第三十五章——过滤器和监听器

过滤器代码示例：

package com.hanqi.maya.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.annotation.WebFilter;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet Filter implementation class SessionFilter
 */
@WebFilter(filterName="sessionFilter",
    value={"/*"}, initParams={@WebInitParam(name="initp", value="message.jsp;login.jsp;LoginOrRegisterServlet")})
public class SessionFilter implements Filter {

    private String initParams;

    /**
     * Default constructor.
     */
    public SessionFilter() {
        // TODO Auto-generated constructor stub
    }

    /**
     * @see Filter#destroy()
     */
    public void destroy() {
        // TODO Auto-generated method stub
    }

    /**
     * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
     */
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest)req;
        HttpServletResponse response = (HttpServletResponse)resp;

        String[] ss = initParams.split(";");

        String reqUrl = request.getRequestURI();
        for(String s : ss) {
            if(reqUrl.indexOf(s)!=-1) {
                chain.doFilter(request, response);
                return;
            }
        }

        Object obj = request.getSession().getAttribute("currentUser");
        if(obj==null) {
            response.sendRedirect("login.jsp");
        } else {
            chain.doFilter(request, response);
        }
    }

    /**
     * @see Filter#init(FilterConfig)
     */
    public void init(FilterConfig fConfig) throws ServletException {
        initParams = fConfig.getInitParameter("initp");
    }

}

监听器：