redirectError example is confusing

[micobarac]

In the following example, the console gets all the output, but the String output value remains empty:

String output = new ProcessExecutor().command("java", "-version")
        .redirectError(Slf4jStream.of(getClass()).asInfo())
        .readOutput(true).execute()
        .outputUTF8();

Output:

2021-12-30 12:51:32.150 DEBUG 43928 --- [  XNIO-1 task-1] org.zeroturnaround.exec.ProcessExecutor  : Executing [java, -version].
2021-12-30 12:51:32.177 DEBUG 43928 --- [  XNIO-1 task-1] org.zeroturnaround.exec.ProcessExecutor  : Started java.lang.UNIXProcess@56e2d396
2021-12-30 12:51:32.296  INFO 43928 --- [      Thread-56] c.l.openmx.service.mapper.AccountMapper  : openjdk version "1.8.0_292"
2021-12-30 12:51:32.297  INFO 43928 --- [      Thread-56] c.l.openmx.service.mapper.AccountMapper  : OpenJDK Runtime Environment (AdoptOpenJDK)(build 1.8.0_292-b10)
2021-12-30 12:51:32.297  INFO 43928 --- [      Thread-56] c.l.openmx.service.mapper.AccountMapper  : OpenJDK 64-Bit Server VM (AdoptOpenJDK)(build 25.292-b10, mixed mode)
2021-12-30 12:51:32.300 DEBUG 43928 --- [  XNIO-1 task-1] org.zeroturnaround.exec.WaitForProcess   : java.lang.UNIXProcess@56e2d396 stopped with exit code 0

Without redirectError, the String output gets the output value:

String output = new ProcessExecutor().command("java", "-version")
        .readOutput(true).execute()
        .outputUTF8();

Output:

openjdk version "1.8.0_292"
OpenJDK Runtime Environment (AdoptOpenJDK)(build 1.8.0_292-b10)
OpenJDK 64-Bit Server VM (AdoptOpenJDK)(build 25.292-b10, mixed mode)

Questions:

1. Does redirectError work just in case of errors?
2. Should String output get the output value with redirectError in place?

[nemecec]

You see a combination of two aspects:

1. java -version command prints the version information to standard error stream.
2. Unless an explicit handler for standard error stream has been specified, the ProcessExecutor by default redirects standard error stream into the standard output stream and returns the merged result as "output".

[panchenko]

This example is taken from the README file, would be good replacing it with something which makes more sense.

[nemecec]

Well, the README does describe the behaviour:

• Pumping the stderr to a logger
• Returning the output as UTF8 String

Maybe should replace the second line with "Returning the output as UTF-8 String (empty in this case as the version is printed to stderr)". Would this be enough?