Redirect batch stderr to file

Question

I have a batch file that executes a java application. I'm trying to modify it so that whenever an exception occurs, it'll write the STDERR out to a file.

It looks something like this:

start java something.jar method %1 %2 2>> log.txt

Is there a way I can write the arguments %1 and %2 to the log.txt file as well? I don't want to write it to the log file everytime this batch file gets called, only when an exception occurs.

I tried searching for a way to redirect STDERR into a variable, but I couldn't figure it out. Ideally I'd like the log file to look something like:

Batch file called with parameters:
- "first arg"
- "second arg"
Exception: 
java.io.exception etc...

------------------------------------

Batch file called with parameters:
- "first arg"
- "second arg"
Exception: 
java.io.exception etc...

Answer 1

Something like this might work:

javastart.cmd

@echo off
set params=%*
for /f "delims=" %%e in ('java something.jar method %1 %2 ^>nul') do (
    echo Batch file called with parameters:>>log.txt
    echo - Args[]: %*>>log.txt
    echo - Arg[1]: %1>>log.txt
    echo - Arg[2]: %2>>log.txt
    echo Exception: %%e
)

I am not a java programmer myself, I cannot test this output/situation but:

1: %* means every parameters, from 1st to last (even %12 although it's not directly available.. ) whatever the formating. Might be better to use this than delimit those. In the even of bad spacing/quoting, you would have the full parameters too. I added a line in the log, to show the full line then the parameters. You can see where the problem was if it's a matter of bad arguments.

2: sending the stdout to null (^>nul) will only keep the stderr output, set into %%e

3: Whatever is in the do part will only happen is the for test statement actually has anything as an output, i.e. if %%e is set.

With those being said, you have to test the script and see if the exception is actually sent to stderr or, like some other softwares, to stdout even if an error occured.

I hope this helps.