Mar 24

You need to read any output from standard output or standard error when running a process using Runtime.exec(). If you don’t the buffers may fill up causing the process to lock up.

The following code can be used to handle reading the process output, and the linked article provides a lot of great insight into the correct usage of Runtime.exec().

/** code copied from
 *  http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html
 *  When Runtime.exec() won't: Navigate yourself around pitfalls
 *  related to the Runtime.exec() method
 *  @author Michael Daconta
 */
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;
    }
    
    /** creates readers to handle the text created by the external program
    */		
    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();  
            }
    }
}

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Sep 09

Write your input to the output stream returned by the getOutputStream() method of the java.util.Process.


// Execute command

Process process = Runtime.getRuntime().exec(command);

// Get output stream to send command to process
     
OutputStream out = process.getOutputStream();

// send command
    
out.write("input text".getBytes());
out.close();

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