Redirecting standard I/O
The Java System class allows you to redirect the standard input, output, and error I/O streams using simple static method calls:
setIn(InputStream)
setOut(PrintStream)
setErr(PrintStream)
Redirecting output is especially useful if you suddenly start creating a large amount of output on your screen, and it’s scrolling past faster than you can read it.[64] Redirecting input is valuable for a command-line program in which you want to test a particular user-input sequence repeatedly. Here’s a simple example that shows the use of these methods:
//: c12:Redirecting.java
// Demonstrates standard I/O redirection.
// {Clean: test.out}
import java.io.*;
public class Redirecting {
// Throw exceptions to console:
public static void main(String[] args)
throws IOException {
PrintStream console = System.out;
BufferedInputStream in = new BufferedInputStream(
new FileInputStream("Redirecting.java"));
PrintStream out = new PrintStream(
new BufferedOutputStream(
new FileOutputStream("test.out")));
System.setIn(in);
System.setOut(out);
System.setErr(out);
BufferedReader br = new BufferedReader(
new InputStreamReader(System.in));
String s;
while((s = br.readLine()) != null)
System.out.println(s);
out.close(); // Remember this!
System.setOut(console);
}
} ///:~
This program attaches standard input to a file and redirects standard output and standard error to another file.
I/O redirection manipulates streams of bytes, not streams of characters, thus InputStreams and OutputStreams are used rather than Readers and Writers.
