Piping input to a Java app with Perl
- by user319479
I need to write a Perl script that pipes input into a Java program. This is related to this, but that didn't help me. My issue is that the Java app doesn't get the print statements until I close the handle. What I found online was that $| needs to be set to something greater than 0, in which case newline characters will flush the buffer. This still doesn't work.
This is the script:
#! /usr/bin/perl -w
use strict;
use File::Basename;
$|=1;
open(TP, "| java -jar test.jar") or die "fail";
sleep(2);
print TP "this is test 1\n";
print TP "this is test 2\n";
print "tests printed, waiting 5s\n";
sleep(5);
print "wait over. closing handle...\n";
close TP;
print "closed.\n";
print "sleeping for 5s...\n";
sleep(5);
print "script finished!\n";
exit
And here is a sample Java app:
import java.util.Scanner;
public class test{
public static void main( String[] args ){
Scanner sc = new Scanner( System.in );
int crashcount = 0;
while( true ){
try{
String input = sc.nextLine();
System.out.println( ":: INPUT: " + input );
if( "bananas".equals(input) ){
break;
}
} catch( Exception e ){
System.out.println( ":: EXCEPTION: " + e.toString() );
crashcount++;
if( crashcount == 5 ){
System.out.println( ":: Looks like stdin is broke" );
break;
}
}
}
System.out.println( ":: IT'S OVER!" );
return;
}
}
The Java app should respond to receiving the test prints immediately, but it doesn't until the close statement in the Perl script. What am I doing wrong?
Note: the fix can only be in the Perl script. The Java app can't be changed. Also, File::Basename is there because I'm using it in the real script.
