Question

import java.io.*;

public class Demo{

    public static void main(String[] args){
        File f = new File("abc.txt") ;

        try{
            System.setOut(new PrintStream( new FileOutputStream(f) ) ) ;
        }
        catch(FileNotFoundException fnfe){
            System.out.println(fnfe.getMessage()) ;
        }

        System.out.println("Hello\n") ;

        try{
            //throwing exception,
            //is there any method to close the f File,
            //before we try to open the file referred by f.
            Process p = Runtime.getRuntime().exec(f.getPath()) ;
        }
        catch(IOException io){
            System.out.println(io.getMessage()) ;
        }
    }

}

and the content of abc.txt after executing Demo is:-

Hello

Cannot run program “abc.txt”: CreateProcess error=32, The process cannot access the file because it is being used by another process

how to avoid the exception…..

as many people here suggested, i have tried the following code,
but sadly, even that is also throwing excption….:-(

import java.io.*;

class Demo{

    public static void main(String[] args){
        File f = new File("abc.txt") ;

        FileOutputStream fos = null ;
        try{
            fos = new FileOutputStream(f) ; 
        }
        catch(FileNotFoundException fnfe){
            System.out.println(fnfe.getMessage()) ;
        }

        PrintStream ps = new PrintStream(fos) ;
        ps.println("Hello") ;

        try{
            fos.close() ;

            //throwing exception again
            Process p = Runtime.getRuntime().exec(f.getAbsolutePath()) ;
        }
        catch(IOException io){
            System.out.println(io.getMessage()) ;
        } 
    }
}

??????????

Answer 1

I am assuming that the reason for calling Runtime.getRuntime().exec(f.getPath()); is to open up the abc.txt file in a text editor. It would be better to provide complete command for opening the text editor along with the file path. I tried this with notepad.exe (windows) and it worked.

import java.io.*;

public class Demo{

    public static void main(String[] args){
        File f = new File("abc.txt") ;

        try{
                System.setOut(new PrintStream( new FileOutputStream(f) ) ) ;
        }
        catch(FileNotFoundException fnfe){
                System.out.println(fnfe.getMessage()) ;
        }

        System.out.println("Hello\n") ;

        try{
                Process p = Runtime.getRuntime().exec("notepad.exe " + f.getPath()) ;
        }
        catch(IOException io){
                System.out.println(io.getMessage()) ;
        }
    }

}

Following code dynamically generates java code and uses javac to compile it

import java.io.*;

public class Demo{

    public static void main(String[] args){

        File f = new File("Abc.java") ;
        PrintWriter writer = null;
        BufferedReader reader = null;
        InputStream pStream = null;

        try{
                // Open File Stream and write code
                writer = new PrintWriter( new FileOutputStream(f) );
                String javaCode = "public class Abc { \r\n" +
                                  "public static void main(String[] args) {\r\n" +
                                  "System.out.println(\"Hello World!\");\r\n" +
                                  "}\r\n" +
                                  "}\r\n";

                writer.println(javaCode) ;
                writer.close();

                // Run Javac to compile the code
                Process p = Runtime.getRuntime().exec("javac " + f.getPath()) ;
                p.waitFor();

                // status = 0 => Process executed without errors
                //        = 1 => Process executed with errors
                int status = p.exitValue();
                if( status ==  0 )
                {
                    pStream = p.getInputStream();
                }
                else
                {
                    pStream = p.getErrorStream();
                }

                // Display the output from the process
                reader = new BufferedReader(new InputStreamReader(pStream));
                String ln = null;
                while( (ln = reader.readLine()) != null )
                {
                    System.out.println(ln);
                }
        }
        catch(Exception ex){
                System.out.println(ex.getMessage()) ;
        }
        finally{
            try{
               if( writer != null ){writer.close();}
                if( pStream != null ){pStream.close();}
                if( reader != null ){reader.close();}
            }
            catch(Exception ex){
                System.out.println(ex.getMessage()) ;
            }
        }
    }
}