如何阅读下一行 BufferedReader？答案

【问题标题】：How do I read the next line BufferedReader?如何阅读下一行 BufferedReader？
【发布时间】：2021-10-23 02:43:20
【问题描述】：

我遇到了一个问题，在我检索到第一行后它没有读取下一行。主要问题是，在我从 txt 文件中获取第一行数据后，基本上是这样的：

admin,password  
nameone,passtwo  
nametwo,passthree

等等。等等

我遇到的问题是它在admin,password 之后无法读取。如何解决这个问题？

else if (userName.equals(u) && passWord.equals(p)) {  
    http.setAttribute("username", userName);  
    getServletContext().getRequestDispatcher("/WEB-INF/inventory.jsp").forward(request, response);

那行代码应该在第一行之后读取数据，但我不太确定如何修复它。任何帮助，将不胜感激。谢谢！

 protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        HttpSession http = request.getSession();

        String path = getServletContext().getRealPath("/WEB-INF/users.txt");
        BufferedReader br = new BufferedReader(new FileReader(new File(path)));

        String userName = request.getParameter("username");
        String passWord = request.getParameter("password");

        String account = br.readLine();
        String split[] = account.split(",");

        int i = 0;
        String u = split[i];
        String p = split[i + 1];

        while ((account = br.readLine()) != null) {

            if (userName.equals(u) && passWord.equals(p)) {
                http.setAttribute("username", userName);
                getServletContext().getRequestDispatcher("/WEB-INF/admin.jsp").forward(request, response);
                // response.sendRedirect("inventory");
            } else if (userName.equals(u) && passWord.equals(p)) {
                http.setAttribute("username", userName);
                getServletContext().getRequestDispatcher("/WEB-INF/inventory.jsp").forward(request, response);
            } else {
                request.setAttribute("message", "The wrong username or password have been entered.");
                getServletContext().getRequestDispatcher("/WEB-INF/login.jsp").forward(request, response);
            }
            account = br.readLine();
        }

        HttpSession session = request.getSession();
        session.setAttribute("username", userName);
        response.sendRedirect("inventory");
    }

【问题讨论】：

stackoverflow.com/questions/28999757/…
您不会在循环中拆分刚刚读取的字符串，因此userName 和passWord 永远不会改变。您还在循环中阅读了两次，因此您将错过每一行。为什么要对它们进行两次测试是另一个谜。
您也没有关闭阅读器 - 使用“try-with-resources”块。使用Files.readAllLines 比BufferedReader 简单很多

标签： java bufferedreader

【解决方案1】：

 while ((account = br.readLine()) != null) {
            account = br.readLine(); //duplicated here.
        }

从您的代码中，您 readLine 两次。您应该删除 end 命令。

 while ((account = br.readLine()) != null) {             
        }

够了。您可以打印帐户进行调试，以确保您是否怀疑数据。

顺便说一句，两个if条件是一样的。请重构您的代码...

【讨论】：

【解决方案2】：

您永远不会刷新实际值，只读取该行而不对它们做任何事情。修复：

 protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        HttpSession http = request.getSession();

        String path = getServletContext().getRealPath("/WEB-INF/users.txt");
        BufferedReader br = new BufferedReader(new FileReader(new File(path)));

        String userName = request.getParameter("username");
        String passWord = request.getParameter("password");

        String account = "", u = "", p = "";

        while ((account = br.readLine()) != null) {
        String split[] = account.split(",");

        int i = 0;
        u = split[i];
        p = split[i + 1];

            if (userName.equals(u) && passWord.equals(p)) {
                http.setAttribute("username", userName);
                getServletContext().getRequestDispatcher("/WEB-INF/admin.jsp").forward(request, response);
                // response.sendRedirect("inventory");
            } else if (userName.equals(u) && passWord.equals(p)) {
                http.setAttribute("username", userName);
                getServletContext().getRequestDispatcher("/WEB-INF/inventory.jsp").forward(request, response);
            } else {
                request.setAttribute("message", "The wrong username or password have been entered.");
                getServletContext().getRequestDispatcher("/WEB-INF/login.jsp").forward(request, response);
            }
            account = br.readLine();
        }

【讨论】：

【解决方案3】：

我建议你真的想检查一下 BufferedReader 是否不起作用。处理这段代码。我认为如果代码很复杂，你最好对部分进行测试。

public static void main(String[] args) throws IOException {
    String path = "useres.txt";
    File file = new File(path);
    FileReader fr = new FileReader(file);

    BufferedReader br = new BufferedReader(fr);

    String account = null;
    while ((account = br.readLine()) != null) {
        System.out.println(account);
    }

    br.close();
}

输出是

admin,password
nameone,passtwo
nametwo,passthree
etc,etc

【讨论】：