package com.base.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 javax.servlet.http.HttpSession;
import com.base.constants.SessionKeyConstants;
import com.mvc.entity.User;
public class SessionFilter implements Filter {
  public void destroy() {
    // 過濾器銷毀，一般是釋放資源
  }
  /**
   * 某些url需要登陸才能訪問（session驗(yàn)證過濾器）
   */
  public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
      throws IOException, ServletException {
    HttpServletRequest request = (HttpServletRequest) arg0;
    HttpServletResponse response = (HttpServletResponse) arg1;
    HttpSession session = request.getSession();
    //判斷session是否過期
    if ((User) session.getAttribute(SessionKeyConstants.LOGIN) == null) {
      String errors = "您還沒有登錄，或者session已過期。請(qǐng)先登陸!";
      request.setAttribute("Message", errors);
      //跳轉(zhuǎn)至登錄頁面
      request.getRequestDispatcher("/login.jsp").forward(request, response);
    } else {
      arg2.doFilter(request, response);
    }
  }
  public void init(FilterConfig arg0) throws ServletException {
    // 初始化操作，讀取web.xml中過濾器配置的初始化參數(shù)，滿足你提的要求不用此方法
  }
}

<!-- 設(shè)置session過期時(shí)間為30分鐘 -->
<session-config>
    <session-timeout>30</session-timeout>
</session-config>
<!-- session過濾器配置相關(guān) -->
<filter>
    <filter-name>SessionFilter</filter-name>
    <filter-class>com.base.filter.SessionFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>SessionFilter</filter-name>
    <url-pattern>/contract/*</url-pattern>
    <url-pattern>/user/*</url-pattern>
    <dispatcher>FORWARD</dispatcher>
    <!--在這種情況下，如果請(qǐng)求是以/contract/…或者/user/…開頭的，并且是通過request dispatcher的forward方法傳遞過來或者直接從客戶端傳遞過來的，則必須經(jīng)過這個(gè)過濾器。-->
    <dispatcher>REQUEST</dispatcher>
</filter-mapping>