How can I get output from subprocess.check_output if the subprocess is a java program(with Command-line arguments)?

Question

I have the following java code: (HelloWorld.class is in bin folder):

package Hello;
public class HelloWorld {
    public static void main(String[] args) {
    System.out.println("Hello World" + args[1]);
    }
}

I want to call this java code from a python script and pass some command-line arguments to it.

So my python code is:

cmd = ["java","-classpath","bin/","Hello.HelloWorld","arguement1","arguement2"]
try:
    print subprocess.check_output(cmd,stderr=subprocess.STDOUT)
except: subprocess.CalledProcessError:
    print ('calling '+ ' '.join(cmd) +' failed\n')

If I run this code, I will get the no output from java code, and also get output "calling java -classpath bin/ Hello.HelloWorld arguement1 arguement2 failed".

But if I run:

java -classpath bin/ Hello.HelloWorld arguement1 arguement2 

in terminal, the java code will print the string.

So where is wrong of my python code?

Answer 1

You don't see the output because both stdout and stderr are captured by check_output(stderr=STDOUT) and java exits with a non-zero exit status that leads to the exception and that is why you see ".. failed" message.

To get subprocess' output in the exception handler except CalledProcessErrror as e: , access e.output attribute.

If you don't need to capture the output then just call call() instead:

import subprocess

subprocess.check_call(cmd)