Changing the current working directory in Java

Question

How can I change the current working directory from within a Java program  Everything I ve been able to find about the issue claims that you simply can t do it  but I can t believe that that s really the case   I have a piece of code that opens a file using a hard-coded relative file path from the directory it s normally started in  and I just want to be able to use that code from within a different Java program without having to start it from within a particular directory  It seems like you should just be able to call System setProperty   user dir     path to dir     but as far as I can figure out  calling that line just silently fails and does nothing   I would understand if Java didn t allow you to do this  if it weren t for the fact that it allows you to get the current working directory  and even allows you to open files using relative file paths

User · Answer

It is possible to change the PWD  using JNA JNI to make calls to libc  The JRuby guys have a handy java library for making POSIX calls called jna-posix Here s the maven info  You can see an example of its use here  Clojure code  sorry   Look at the function chdirToRoot

User · Answer

There is no reliable way to do this in pure Java  Setting the user dir property via System setProperty   or java -Duser dir     does seem to affect subsequent creations of Files  but not e g  FileOutputStreams   The File String parent  String child  constructor can help if you build up your directory path separately from your file path  allowing easier swapping   An alternative is to set up a script to run Java from a different directory  or use JNI native code as suggested below   The relevant Sun bug was closed in 2008 as  will not fix

User · Answer

You can use      new File  relative path   getAbsoluteFile      after      System setProperty  user dir     some directory     System setProperty  user dir    C  OtherProject    File file   new File  data data csv   getAbsoluteFile    System out println file getPath       Will print  C  OtherProject data data csv

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The other possible answer to this question may depend on the reason you are opening the file   Is this a property file or a file that has some configuration related to your application   If this is the case you may consider trying to load the file through the classpath loader  this way you can load any file Java has access to

User · Answer

Use FileSystemView   private FileSystemView fileSystemView  fileSystemView   FileSystemView getFileSystemView    currentDirectory   new File         listing currentDirectory File   filesAndDirs   fileSystemView getFiles currentDirectory  false   fileList   new ArrayList lt File gt     dirList   new ArrayList lt File gt     for  File file   filesAndDirs    if  file isDirectory        dirList add file   else     fileList add file     Collections sort dirList   if   fileSystemView isFileSystemRoot currentDirectory       dirList add 0  new File         Collections sort fileList     change currentDirectory   fileSystemView getParentDirectory currentDirectory

User · Answer

If I understand correctly  a Java program starts with a copy of the current environment variables  Any changes via System setProperty String  String  are modifying the copy  not the original environment variables  Not that this provides a thorough reason as to why Sun chose this behavior  but perhaps it sheds a little light

User · Answer

The smarter easier thing to do here is to just change your code so that instead of opening the file assuming that it exists in the current working directory  I assume you are doing something like new File  blah txt    just build the path to the file yourself   Let the user pass in the base directory  read it from a config file  fall back to user dir if the other properties can t be found  etc  But it s a whole lot easier to improve the logic in your program than it is to change how environment variables work

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If you run your commands in a shell you can write something like  java -cp  and add any directories you want separated by     if java doesnt find something in one directory it will go try and find them in the other directories  that is what I do

User · Answer

The working directory is a operating system feature  set when the process starts    Why don t you just pass your own System property  -Dsomeprop  my path  and use that in your code as the parent of your File   File f   new File   System getProperty  someprop    myFilename

User · Answer

As mentioned you can t change the CWD of the JVM but if you were to launch another process using Runtime exec   you can use the overloaded method that lets you specify the working directory  This is not really for running your Java program in another directory but for many cases when one needs to launch another program like a Perl script for example  you can specify the working directory of that script while leaving the working dir of the JVM unchanged   See Runtime exec javadocs  Specifically   public Process exec String   cmdarray String   envp  File dir  throws IOException   where dir is the working directory to run the subprocess in

User · Answer

I have tried to invoke  String oldDir   System setProperty  user dir   currdir getAbsolutePath      It seems to work  But   File myFile   new File  localpath ext     InputStream openit   new FileInputStream myFile    throws a FileNotFoundException though  myFile getAbsolutePath    shows the correct path   I have read this  I think the problem is    Java knows the current directory with the new setting  But the file handling is done by the operation system  It does not know the new set current directory  unfortunately     The solution may be    File myFile   new File System getPropety  user dir     localpath ext     It creates a file Object as absolute one with the current directory which is known by the JVM  But that code should be existing in a used class  it needs changing of reused codes       JcHartmut

User · Answer

You can change the process s actual working directory using JNI or JNA    With JNI  you can use native functions to set the directory  The POSIX method is chdir    On Windows  you can use SetCurrentDirectory      With JNA  you can wrap the native functions in Java binders   For Windows   private static interface MyKernel32 extends Library       public MyKernel32 INSTANCE    MyKernel32  Native loadLibrary  Kernel32   MyKernel32 class            BOOL SetCurrentDirectory  LPCTSTR lpPathName           int SetCurrentDirectoryW char   pathName       For POSIX systems   private interface MyCLibrary extends Library       MyCLibrary INSTANCE    MyCLibrary  Native loadLibrary  c   MyCLibrary class            int chdir const char  path          int chdir  String path

User · Answer

If you run your legacy program with ProcessBuilder  you will be able to specify its working directory

User · Answer

There is a way to do this using the system property  user dir    The key part to understand is that getAbsoluteFile   must be called  as shown below  or else relative paths will be resolved against the default  user dir  value   import java io     public class FileUtils       public static boolean setCurrentDirectory String directory name                boolean result   false      Boolean indicating whether directory was set         File    directory           Desired current working directory          directory   new File directory name  getAbsoluteFile            if  directory exists      directory mkdirs                          result    System setProperty  user dir   directory getAbsolutePath       null                      return result             public static PrintWriter openOutputFile String file name                PrintWriter output   null      File to open for writing          try                       output   new PrintWriter new File file name  getAbsoluteFile                       catch  Exception exception              return output             public static void main String   args  throws Exception               FileUtils openOutputFile  DefaultDirectoryFile txt            FileUtils setCurrentDirectory  NewCurrentDirectory            FileUtils openOutputFile  CurrentDirectoryFile txt

[java] Changing the current working directory in Java?

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