I have a bash script (named opsin) which only manages the calling of Java binary. All arguments are forwarded with ${@:1} to Java binary.

#!/bin/bash
DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
java -jar $DIR/../bin-java/opsin/opsin.jar ${@:1}

This binary, opsin.jar, also accepts stdin so you can do

echo "abcd" | java -jar opsin.jar

But I can do the same with bash script above:

echo "abcd" | opsin

How is the stdin passed to

java -jar $DIR/../bin-java/opsin/opsin.jar ${@:1}

in bash script?