter(request, response);
}else{
//没有登录，跳转到登录页面
response.sendRedirect(request.getContextPath() + "/sys/login_toLoginUI.action");
}
}else{
//登录请求，直接放行
chain.doFilter(request, response);
}
}

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

}

}

<filter>
<filter-name>loginFilter</filter-name>
<filter-class>cn.buaa.core.filter.LoginFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>loginFilter</filter-name>
<url-pattern>*.action</url-pattern>
</filter-mapping>