redirect conosle result

[iyappan sankaran]

hai
how to redirect the console result to a application.

[Stan James]

One neat way is to run the command with runtime.exec and connect readers to the stdout and errout of the command. You can also connect a writer to the stdin of the program and interact with prompts and responses and such. You kinda need to get into some threading tricks to make it all work, so it's not quite a trivial task. Let us know if you'd like samples.

[Stefan Wagner]

java Producer | java Consumer

[ October 05, 2004: Message edited by: Stefan Wagner ]

[Joaquin Morcate]

I'm trying to capture the output of a process that I started using exec(), and I have observed a different behaviour between stdin and stderr.

I have de following C code: (HelloWorld.c)

 
#include <stdio.h>
int 
main(int argc, char **argv) 
{
   int i;
   for (i=0; i<10 ;i++) {
fprintf(stderr, "HelloWorld stdout\n");
printf("HelloWorld stdin\n");
sleep(2);
   }
   printf("Good bye!\n");

}
 

and to capture output: (TheLaucher.java)

 
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
 
public class TheLauncher {
    
    public static void main(String[] args) throws IOException {
        System.out.println("Launcher --  begin");
       
        Process pc = Runtime.getRuntime().exec("HelloWorld");
        BufferedReader is = new BufferedReader(new InputStreamReader(pc.getInputStream()));
        String line;
        while ((line = is.readLine())!=null){
            System.out.println(line);
        }
 
        System.out.println("Launcher --  end");
    }
    
 
}

In this case I have to wait till the end of the process to get the output but if I use the stderr changing:

 
 BufferedReader is = new BufferedReader(new InputStreamReader(pc.getInputStream()));

for

 
 BufferedReader is = new BufferedReader(new InputStreamReader(pc.getErrorStream()));

I get the strings as they are available.
How can I get the same behaviour with the stdout, i.e. to get all the messages as they are produced? Why are they different?

Thanks

Joaquin Morcate
[ November 17, 2005: Message edited by: Joaquin Morcate ]

[Rob Spoor]

Processes can output to 2 distinct streams, stdout and stderr. While you see these two as one in a command box, they are still distinct. When reading one, you will not see the results of the other.

There are ways to redirect them, so that they both go to the same stream:
- in Java, use System.setOut(System.err) or System.setErr(System.out).
- if that is not possible, you can use OS redirection. After your command you add a 2>&1 to redirect the error stream to the output stream and >&2 for the other way around. E.g, "someCommand -paramater value <any other input to the command here> 2>&1". There cannot be any spaces around the >.