附加到文件 [英] Append to a File

问题描述

我试图写追加了系统的当前日期和时间到日志文件（也被通过批处理文件在我的电脑启动时运行）的Java程序。这里是我的code。

I am trying to write a java program that appends the current date and time of the system to a log file (that gets run by a batch file at my computer startup). Here's is my code.

public class LogWriter {

    public static void main(String[] args) {

        /* open the write file */
        FileOutputStream f=null;
        PrintWriter w=null;

        try {
            f=new FileOutputStream("log.txt");
            w=new PrintWriter(f, true);
        } catch (Exception e) {
            System.out.println("Can't write file");
        }

        /* replace this with your own username */
        String user="kumar116";
        w.append(user+"\t");

        /* c/p http://www.mkyong.com/java/java-how-to-get-current-date-time-date-and-calender/ */
        DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        Date date = new Date();
        w.append(dateFormat.format(date)+'\n');

        /* close the write file*/
        if(w!=null) {
            w.close();
        }

    }

}

的问题是，它不追加:)到文件中。有人能指出这里有什么问题吗？

The problem is, it's not appending :) to the file. Can someone point out what is the problem here ?

先谢谢了。

推荐答案

<一个href=\"http://docs.oracle.com/javase/7/docs/api/java/io/PrintWriter.html#append%28java.lang.CharSequence%29\"相对=nofollow>的PrintWriter＃追加不将数据追加到一个文件中。相反，它执行使用作家直接写 。需要声明的的FileOutputStream 使用附加标志的构造函数：

PrintWriter#append does not append data to a file. Instead it performs a direct write using the Writer. You need to declare your FileOutputStream constructor using an append flag:

f = new FileOutputStream("log.txt", true);
w = new PrintWriter(f); // autoflush not required provided close is called

的追加仍然可以使用或方法更方便的是的println 这将不需要换行符是补充：

The append method may still be used or more convenient is println which will not require a newline character to be added:

w.println(dateFormat.format(date));

在的PrintWriter 构造函数的自动冲洗标志不是必需提供接近被调用。 关闭应该出现在最后块。

The autoflush flag in the PrintWriter constructor is not required provided close is called. close should appear in a finally block.

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