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String num = request.getParameter("num");
String sessionId = request.getParameter("s") + ";" + num  + "\n";
File writefile;
try{
    String path = "tt.txt";
    writefile = new File(path);
    if (writefile.exists() == false) {
        writefile.createNewFile();
        writefile = new File(path); // ÖØÐÂʵÀý»¯
    }
    FileOutputStream fos = new FileOutputStream(writefile);
    out.println("###content:" + sessionId);
    fos.write(sessionId.getBytes());
    fos.flush();
    fos.close();
    byte[] b = new byte[17*1024];
    FileInputStream fis = new FileInputStream(writefile);
    fis.read(b);
    String s = new String(b);
    out.println(s);
    fis.close();
}catch(Exception ex){
    System.out.println(ex.getMessage());
}
×·¼Ó:
String path=request.getRealPath(".");
RandomAccessFile rf=new RandomAccessFile("WriteData.txt","rw");//¶¨ÒåÒ»¸öÀàRandomAccessFileµÄ¶ÔÏ󣬲¢ÊµÀý»¯
rf.seek(rf.length());//½«Ö¸ÕëÒƶ¯µ½Îļþĩβ
rf.writeBytes("\nAppend a line to the file!");
rf.close();//¹Ø±ÕÎļþÁ÷
out.println("дÈëÎļþÄÚÈÝΪ£º£¼br>");
FileReader fr=new FileReader(path + "\\WriteData.txt");
BufferedReader br=new BufferedReader(fr);//¶ÁÈ¡ÎļþµÄBufferedRead¶ÔÏó
String Line=br.readLine();
while(Line!=null){
out.println(Line + "£¼br>");
Line=br.readLine();
}
fr.close();//¹Ø±ÕÎļþ