用Filter防止用户访问一些未被授权的资源,比如一个用户未登录就不允许访问网站的某些页面,并将页面重定向到需要用户登录的页面,下面是一个相关的例子:
package com.drp.util.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;
importjavax.servlet.http.HttpServletRequest;
importjavax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class AuthFilter implements Filter {
public void destroy() {
}
public void doFilter(ServletRequest servletRequest,ServletResponse servletResponse,
FilterChain filterChain) throws IOException, ServletException{
HttpServletRequest request =(HttpServletRequest)servletRequest;
HttpServletResponse response =(HttpServletResponse)servletResponse;
String currentURL = request.getRequestURI();//取得根目录所对应的绝对路径:
String targetURL =currentURL.substring(currentURL.indexOf("/",1),
currentURL.length()); //截取到当前文件名用于比较
HttpSession session =request.getSession(false);
if (!"/login.jsp".equals(targetURL)) {
//判断当前页是否是重定向以后的登录页面页面,如果是就不做session的判断,防止出现死循环
if (session == null || session.getAttribute("user") == null){
/
}
public void init(FilterConfig filterConfig) throwsServletException {
}
}
然后在配置文件web.xml里添加:(请注意,过滤是在serlvet规范2.3版中初次引入的。因此,web.xml文件必须使用DTD的2.3以上版本。)
<filter>
<filter-name>AuthFilter</filter-name>
<filter-class>com.drp.util.filter.AuthFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>AuthFilter</filter-name>
<url-pattern>*.jsp</url-pattern>//表示对所有jsp文件有效
</filter-mapping>
这样用户没有登录的情况下就会转到登录页面。