[java] ProcessBuilder: Forwarding stdout and stderr of started processes without blocking the main thread

There is a library that provides a better ProcessBuilder, zt-exec. This library can do exactly what you are asking for and more.

Here's what your code would look like with zt-exec instead of ProcessBuilder :

add the dependency :

<dependency>
  <groupId>org.zeroturnaround</groupId>
  <artifactId>zt-exec</artifactId>
  <version>1.11</version>
</dependency>

The code :

new ProcessExecutor()
  .command("somecommand", "arg1", "arg2")
  .redirectOutput(System.out)
  .redirectError(System.err)
  .execute();

Documentation of the library is here : https://github.com/zeroturnaround/zt-exec/