如何将调用的命令/程序的输出重定向到log4j？

Question

I write a program and handle my logs with a logging tool (eg, Java's log4j or Python's logging ), so all logs produced by myself can go to a log file managed by the logging tool.

I'd also invoke a command or a third party program in my program, which writes all its outputs to the console by default. How can I redirect those outputs to the log file managed by the logging tool (and make them conform to the logging format if possible)?

Answer 1

In java, you could use IoBuilder from log4j to build your PrintStream. IoBuilder is included in Apache's Log4j Streaming Interface, an addition to Log4J.

Once you have your PrintStream, you can set the system's default PrintStream...

 IoBuilder builder = IoBuilder.forLogger(MyClass.class);
 PrintStream myPrintStream = builder.buildPrintStream();
 System.out = myPrintStream;

This way, if other library goes System.out.print() or println() it will be logged through your logger, with your logger format.

Answer 2

To redirect all standard output of an external process to a file in Python:

#!/usr/bin/env python
from subprocess import check_call, STDOUT

with open('log', 'ab', 0) as file:
    check_call(['program', 'arg 1', 'arg 2'], stdout=file, stderr=STDOUT)

The output is redirected as is. To make it conform to the logging format, you might need it to pass through your program explicitly:

#!/usr/bin/env python3
import logging
from subprocess import Popen, PIPE, STDOUT

logging.basicConfig(filename='log',level=logging.DEBUG)
with Popen(['program', 'arg 1', 'arg 2'], stdout=PIPE, stderr=STDOUT, bufsize=1,
           universal_newlines=True) as process:
    for line in process.stdout:
        logging.debug('program output %s', line.rstrip('\n'))

The code decodes program's standard output using locale.getpreferredencoding(False) and appends lines to the log file using logging module (you could configure whatever logging format you like using standard logging tools).