java: how to both read and write to & from process thru pipe (stdin/stdout)
Question: (i'm new to java) I need to start a process and receive 2 or 3 handles: for
STDIN, STDOUT, (and STDERR), so I can write input to the process and receive
its output, the same way command line pipes behave (e.g. "grep")

in Python this is acheived with the following code:

    
    
    from subprocess import Popen, PIPE
    p = Popen(cmd, shell=True, stdin=PIPE, stdout=PIPE)
    (child_stdin, child_stdout) = (p.stdin, p.stdout)
    child_stdin.write('Yoram Opposum\n')
    child_stdin.flush()
    child_stdout.readlines()
    

What's the Java equivalent??

I've tried so far

    
    
    Process p = Runtime.getRuntime().exec(cmd);
    BufferedReader inp = new BufferedReader( new InputStreamReader(p.getInputStream()) );
    BufferedWriter out = new BufferedWriter( new OutputStreamWriter(p.getOutputStream()) );
    out.write( "Some Text!\n\n" );
    out.flush();
    line = inp.readLine();
    print("response1: " + line );   // that's ok
    out.write( "Second Line...\n" );
    out.flush();
    line = inp.readLine();
    print("response2: " + line );    // returns an empty string, if it returns,,,
    inp.close();
    out.close();
    

BTW the first try works only with \n\n, but doesn't work with single \n (why?)

the following code works, but all input is given in advance, not the behavior
i'm looking for:

    
    
    out.write( "Aaaaa\nBbbbbb\nCcccc\n" );
    out.flush();
    line = inp.readLine();
    print("response1: " + line );
    line = inp.readLine();
    print("response2: " + line );
    line = inp.readLine();
    print("response3: " + line );
    line = inp.readLine();
    print("response4: " + line );
    

output:

    
    
    response1: AAAAA
    response2: 
    response3: bbbbbb
    response4: 
    

the process being run looks like that:

    
    
    s = sys.stdin.readline()
    print s.upper()
    s = sys.stdin.readline()
    print s.lower()
    


Answer: ok, it was also my python's code fault, but opposite to @Jon's answer, there
was an EXTRA newline (0xA0 to be exact, which isn't Windows' standard).

once i'm strip()ing the extra 0xA0 from the line i get from Java, python adds
a single "normal" \n to Java on the way back, and things run smoothly.

for the completeness of the question and answer, here's a working Java code:

    
    
    import java.io.*;
    import java.util.*;
    
    public class Main {
    
        public static BufferedReader inp;
        public static BufferedWriter out;
    
        public static void print(String s) {
        System.out.println(s);
        }
    
        public static String pipe(String msg) {
        String ret;
    
        try {
            out.write( msg + "\n" );
            out.flush();
            ret = inp.readLine();
            return ret;
        }
        catch (Exception err) {
    
        }
        return "";
        }
    
    
    
        public static void main(String[] args) {
    
        String s;
        String cmd = "c:\\programs\\python\\python.exe d:\\a.py";
    
        try {
    
            print(cmd);
            print(System.getProperty("user.dir"));
            Process p = Runtime.getRuntime().exec(cmd);
    
            inp = new BufferedReader( new InputStreamReader(p.getInputStream()) );
            out = new BufferedWriter( new OutputStreamWriter(p.getOutputStream()) );
    
            print( pipe("AAAaaa") );
            print( pipe("RoteM") );
    
            pipe("quit")
            inp.close();
            out.close();
        }
    
        catch (Exception err) {
            err.printStackTrace();
        }
        }
    }
    

and this is the python code

    
    
    import sys
    s = sys.stdin.readline().strip()
    while s not in ['break', 'quit']:
        sys.stdout.write(s.upper() + '\n')
        sys.stdout.flush()
        s = sys.stdin.readline().strip()
    

