在Linux中的Java中运行CPU利用率命令

Question

I am writing a Java program which will be run in a Linux machine. I wanted to get the CPU utilization of the system. For getting the cpu utilization of the machine I use the command :

top -bn 2 -d 0.01 | grep '^Cpu.s.' | tail -n 1 | gawk '{print $2+$4+$6}'

Then I call this command from the java code, but I do not get any output. Normal linux commands such as ls works for me.

My code is:

public class HelloWorld{

     public static void main(String []args){
         String s;
        Process p;
        try {
           p = Runtime.getRuntime().exec("top -bn 2 -d 0.01 | grep '^Cpu.s.' | tail -n 1 | gawk '{print $2+$4+$6}'");


            BufferedReader br = new BufferedReader(
                new InputStreamReader(p.getInputStream()));
            while ((s = br.readLine()) != null)
                System.out.println("line: " + s);
             p.waitFor();
            System.out.println ("exit: " + p.exitValue());
            p.destroy();
        } catch (Exception e) {}
     }
}

Answer 1

To use pipes, you need run your command from within a shell:

ProcessBuilder b = new ProcessBuilder("/bin/sh", "-c",
      "top -bn 2 -d 0.01 | grep '^Cpu.s.' | tail -n 1 | gawk '{print $2+$4+$6}'");

p = b.start();

Also, please be aware that your command fails on a different locale. And the output of top may vary too.