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Using MS-DOS Commands Within Java App to Create Files

Posted on 2013-01-23
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Last Modified: 2013-01-23
I am using the Runtime.getRuntime().exec() method to run MS-DOS commands to, for example, create files.  One example is to execute “dir *abc* /s /b > abc.txt” to create a text file containing the full path names of every file whose filename contains the characters “abc”.

After the successful execution of that command, the Java app does not know that the new file, abc.txt, exists.

Is there something else that must be done to let Java know that this file exists?
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Question by:david_m_jacobson
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9 Comments
 
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Expert Comment

by:krakatoa
ID: 38811100
You need to make Java see the new file after the exec() returns.

Should be as easy as :

File f = new File("abc.txt");
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LVL 86

Expert Comment

by:CEHJ
ID: 38811265
a. you would need to execute a shell to use stream redirection successfully (i.e. your command must begin with cmd.exe)
b. you don't need to do that to produce a file of paths - Java already has the power to do that without invoking the OS
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Author Comment

by:david_m_jacobson
ID: 38812135
Thank you for that suggestion, but it doesn't work for me.  Here is a snippet of code I am using:

commandLine = "cmd /c dir *\"" + param[0] + "\"* /s /b > \"" + input_filename + "\"";
System.out.println(commandLine);
process = Runtime.getRuntime().exec(commandLine, null, pictures_directoryName_File);
File aFile = new File(input_filename);
if (aFile.exists())
      System.out.println(input_filename + " exists");
else
      System.out.println(input_filename + " does NOT exist");
System.exit(0);

The output looks as follows:

cmd /c dir *"abc"* /s /b > "C:\Users\my_user_name\Desktop\Temporary\abc.txt"
C:\Users\my_user_name\Desktop\Temporary\abc.txt does NOT exist

So clearly, Java doesn't know that 'abc.txt' exists; yet it does exist.

Any other suggestions?
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LVL 86

Accepted Solution

by:
CEHJ earned 500 total points
ID: 38812176
If you're determined to do it that way, you need to do it right. See
http://technojeeves.com/joomla/index.php/free/52-runtimeexec
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Author Comment

by:david_m_jacobson
ID: 38812364
Thank you very much.  Reading through the suggested "theory" link brought my attention of the 'waitFor()' method of the Process class, and appears to have solved my problem.

Thank you very much!!
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Author Comment

by:david_m_jacobson
ID: 38812387
I've requested that this question be closed as follows:

Accepted answer: 0 points for david_m_jacobson's comment #a38812364

for the following reason:

I was not rating my own comment here, but rather the Expert's previous comment.
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LVL 86

Expert Comment

by:CEHJ
ID: 38812388
I think you might have closed the question in a way you didn't intend ...
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Author Comment

by:david_m_jacobson
ID: 38812723
You are right.  I am about to correct that.  Thank you again.
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Author Closing Comment

by:david_m_jacobson
ID: 38812725
Thank you very much.
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