从Java文件中删除最后一个换行符

Question

我想使用Java删除文件中存在的最后一个换行符。 我的意思是，文件的末尾有一个换行符，我想删除它。

我尝试了许多在线提供的解决方案，但是没有任何效果。

下面的代码从文件中删除所有换行符

trimm.replace("\n", "").replace("\r", "");

示范文本：

ABC 123|1|2 ABC '123|1|2|"Jan 30 2018  2:34:13:000AM"|dd1|1|"Jan 30 2018  2:56:08:000AM"|EST' ABC 20180821
ABC 123|1|2 ABC '123|1|2|"Jan 30 2018  2:34:13:000AM"|dd1|1|"Jan 30 2018  2:56:08:000AM"|EST' ABC 20180821

上面的示例末尾有换行符。 我已引用以下网址：

http://www.avajava.com/tutorials/lessons/how-do-i-remove-a-newline-from-the-end-of-a-string.html

https://www.java-forums.org/new-java/22655-removing-last-blank-line-txt-file.html

我无法在\\n后使用split() ，因为许多raws具有相同的单词

我的代码：

    String actual ="ABC 123|1|2 ABC '123|1|2|\"Jan 30 2018  2:34:13:000AM\"|dd1|1|\"Jan 30 2018  2:56:08:000AM\"|EST' ABC 20180821\r\n" + 
            "ABC 123|1|2 ABC '123|1|2|\"Jan 30 2018  2:34:13:000AM\"|dd1|1|\"Jan 30 2018  2:56:08:000AM\"|EST' ABC 20180821\r\n";
    try {
          File fout = new File("I:\\demo\\S2.txt");
          FileOutputStream fos = new FileOutputStream(fout);
          BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(fos));
          String trimm= actual;
/*            StringBuilder sb = new StringBuilder(trimm);
              int lastEnterPosition = trimm.lastIndexOf("\r\n");
              sb.replace(lastEnterPosition, lastEnterPosition + 1, "");
              trimm = sb.toString();*/
              trimm = trimm.replaceAll("[\n\r]+$", "");
              bw.write(trimm);
              bw.newLine();
              bw.close();
            } catch (FileNotFoundException e){
              // File was not found
              e.printStackTrace();
            } catch (IOException e) {
              // Problem when writing to the file
              e.printStackTrace();
            }

任何解决方法都将有所帮助。

Answer 1

您可以使用replaceFirst ，它在此[\\n\\r]+$使用正则表达式，如下所示：

trimm = trimm.replaceFirst("[\n\r]+$", "");

完整代码

我尝试了这段代码：

public static void main(String[] args) throws Exception {
    String trimm = "ABC 123|1|2 ABC '123|1|2|\"Jan 30 2018  2:34:13:000AM\"|dd1|1|\"Jan 30 2018  2:56:08:000AM\"|EST' ABC 20180821\n" +
            "ABC 123|1|2 ABC '123|1|2|\"Jan 30 2018  2:34:13:000AM\"|dd1|1|\"Jan 30 2018  2:56:08:000AM\"|EST' ABC 20180821\r\n";

    System.out.println("---------------------------------------------------Before replace Start of the input---------------------------------------------------");
    System.out.println(trimm);
    System.out.println("---------------------------------------------------Before replace End of the input---------------------------------------------------");

    System.out.println("---------------------------------------------------After replace Start of the input---------------------------------------------------");
    trimm = trimm.replaceFirst("[\n\r]+$", "");
    System.out.println(trimm);
    System.out.println("---------------------------------------------------After replace End of the input---------------------------------------------------");

}

输出 ：

---------------------------------------------------Before replace Start of the input---------------------------------------------------
ABC 123|1|2 ABC '123|1|2|"Jan 30 2018  2:34:13:000AM"|dd1|1|"Jan 30 2018  2:56:08:000AM"|EST' ABC 20180821
ABC 123|1|2 ABC '123|1|2|"Jan 30 2018  2:34:13:000AM"|dd1|1|"Jan 30 2018  2:56:08:000AM"|EST' ABC 20180821

---------------------------------------------------Before replace End of the input---------------------------------------------------
---------------------------------------------------After replace Start of the input---------------------------------------------------
ABC 123|1|2 ABC '123|1|2|"Jan 30 2018  2:34:13:000AM"|dd1|1|"Jan 30 2018  2:56:08:000AM"|EST' ABC 20180821
ABC 123|1|2 ABC '123|1|2|"Jan 30 2018  2:34:13:000AM"|dd1|1|"Jan 30 2018  2:56:08:000AM"|EST' ABC 20180821
---------------------------------------------------After replace End of the input---------------------------------------------------

---

请注意，在替换之前有一个换行符，在替换之后只有最后一个换行符被删除。

Ideone演示

---

更多细节

我尝试了以下三种解决方案：

代码1（您的代码）

public static void main(String[] args) throws Exception {
    String trimm = "ABC 123|1|2 ABC '123|1|2|\"Jan 30 2018  2:34:13:000AM\"|dd1|1|\"Jan 30 2018  2:56:08:000AM\"|EST' ABC 20180821\n" +
            "ABC 123|1|2 ABC '123|1|2|\"Jan 30 2018  2:34:13:000AM\"|dd1|1|\"Jan 30 2018  2:56:08:000AM\"|EST' ABC 20180821\r\n";

    try {
        File fout = new File("path");
        FileOutputStream fos = new FileOutputStream(fout);
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(fos));
        trimm = trimm.replaceAll("[\n\r]+$", "");
        bw.write(trimm);
        //bw.newLine();//<-----------------------note this
        bw.close();
    } catch (FileNotFoundException e) {
        // File was not found
        e.printStackTrace();
    } catch (IOException e) {
        // Problem when writing to the file
        e.printStackTrace();
    }
}

代码2

public static void main(String[] args) throws Exception {
    String trimm = "ABC 123|1|2 ABC '123|1|2|\"Jan 30 2018  2:34:13:000AM\"|dd1|1|\"Jan 30 2018  2:56:08:000AM\"|EST' ABC 20180821\n" +
            "ABC 123|1|2 ABC '123|1|2|\"Jan 30 2018  2:34:13:000AM\"|dd1|1|\"Jan 30 2018  2:56:08:000AM\"|EST' ABC 20180821\r\n";

    Path path = Paths.get("path");

    try (BufferedWriter writer = Files.newBufferedWriter(path))
    {
        writer.write(trimm.replaceFirst("[\n\r]+$", ""));
    }
}

代码3

public static void main(String[] args) {
    String trimm = "ABC 123|1|2 ABC '123|1|2|\"Jan 30 2018  2:34:13:000AM\"|dd1|1|\"Jan 30 2018  2:56:08:000AM\"|EST' ABC 20180821\n" +
            "ABC 123|1|2 ABC '123|1|2|\"Jan 30 2018  2:34:13:000AM\"|dd1|1|\"Jan 30 2018  2:56:08:000AM\"|EST' ABC 20180821\r\n";

    try {
        Files.write(Paths.get("path"), trimm.replaceFirst("[\n\r]+$", "").getBytes());
    } catch (IOException e) {
        e.printStackTrace();
    }
}

这三个代码都给我：

Answer 2

如果您知道字符串将始终以\\r\\n结尾，则给定

String test = "your string that ends with a newline\r\n";

您可以使用类似

String eol = "\r\n";
int eolLen = eol.length();
String tmp = test.substring(0, test.length()-eolLen);

使用正则表达式似乎有点矫kill过正。 您可以选择检查字符串是否真的以换行符结尾，并在可能输入错误的情况下抛出某种异常。 就像是：

String check = test.substring(test.length() - eolLen);
if (!eol.equals(check)) {
    throw new Exception(String.format("Expected newline, found %s", check));
}