写入后如何清除PrintWriter的内容

Question

晚上好，我想知道如何清除写入到PrintWriter的数据，即是否可以在打印后从PrintWriter删除数据？

在此servlet中，我在响应中打印一些文本，并在＃表示的行上希望删除所有先前打印的数据并打印新内容：

protected void doGet(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {
    PrintWriter out = response.getWriter();
    String uName = request.getParameter("uName");
    String uPassword = request.getParameter("uPassword");

    if (uName .equals("Islam")) {
        out.println("Valid-Name");
        if (uPassword !=null) {
            if (uPassword .equals("Islam")) {
                // # clear the writer from any printed data here
                out.println("Valid-password");
            } else {
                out.println("");
                out.println("InValid-password");
            }
        }
    } else {
        out.println("InValid-Name");

    }

}

注意：我尝试过out.flush（），但旧的打印文本仍然保留

Answer 1

创建一个内存PrintWriter使用StringWriter。您可以从获取底层缓冲区，StringWriter并在需要时清除它。

StringWriter sr = new StringWriter();
PrintWriter w = new PrintWriter(sr);

w.print("Some stuff");
// Flush writer to ensure that it's not buffering anything
w.flush();
// clear stringwriter
sr.getBuffer().setLength(0);

w.print("New stuff");

// write to Servlet out
w.flush();
response.getWriter().print(sr.toString());