protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub //response.getWriter().append("Served at: ").append(request.getContextPath()); request.setCharacterEncoding("utf-8"); response.setContentType("text/html;charset=utf-8"); response.setCharacterEncoding("utf-8");//解码 //向网页输出内容 PrintWriter out=response.getWriter(); //获取用户的姓名和密码 String b_username = request.getParameter("b_username"); String b_password = request.getParameter("b_password"); System.out.println(b_password+" "+b_username+"==="); //调用Login方法进行判断 BuyerobjDao dao = new BuyerobjDao(); boolean success = dao.login(b_username, b_password); System.out.println(success); if(success==true){ System.out.println("登录成功"); response.sendRedirect("shouyu.html"); }else{ System.out.println("登录失败"); response.sendRedirect("jingdong.jsp"); } } 改错

代码中主要存在的问题是：

1. doGet方法中的response.getWriter()方法只能调用一次，不能重复调用，否则会报错。

2. 在设置response的字符编码时，应该在获取PrintWriter对象之前进行设置，否则会无效。

修改后的代码如下：

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    request.setCharacterEncoding("utf-8");
    response.setContentType("text/html;charset=utf-8");
    response.setCharacterEncoding("utf-8");
    //向网页输出内容
    PrintWriter out = response.getWriter();

    //获取用户的姓名和密码
    String b_username = request.getParameter("b_username");
    String b_password = request.getParameter("b_password");
    System.out.println(b_password + " " + b_username + "===");

    //调用Login方法进行判断
    BuyerobjDao dao = new BuyerobjDao();
    boolean success = dao.login(b_username, b_password);
    System.out.println(success);

    if (success) {
        System.out.println("登录成功");
        response.sendRedirect("shouyu.html");
    } else {
        System.out.println("登录失败");
        response.sendRedirect("jingdong.jsp");
    }
    out.close();
}

修改的主要内容包括：

1. 删除了无用的注释和代码。

2. 将获取PrintWriter对象的代码移到设置response字符编码的前面。

3. 修改了if语句中的判断条件，使其更加简洁。