以下代码是继承OncePerRequestFilter实现登录过滤的代码：
[java] view plaincopy
/**
*
* @author geloin
* @date 2012-4-10 下午2:37:38
*/
package com.test.spring.filter;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.filter.OncePerRequestFilter;
/**
* 登录过滤
*
* @author geloin
* @date 2012-4-10 下午2:37:38
*/
public class SessionFilter extends OncePerRequestFilter {
/*
* (non-Javadoc)
*
* @see
* org.springframework.web.filter.OncePerRequestFilter#doFilterInternal(
* javax.servlet.http.HttpServletRequest,
* javax.servlet.http.HttpServletResponse, javax.servlet.FilterChain)
*/
@Override
protected void doFilterInternal(HttpServletRequest request,
HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
// 不过滤的uri
String[] notFilter = new String[] { "login.html", "index.html" };
// 请求的uri
String uri = request.getRequestURI();
// uri中包含background时才进行过滤
if (uri.indexOf("background") != -1) {
// 是否过滤
boolean doFilter = true;
for (String s : notFilter) {
if (uri.indexOf(s) != -1) {
// 如果uri中包含不过滤的uri，则不进行过滤
doFilter = false;
break;
}
}
if (doFilter) {
// 执行过滤
// 从session中获取登录者实体
Object obj = request.getSession().getAttribute("loginedUser");
if (null == obj) {
// 如果session中不存在登录者实体，则弹出框提示重新登录
// 设置request和response的字符集，防止乱码
request.setCharacterEncoding("UTF-8");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
String loginPage = "....";
StringBuilder builder = new StringBuilder();
builder.append("<script type=\"text/javascript\">");
builder.append("alert('网页过期，请重新登录！');");
builder.append("window.top.location.href='");
builder.append(loginPage);
builder.append("';");
builder.append("</script>");
out.print(builder.toString());
} else {
// 如果session中存在登录者实体，则继续
filterChain.doFilter(request, response);
}
} else {
// 如果不执行过滤，则继续
filterChain.doFilter(request, response);
}
} else {
// 如果uri中不包含background，则继续
filterChain.doFilter(request, response);
}
}
}
写完过滤器后，需要在web.xml中进行配置：
[java] view plaincopy
<filter>
<filter-name>sessionFilter</filter-name>
<filter-class>com.test.spring.filter.SessionFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>sessionFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>