过滤器和监听器

过滤器：

对过滤的所有文件设置字符编码

package Filter;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import javax.servlet.annotation.WebFilter;

//要过滤的文件路径
@WebFilter("/*")
public class CharacterEncodeing implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        //初始化过滤器，由jvm自动加载
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        HttpServletRequest req = (HttpServletRequest) servletRequest;
        HttpServletResponse resp = (HttpServletResponse) servletResponse;
        //设置字符编码
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        //设置响应时的数据格式
        resp.setContentType("text/html;charset=utf-8");
        filterChain.doFilter(req,resp);
    }

    @Override
    public void destroy() {
        //销毁过滤器，由jvm自动加载
    }
}

过滤目录下的jsp页面是否已经登录，否则跳转会登录页面

package Filter;
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import javax.servlet.annotation.WebFilter;
@WebFilter("/newspages/*")
public class LoginFilter implements Filter {//过滤器
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) servletRequest;
        HttpServletResponse resp = (HttpServletResponse) servletResponse;
        Object uname = req.getSession().getAttribute("uname");
        if(uname!=null){
            filterChain.doFilter(req,resp);
        }else{
           resp.sendRedirect(req.getContextPath()+"/IndexServlet");
        }
    }
    @Override
    public void destroy() {
    }
}

监听器：

import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

/**
 * 监听session作用域变化的监听器
 */
@WebListener
public class AttributeListener implements HttpSessionAttributeListener{
    @Override
    public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {

         //判断哪个用户完成了登录操作
         System.err.println("key:"+httpSessionBindingEvent.getName()+",用户:"+httpSessionBindingEvent.getValue()+"进行了登录操作");
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {
         //移除作用域中的值
         System.err.println("key:"+httpSessionBindingEvent.getName()+",用户:"+httpSessionBindingEvent.getValue()+"进行了注销操作");
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {

    }
}

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;
import java.util.Arrays;
import java.util.List;
@WebListener
public class FirstListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        //在servletContext对象初始化时执行的操作
        List<String> strings = Arrays.asList("张三", "李四", "王二麻子");
        //把lists集合存入到ServletContext作用域
        servletContextEvent.getServletContext().setAttribute("lists",strings);

    }
    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.out.println("ServletContext对象已销毁====");
    }
}