如何使用 Java 获取带有模式的子字符串

Question

我有一个包含如下记录的文件：

drwxr-xr-x   - root supergroup          0 2015-04-05 05:26 /user/root
drwxr-xr-x   - hadoop supergroup          0 2014-11-05 11:56 /user/root/input
drwxr-xr-x   - hadoop supergroup          0 2014-11-05 03:06 /user/root/input/foo
drwxr-xr-x   - hadoop supergroup          0 2015-04-28 03:06 /user/root/input/foo/bar
drwxr-xr-x   - hadoop supergroup          0 2013-11-06 15:54 /user/root/input/foo/bar/20120706
-rw-r--r--   3 hadoop supergroup          0 2013-11-06 15:54 /user/root/input/foo/bar/20120706/_SUCCESS
drwxr-xr-x   - hadoop supergroup          0 2013-11-06 15:54 /user/root/input/foo/bar/20120706/_logs
drwxr-xr-x   - hadoop supergroup          0 2013-11-06 15:54 /user/root/input/foo/bar/20120706/_logs/history

在Java代码中，我使用Pattern和Matcherclass来获取我想稍后处理的子字符串。代码如清单：

String filename = "D:\temp\files_in_hadoop_temp.txt";
Pattern thePattern
    = Pattern.compile("[a-z\-]+\s+(\-|[0-9]) (root|hadoop)\s+supergroup\s+([0-9]+) ([0-9\-]+) ([0-9:]+) (\D+)\/?.*");

    try
    {
        Files.lines(Paths.get(filename))
                .map(line -> thePattern.matcher(line))
                .collect(Collectors.toList())
                .forEach(theMather -> {
                    if (theMather.find())
                    {
                        System.out.println(theMather.group(3) + "-" + theMather.group(4) + "-" + theMather.group(6));
                    }
                });
    } catch (IOException e)
    {
        e.printStackTrace();
    }

结果如下：

0-2015-04-05-/user/root
0-2014-11-05-/user/root/input
0-2014-11-05-/user/root/input/foo
0-2015-04-28-/user/root/input/foo/bar
0-2013-11-06-/user/root/input/foo/bar/
0-2013-11-06-/user/root/input/foo/bar/
0-2013-11-06-/user/root/input/foo/bar/
0-2013-11-06-/user/root/input/foo/bar/

但我预期的结果是前三行没有尾部“/”。我尝试了很多模式来去除尾部“/”但都失败了。

能否请您提供一些关于去除尾部“/”的模式的建议。

非常感谢。

Answer 1

您可以做的是检查一个简单的 if 语句，如果最后一个字符是斜杠，并使用子字符串获取新字符串：

if (theMather.find())
   {
       String data = theMather.group(3) + "-" + theMather.group(4) + "-" + theMather.group(6);
       //String data = theMather.group(3) + "-" + theMather.group(4) + "-" + theMather.group(6);
       if(data.charAt(data.length() - 1) == '/')
        data = data.substring(0, data.length() - 1);

       System.out.println(data);
   }

Answer 2

使用字符集确保最后一个字符不是斜线。因此，而不是

(\D+)\/?.*"

尝试

(\D*[^\d/]).*

圆括号中的部分匹配最长的非数字子串，附加的限制是最后一个字符不能是斜杠。

注：已测试。

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