How to run python within java?

abc73 · Nov 28, 2004

I want to run python command within java. Not sure how to do this. Seems like runtime.getRuntime.exec() is something that I can use. Can I run python command using getRuntime().. Please let me know. I am trying to change the file permission using python, now I need to call the python within java. Can anyone help plz.

Thank

sedj · Nov 28, 2004

I will not try to understand why you would want to do something in python from Java ... in any case, if you can run your python command from the shell/command line console, then you can run it by using Runtime.exec().

--------------------------------------------------
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http://www.primrose.org.uk

jwenting · Nov 29, 2004

You can use Jython which is a Python implementation in Java.
Haven't tried interaction between Jython and a host application yet but it is designed to plug into Java applications so it shouldn't be hard.

http://www.jython.org

Note: Jython does at this time lag quite seriously to Python development

abc73 · Nov 29, 2004

I am trying to execute some code written in python inside java. But so far no success. Here is the sample I am trying to run. Please see the below code:

I get the following exception at runtime and my python is not being executed. I am on windows and python is in the path.

Code:

java.io.IOException: CreateProcess: C:\Documents and Settings\TEST\Desktop\PYTHON\c.py error=193

int java.lang.Win32Process.create(java.lang.String, java.lang.String, java.lang.String, java.io.FileDescriptor, java.io.FileDescriptor, java.io.FileDescriptor)

void java.lang.Win32Process.<init>(java.lang.String[], java.lang.String[], java.lang.String)

java.lang.Process java.lang.Runtime.execInternal(java.lang.String[], java.lang.String[], java.lang.String)

java.lang.Process java.lang.Runtime.exec(java.lang.String[], java.lang.String[], java.io.File)

java.lang.Process java.lang.Runtime.exec(java.lang.String, java.lang.String[], java.io.File)

java.lang.Process java.lang.Runtime.exec(java.lang.String, java.lang.String[])

java.lang.Process java.lang.Runtime.exec(java.lang.String)

void RuntimeTest.main(java.lang.String[])

Now here is the java code that I am trying to execute:

Code:

import java.io.*;

public class RuntimeTest
{
public static void main(String[] args)
{ 
try 
{
Runtime r = Runtime.getRuntime();
Process p = r.exec("C:\\Documents and Settings\\TEST\\Desktop\\PYTHON\\c.py");
p.waitFor();
} 
catch (Exception e) 
{
e.printStackTrace();
}
}
}

And here is the python code that I am trying to run inside java:

Code:

import os
from stat import *

print "SUCCESS"

Thanks for the help.

sedj · Nov 29, 2004

How do you run the code from the command line ? Post that.

There are several problems anyway :

1) Your use of spaces in the file to the .py file are problematic - try not to use them. If you do, you will need to encapsualte them in quotes.
2) It looks like you are trying to execute a file - where is the command to invoke the python interpreter ?
3) You need to invoke a new shell, not use the existing shell when working on Win32.

EG:

Code:

Process p = Runtime.getRuntime().exec("cmd /c dir \"C:/Documents and Settings\"");
BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
String line = "";
while ((line = br.readLine()) != null) {
	System.out.println(line);
}

--------------------------------------------------
Free Database Connection Pooling Software

http://www.primrose.org.uk

abc73 · Nov 29, 2004

I got execution part working. I am trying to make a read only file to writable. As I can't find a method to set a read only file to writable in java so I was trying to use python and invoke it inside java. Right now python code is being executed but it's npt changing the file permission. If I run the python code stand alone it changes the file permission but invoking inside java doesn't change the file permission. Can you please help. Here is my python code:

Code:

import os
from stat import *

os.chmod("test.txt",666)
print "SUCCESS"

And here is the java code, modified according to the above suggestions (Thanks):

Code:

import java.io.*;

public class pythonTest
{
	public static void main(String[] args)
	{ 
		try 
		{
			Runtime r = Runtime.getRuntime();
			Process p = r.exec("cmd /c C:\\c.py");
			p.waitFor();
			BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
			String line = "";
			while ((line = br.readLine()) != null)
			{
    			System.out.println(line);
			}
			p.waitFor();

		} 
		catch (Exception e) 
		{
			e.printStackTrace();
		}
	}
}

Thanks for helping me out.

sedj · Nov 29, 2004

Why are you doing p.waitFor(); twice ?

Perhaps you should change the file to its full path in this line :

os.chmod("test.txt",666)

--------------------------------------------------
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http://www.primrose.org.uk

Diancecht · Nov 29, 2004

Well, if you have already lost cross-platform issue, I don't think you need Python anymore.

You can change file permission by executing in Windows attrib +r filename, that would make things easier.

Runtime.getRuntime().exec("cmd / c attrib +R file.ext");

Btw, did you try the API someone mentioned in your other post? Did it work? I'm a bit curious about it.

Cheers.

Dian

sedj · Nov 29, 2004

Nice suggestion on the attrib Dian ! My DOS is not up to much !

I bet that other API does something similar to this :

Code:

		String file = "C:/permissions.txt";

		// RW
		if (System.getProperty("os.name").indexOf("Windows") != -1) {
			Runtime.getRuntime().exec("cmd /c attrib -R " +file);
		} else {
			Runtime.getRuntime().exec("chmod -R 775 " +file);
		}

		// RO
		if (System.getProperty("os.name").indexOf("Windows") != -1) {
			Runtime.getRuntime().exec("cmd /c attrib +R " +file);
		} else {
			Runtime.getRuntime().exec("chmod -R 444 " +file);
		}

--------------------------------------------------
Free Database Connection Pooling Software

http://www.primrose.org.uk

abc73 · Nov 29, 2004

PeDidn't specify the full path in this line :

os.chmod("test.txt",666)

Thanks for all the help.

Diancecht · Nov 29, 2004

He he, when I started with this computer thingie, there was no mouse to right-click anything, so command line was the only option. Even today, give a MS-DOS command or Unix shell and I'll give you my mouse

Btw, good suggestion for the API sedj, I find it really interesting, dealing with native filesystem is always a headache when you need cross-platform, but atm I have no time to take a look at that. Will put it on the TODO list.

Cheers.

Dian

sedj · Nov 29, 2004

Diancecht :

>>>> He he, when I started with this computer thingie, there was no mouse to right-click anything

Double Hehehehe - when I started there was bairly a cmd shell left in Windows !!

rockets12345 :

I would dump using Python. Its bad enough shelling out to run OS commands, without shelling out to run another interpreted langauge, which will ultimately just run the OS command anyway !

--------------------------------------------------
Free Database Connection Pooling Software

http://www.primrose.org.uk

abc73 · Nov 29, 2004

Anyways I did triee the following earlier too but somehow doesn't work: (file = permissions to be changed)

Runtime.getRuntime().exec("cmd /c attrib -R " +file);

I even tried:
Runtime.getRuntime().exec("cmd /c attrib +R " +file);

and no effect, that's why I used python and it does change the file permission.

Thanks

sedj · Nov 29, 2004

This will make your file read-write :
Runtime.getRuntime().exec("cmd /c attrib -R " +file);

This will make your file read-only :
Runtime.getRuntime().exec("cmd /c attrib +R " +file);

I can assure you it works ... are you passing in the whole path to the file ?

--------------------------------------------------
Free Database Connection Pooling Software

http://www.primrose.org.uk

abc73 · Nov 29, 2004

thanks my problem spacing. I got it thanks.

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