Java ProcessBuilder not able to run Python script in Java

Question

null from bfr.readLine()

However, there is no problem if I run the python file directly on terminal by firing:

python C:/Machine_Learning/Text_Analysis/Ontology_based.py

The last line in my Python script is >> print(data)

The result of the following code is:

Running Python starts:

First Line: null

Picked up _JAVA_OPTIONS: -Xmx512M

package text_clustering;

import java.io.*;

public class Similarity {

    /**
     * 
     * @param args
     * 
     */
    public static void main(String[] args){
        try{
            String pythonPath = "C:/Machine_Learning/Text_Analysis/Ontology_based.py";
            //String pythonExe = "C:/Users/AppData/Local/Continuum/Anaconda/python.exe";
            ProcessBuilder pb = new ProcessBuilder("python", pythonPath);
            Process p = pb.start();
            
            BufferedReader bfr = new BufferedReader(new InputStreamReader(p.getInputStream()));
            String line = "";
            System.out.println("Running Python starts: " + line);
            line = bfr.readLine();
            System.out.println("First Line: " + line);
            while ((line = bfr.readLine()) != null){
                System.out.println("Python Output: " + line);
                
                
            }

        }catch(Exception e){System.out.println(e);}
    }

}

You'd better grab the error stream as well and check what it's putting out as you may have an error situation. Alternatively you could combine the error stream with the input stream, and read that. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Oct 3, 2014 at 1:01
@HovercraftFullOfEels,THANKS! Sorry, I am a newbie in both Java and Python... so do u mean that in the Java code block, instead of catch Exception, I throw Exception? Many Thanks again! — Yue Harriet Huang
– Yue Harriet Huang, Commented Oct 3, 2014 at 1:05
No. Change your catch block though to e.printStackTrace() for more information, but that's a separate issue. I mean that you should capture the ErrorStream just as you do the InputStream. But easiest just to call pb.redirectErrorStream(true); to redirect the error stream into the input stream. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Oct 3, 2014 at 1:10
hmmm, I added pb.redirectErrorStream(true) in the try{} block and e.printStackTrace() in the catch{} block... but it seems nothing chance? Am I missing something? would you mind showing an example please? Thanks so much — Yue Harriet Huang
– Yue Harriet Huang, Commented Oct 3, 2014 at 1:18
My recommendation was only to see if errors were occurring that you did not see. As long as you're redirecting the error stream immediately after creating your ProcessBuilder object, you're following my recommendations. Then something else might be wrong. How do you run your python script if you weren't using Java? Do you need to give the full path to python.exe? — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Oct 3, 2014 at 1:24

shazin · Accepted Answer · 2014-10-03 07:18:16Z

Usually when executing commands using ProcessBuilder, PATH variable is not taken into consideration. Your python C:/Machine_Learning/Text_Analysis/Ontology_based.py is directly working in your CMD shell because it can locate the python executable using the PATH variable. Please provide the absolute path to python command in your Java code. In below code replace <Absolute Path to Python> with the path to python command and its libraries. Usually it will something like C:\Python27\python in Windows by default

package text_clustering;

import java.io.*;

public class Similarity {

    /**
     * 
     * @param args
     * 
     */
    public static void main(String[] args){
        try{
            String pythonPath = "C:/Machine_Learning/Text_Analysis/Ontology_based.py";
            //String pythonExe = "C:/Users/AppData/Local/Continuum/Anaconda/python.exe";
            ProcessBuilder pb = new ProcessBuilder(Arrays.asList("<Absolute Path to Python>/python", pythonPath));
            Process p = pb.start();

            BufferedReader bfr = new BufferedReader(new InputStreamReader(p.getInputStream()));
            String line = "";
            System.out.println("Running Python starts: " + line);
            int exitCode = p.waitFor();
            System.out.println("Exit Code : "+exitCode);
            line = bfr.readLine();
            System.out.println("First Line: " + line);
            while ((line = bfr.readLine()) != null){
                System.out.println("Python Output: " + line);


            }

        }catch(Exception e){System.out.println(e);}
    }

}

Enno Shioji · Accepted Answer · 2014-10-03 07:07:43Z

0

Reading from stdin returns null when the script is killed/dies. Do a Process#waitFor and see what the exitValue is. If it isn't 0 then it's highly probable that your script is dying.

I'd try making it work with a dumb script that only writes a value. Make sure that you print all error information from python.

answered Oct 3, 2014 at 7:07

Enno Shioji

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Comments

Petter Friberg · Accepted Answer · 2016-10-05 08:39:44Z

0

try {

    Process p = Runtime.getRuntime().exec(
            "python   D://input.py   ");
    BufferedReader in = new BufferedReader(new InputStreamReader(
            p.getInputStream()));

    String line;  
        while ((line = in.readLine()) != null) {  
            System.out.println(line);  
        }  
        in.close();
        p.waitFor();



} catch (Exception e) {
}

edited Oct 5, 2016 at 8:39

Petter Friberg

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answered Oct 5, 2016 at 8:36

bob90937

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Comments

Arayan Singh · Accepted Answer · 2020-01-10 08:28:03Z

0

try {
    ProcessBuilder pb = new ProcessBuilder("C:/Python27/python", "D://searchTestJava//input.py");
    Process p = pb.start();
    BufferedReader bfr = new BufferedReader(new InputStreamReader(p.getInputStream()));

    System.out.println(".........start   process.........");
    String line = "";
    while ((line = bfr.readLine()) != null) {
        System.out.println("Python Output: " + line);
    }

    System.out.println("........end   process.......");

} catch (Exception e) {
    System.out.println(e);
}

edited Jan 10, 2020 at 8:28

Arayan Singh

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answered Oct 5, 2016 at 9:02

bob90937

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1 Comment

croxy Over a year ago

A little explanation of what your code does wouldn't be bad.

Arayan Singh · Accepted Answer · 2020-01-14 07:22:34Z

I tried this one. This script runs a python file with the argument in Java. It also logs about which line, your program is executing. Hope this Helps.

    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStreamReader;
    import java.io.Reader;

    public class Test {
      public static void main(String... args) throws IOException {

        ProcessBuilder pb =
                new ProcessBuilder("python","samples/test/table_cv.py","1.pdf");

        pb.redirectErrorStream(true);
        Process proc = pb.start();

        Reader reader = new InputStreamReader(proc.getInputStream());
        BufferedReader bf = new BufferedReader(reader);
        String s;
        while ((s = bf.readLine()) != null) {
            System.out.println(s);
        }
    }
  }

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