Executing An External Process

Illustrates the monitoring of an external process as well as input and output error streams.

Overview

To execute an external process you have to create an instance of the TerminalMonitoredProcess class. The constructor requires the following parameters:

1. A String[] – Command line arguments to be executed.
2. java.io.File – The working directory of the sub process providing listing of the root folder. You can pass null for this parameter.
3. A long – Used to set the period of time for which the monitored process waits to reduce the CPU load.
4. A boolean – Running the garbage collector after the process is closed.
5. An instance of a class implementing the TerminalMonitoredProcessCallback interface – To provide an event handler, called when a process monitoring event occurs. It executes one of the four methods depending on the process. null can be passed for this parameter.

The following example shows the creation of an external process. At the end of this example when call TerminalMonitoredProcess.destroy, one of the methods will be executed onClose with terminal output for the external process.

The example below uses the Terminal Monitored Process:

     . . .
TerminalMonitoredProcess process = new TerminalMonitoredProcess(//
      new String[] {         // command line parameters - execute "ls -l /"
        "/bin/ls", "-l", "/" // provides listing of the root folder
        },
        300,                 // a small period that monitored process waits to reduce CPU load
        true,                // run Garbage Collector after process exits
       new TerminalMonitoredProcessCallback() {
       public void onErrLine(String line, TerminalMonitoredProcess process) {
            System.out.println("ERR: " + line);
          }
       public void onOutLine(String line, TerminalMonitoredProcess process) {
            System.out.println("OUT: " + line);
          }
       public void onClose(MonitoredProcess process) {
            System.out.println("Process closed: " + process);
          }
       public void onCloseHang(MonitoredProcess process) {
            System.out.println("Process hanged: " + process);
          }
        });
    // let the process execute for maximum 4 seconds
    process.waitFor(4000);

    // make sure process is destroyed
    int exitValue = process.destroy(1000);

    System.out.println("Process closed with exit value " + exitValue);
  }

      . . .
  

The console/terminal output when executing external process is shown below:

OUT: drwxr-xr-x  2 root root 4096 2015-03-08 00:58 selinux
OUT: drwxr-xr-x  2 root root 4096 2014-04-02 13:08 srv
OUT: drwxr-xr-x 11 root root    0 2014-07-13 14:43 sys
OUT: drwxrwxrwt  8 root root 4096 2014-10-03 15:22 tmp
OUT: drwxrwxr-x  3 root root 4096 2014-09-21 12:23 tools
OUT: drwxr-xr-x 12 root root 4096 2015-01-17 11:22 usr
OUT: drwxr-xr-x 13 root root 4096 2015-02-12 13:16 var
OUT: lrwxrwxrwx  1 root root   25 2015-03-02 13:08 vmlinuz -> boot/vmlinuz-2.6.26-2-686
Process closed: com.prosyst.util.process.TerminalMonitoredProcess@586a50
Process closed with exit value 0
Bundle with ID 20 was started.
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