高分请教

Question

Listing 4.7 properly redirects the standard output stream of the jecho process into a file. Listing 4.7 GoodWinRedirect.java import java.util.*;
import java.io.*;class StreamGobbler extends Thread
{
    InputStream is;
    String type;
    OutputStream os;
    
    StreamGobbler(InputStream is, String type)
    {
        this(is, type, null);
    }    StreamGobbler(InputStream is, String type, OutputStream redirect)
    {
        this.is = is;
        this.type = type;
        this.os = redirect;
    }
    
    public void run()
    {
        try
        {
            PrintWriter pw = null;
            if (os != null)
                pw = new PrintWriter(os);
                
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line=null;
            while ( (line = br.readLine()) != null)
            {
                if (pw != null)
                    pw.println(line);
                System.out.println(type + ">" + line);    
            }
            if (pw != null)
                pw.flush();
        } catch (IOException ioe)
            {
            ioe.printStackTrace();  
            }
    }
}public class GoodWinRedirect
{
    public static void main(String args[])
    {
        if (args.length < 1)
        {
            System.out.println("USAGE java GoodWinRedirect <outputfile>");
            System.exit(1);
        }
        
        try
        {            
            FileOutputStream fos = new FileOutputStream(args[0]);
            Runtime rt = Runtime.getRuntime();
            Process proc = rt.exec("java jecho 'Hello World'");
            // any error message?
            StreamGobbler errorGobbler = new 
                StreamGobbler(proc.getErrorStream(), "ERROR");            
            
            // any output?
            StreamGobbler outputGobbler = new 
                StreamGobbler(proc.getInputStream(), "OUTPUT", fos);
                
            // kick them off
            errorGobbler.start();
            outputGobbler.start();
                                    
            // any error???
            int exitVal = proc.waitFor();
            System.out.println("ExitValue: " + exitVal);
            fos.flush();
            fos.close();        
        } catch (Throwable t)
          {
            t.printStackTrace();
          }
    }
}