CODEWITHSUNDEEP
java
Myrna
Myrna

Reputation: 41

Java Process Builder

I have a project where program has to open notepad file and after entering text and saving that notepad file program should display number of words in that file and it should delete the entered content in the file. iam getting this error Error not derjava.lang.NullPointerException after running the program. though after entering some text in Mytext.txt and saving it? my question is why BufferedReader is reading empty file even though iam saving the file with some content. Appreciate the help..

public class Notepad_Example {
    public static void main(String[] jfb) {
        try {
            ProcessBuilder proc = new ProcessBuilder("notepad.exe", "C:\\Java Projects\\Reverse String\\src\\Mytext.txt");
            proc.start();
            BufferedReader br;
            String s;

            br = new BufferedReader(new FileReader("C:\\Java Projects\\Reverse String\\src\\Mytext.txt"));
            s = br.readLine();

            char c[] = new char[s.length()];
            int j = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) != ' ') {
                    c[i] = s.charAt(i);

                } else {
                    j++;
                }
            }
            System.out.println("number of words are " + (j + 1));
            br.close();

        } catch (Exception hj) {
            System.out.println("Error not der" + hj);
        }

        try {
            FileWriter fw = new FileWriter("C:\\Java Projects\\Reverse String\\src\\Mytext.txt");
            fw.close();
        } catch (Exception hj) {
            System.out.println("Error not der" + hj);
        }
    }
}

Upvotes: 1

Views: 682

Answers (3)

Martin Frank
Martin Frank

Reputation: 3454

NOTE

we have had some weird behaviour when using the process builder... we used to start the process with a

new ProcessBuilder("notepad.exe", "C:\\Java Projects\\Reverse String\\src\\Mytext.txt");

but that started to fail wen we upgraded to Win7 and Java7 - we we not sure where this problem really originated, but we changed out Code like this:

String[] cmd = new String[]{"notepad.exe", "C:\\Java Projects\\Reverse String\\src\\Mytext.txt"};
new ProcessBuilder(cmd);

and since then it worked correct!

Upvotes: 0

Matthias
Matthias

Reputation: 3592

The issue you are having is here:

 ProcessBuilder proc=new ProcessBuilder("notepad.exe","C:\\Java Projects\\Reverse String\\src\\Mytext.txt"); 
 proc.start();

proc.start() is returning the freshly started process. You'll have to give the user the chance to edit and save the file and close the editor before you can read from that file. That is you have to wait for that process to finish before you can start using the results (the saved file) of that process.

So do instead something like this:

Process process = proc.start();
int result = process.waitFor();
if (result == 0) {
  // Do your rest here
} else {
 // give error message as the process did not finish without error.
}

Some further remarks:

The rest of your code also appears to have some issues.

  • You are only reading one line of that file. What if the user is using new lines?
  • The exception handling is not very good, at the very least print the stack trace of the exception which will give you further hints of where an exception was occuring
  • If you are using Java 7, read on try with resources; if you are using Java 6, add finally blocks to make sure your resources (the streams) are getting closed.

Upvotes: 2

Scary Wombat
Scary Wombat

Reputation: 44813

When you run proc.start(); it is not going to block and waitfor the process to end, it will continue running.

You will need to call the proc.waitFor() method, to block until it has finished.

Upvotes: 0

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