I'm solving this problem in my own way. I'm trying to split the file path into Drive, folders, and file name, all into an array.
Complete class. (Github)
The problem:
String regex = "\\";
String [] divisions = path.split (regex);
This gives me an java.util.regex.PatternSyntaxException. I looked up the wiki and found [\b]
String regex = "[\b]";
String [] divisions = path.split (regex);
This doesn't work. It doesn't throw an exception, nor does it split my file path based on backspace.
Input:
► Enter path --
C:\User\Admin\NekedGaben.jpg
Output:
→ Path = C:\User\Admin\NekedGaben.jpg
→ File name = C:\User\Admin\NekedGaben
→ Extension = .jpg
My questions:
Why does "\\" throw an exception, while "[\b]" doesn't?
Why doesn't the split() split the Path string?
You should use double escaping in Java regex, i.e.:
String regex = "\\\\";
Or use static Pattern.quote(String) method:
String regex = Pattern.quote("\\");
Because \b is a single character, the compiler knows it, they're friends.
However backslash (\) is represented by \\ in Java, and \ is invalid regex, in order to escape it, you should use:
\\\\
↓ ↓
escaping
Solution:
Escape it as shown above
Don't escape, let Pattern#quote handle this for you
Related
I'm trying to build a Java regex to search a .txt file for a Windows formatted file path, however, due to the file path containing literal backslashes, my regex is failing.
The .txt file contains the line:
C\Windows\SysWOW64\ntdll.dll
However, some of the filenames in the text file are formatted like this:
C\Windows\SysWOW64\ntdll.dll (some developer stuff here...)
So I'm unable to use String.equals
To match this line, I'm using the regex:
filename = "C\\Windows\\SysWOW64\\ntdll.dll"
read = BufferedReader.readLine();
if (Pattern.compile(Pattern.quote(filename), Pattern.CASE_INSENSITIVE).matcher(read).find()) {
I've tried escaping the literal backslashes, using the replace method, i.e:
filename.replace("\\", "\\\\");
However, this is failing to find, I'm guessing this is because I need to further escape the backslashes after the Pattern has been built, I'm thinking I might need to escape upto an additional four backslashes, i.e:
Pattern.replaceAll("\\\\", "\\\\\\\\");
However, each time I try, the pattern doesn't get matched. I'm certain it's a problem with the backslashes, but I'm not sure where to do the replacement, or if there's a better way of building the pattern.
I think the problem is further being compounded as the replaceAll method also uses a regex, with means the pattern will have it's own backslashes in there, to deal with the case insensitivity.
Any input or advice would be appreciated.
Thanks
Seems like you're attempting to to a direct comparison of String against another. For exact matches, you could do (
if (read.equalsIgnoreCase(filename)) {
of simply
if (read.startsWith(filename)) {
Try this :
While reading each line from the file, replace '\' by '\\'.
Then :
String lLine = "C\\Windows\\SysWOW64\\ntdll.dll";
Pattern lPattern = Pattern.compile("C\\\\Windows\\\\SysWOW64\\\\ntdll\\.dll");
Matcher lMatcher = lPattern.matcher(lLine);
if(lMatcher.find()) {
System.out.println(lMatcher.group());
}
lLine = "C\\Windows\\SysWOW64\\ntdll.dll (some developer stuff here...)";
lMatcher = lPattern.matcher(lLine);
if(lMatcher.find()) {
System.out.println(lMatcher.group());
}
The correct usage will be:
String filename = "C\\Windows\\SysWOW64\\ntdll.dll";
String file = filename.replace('\\', ' ');
This is how i try to make sure a path given in a property file is a valid java path (with \\ instead of \) :
String path = props.getProperty("path");
if (path.length()>1) path=path.replaceAll("\\\\", "\\");
if (path.length()>1) path=path.replaceAll("\\", "\\\\");
in the first replace im making sure that if the path already valid (has \\ instead of \) then it wont get doubled to \\\\ instead of \\ in the second replace...
anyway i get this weird exception :
java.lang.StringIndexOutOfBoundsException: String index out of range: 1
at java.lang.String.charAt(Unknown Source)
at java.util.regex.Matcher.appendReplacement(Unknown Source)
at java.util.regex.Matcher.replaceAll(Unknown Source)
at java.lang.String.replaceAll(Unknown Source)
at com.hw.Launcher.main(Launcher.java:56)
can anyone tell why?!
replaceAll expects RegExes, use replace instead.
You can find the JavaDocs here
If you want to be sure the path is valid, how about trying
File f = new File("c:\\this\\that");
f.getCanonicalPath();
The File class is made for taking apart paths. It's probably the best way to verify that a path is valid.
(Let me spell it out for newbies too.)
If you have a text file or a String, normally only a single backslash should occur.
In java source code, a string or character denotation, backslash is the escape character, transforming the next one into a special meaning. Backslash itself should be given doubled, as \\. The string value itself will have only one backslash character.
If you read special text, using backslash escaping (like \n for a line break), then use the non-regex replace of strings:
// First escapes of other:
path = path.replace("\\n", "\n"); // Text `\n` -> linefeed
path = path.replace("\\t", "\t"); // Text `\t` -> tab
// Then escape of backslash:
path = path.replace("\\\\", "\\"); // Text `\\` -> backslash
For file paths only the last might make sense, but it should not have been needed.
I have a String as folder/File Name. I am creating folder , file with that string. This string may or may not contain some charters which may not allow to create desired folder or file
e.g
String folder = "ArslanFolder 20/01/2013";
So I want to remove these characters with "_"
Here are characters
private static final String ReservedChars = "|\?*<\":>+[]/'";
What will be the regular expression for that? I know replaceAll(); but I want to create a regular expression for that.
Use this code:
String folder = "ArslanFolder 20/01/2013 ? / '";
String result = folder.replaceAll("[|?*<\":>+\\[\\]/']", "_");
And the result would be:
ArslanFolder 20_01_2013 _ _ _
you didn't say that space should be replaced, so spaces are there... you could add it if it is necessary to be done.
I used one of this:
String alphaOnly = input.replaceAll("[^\\p{Alpha}]+","");
String alphaAndDigits = input.replaceAll("[^\\p{Alpha}\\p{Digit}]+","");
See this link:
Replace special characters
Try this :
replaceAll("[\\W]", "_");
It will replace all non alphanumeric characters with underscore
This is correct solution:
String result = inputString.replaceAll("[\\\\|?\u0000*<\":>+\\[\\]/']", "_");
Kent answer is good, but he isnt include characters NUL and \.
Also, this is a secure solution for replacing/renaming text of user-input file names, for example.
I am trying to replace '\\'with '/' in java(Android) and this does not seem to work!
String rawPath = filePath.replace("\\\\", "/");
What is wrong with this ? I have escaped "\" and tried escaping '/' but to no use. Nothing happens to the original string.
filePath = abc\\xyz(not after escaping two \\, the original string is with two \\)
rawPath = abc \ xyz
expected = abc/xyz
Whats the correct way of doing this? (Another Windows file to Android path conversion prob)
When using String.replace(String, String) the backslash doesn't need to be escaped twice (thats when using replaceAll - it deals with regex). So:
String rawPath = filePath.replace("\\", "/");
Or using char version:
String rawPath = filePath.replace('\\', '/');
You do not need the quad-druple escape,
\\\\
, just simply
\\
.
escape with single slash should be enough. Following is working fine for me.
String rawPath = filePath.replace("\\", "/");
public static void main(String[] args) {
String s = "foo\\\\bar";
System.out.println(s);
System.out.println(s.replace("\\\\", "/"));
}
will print
foo\\bar
foo/bar
If you want to replace a sequence of 2 backslashes in your original string with a single forward slash, this should work:
String filePath = "abc\\\\xyz";
String rawPath = filePath.replace("\\\\", "/");
System.out.println(filePath);
System.out.println(rawPath);
outputs:
abc\\xyz
abc/xyz
Do you really have two backslashes in the String in the first place? That only appears in Java source code. At runtime there will only be one backslash. So the task reduces to changing backslashes to forward slashes (why?). For which you need a regex if you are using replaceAll(), which would require four of them: two for the compiler, and two for the regex, but you aren't using that, you are using replace(), which isn't a regex, so you only need two, one for the compiler and one for itself.
Why are you doing this? It is never necessary to use a backslash in a File path in Java at all, and it is also never necessary to translate them to / unless you are doing URL-like things with them, in which case there are File.toURI() methods and URI and URL classes for that.
Here is a very small method to get the desktop path and show you how to replace them in the return statement.
public static String getDesktopPath() {
String desktopPath = System.getProperty("user.home") + "/Desktop";
return desktopPath.replace("\\", "/");
}
I have a complete file path and I want to get the file name.
I am using the following instruction:
String[] splittedFileName = fileName.split(System.getProperty("file.separator"));
String simpleFileName = splittedFileName[splittedFileName.length-1];
But on Windows it gives:
java.util.regex.PatternSyntaxException: Unexpected internal error near index 1
\
^
Can I avoid this exception? Is there a better way to do this?
The problem is that \ has to be escaped in order to use it as backslash within a regular expression. You should either use a splitting API which doesn't use regular expressions, or use Pattern.quote first:
// Alternative: use Pattern.quote(File.separator)
String pattern = Pattern.quote(System.getProperty("file.separator"));
String[] splittedFileName = fileName.split(pattern);
Or even better, use the File API for this:
File file = new File(fileName);
String simpleFileName = file.getName();
When you write a file name, you should use System.getProperty("file.separator").
When you read a file name, you could possibly have either the forward slash or the backward slash as a file separator.
You might want to try the following:
fileName = fileName.replace("\\", "/");
String[] splittedFileName = fileName.split("/"));
String simpleFileName = splittedFileName[splittedFileName.length-1];
First of all, for this specific problem I'd recommend using the java.util.File class instead of a regex.
That being said, the root of the problem you're running into is that the backslash character '\' signifies an escape sequence in Java regular expressions. What's happening is the regex parser is seeing the backslash and expecting there to be another character after it which would complete the escape sequence. The easiest way to get around this is to use the java.util.regex.Pattern.quote() method which will escape any special characters in the string you give it.
With this change your code becomes:
String splitRegex = Pattern.quote(System.getProperty("file.separator"));
String[] splittedFileName = fileName.split(splitRegex);
String simpleFileName = splittedFileName[splittedFileName.length-1];
Another simpler way could be to do
File f = new File(path);
String fileName = f.getName();
I believe this will work provided the paths are compatible with the platform, i.e. not sure if path "c:\file.txt" will work on Linux or not.