Java execute BAT have no response

[niqi li]

Hi

I am writing a program to execute a .bat to call another java program. The reason is I want to set the JVM heap space to larger. Here's an example I've tried. I am only testing on small files so I haven't put the JVM setting commands in. For now my purpose is to have a copied of the target file when I run the java...

The problem is that when I run the first java to call bat, it only shows the header message, seems it does not run the file properly. The command line hangs and I cannot type any things. By looking at the task panel, I found a new cmd process and java thread is called and I know the code does something, but why this happens? I am quite new to java and hope could have your help. Any ideas what's going on?

Your comments are welcome and appreciate. Thanks indeed.

Here's the code

The Helloworld.java

    
import java.io.*;

public class HelloWorld {
    public static void main(String[] args){
        System.out.println("Hello World");
String s = null;
        try{

		Process p = Runtime.getRuntime().exec("cmd c/ callJava.bat");
		
                 BufferedReader stdInput = new BufferedReader(new 
                 InputStreamReader(p.getInputStream()));

            BufferedReader stdError = new BufferedReader(new 
                 InputStreamReader(p.getErrorStream()));

            // read the output from the command
            
            System.out.println("Here is the standard output of the command:\n");
            while ((s = stdInput.readLine()) != null) {
                System.out.println(s);
            }
            
            // read any errors from the attempted command

            System.out.println("Here is the standard error of the command (if any):\n");
            while ((s = stdError.readLine()) != null) {
                System.out.println(s);
            }

    		p.waitFor();
                System.out.println("comand ok");
        }
        catch(Exception ex){
            System.out.println("Exception in command");
            ex.printStackTrace();
        }
    }
}

The bat file, same dir with Helloworld.java

    
java ResizeImage c:\iuCache\a.txt c:\iuCache\b.txt

and finally the ResizeImage.java

    
import java.io.*;
public class ResizeImage {
    public static void main(String[] args){

        try{
             File inputFile = new File(args[0]);
             File outputFile = new File(args[1]);

             FileReader in = new FileReader(inputFile);
             FileWriter out = new FileWriter(outputFile);
             int c;

             while ((c = in.read()) != -1) {
                out.write(c);
             }

             in.close();
             out.close();
         }
         catch(Exception ex ){
             System.out.println("Exception in resize image: "+ex.getMessage());
         }

    }
}

[William Brogden]

Your code depends on the Process writing all the stdout first, followed by the std err output. The process may be stuck trying to write to stderr first.

To cover all possibilities, you should be starting two Threads, one to read stdout and one to read stderr. As I recall the javadocs for Process talk about this.

Bill