如何将文本追加到Java中的现有文件 [英] How to append text to an existing file in Java

问题描述

我需要重复追加文本到Java中的现有文件。如何做到这一点？

解决方案

如果是这样，有这个的几个库。其中两个最受欢迎的是 Log4j 和 Logback 。

Java 7 +

需要这样做一次，文件类使得这一点变得简单：

$ p $ try {
Files.write（Paths.get（myfile.txt ），文本.getBytes（），StandardOpenOption.APPEND）;
} catch（IOException e）{
//将异常处理留作练习读者
}


<sup>小心：如果文件不存在，上面的方法会抛出 NoSuchFileException 它也不会自动追加一个换行符（当你追加到一个文本文件时你经常需要这个换行符）。 史蒂夫钱伯斯的答案涵盖了如何使用 Files 类来做到这一点。然而，如果你要多次写入同一个文件，上面必须多次打开和关闭磁盘上的文件，这就是一个缓慢的操作。在这种情况下，一个缓冲的作家是更好的：

$ $ p $ try（FileWriter fw = new FileWriter（myfile.txt，true） ;
BufferedWriter bw = new BufferedWriter（fw）;
PrintWriter out = new PrintWriter（bw））
{
out.println（text）;
//更多的代码
out.println（more text）;
//更多的代码
} catch（IOException e）{
//异常处理留给读者练习
}</sup>


$ b 对 FileWriter 构造函数的第二个参数会告诉它追加到文件中，而不是写入一个新文件。 （如果该文件不存在，将会被创建。）

对于一个昂贵的编写器（例如，使用 BufferedWriter FileWriter ）。

使用 PrintWriter 可以访问 println 语法，您可能习惯于从 System.out 。

BufferedWriter 和 PrintWriter 包装并不是必须的。

---

旧版Java

  try {
 PrintWriter out = new PrintWriter（new BufferedWriter（new FileWriter（myfile.txt，true）））; 
 out.println（text）; 
 out.close（）; 
} catch（IOException e）{
 //将异常处理留作练习读者
} 
  

---

异常处理

如果您需要对较老的Java进行健壮的异常处理，非常详细：

  FileWriter fw = null; 
 BufferedWriter bw = null; 
 PrintWriter out = null; 
尝试{
 fw = new FileWriter（myfile.txt，true）; 
 bw = new BufferedWriter（fw）; 
 out = new PrintWriter（bw）; 
 out.println（text）; 
 out.close（）; 
} catch（IOException e）{
 //异常处理留给练习读者
} 
 finally {
 try {
 if（out ！= null）
 out.close（）; 
} catch（IOException e）{
 //将异常处理留给练习读者
} 
 try {
 if（bw！= null）
 bw.close（）; 
} catch（IOException e）{
 //将异常处理作为练习留给读者
} 
 try {
 if（fw！= null）
 fw.close（）; 
} catch（IOException e）{
 //将异常处理留作练习读者
} 
} 
  

I need to append text repeatedly to an existing file in Java. How do I do that?

解决方案

Are you doing this for logging purposes? If so there are several libraries for this. Two of the most popular are Log4j and Logback.

Java 7+

If you just need to do this one time, the Files class makes this easy:

try {
    Files.write(Paths.get("myfile.txt"), "the text".getBytes(), StandardOpenOption.APPEND);
}catch (IOException e) {
    //exception handling left as an exercise for the reader
}

^{Careful: The above approach will throw a NoSuchFileException if the file does not already exist. It also does not append a newline automatically (which you often want when appending to a text file). Steve Chambers's answer covers how you could do this with Files class.}

However, if you will be writing to the same file many times, the above has to open and close the file on the disk many times, which is a slow operation. In this case, a buffered writer is better:

try(FileWriter fw = new FileWriter("myfile.txt", true);
    BufferedWriter bw = new BufferedWriter(fw);
    PrintWriter out = new PrintWriter(bw))
{
    out.println("the text");
    //more code
    out.println("more text");
    //more code
} catch (IOException e) {
    //exception handling left as an exercise for the reader
}

Notes:

• The second parameter to the FileWriter constructor will tell it to append to the file, rather than writing a new file. (If the file does not exist, it will be created.)
• Using a BufferedWriter is recommended for an expensive writer (such as FileWriter).
• Using a PrintWriter gives you access to println syntax that you're probably used to from System.out.
• But the BufferedWriter and PrintWriter wrappers are not strictly necessary.

---

Older Java

try {
    PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("myfile.txt", true)));
    out.println("the text");
    out.close();
} catch (IOException e) {
    //exception handling left as an exercise for the reader
}

---

Exception Handling

If you need robust exception handling for older Java, it gets very verbose:

FileWriter fw = null;
BufferedWriter bw = null;
PrintWriter out = null;
try {
    fw = new FileWriter("myfile.txt", true);
    bw = new BufferedWriter(fw);
    out = new PrintWriter(bw);
    out.println("the text");
    out.close();
} catch (IOException e) {
    //exception handling left as an exercise for the reader
}
finally {
    try {
        if(out != null)
            out.close();
    } catch (IOException e) {
        //exception handling left as an exercise for the reader
    }
    try {
        if(bw != null)
            bw.close();
    } catch (IOException e) {
        //exception handling left as an exercise for the reader
    }
    try {
        if(fw != null)
            fw.close();
    } catch (IOException e) {
        //exception handling left as an exercise for the reader
    }
}

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