This question looks like very similar to: Concatenating null strings in Java
But my issue is some different.
I want to build an absolute path to a file:
String path = properties.get("path"); // returns /home/myuser/relativepath/ , ends with bar /
String file = currentFile; // currentFile values "file.txt"
String result = path + file; // this results in /home/myuser/relativepath/nullfile.txt
Why is there than 'null' text? That's the reason my application does not work now.
I have review it in Windows and Linux.
In Windows it works perfectly.
In Linux, I have this issue.
I uploaded properties file and then, edited with vi command.
Maybe is this the problem?
Shouldn't I use this way to generate an absolute path, and use File.Separator property in Java?
EDIT: I have post my final right answer with detailed steps. I hope it would be useful.
My bet (though I have not seen Java behave this way) is there's a null-ish character (such as a carriage return) of some sort in your properties file which Windows handles at the OS level so Java/Properties doesn't see it.
As a first pass, try printing the length and last few characters of your path string, e.g.:
for(int i = Math.max(0, path.length()-5); i < path.length(); i++) {
System.out.print(path.charAt(i)+":"+((int)path.charAt(i))+" ");
}
System.out.println(path.length());
Willing to bet the last character, on Linux, is not what you'd expect. The right fix would then be to clean up your properties file so that it's compatible on both OSes.
Well, the complete and detailed steps to fix my issue are these (maybe any of them could not be necessary, but I prefer to write them all):
Create config file in Linux with vi, emacs, ... (not upload file from Windows).
Edit file with vi, emacs... At the end of each path, do not include directory separator character ( / ).
Check variables before contatenate them. Make sure they don't have any space and other unexpected character.
Concatenate variables with:
String result = path + File.separator + file;
I hope this would be useful. Thank you all for your suggestions.
Regards
What do you expect?
Yo´re doing a String result = path + result;
int a = 1 + a would be similar... don´t use a variable to init itself.
(That can´t be your code in the first place, if you´re getting this output.)
result is path+file :
String path = properties.get("path");
String file = currentFile;
String result = path + file;
^
change here
the result is: /home/myuser/relativepath/file.txt
Related
I am making an HTTP Server in Java so that (on start) it finds all files in a directory (and it's sub-directories) and adds them to the server. But when getting the path of a file and trying to give it to HttpServer.createContext(), it throws a java.lang.IllegalArgumentException: Illegal value for path or protocol. (with the string argument, say "\folder/index.html"). To get this value, I used
file.getParent().substring(24) + "/" + file.getName()
I used substring because I had to exclude the folder the web server is in. The illegal character is the backslash. I have tried extending File to change separator and separatorChar, but that only created 2 new variables. While using String.replace() didn't seem to have any effect. Is there a different method than File.getParent or File.getPath that I can use, or is there a way to use String.replace that I am not seeing?
EDIT:
String.replace() seems to be the best answer... But I am not completely sure how to use it.
EDIT 2: For some reason the backslash isn't showing up, so I changed it.
You have to use the java System.getProperty.
Notice that, in this context, "file.separator" is a key which we are
using to get this property from current system executing the java VM.
Insteady of using a slash (/), you should choose a platform agnostic file separator, as an example it should be:
String separator = System.getProperty("file.separator");
System.out.println(separator);
// unix / , windows \
Have a look at Paths.get(...)
Try Paths.get(".") // current working directory.
Or tell it, on which path it should start:
Use System.getProperty("user.dir"), for current loged in user, home directory.
String pathStr = "/";
Path homeDir = Paths.get(System.getProperty("user.dir"))
Getting from the user directory into the data directory: homeDir.get("data")
Path dataPath = Paths.get(System.getProperty("user.dir"));
File dataFile = dataPath.toFile();
Now use operations on dataFile, to check what files and directories there are, on that location of the file system.
I am making a simple MP3 player and have imported mp3 files from a certain directory. I want to change the path to have double backslashes, however it's not registering.
matchingFiles = dir.listFiles(textFilter);
for(int i = 0; i<matchingFiles.length; i++){
String s = matchingFiles[i].toString();
String t = s.replace("\\", "\\\\");
matchingFiles[i] = new File(t);
System.out.println(matchingFiles[i]);
fileList.add(matchingFiles[i]);
}
The print gives single backslashes, while t has double. File.renameTo() didn't seem to work either, so I'm wondering how to change the path in an existing File.
The File class aims at representing system paths in its own way, well, the system way. In other words, File understands paths as folders seperated by \, not \\. You can't change that. The question is, why would you?
I am working in a java code that was designed to run on windows and contains a lot of references to files using windows style paths "System.getProperty("user.dir")\trash\blah". I am in charge to adapt it and deploy in linux. Is there an efficient way to convert all those paths(\) to unix style (/) like in "System.getProperty("user.dir")/trash/blah". Maybe, some configuration in java or linux to use \ as /.
My approach is to use the Path object to hold the path information, handle concatenate and relative path. Then, call Path's toString() to get the path String.
For converting the path separator, I preferred to use the apache common io library's FilenameUtils. It provides the three usefule functions:
String separatorsToSystem(String path);
String separatorsToUnix(String path);
String separatorsToWindows(String path)
Please look the code snippet, for relative path, toString, and separator changes:
private String getRelativePathString(String volume, Path path) {
Path volumePath = Paths.get(configuration.getPathForVolume(volume));
Path relativePath = volumePath.relativize(path);
return FilenameUtils.separatorsToUnix(relativePath.toString());
}
I reread your question and realize you likely don't need help writing paths. For what you're trying to do I am not able to find a solution. When I did this in a project recently I had to take time to convert all paths. Further, I made the assumption that working out of the "user.home" as a root directory was relatively sure to include write access for that user running my application. In any case, here are some path problems I addressed.
I rewrote the original Windows code like so:
String windowsPath = "C:\temp\directory"; //no permission or non-existing in osx or linux
String otherWindowsPath = System.getProperty("user.home") + "\Documents\AppFolder";
String multiPlatformPath = System.getProperty("user.home") + File.separator + "Documents" + File.separator + "AppFolder";
If you're going to be doing this in a lot of different places, perhaps write a utility class and override the toString() method to give you your unix path over and over again.
String otherWindowsPath = System.getProperty("user.home") + "\Documents\AppFolder";
otherWindowsPath.replace("\\", File.separator);
Write a script, replace all "\\" with a single forward slash, which Java will convert to the respected OS path.
I have a file path location as such:
Properties readProp = \\192.168.41.84\dev\config\dev\config.properties
how can I manipulate it so I remove the portion of config.properties
and replace it with test\config.properties
so the new Properties location would be:
Properties readProp = \\192.168.41.84\dev\config\dev\test\newconfig.properties
?
thanks for your time and effort
Make sure you escape any backslashes you have as you build the string.
String path = "\\\\192.168.41.84\\dev\\config\\dev\\config.properties";
System.out.println(path);
int lastBackSlash = path.lastIndexOf("\\");
//+1 to include lastBackSlash
String newPath = path.substring(0, lastBackSlash + 1) + "test" + path.substring(lastBackSlash);
System.out.println(newPath);
Prints
\\192.168.41.84\dev\config\dev\config.properties
\\192.168.41.84\dev\config\dev\test\config.properties
This article like this is also decent read. Treating paths as strings can be dangerous.
http://twistedoakstudios.com/blog/Post4872_dont-treat-paths-like-strings
However, if your careful, know what how your string functions behave(or look them up), and you don't have off by 1 errors... then treating the paths like strings should be pain free. But you will have no guarantee that the path is valid... while a path builder library would give you that assurance.
I am trying to list the number of files in a directory. But I am unable to get so and I suspect it has got to do with the white space in the parent directory names.
What I am doing is in a .properties file I set the value as -
dir.loc=H:/Main/dir one/dir - two/dir3/dir four
dir.name=Run
Now in a jave file I set these values to String variables as -
String s1 = properties.getProperty("dir.loc");
String s2 = properties.getProperty("dir.name");
I create a File object as -
File f = new File(s1, s2);
File[] fList = f.listFiles();
Now here the fList is null;
The H drive is on another remote machine and I reckon the java program tries to locate the 'Run' directory locally rather than finding it on H drive and because it does not find 'Run' the list return null.
When I tried in a simple java class as -
File f = new File("H:/Main/dir one/dir - two/dir3/dir four", "Run");
then I do get the result with f.listFiles().length;
So I guess it might have to do something with extracting the value from properties file and assigning it to a String variable.
Am I correct in my assumption?
What could be possible solution to this problem?
Yes, you are right. Values are screwed up when reading them from the properties file.
Do this instead:
dir.loc="H:/Main/dir one/dir - two/dir3/dir four"
Ok, I found the solution for my problem, quite simple actually.
I did the following -
In properties file -
dir.loc=H:/Main/dir one/dir - two/dir3/dir four/Run
In a config java file -
String s1 = properties.getProperty("dir.loc");
In my java program -
File tempF = new File(s1);
File dirLoc = new File(tempF.getAbsolutePath());
dirLoc.listFiles().length; gives out a number.
The comment by #barti_ddu about getAbsolutePath() got me into bit of thinking about may be using that.
Is anything wrong with this solution or is not quite a decent one?
Thank you all.
It looks like you simply need to trim the value of your properties.
In the code you have shown, the
dir.loc=H:/Main/dir one/dir - two/dir3/dir four
has trailing spaces.
Does this:
String s1 = properties.getProperty("dir.loc").trim();
String s2 = properties.getProperty("dir.name").trim();
fix it?