程序终止，没有任何错误

Question

I am trying to run this Python program in Java.

Issue: When i run this program from Commandline: Python msp.py dennys-san-jose-2 - it WORKS

When I call the same script through this java program. It just terminates. I tested other python scripts and they work!

public void pythonrun(String args) throws IOException, InterruptedException
{
    String pythonScriptPath = "/yelp/msp.py";
    String[] cmd = new String[2 + args.length()];
    cmd[0] = "C:\\Python27\\python.exe";
    cmd[1] = pythonScriptPath;
    for(int i = 0; i < args.length(); i++) {
    cmd[i+2] = args;
    }

    // create runtime to execute external command
    Runtime rt = Runtime.getRuntime();
    Process pr = rt.exec(cmd);
    //pr.waitFor();

    // retrieve output from python script
    BufferedReader bfr = new BufferedReader(new InputStreamReader(pr.getInputStream()));
    String line = "";
    while((line = bfr.readLine()) != null) {
    // display each output line form python script
    System.out.println(line);
    }
}

public static void main(String args[]) throws IOException, InterruptedException {
YelpPython demo = new YelpPython();
demo.pythonrun("dennys-san-jose-2");
}

Script (msp.py):

What it does? (in short, the script goes to a page and scrapes the reviews)

from bs4 import BeautifulSoup
from urllib import urlopen
import sys
queries = 0
while queries <201:
    stringQ = sys.argv[1]
    page = urlopen('http://www.yelp.com/biz/' + stringQ)

    soup = BeautifulSoup(page)
    reviews = soup.findAll('p', attrs={'itemprop':'description'})
    authors = soup.findAll('span', attrs={'itemprop':'author'})

    flag = True
    indexOf = 1

    for review in reviews:
        dirtyEntry = str(review)
        while dirtyEntry.index('<') != -1:
            indexOf = dirtyEntry.index('<')
            endOf = dirtyEntry.index('>')
            if flag:
                dirtyEntry = dirtyEntry[endOf+1:]
                flag = False
            else:
                if(endOf+1 == len(dirtyEntry)):
                    cleanEntry = dirtyEntry[0:indexOf]
                    break
                else:
                    dirtyEntry = dirtyEntry[0:indexOf]+dirtyEntry[endOf+1:]
        f=open("reviews.txt", "a")
        f.write(cleanEntry)
        f.write("\n")
        f.close
    queries = queries + 40

Problem (In short):

When I run this script through command line it works and it finally stores a reviews.txt file. But when I run it through this program nothing happens.

I have played with pr.wait() and pr.waitfor() and yet nothing happens.

Please advice.

Thank you.

Answer 1

public void pythonrun(String args) throws IOException, InterruptedException {
    String pythonScriptPath = "/yelp/msp.py";
    String[] cmd = new String[2 + args.length()];
    cmd[0] = "C:\\Python27\\python.exe";
    cmd[1] = pythonScriptPath;
    for(int i = 0; i < args.length(); i++) {
        cmd[i+2] = args;
    }
    :
}

That doesn't look quite right. You're creating a string array with a size based on the size of the string being passed in.

That means that pythonrun("1234") will end up executing:

C:\Python27\python.exe /yel/msp.py 1234 1234 1234 1234

If you just want to pass in a single argument for the script, you would do something like:

public void pythonrun(String args) throws IOException, InterruptedException {
    String pythonScriptPath = "/yelp/msp.py";
    String[] cmd = new String[3];
    cmd[0] = "C:\\Python27\\python.exe";
    cmd[1] = pythonScriptPath;
    cmd[2] = args;
    :
}

If you wanted to pass in an array of arguments, something like this would be better:

public void pythonrun(String [] args) throws IOException, InterruptedException {
    String pythonScriptPath = "/yelp/msp.py";
    String[] cmd = new String[2 + args.length()];
    cmd[0] = "C:\\Python27\\python.exe";
    cmd[1] = pythonScriptPath;
    for(int i = 0; i < args.length(); i++) {
        cmd[i+2] = args[i];
    }
    :
}

You can tell exactly what parameters are being used for the process by placing the following code after the code where you set them:

for (int i = 0; i < cmd.length(); i++)
    System.out.println ("DEBUG " + i + ": [" + cmd[i] + "]");

---

Beyond that, there may be discrepencies between your command line version and the one called from your Java program.

For one thing, your Java program is calling /yelp/msp.py whereas your command line version call msp.py directly. Are you sure that your msp.py script is actually in /yelp ?

Also make sure that C:\\Python27\\python.exe is the correct Python interpreter.

And, one last thing, check which directory you're in when the Java program is running. If it's not what you expect, you may well be creating reviews.txt in a totally unexpected place.

Answer 2

String python_script_path ="Path to Python script/";
ProcessBuilder pb = new ProcessBuilder("python","msp.py","parameter1","parameter2");
 pb.directory(new File(python_script_path));
Process process = pb.start();
InputStream is = process.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br1 = new BufferedReader(isr);
String line1;
 while ((line1 = br1.readLine()) != null) {
 System.out.println(line1);
 }

Use Processbuilder and set path variables

Answer 3

I have managed to find the solution for this one although I still don't get it.

I used the same code and it works on Ubuntu.

cmd[0] = "python";

This is all I modified and I ran the same script and b00m and it works!

The question is WHY?