登陆页面的搭建

function login(){
    var th=document.form1;
    if(th.username.value==""){
        alert("用户名不能为空！");
        th.username.focus();
        return; 
    }
    if(th.pswd.value==""){
        alert("密码不能为空！");
        th.pswd.focus();
        return;
    }
    th.action="<%=path%>/servlet/LoginAction";
    th.submit();
    
}

package com.servlet.login.service;

import java.util.List;
import java.util.Map;

public interface LoginService {
    public boolean userLogin(List<Object> params);
}

package com.servlet.login.dao;

import java.sql.SQLException;
import java.util.List;
import java.util.Map;

import com.jdbc.util.MySqlConnect;
import com.servlet.login.service.LoginService;

public class LoginDao implements LoginService {
    private MySqlConnect conn = null;

    public LoginDao() {
        conn = new MySqlConnect();
    }

    public boolean userLogin(List<Object> params) {
        //连接数据库
        conn.getConnect();
        boolean flag = false;
        String sql = "select * from userinfo where username= ? and password=? ";
        try {
            Map<String, Object> map = conn.queryBySimpleResult(sql, params);
            flag = !map.isEmpty() ? true : false;
        } catch (SQLException e) {
            e.printStackTrace();
        }finally{
            conn.releaseConnect();
        }
        return flag;
    }

}

package com.servlet.login.action;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.servlet.login.dao.LoginDao;
import com.servlet.login.service.LoginService;

public class LoginAction extends HttpServlet {

    private static final long serialVersionUID = 1L;
    private LoginService service;

    public LoginAction() {
        service=new LoginDao();
    }

    public void destroy() {
        super.destroy(); 
    }
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doPost(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String path=request.getContextPath();
        response.setContentType("text/html;charset=utf-8");
        
        String username=request.getParameter("username");
        String password=request.getParameter("pswd");
        List<Object>params=new ArrayList<Object>();
        params.add(username);
        params.add(password);
        boolean flag=service.userLogin(params);
        if(flag){
            request.getSession().setAttribute("username",username);
            response.sendRedirect(path+"/main.jsp");
        }
        
    }

    
    public void init() throws ServletException {
    }

}

package com.servlet.login.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;

public class MyFilter implements Filter {

    public MyFilter() {
    }

    public void destroy() {

    }

    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        HttpServletRequest httpServletRequest = (HttpServletRequest) request;
        HttpServletResponse httpServletResponse = (HttpServletResponse) response;
        String path = httpServletRequest.getContextPath();
        httpServletRequest.setCharacterEncoding("utf-8");
        httpServletResponse.setCharacterEncoding("utf-8");
        String username = (String) httpServletRequest.getSession()
                .getAttribute("username");
        if (username == null) {
            httpServletResponse.sendRedirect(path + "/index.jsp");
        }
        chain.doFilter(httpServletRequest, httpServletResponse);
    }

    public void init(FilterConfig arg0) throws ServletException {

    }

}

<filter>
    <filter-name>MyFilter</filter-name>
    <filter-class>com.servlet.login.filter.MyFilter</filter-class>
    </filter>
    

    <filter-mapping>
    <filter-name>MyFilter</filter-name>
    <url-pattern>/main.jsp</url-pattern>
    </filter-mapping>